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  Topic: Sharks, and why some of us are interested in them.< Next Oldest | Next Newest >  
Ichthyic



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Joined: May 2006

(Permalink) Posted: June 11 2007,16:55   

Ok, a couple of folks have asked me to make a post about sharks, what I did with them and why.  This has taken a while to post, partly because the machine I originally composed it on crashed, and partly because I was trying to find some of my original photos (all on slides it turns out, unfortunately).

I'm not going to go into the current status of research on shark evolution and cladistics, as that has been covered in other places, and it was never my focus anyway.

you can get a brief overview of that subject here:

http://www.elasmo-research.org/educati....yst.htm

...and an old paleo friend of mine from Berkeley days specialized in this area as well, so if you're curious about that particular aspect, I can try to track down where he's at these days, or you can yourself (he's a nice guy, I swear!):

http://www.ucmp.berkeley.edu/vertebrates/Doug/doug.html

For a few years, back in the early-mid 90's, I worked as the Science Director for an NGO that was primarily oriented towards researching shark behavior and migration patterns.  It still exists (such as it is), in fact, and you can visit the website here:

http://www.pelagic.org/

However, at the same time, I would rather recommend its inevitable replacement:

http://psrc.mlml.calstate.edu/neweve.htm

which contains much more complete references, and many that will give a good start to anyone thinking about this issue (check the recommended reading link).

Here, I'm going to go into why we were looking at migration patterns, and a bit about the biology of sharks that's relevant to the issue.

In case you want to bypass all my text and just look at the pictures, you can grab an excellent in depth explanation of why there is interest in studying shark populations for later perusal in this report:

Branstetter, S. (ed.). 1993. Conservation biology of elasmobranchs. NOAA Technical Report NMFS, U.S. Department of Commerce, no. 115, 99 pp.

which, IIRC, you can either grab directly or order from here:

http://spo.nwr.noaa.gov/trlist.htm

Let's start with some of the fun stuff:



This is a pic of one of the most common pelagic (open ocean) sharks in the Pacific, the blue shark (Prionace glauca ).

It's a great species to work with for tagging studies, as it is quite common and often caught as a bycatch of the longline and gillnet fisheries.

So why bother to tag them?

Well, a number of reasons really.  One is that pelagic sharks like blues are far ranging, and often follow important species of food fish that are also pelagic (like tunas), so it is good to know where they cross over national boundaries.  Different countries have different fishing regulations, but they may affect the same populations if those populations range widely.  So, it's important to know which specific fisheries the sharks are subject to, as this gives us important information in figuring out how best to conserve them.  It would be nice to think that just changing fishing regulations in this country would solve population problems in any given fishery, but studying the blue shark (and tuna too), suggests this is not the case for such far ranging animals, and the data gained from tags recovered from captured animals indicates which countries must be included in an overal species conservation plan.

Another reason is that blues, like most large pelagic sharks, are essentially apex predators in the systems they are found in.  As such, their role in maintaining the biodiversity of any given system should logically play a significant role.  Rough estimates of population sizes and migratory patterns garnered from tag data is at least a start in objectively examining what relative impacts they may have, which areas they are likely to have an impact on, as well as what might be the effects of significant removals.

Why sharks though?  

One thing that sharks in particular are noted for, is that they are typically slow breeders.  For example, in blue sharks gestation is takes 8-10 months, and it often takes a dozen or more years to reach maturity.  As such, fishing pressures that would normally be sustainable in faster breeding species are entirely unsustainable in sharks.  A great case on point was the opening of the Angel Shark fishery in CA by CA Fish and Game in the early-mid 80's.  Data on how rockfish responded to various levels of fishing pressure were not applicable at all to the newly opened fishery for angel sharks, and the populations quickly collapsed under the pressure.

In addition, sharks are fairly unique as targets of the fishing industry in that there is a market for mere pieces of them (namely, fins for shark fin soup and for the cartilage market - which is huge).  What this does is allow a fishing fleet to concentrate on storage of the most profitable bits of the sharks, and thus take many, many, more individuals than they normally would be able to if they had to take the whole animal.  We often see fishing fleets simply slicing the fins from live sharks, and dumping the rest of the animal back into the water.  This of course puts even heavier pressure on shark populations than would be normal for a standard food fish.

Being an apex level predator, sharks are also of interest in the study of how introduced toxins bioaccumulate, and we also were involved in taking many, many blood samples for analysis.  PCB's, Metals, and other pollutants are carried in the sharks blood. The samples collected from pelagic blue sharks can be compared with samples taken from benthic sharks and estuarine sharks to analyze differences in the levels of contamination, as well as giving clues as to what toxins are being accumulated in any given ecosystem.

We also worked with estuarine sharks like leopard sharks ( Triakis semifasciatus ) and grey smoothounds ( Mustelus californicus ), deepwater sharks like sixgill sharks ( Hexanchus griseus ), and "coastal" sharks like the white ( Carcharodon carcharias ); even spent time looking at basking sharks ( Cetorhinus maximus ), but by the time i really got rolling there, basking sharks had become inordinately hard to find.  I'm still unsure if this was due to some particularly heavy fishing pressure (we did find basking shark fins for sale in some markets in San Francisco), or whether something else has changed in the distribution of their favored prey items that simply means they hadn't come around much in several years.  Populations around the UK have show fluctuations as well, but not nearly as dramatic as those observed in CA.

We typically did the tag/release studies and took blood samples from ALL the species we looked at, but other studies varied from species to species.  For example, I was primarily focused on analyzing severe sex ratio bias in the populations of grey smoothhounds captured in the Elkhorn Slough area, while others were focused on researching habitat utilization patterns in populations of white sharks around areas north of Santa Cruz, and at the Faralon Islands (near San Francisco).  Still others were working on analyzing tissue samples to examine population genetics (Giacomo Bernardi for example: http://bio.research.ucsc.edu/people/bernardi/Bernardi/ ), and again for use in toxicology studies.

When tagging the sharks, we typically used standard CA Fish and Game tags (commonly known as "spagheti" tags) that we placed typically at the base of the dorsal fin.

here's an example (also known as a Floy tag):



though the ones we used are of course larger, heavier, and with stainless steel anchors instead.

I'm going to cut this off at this point, and just answer specific questions, otherwise I'll just ramble on and on.  I wish I had more perty piktures, but all my stuff is still in slide form, and my scanner broke ages ago.  a lot of it is on the psrf site, and there are far better photographs available than that ones I had anyway (Callaghan Fritz-Cope took most of the pics you see there)

I would suggest that anybody interested in shark conservation, population biology, or just anything having to do with sharks in general start with an email to Greg Caillet at Moss Landing Marine Station near Monterey, CA.  To get an idea of the kind of work that started much of the interest in elasmobranch conservation biology, you might try locating this paper:

Caillet, G. M. (1982). Age and growth of pelagic sharks: Management information for California's emerging fisheries, Sea Grant Report.

please feel free to post questions if you have any.  I'm more than happy to answer any I can.

cheers

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"And the sea will grant each man new hope..."

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Lou FCD



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(Permalink) Posted: June 11 2007,19:18   

Thanks for all that, Ich.  Do continue.

I was about ten when I saw Jaws at the drive in movies.  That sucker was huge.

With that permanent scarring in mind, here's my thing about sharks...

Sharks come in two basic flavors:

Hammerheads, which look really cool but want to eat me for lunch.

All the Rest.

The "All the Rest" flavor can be broken down into two subflavors...

The kinds that want to eat me.

and

The other kinds that want to eat me.

They are very cool to look at as long as they're behind the aquarium glass, but in case I haven't made it clear, I'm afeared o' sharks.  They want to eat me.

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Lou FCD is still in school, so we should only count him as a baby biologist. -carlsonjok -deprecated
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Ichthyic



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(Permalink) Posted: June 11 2007,19:43   

actually, very few species of sharks are considered at all dangerous.

there are only about 15 species that have ever been confirmed to attack humans, out of about 500 or so.

they range in size from the pygmy shark, at around 8-10", to the whale shark, which is by far and away the largest fish in the ocean at over 40'.

even if you are hanging in waters where dangerous species are relatively common, your chances of being attacked are about the same as being struck by lightning during a standard rainstorm (VERY low).

moreover, fatalities are extremely rare, even among those that have been attacked.

there is no evidence that sharks regularly hunt humans for food; typically most attacks are either:

defensive (reef sharks will sometimes attack divers or snorkelers that encroach on their territories)

mistaken identity (sharks often hunt in turbid waters, which helps hide them from their prey, but also makes visibility poor for the shark)

investigation (sharks appear to often be curious about uncommon objects in their environment, and much of their sensory equipment is in and around their mouths; they don't have hands and fingers, after all.  But then, even human babies like to put things in their mouths to investigate).

If you are interested, you can get great information on shark attack statistics (and how best to avoid being a statistic) on George Burgess' site:

http://www.flmnh.ufl.edu/fish/sharks/isaf/isafabout.htm

just be aware that the statistics don't support the level of hysteria associated with sharks, as an order of magnitude more people are killed each year by bees, for example.

I've logged thousands of hours in and under waters where even whites are relatively common (they really aren't all that common anywhere), as have many of my acquaintances, and over 25 years of diving, and tens of thousands of hours logged between myself and all of my acquaintances, I only count ONE instance of a shark attack in that whole time.

that guy was riding an underwater scooter (bright yellow, no less), in an area he had been warned earlier a white shark had been sighted.

He must have looked like a giant bass plug!

end result:

the scars he received vastly improved his sex life.

:)

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"And the sea will grant each man new hope..."

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Lou FCD



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(Permalink) Posted: June 11 2007,19:59   

Thanks Ichthyic.  I've actually been told most all of that before by other folks who also know what they're talking about.

I really appreciate your efforts, but my fear of sharks has nothing whatever to do with reality or reason.  I'm perfectly aware of that, as well.  They still want to eat me, though.  I can see it in their soulless black eyes.

 
Quote
Sometimes that shark he looks right into ya. Right into your eyes. And, you know, the thing about a shark... he's got lifeless eyes. Black eyes. Like a doll's eyes.

When he comes at ya, doesn't seem to be living... until he bites ya, and those black eyes roll over white and then... ah then you hear that terrible high-pitched screamin'. The ocean turns red, and despite all the poundin' and the hollerin', they all come in and they... rip you to pieces.

You know by the end of that first dawn, lost a hundred men. I don't know how many sharks, maybe a thousand.

I know how many men, they averaged six an hour.

On Thursday morning, Chief, I bumped into a friend of mine, Herbie Robinson from Cleveland. Baseball player. Boatswain's mate. I thought he was asleep. I reached over to wake him up. Bobbed up, down in the water just like a kinda top. Upended. Well, he'd been bitten in half below the waist.

Noon, the fifth day, Mr. Hooper, a Lockheed Ventura saw us. He swung in low and he saw us... he was a young pilot, a lot younger than Mr. Hooper. Anyway, he saw us and he come in low and three hours later a big fat PBY comes down and starts to pick us up.

You know that was the time I was most frightened... waitin' for my turn. I'll never put on a lifejacket again. So, eleven hundred men went in the water; 316 men come out and the sharks took the rest, June the 29th, 1945


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Lou FCD is still in school, so we should only count him as a baby biologist. -carlsonjok -deprecated
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J-Dog



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(Permalink) Posted: June 11 2007,20:02   

Remember that scene in Jaws, when Quint was describing the fate of the crew of the Indianapolis?  Yeah.  I thought so; one of the best scenes in the movie.  

From the Jaws Trivia Page:
Quint's tale of the USS Indianapolis was conceived by playwright Howard Sackler, lengthened by screenwriter John Milius and rewritten by Robert Shaw following a disagreement between screenwriters Peter Benchley and Carl Gottlieb. Shaw presented his text, and Benchley and Gottlieb agreed that this was exactly what was needed. Whoever was responsible, Quint got the date of the sinking wrong, claiming it was June 29, 1945, when in reality it was 12:14 am on July 30th, 1945. Universal has toyed with the idea of making the "Indianapolis" incident into a film, using a young Quint as the lead, ever since. Note that June 29, however, is the date (in the film) that the young boy was eaten by the shark, as can be seen in the hand-written "reward" notice.

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Albatrossity2



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(Permalink) Posted: June 11 2007,20:15   

Sharks are pretty cool, but sadly missing (for at least the past 60 million years or so) from my part of the galaxy. But I did have the pleasure of graduating from the same Biology department as Leonard Compagno, who went on to become a famous shark biologist. I think he is now at some shark research institute in South Africa. He probably still has the dubious record of being the graduate student who took longest to get his doctoral degree in Stanford Biology (starting in the mid 1960's sometime and finishing in 1979), due in no small measure to the difficulty of the dissertation topic. That would be shark demographics, tag and release and wait for the data to come in... I wish I had been around to hear his dissertation defense, but I was already at a post-doc and never had the chance.

Shark fear is an interesting and perhaps primal fear, if my youngest daughter is any indication. When she was about 2 years old, I attended a Biophysical Society meeting in Baltimore. We had a chance to visit the then-new Baltimore Aquarium, which has a large circular tank with sharks and a spiral ramp down the middle of the tank. So the sharks basically circle you in the tank as you walk along. My daughter was excited about most of the interesting fish that swam by, but would recoil and cling to me every time a big shark came by. I always wondered if anyone knew any more about this sort of reaction.  When (at what age) does it kick in?  Is it universal?  Who knows?

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As the only possible proof of its own inheritance.
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Lou FCD



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(Permalink) Posted: June 11 2007,20:17   

Quote (J-Dog @ June 11 2007,20:02)
Remember that scene in Jaws, when Quint was describing the fate of the crew of the Indianapolis?  Yeah.  I thought so; one of the best scenes in the movie.  

From the Jaws Trivia Page:
Quint's tale of the USS Indianapolis was conceived by playwright Howard Sackler, lengthened by screenwriter John Milius and rewritten by Robert Shaw following a disagreement between screenwriters Peter Benchley and Carl Gottlieb. Shaw presented his text, and Benchley and Gottlieb agreed that this was exactly what was needed. Whoever was responsible, Quint got the date of the sinking wrong, claiming it was June 29, 1945, when in reality it was 12:14 am on July 30th, 1945. Universal has toyed with the idea of making the "Indianapolis" incident into a film, using a young Quint as the lead, ever since. Note that June 29, however, is the date (in the film) that the young boy was eaten by the shark, as can be seen in the hand-written "reward" notice.

Heh, I was just reading a web page about the real story.  Interesting stuff.

And I'd say that that's one of the best scenes in movie history.  Shaw did an awesome job with that.  Oddly enough, Jaws is one of my favorite movies EVAH.

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Lou FCD is still in school, so we should only count him as a baby biologist. -carlsonjok -deprecated
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Lou FCD



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(Permalink) Posted: June 11 2007,20:22   

Quote (Albatrossity2 @ June 11 2007,20:15)
Shark fear is an interesting and perhaps primal fear, if my youngest daughter is any indication. When she was about 2 years old, I attended a Biophysical Society meeting in Baltimore. We had a chance to visit the then-new Baltimore Aquarium, which has a large circular tank with sharks and a spiral ramp down the middle of the tank. So the sharks basically circle you in the tank as you walk along. My daughter was excited about most of the interesting fish that swam by, but would recoil and cling to me every time a big shark came by. I always wondered if anyone knew any more about this sort of reaction.  When (at what age) does it kick in?  Is it universal?  Who knows?

Very cool, though.  There's a tank with sharks at the aquarium in Wilmington (just south of here), and last time I was there there were two divers in the tank.  Their scuba gear was wired up so they were giving a talk to some elementary school kids who were all sitting on the carpet in rapt attention.

I had to stop and listen, and the kids got to ask some questions of the divers.  Really good questions, too.  It was neat.

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Lou FCD is still in school, so we should only count him as a baby biologist. -carlsonjok -deprecated
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Ichthyic



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(Permalink) Posted: June 11 2007,20:23   

Compagno helped pioneer the study of shark population biology that Greg Caillet ended up becoming likely the current world's leading expert on.

Greg is about done, however, sorry to say.  Poor guy has had a heart attack, and STILL juggles three major research related functions.  I can't imagine he'll keep that up much longer.

I'm at a loss to say who will be considered the next generation's leading shark expert.

any guesses?

here's where Leonard is now, btw:

http://www.amonline.net.au/fishes/about/visitors/compagno.htm

actually, even that's dated.

hmm, then i would try here:

http://www.iziko.org.za/nh/research/src/index.html

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skeptic



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(Permalink) Posted: June 11 2007,21:08   

Ichy, I'm going to have to take back everything I ever said or thought about you.  This is the most content and substance I've ever seen you post.  To be honest I didn't think you were capable and I'm pleased to be wrong.  Great stuff, thanks for the post.

  
Ichthyic



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(Permalink) Posted: June 11 2007,21:12   

sorry to say it, but this isn't even the work that I published on my thesis that I put up here a while back.

you keep seeming to think that my responses to YOU are indicative of anything other than what they are:

responses to YOU.

that said, did you actually HAVE a question?

otherwise, I'm not particularly partial to backhanded compliments.

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"And the sea will grant each man new hope..."

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skeptic



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(Permalink) Posted: June 12 2007,00:41   

No, actually I just enjoyed reading.  I'm kinda partial to the subject after a few close encounters and I can see your passion in you're writing.  It's always enjoyable to read a topic that the writer really enjoys, much more incitful, I think.  No backhanded compliment there, just the honest truth.

  
khan



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(Permalink) Posted: June 12 2007,08:49   

Quote
just be aware that the statistics don't support the level of hysteria associated with sharks, as an order of magnitude more people are killed each year by bees, for example.


I recall reading something several years ago.  Some folks were all upset because two people had been killed by sharks off Hawaii.  It was then noted that more than 40 people had drowned in the same time frame and location.  If you want to save lives, close the beaches.

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skeptic



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(Permalink) Posted: June 12 2007,09:03   

I think you can refer back to what Alba2 indicated.  There's something primal about the reaction and this far precedes Jaws.  Even in cultures where the shark is reverred it attains a near diety-like or supernatural position.

  
Lou FCD



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(Permalink) Posted: June 12 2007,10:42   

I think it's just all those nasty looking teeth.

And the fact that they're (for all intents and purposes) invisible... until they eat me.

I'm not so scared I don't go to the beach or swim in the ocean, but I'd have serious doubts about taking a swim from a boat on the ocean, even if I could see the shore line.

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Lou FCD is still in school, so we should only count him as a baby biologist. -carlsonjok -deprecated
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Ichthyic



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(Permalink) Posted: June 12 2007,14:39   

Quote (khan @ June 12 2007,08:49)
Quote
just be aware that the statistics don't support the level of hysteria associated with sharks, as an order of magnitude more people are killed each year by bees, for example.


I recall reading something several years ago.  Some folks were all upset because two people had been killed by sharks off Hawaii.  It was then noted that more than 40 people had drowned in the same time frame and location.  If you want to save lives, close the beaches.

there's a very interesting addition to that story actually.

turns out that the attack you are thinking about (or one similar) happened quite some time ago (late 80's, IIRC).  There was indeed a mass hysteria that happened after that, with many islanders insisting that there be a massive hunt for all sharks around the islands (especially tiger sharks).  

In the 10 or so intervening years between that and the next fatal shark attack, biologists (OK, Ichthyologists) at the University of Hawaii had been able to conclusively show how the sharks were extremely important in maintaining populations of important food fishes around the islands (I can probably dig up the reference, if anyone wants), and started an outreach program to inform people about the importance of sharks to the local environment.

Lo and behold, after that next fatal shark attack, people who wrote in to the local papers insisting that the sharks be hunted down were actually shouted down by the now vast majority who thought they should be left alone.

It's a great story of how good science CAN change people's attitudes drastically, as well as a rare positive story from the world of conservation biology.

All too infrequent, but things like that give hope that irrational attitudes and concepts can be overcome with solid information and outreach.  Provided, of course, that a direct impact on people can be demonstrated.

Same techniques are being tried to curb the "snake roundup" folks in the SW USA, who prey on people's irrational fear of snakes in order to turn a tidy profit and wipe out vast numbers of rattlesnakes in the process.

It also reminds that because of the importance of providing a direct "connection" to personal interests when trying to sway the way someone thinks, it should be no surprise to hear the DI utilizing people like Michael Egnor in order to try and minimize the importance of the ToE wrt to things people take a direct interest in, like their health.

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"And the sea will grant each man new hope..."

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Stephen Elliott



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(Permalink) Posted: June 12 2007,14:42   

I would like to ask a question. More about you Ichy than sharks really. Do you not get the feeling of fear when viewing them whilst in the water?

I have only ever encountered sharks twice while in their habitat (I am not counting seeing them in an "aquarium" here). Both times I experienced an irational fear that was a tad uncontrolable. I know they are unlikely to atack, I had a clue how the odds stacked, yet upon seing them I was afraid. Did they not "bother" you at all?

EDIT: Don't get me wrong here. They did look cool as Hell and I loved having seen them in the wild in retrospect. Just that at the time I was scared.

  
Ichthyic



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(Permalink) Posted: June 12 2007,14:48   

Quote
And the fact that they're (for all intents and purposes) invisible... until they eat me.


hmm, let me share something with you:

I learned to scuba dive when I was about 15.

I noticed an immediate difference in "comfort" levels between when I was underwater as opposed to on top of the water...

when you are snorkeling, you can only really look down, and with low visibility, you often can't see the bottom.

that can be unnerving;  the same can be said when you are in a boat - you can't see the bottom, so it's like being in the dark - you just don't "know" what could be down there.

However, when you are UNDER water, scuba diving, all that anxiety disappears, as just like on land, you are now able to see 360 all around, just by turning your head.  No more not knowing what is beneath you.

anywho, I would recommend if you want to rid yourself of a fear of sharks, you might actually want to take up scuba diving.

sounds counterintuitive on the surface, but it really does remove an awful lot of anxiety.

I have several stories of diving with sharks I could share, if you want.

--------------
"And the sea will grant each man new hope..."

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Lou FCD



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(Permalink) Posted: June 12 2007,14:53   

Quote (Ichthyic @ June 12 2007,14:48)
I have several stories of diving with sharks I could share, if you want.

Please do..

As for scuba diving, I'm afraid that although I always wanted to take a proper course and take it up, I waited too long.

My spinal issues would never let me do that now.

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Lou FCD is still in school, so we should only count him as a baby biologist. -carlsonjok -deprecated
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cogzoid



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(Permalink) Posted: June 12 2007,14:59   

I have some questions about sharks as well.

My girlfriend is really afraid of sharks.  We like to surf.  You can already see the problem.  Most of the time she's fine, especially if the water is clear.  Knowing that she has a chance of spotting an approaching shark helps her cope.  But, she's always sort of afraid of sharks.  And we got to brainstorming about ways to diminish attacks.  I remember some "Discovery Channel fact" about sharks having a keen sensitivity to electricity in the water.  How sensitive are they?  Can they be driven away by an annoying amount of electrical signals?  Or will it just attract them?  I'm a pretty hands-on type of guy and I told her I'd be willing to put an electrical device into her surfboard if it'd help keep her mind at ease.  I just want to make sure that I won't turn her into shark bait in the process.

Thanks.

  
Ichthyic



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(Permalink) Posted: June 12 2007,15:10   

Quote (Stephen Elliott @ June 12 2007,14:42)
I would like to ask a question. More about you Ichy than sharks really. Do you not get the feeling of fear when viewing them whilst in the water?

I have only ever encountered sharks twice while in their habitat (I am not counting seeing them in an "aquarium" here). Both times I experienced an irational fear that was a tad uncontrolable. I know they are unlikely to atack, I had a clue how the odds stacked, yet upon seing them I was afraid. Did they not "bother" you at all?

EDIT: Don't get me wrong here. They did look cool as Hell and I loved having seen them in the wild in retrospect. Just that at the time I was scared.

there's really not a simple answer to that.

I've been diving right next to large reef sharks and blue sharks and hadn't the slightest bit of anxiety (well, other than occasional "jack in the box" moments where they seem to appear out of nowhere right next to you).

In fact, the more time you spend with them, the more you begin to accept, even at a "deep" level, that they simply have no interest in you whatsoever.

Example:

As a first year grad student at Berkeley, I spent my first field season (3 months) at the research station Berkeley owned on the island of Moorea, which is a short hop from Tahiti in French Polynesia.  

I was there to study damselfish (I posted a paper of mine I published on the topic here a couple years back), but spent a lot of time exploring the different reef systems around the island, often in the company of the equivalent French graduate students on the other side of the Island.

One day, they invited me to come with them on a specimen collecting mission for the Ichthyology museum on Tahiti.  We were doing a deep dive (110 feet) to collect a list of fish for their collection (not live).  So we were using spears to collect the fish specimens, then stuffing them into heavy plastic bags for storage until we were done.  

An interesting side-note is that fish blood looks chartreuse green at that depth, since there is functionally no red light left (or orange, for that matter).  However, the water is so clear that even at 100 feet, it's quite bright and easy to see.

Anyway, about 15 minutes into our collections, the speared fish started to attract the local reef sharks.  We were using "paralyzer" style pole spears (which means they kind of look like a trident, but instead the points are arranged into essentially a cone, widening as you get towards the tips).  Sometimes, a speared fish will manage to get itself off of the spear, and then you have to try and chase it down.

Well, one large surgeonfish i speared managed to do just that, and so I was closely following the trail of green and not paying much attention to anything else.  I stopped once and lifted my head up, and could see that the injured fish had hidden itself inside a coral head about 20 yards further on, as soon as i had done that, I saw a movement out of the corner of my eye, and turned my head right... to find out that a 7 foot gray reef shark was doing the EXACT same thing I was, and was basically no further than 2 feet away on my right.

the shark, just like myself, was totally oblivious to anything but following that green trail.

Well, I decided the shark should have "the right of way", so to speak, and it must have too, because it pulled right in front of me and proceeded straight to the coral head.

Shortly thereafter, there was a cloud of green and fish scales, and the shark moved off.

Other than the shock of seeing the shark right next to me, when I hadn't the slightest clue it was there, I had no feelings of trepidation or anxiety.  Really, it was obvious the shark had absolutely no interest in me whatsoever.  It only wanted the fish.

Nothing like direct experience to really gain an understanding.

At the same time, while the fear factor tends to die down with experience, you also start garnering a respect for them.

Just like any large predator, they can obviously cause serious damage under the wrong circumstances.

For example, I've looked eye to eye with a 16' white shark, and not felt any fear whatsoever.  But, I was on a boat at the time.  I wouldn't go diving with a white shark when it is in a habitat where it is hunting for seals, any more than I would jump into a bear cage during feeding time.

so I'd say it is more respect, than fear.

oh, btw, here is the white shark that gave me my "chumming from the back of the Orca" moment (for those of you who remember that scene with Roy Scheider from Jaws):



seriously, that shark was 16' long, and I was sitting on the transom of the boat, swapping a lens on my camera, and this girl stuck her head about 4 feet out of the water no less than 3 feet away from me, and just looked right at me.  Then started to slide over and fall back down (that's this shot).

They appear to be quite curious.

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Ichthyic



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(Permalink) Posted: June 12 2007,15:41   

Quote (cogzoid @ June 12 2007,14:59)
I have some questions about sharks as well.

My girlfriend is really afraid of sharks.  We like to surf.  You can already see the problem.  Most of the time she's fine, especially if the water is clear.  Knowing that she has a chance of spotting an approaching shark helps her cope.  But, she's always sort of afraid of sharks.  And we got to brainstorming about ways to diminish attacks.  I remember some "Discovery Channel fact" about sharks having a keen sensitivity to electricity in the water.  How sensitive are they?  Can they be driven away by an annoying amount of electrical signals?  Or will it just attract them?  I'm a pretty hands-on type of guy and I told her I'd be willing to put an electrical device into her surfboard if it'd help keep her mind at ease.  I just want to make sure that I won't turn her into shark bait in the process.

Thanks.

Most of the time she's fine, especially if the water is clear.

yes, note what I was saying in the previous post; once you can see there is nothing "in the dark" that isn't there in the light, the anxiety tends to dissipate.

There is only one way to conquer that, and that is to know exactly what kinds of sharks are in the areas you like to surf, and how likely an attack REALLY is.  99.99% of the time, there really is no significant risk, but there are times and places where it just would not be advisable to shred some tasty waves...

going back to the white shark example, they often come close to shore to hunt pinnipeds in areas where they haul out (for example, the beaches a dozen or so miles north of Santa Cruz, CA).  Since the pinnipeds are only there in numbers at a certain time period (October through March), other times of the year, there is extremely low probability you will run into a white shark in these areas.

familarize yourself with the link to george burgess' site I put in the main post; it will give you the best available information on exactly what the real risks are in your area, and hopefully, armed with the real information, you can overcome any fears you might have.

I remember some "Discovery Channel fact" about sharks having a keen sensitivity to electricity in the water.  How sensitive are they?  Can they be driven away by an annoying amount of electrical signals?  Or will it just attract them?

yes, sharks have sense organs in small pits on their face known as ampulae of lorenzini which are used to detect very small changes in electrical fields typically generated by muscles in fish.  This helps them locate prey items when they are very close to the mouth, as they no longer can see them with their eyes.  Some benthic sharks and most rays also can use this to locate prey items buried in the sand.

There has been debatable success in producing various electronic devices that utilize electrical fields to drive away sharks.  They seem to both attract AND repel.  Sometimes, they will actually attract sharks from a distance, but then when they get closer, will work to repel them.

To the best of my knowledge, most of the sharks that work by ambush or quick-strike of large prey items (makos, whites, sometimes tigers) are not much affected by these things.  However, there is some evidence to indicate they might be effective for smaller species and reef sharks.

the units i examined a few years back were pretty bulky, and mostly designed for divers, not swimmers or surfers.  Mounting one on a surfboard is a novel idea, but the weight of it might tweak the characteristics of the board too much.

things might have changed since the last time I looked, though.  I think there is a link to one or two of the product developers on the wiki page i linked to above.

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PennyBright



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(Permalink) Posted: June 12 2007,16:03   

I can remember seeing sharks at the boston aquarium when I was a tiny girl - I couldn't have been more then 5 years old.   What struck me most - I can still see it in my minds eye - is how "not fish" they looked.   Very very different then anything else I've ever seen.

It wasn't frightening, exactly -- just an intense awareness of difference.  And size -- even through the distortion of the window (curving slightly along the ramp).

Hmm.... googling in another tab, I find that what I remember as the boston aquarium is now called (maybe always was) the New England Aquarium.   And they've got a webcam, on which I have just watched a shark swim past.

http://www.neaq.org/webcams/gotcam.php  - the static cam I can use with my dinky dialup connection.

http://www.neaq.org/webcams/ - the static and streaming cams.

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Lou FCD



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(Permalink) Posted: June 12 2007,16:08   

Okee doke.  I have a few questions...

Is that blood hanging out of her nostril looking thing?  (And what is that structure?  Since they don't breathe air, it seems like there wouldn't be much need for a nostril per se, unless that's their super duper sniffer thing that lets them smell Lou FCDs in the water from miles away... in which case it would seem that sniffers evolved quite a little while ago, seeing as how they have them on the front of their face, just like us mammal types.)

That red stuff in between her teeth is suspiciously reminiscent of the mental picture I have of my own large intestine.  Is that chum or do they always look like they just ate somebody?

What's up with that bite mark looking thing back by where I would guess her gills are?  Is that normal looking, or is that some sort of injury?

How do you know she was a she?  Are reproductive organs that noticeable on sharks?  Or is there some other obvious characteristic of sharks that identifies gender?



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Lou FCD



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(Permalink) Posted: June 12 2007,16:17   

Quote (PennyBright @ June 12 2007,16:03)
Hmm.... googling in another tab, I find that what I remember as the boston aquarium is now called (maybe always was) the New England Aquarium.   And they've got a webcam, on which I have just watched a shark swim past.

http://www.neaq.org/webcams/gotcam.php  - the static cam I can use with my dinky dialup connection.

http://www.neaq.org/webcams/ - the static and streaming cams.

Oh, thanks for that.  I just saw a shark, too!  Creepy.

I recommend broadband if for no other reason...

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Ichthyic



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(Permalink) Posted: June 12 2007,16:28   

Quote (Lou FCD @ June 12 2007,16:08)
Okee doke.  I have a few questions...

Is that blood hanging out of her nostril looking thing?  (And what is that structure?  Since they don't breathe air, it seems like there wouldn't be much need for a nostril per se, unless that's their super duper sniffer thing that lets them smell Lou FCDs in the water from miles away... in which case it would seem that sniffers evolved quite a little while ago, seeing as how they have them on the front of their face, just like us mammal types.)

That red stuff in between her teeth is suspiciously reminiscent of the mental picture I have of my own large intestine.  Is that chum or do they always look like they just ate somebody?

What's up with that bite mark looking thing back by where I would guess her gills are?  Is that normal looking, or is that some sort of injury?

How do you know she was a she?  Are reproductive organs that noticeable on sharks?  Or is there some other obvious characteristic of sharks that identifies gender?


Is that blood hanging out of her nostril looking thing?  (And what is that structure?

possibly, she recently fed so there might have been some "backwash"

:)

you are correct; sharks have nares (nostrils).  also one of the best senses of smell you're likely to find.  can 'smell' blood at the parts per million level.

as to why they are located where they are, it's very much like why you eyes are located on the front of your head; essentially they have "stereoscopic" smell, which allows for better directional location of source.


That red stuff in between her teeth is suspiciously reminiscent of the mental picture I have of my own large intestine.  Is that chum or do they always look like they just ate somebody?


this one had indeed recently just fed, as noted above.  they don't normally look like that.

What's up with that bite mark looking thing back by where I would guess her gills are?  Is that normal looking, or is that some sort of injury?

excellent observation.  It is indeed an injury.  The critters these guys commonly feed on (elephant seals), are rather large and nasty in and of themselves, and most white sharks have scars from where their prey items have managed to get a hit or two in (typically, you will see parallel lines where the claws from the seal dragged across the skin, or puncture marks near the jaw area from bites).

some of the scars are possibly also scars from other white sharks, either from rare scuffles, or mating scars from where males have bitten them to hang on (note that this has not been observed directly in white sharks, but it has for other species).

How do you know she was a she?  Are reproductive organs that noticeable on sharks?

yes, mature males have what are known as claspers:



which are modifications of the pelvic fins which act as essentially double-jointed penises.  they only use one at a time, however.

oh, btw, yeah, sharks all have internal ferilization, though there is quite a large variability in gestation styles amongst the different species.  some are oviparous (lay eggs), some are ovoviparous (hatch egs internally, and give birth to live young), and some are essentially viviparous, much like mammals, some even with what amounts to a placental system.

IIRC, white sharks are ovoviparous, and they also exhibit what is known as "intrauterine cannibalism", meaning that the embryos tend to munch on each other in the womb.

dog-eat-dog from the get-go, basically.

here's a blurb on it:

http://www.elasmo-research.org/educati....ism.htm

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JohnW



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(Permalink) Posted: June 12 2007,16:48   

Quote (PennyBright @ June 12 2007,16:03)
I can remember seeing sharks at the boston aquarium when I was a tiny girl - I couldn't have been more then 5 years old.   What struck me most - I can still see it in my minds eye - is how "not fish" they looked.   Very very different then anything else I've ever seen.

Speaking as a lay person (and expecting a slapping from Ichthyic if I've got this wrong):  "Fish" is not a very helpful term in taxonomy, and while cartilaginous fish like sharks and rays and bony fish like most of the others share a common ancestor, they've been separate groups for an awfully long time.  You and I are more closely related to a mackerel than Ichthy's toothy friend is.  So it's not surprising that sharks look so different.

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Lou FCD



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(Permalink) Posted: June 12 2007,17:00   

Quote (Ichthyic @ June 12 2007,16:28)
possibly, she recently fed so there might have been some "backwash"

:)

you are correct; sharks have nares (nostrils).  also one of the best senses of smell you're likely to find.  can 'smell' blood at the parts per million level.


I thought I had heard that somewhere, and wondered how accurate that was.


Quote (Ichthyic @ June 12 2007,16:28)
as to why they are located where they are, it's very much like why you eyes are located on the front of your head; essentially they have "stereoscopic" smell, which allows for better directional location of source.


Well that makes sense (no pun intended).  So is that a trait passed down from our common ancestor, or is that something that we and they evolved in parallel?  (I can't put my finger on the real biology term at the moment.  Pain killers.)

Quote (Ichthyic @ June 12 2007,16:28)
this one had indeed recently just fed, as noted above.  they don't normally look like that.


I see.  After thinking about it, it also makes sense seeing as how they tend not to use napkins and such.  Barbarians.


Quote (Ichthyic @ June 12 2007,16:28)
excellent observation.


Thanks.  **sticks chest out proudly**

Quote (Ichthyic @ June 12 2007,16:28)
It is indeed an injury.  The critters these guys commonly feed on (elephant seals), are rather large and nasty in and of themselves, and most white sharks have scars from where their prey items have managed to get a hit or two in (typically, you will see parallel lines where the claws from the seal dragged across the skin, or puncture marks near the jaw area from bites).


Oww.  It's a rough world out there, ain't it?

Quote (Ichthyic @ June 12 2007,16:28)
some of the scars are possibly also scars from other white sharks, either from rare scuffles, or mating scars from where males have bitten them to hang on (note that this has not been observed directly in white sharks, but it has for other species).


Geez, talk about rough sex...

Quote (Ichthyic @ June 12 2007,16:28)
yes, mature males have what are known as claspers:



which are modifications of the pelvic fins which act as essentially double-jointed penises.  they only use one at a time, however.


Y'know, if I... nevermind.

Quote (Ichthyic @ June 12 2007,16:28)
oh, btw, yeah, sharks all have internal ferilization, though there is quite a large variability in gestation styles amongst the different species.  some are oviparous (lay eggs), some are ovoviparous (hatch egs internally, and give birth to live young), and some are essentially viviparous, much like mammals, some even with what amounts to a placental system.

IIRC, white sharks are ovoviparous, and they also exhibit what is known as "intrauterine cannibalism", meaning that the embryos tend to munch on each other in the womb.

dog-eat-dog from the get-go, basically.

here's a blurb on it:


Holy cannibalism, Batman!

Again, thanks for sharing.

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Ichthyic



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(Permalink) Posted: June 12 2007,17:23   

Quote (JohnW @ June 12 2007,16:48)
 
Quote (PennyBright @ June 12 2007,16:03)
I can remember seeing sharks at the boston aquarium when I was a tiny girl - I couldn't have been more then 5 years old.   What struck me most - I can still see it in my minds eye - is how "not fish" they looked.   Very very different then anything else I've ever seen.

Speaking as a lay person (and expecting a slapping from Ichthyic if I've got this wrong):  "Fish" is not a very helpful term in taxonomy, and while cartilaginous fish like sharks and rays and bony fish like most of the others share a common ancestor, they've been separate groups for an awfully long time.  You and I are more closely related to a mackerel than Ichthy's toothy friend is.  So it's not surprising that sharks look so different.

yes and no.

even ichthyologists still group both chondrichthians (cartiliginous) and osteichthians (bony fish) under the greater heading of "fish".

but, yes, they did indeed separate hundreds of millions of years ago, and while sharks really haven't changed tremendously since (and not much at all in say, the last 140 million years or so), bony fish have tremendous radiation; around 30 thousand species worth at last count.

morphologically, a typical shark and a typical bony fish do share quite a number of features still, but you indeed could make a good argument that even morphologically, a human would be far closer to a bony fish than a cartilaginous one.

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Lou FCD



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(Permalink) Posted: June 12 2007,17:31   

Quote (Ichthyic @ June 12 2007,17:23)
but, yes, they did indeed separate hundreds of millions of years ago, and while sharks really haven't changed tremendously since (and not much at all in say, the last 140 million years or so),

Well, when you're at the top of the food chain in your ecosystem...

"Don't mess with success" and all that.

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Ichthyic



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(Permalink) Posted: June 12 2007,17:39   

yeah, they must have had a meeting where they and the crocs simply said:

"enough is enough; we're plenty fine as is.
screw the rest of you liberal progressives!"

;)

actually, though, the whole "maintaining form" issue has been a hot one in evolutionary biology for decades.

not my area of expertise, but there are plenty of sites that cover the issue, and lots of good papers on the subject out there.

it's covered under the heading:

evolutionary stasis.

here's an example:

http://72.14.253.104/search?....5&gl=us

I think Wes has dabbled in this area as well.

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Lou FCD



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(Permalink) Posted: June 12 2007,18:47   

Quote (Ichthyic @ June 12 2007,17:39)
it's covered under the heading:

evolutionary stasis.

here's an example:

http://72.14.253.104/search?....5&gl=us

I think Wes has dabbled in this area as well.

I'm wading in...  I'm sure I'll be back with questions...

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Lou FCD is still in school, so we should only count him as a baby biologist. -carlsonjok -deprecated
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skeptic



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(Permalink) Posted: June 12 2007,18:48   

Quote (Stephen Elliott @ June 12 2007,14:42)
I would like to ask a question. More about you Ichy than sharks really. Do you not get the feeling of fear when viewing them whilst in the water?

I have only ever encountered sharks twice while in their habitat (I am not counting seeing them in an "aquarium" here). Both times I experienced an irational fear that was a tad uncontrolable. I know they are unlikely to atack, I had a clue how the odds stacked, yet upon seing them I was afraid. Did they not "bother" you at all?

EDIT: Don't get me wrong here. They did look cool as Hell and I loved having seen them in the wild in retrospect. Just that at the time I was scared.

Kinda piggy-backing on Ichy's comment...at 14 I was scuba diving off the south coast of Jamaica and while descending down a reef face I sat square on the back of a hovering 10 ft bull shark.  He barely noticed me and glided away and I was utterly amazed.  I just floated there and watched him unable to move.  It was truely captivating.  Needless to say, my father was about 20 yds went into full meltdown and physically hauled me back to the boat.  It wasn't until a day or two later that the realization hit me that the shark could have turned right around and tore me apart in a split second.  Strangely, I still look back at that with more awe than anything but now that I'm a father, given the same circumstances, I would probably act the same as my Dad did.

  
skeptic



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(Permalink) Posted: June 12 2007,18:56   

Quote (Ichthyic @ June 12 2007,15:10)
As a first year grad student at Berkeley, I spent my first field season (3 months) at the research station Berkeley owned on the island of Moorea, which is a short hop from Tahiti in French Polynesia.

You've got to be kidding me!!  This sure makes my research lab look like a prison sentence.

  
Ichthyic



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(Permalink) Posted: June 12 2007,19:07   

Quote
 It wasn't until a day or two later that the realization hit me that the shark could have turned right around and tore me apart in a split second.


actually, at 10' it would have taken quite a few minutes for a bull shark to accomplish the task.

I'm visualizing it as I write this...

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stevestory



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(Permalink) Posted: June 12 2007,19:16   

I didn't know whales could be 100-200 years old.

   
Ichthyic



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(Permalink) Posted: June 12 2007,19:19   

sharks live a long while too, larger white sharks are commonly thought to reach ages well over 30, and some think as old as 80 or more.

don't know about 200 though.

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Tom



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(Permalink) Posted: June 12 2007,22:23   

Quote
I think it's just all those nasty looking teeth.

And the fact that they're (for all intents and purposes) invisible... until they eat me.

I'm not so scared I don't go to the beach or swim in the ocean, but I'd have serious doubts about taking a swim from a boat on the ocean, even if I could see the shore line.


A few months ago I finished the book "Oceans of Kansas" and after reading it, I wonder if some of the creatures that swam our oceans back then were alive today, would anybody go for a swim in the ocean?  If I knew that liopleurodon or megalodon was somewhere out there cruisin around the oceans, not only would I not go swimming, you couldn't get me on a boat(call me a whimp).

By the way Ichthyic, thanks for putting this thread together.  A very fascinating field of work that you are involved in.  The Discovery Channel's Shark Week gave me a lot of information that I didn't know about sharks and I can see why people like to study them.

  
Ichthyic



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(Permalink) Posted: June 12 2007,22:29   

heh, the guy I used to work with at PSRF is often featured on Shark Week.

look for episodes on white sharks, and if they show the work being done in CA, you likely will catch at least a glimpse of Sean Van Sommeran.

Quote
A few months ago I finished the book "Oceans of Kansas" and after reading it, I wonder if some of the creatures that swam our oceans back then were alive today, would anybody go for a swim in the ocean?


How's that saying go?

It's not the size, but the motion?

You could have a Charcaradon 10 times the size of carcharias, but if it wasn't interested in small mammals, I doubt it would cause me much anxiety.

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PennyBright



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(Permalink) Posted: June 13 2007,09:33   

Quote (Ichthyic @ June 12 2007,17:23)
   
Quote (JohnW @ June 12 2007,16:48)
 
Speaking as a lay person (and expecting a slapping from Ichthyic if I've got this wrong):  "Fish" is not a very helpful term in taxonomy, and while cartilaginous fish like sharks and rays and bony fish like most of the others share a common ancestor, they've been separate groups for an awfully long time.  You and I are more closely related to a mackerel than Ichthy's toothy friend is.  So it's not surprising that sharks look so different.

yes and no.

even ichthyologists still group both chondrichthians (cartiliginous) and osteichthians (bony fish) under the greater heading of "fish".

but, yes, they did indeed separate hundreds of millions of years ago, and while sharks really haven't changed tremendously since (and not much at all in say, the last 140 million years or so), bony fish have tremendous radiation; around 30 thousand species worth at last count.

morphologically, a typical shark and a typical bony fish do share quite a number of features still, but you indeed could make a good argument that even morphologically, a human would be far closer to a bony fish than a cartilaginous one.



This is why I hang out here.   Straightforward informative dialog about things that are interesting.  I think I've learned more about everything lurking around you EvC folks then I ever did in school.

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Ichthyic



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(Permalink) Posted: June 13 2007,13:10   

Quote
I think I've learned more about everything lurking around you EvC folks then I ever did in school.


scary thought.

;)

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Stephen Elliott



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(Permalink) Posted: June 13 2007,13:53   

Quote (Ichthyic @ June 12 2007,14:48)
...
I learned to scuba dive when I was about 15.

I noticed an immediate difference in "comfort" levels between when I was underwater as opposed to on top of the water...

when you are snorkeling, you can only really look down, and with low visibility, you often can't see the bottom.

that can be unnerving;  the same can be said when you are in a boat - you can't see the bottom, so it's like being in the dark - you just don't "know" what could be down there.

However, when you are UNDER water, scuba diving, all that anxiety disappears, as just like on land, you are now able to see 360 all around, just by turning your head.  No more not knowing what is beneath you.

anywho, I would recommend if you want to rid yourself of a fear of sharks, you might actually want to take up scuba diving...

I would agree with that (from my limited experience). Seeing a shark while snorkelling was much scarier than when diving.

Have you dived off Belize Ichy? If not, I am pretty sure that you would love it. The barrier reef is spectacular it was like swimming in a fish tank the sea life being so crowded (at least it was [spectacular], I have heard that it has suffered a lot since I was last there), you would love the blue hole (never dived that myself as I was no-way competent enough).
http://ambergriscaye.com/pages/town/greatbluehole.html

Anyway, as a shark lover Belize would delight you.

  
Ichthyic



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(Permalink) Posted: June 13 2007,14:04   

I've been diving in the Carribean, but only around the Mexico side (like Cozumel).

also the Pacific side of Mexico, much of the Pacific coast from Guerro Negro to British Columbia, several places in the Gulf of CA, most of the Channel Islands off of CA, and French Polynesia.  done several river/stream dives too, looking at salmon runs in WA and British Columbia (Vancouver Island).

Belize has always sounded appealing, just never made it there yet.

I had high hopes of doing some research in New Guinea as well, but after World Wildlife Fund moved in there and took over all the local research facilities, it became a lot harder to get anything done.

Next will be exploring the reef and shark situations in NZ, I think.

There are several already established groups down there I'm trying to plug in to.

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Stephen Elliott



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(Permalink) Posted: June 13 2007,14:20   

Quote (Ichthyic @ June 13 2007,14:04)
...
Belize has always sounded appealing, just never made it there yet...

Try to get there. It is a long time since I was in that country but it was (in my time) pretty cheap for Americans. The rental/hire costs where a fraction of what you paid in the USA and the opportunities where fantastic.

As you know, most marine life is around barrier reefs and Belize had the 2nd largest in the World but with only a small human population. Then the Blue Hole.

If you got bored with that (fat chance) there are the Mayan ruins to see and unspoilt rainforrest.

Oh, and some of the Worlds best game fishing. Blue Marlin/sailfish/swordfish, sharks, baracuda. Best of all (for me) the dolphins. Damn but dolphins (in the wild) are cool.

  
Ichthyic



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(Permalink) Posted: June 13 2007,17:17   

well hell, let's go!

got any contacts left in that part of the world?

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PennyBright



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(Permalink) Posted: June 13 2007,17:46   

Quote (Ichthyic @ June 13 2007,13:10)
 
Quote
I think I've learned more about everything lurking around you EvC folks then I ever did in school.


scary thought.

;)

Yup.    

Of course, that may speak more to my spotty school experiences (moving 20 some times between the ages of 6 and 16,  hopscotching from grade to grade and frequently flat out skipping parts of some years in the process)  then to the quality of public education.  

Out of curiousity - this isn't exactly a shark question - do the anoxic zones from phytoplankon overgrowth have any bearing (yet?) on shark populations.... I know that as an apex predator the effect would be indirect,  and I would guess limited to shark populations that stay pretty much in one region (coastal and estuarine sharks?).    I guess to be more precise, I'm asking if the dead zones are severe enough to be affecting shark populations -- if that's being studied at all.  And if this isn't one of those "so wrong it's not even wrong" kinda questions.

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Ichthyic



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(Permalink) Posted: June 13 2007,17:54   

anoxic zones due to phytoplankton (or dinoflagellate) blooms are relatively common seasonal occurences in a lot of places.

did you have something specific in mind?

I'm not sure exactly what you're getting at.

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PennyBright



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(Permalink) Posted: June 13 2007,18:13   

Hrm.  I don't know enough about what I am asking about to know if it's a sensible question,  much less how to ask it more clearly.

I was reading this recently:  http://daac.gsfc.nasa.gov/oceancolor/scifocus/oceanColor/dead_zones.shtml

and you got to talking about sharks as apex predators,   and I was just wondering if the habit destruction that I was reading about was wide spread and/or serious enough to be affecting shark populations.    I wouldn't think that it is -- but I'm no expert.  I'm no anything, really,  other then a very curious avid reader.    So I thought I'd ask.

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Ichthyic



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(Permalink) Posted: June 13 2007,18:17   

I'll take a look at the link.

ah.  yeah, what you're talking about is unnatural hypoxia that is essentially the same as what I was talking about, but on larger and constant scales.

Yeah, the gulf of Mexico has had that problem for decades as a result of nutrient rich effluent from the Mississippi river.

It affects everything, not just predators.

when a hurricane or even a strong wind occurs in areas that are extremely eutrophic, the upwelling of the anoxic water can cause massive dieoffs.

yes, it's been a problem for many many years, in a great variety of not just coastal waters, but lakes and rivers too.  

and yes, the vast majority of the problem comes from the vast overuse of fertilizers in the agricultural industry.

US government agencies have been extremely slow to change the rules that subsidize farmers for using way too much fertilizer to begin with.  I know that other countries, like NZ, have indeed been working on controlling effluent from all agriculture/farming industries into their watersheds, but the problem is so large and so ubiquitous to just about every country on the planet, that I don't see the efforts amounting to significant change in my lifetime.

Most consider the pollution of waterways with nitrates and phosphates perhaps to be the largest issue for water quality on the entire planet.

However, as one success story, the gradual eutrophication of lake Tahoe in CA is now being reversed successfully, so with effort and the right subsidies, it's clear that reversing the over-usage of fertilizers and other ag chemicals could eventually have an impact on larger scales.

btw, eutrophic is "nutrient heavy" vs. oligotrophic, which is nutrient poor.

this really is a much broader issue than just sharks; it affects all of us directly, especially considering the issue doesn't just affect large-scale coastal environments.

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Ichthyic



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(Permalink) Posted: June 13 2007,19:04   

btw, I mentioned Sean Van Sommeran earlier.

well, Jeff Corwin paid a vist a while back, and I think that episode just so happens to be airing right this very instant on the animal planet channel.

5pm pacific time.

he's in South Africa in the beginning of that episode, but IIRC, he ends up right where we were working in CA.

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Lou FCD



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(Permalink) Posted: June 13 2007,19:26   

Quote (Ichthyic @ June 13 2007,19:04)
btw, I mentioned Sean Van Sommeran earlier.

well, Jeff Corwin paid a vist a while back, and I think that episode just so happens to be airing right this very instant on the animal planet channel.

5pm pacific time.

he's in South Africa in the beginning of that episode, but IIRC, he ends up right where we were working in CA.

Heh.  "Planet Earth"?  I happen to be watching it, purely coincidence.  I missed the first few minutes of it, though.

Mama whale is starving at the moment.  :(

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Ichthyic



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(Permalink) Posted: June 13 2007,19:29   

nope, that's discovery channel.

it's the other one:

Animal Planet.

the show I believe is called "The Corwin Experience"

he goes around the world ala croc hunter, but actually does touch on some science from time to time.

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Lou FCD



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(Permalink) Posted: June 13 2007,19:46   

Ack, it's that east coast west coast satellite thing.  I'm watching Planet Earth on Animal Planet and a great white shark is currently eating a seal about four or five feet above the water's surface...

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Ichthyic



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(Permalink) Posted: June 13 2007,19:54   

fascinating coincidence.

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Steviepinhead



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(Permalink) Posted: June 13 2007,19:59   

Another cool thing about sharks is how well they've adapted to pool halls.

  
Lou FCD



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(Permalink) Posted: June 13 2007,19:59   

Mama and baby humpback made it safely to the Arctic and are feeding like MAD WaLEzzzz on krill.  FYI, in case anyone was worried about them...

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Lou FCD



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(Permalink) Posted: June 13 2007,20:01   

Quote (Ichthyic @ June 13 2007,19:54)
fascinating coincidence.

Indeed.  They just replayed in slow mo the shark breaching the water with the seal in its mouth.

Cool shot.  It took them a month of shooting to get that shot.

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Lou FCD



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(Permalink) Posted: June 14 2007,07:52   

In other shark news...

Ga. Aquarium Probes Whale Shark's Death


Quote
ATLANTA (AP) -- Georgia Aquarium officials say it may be months before they know what caused Wednesday's death of another whale shark, the second this year at the only facility outside Asia that displays the huge, rare fish.

Norton's death also came only a few weeks after two new whale sharks arrived at the aquarium from Taiwan. At the time, Taiwan fishery officials had said they were satisfied the aquarium provided the quality care the young whale sharks - named Yushan, which means "Jade Mountain" and Taroko, named after a national park in Taiwan - would need.

Aquarium officials planned a necropsy Wednesday afternoon for Norton. His death came five months after the death of Ralph, another whale shark that was among the aquarium's first stars after it opened in 2005.


More at the above link...

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J-Dog



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(Permalink) Posted: June 14 2007,11:13   

Sharks, and why some of us are interested in them...



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Ichthyic



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(Permalink) Posted: June 14 2007,12:15   

Quote (Lou FCD @ June 14 2007,07:52)
In other shark news...

Ga. Aquarium Probes Whale Shark's Death


 
Quote
ATLANTA (AP) -- Georgia Aquarium officials say it may be months before they know what caused Wednesday's death of another whale shark, the second this year at the only facility outside Asia that displays the huge, rare fish.

Norton's death also came only a few weeks after two new whale sharks arrived at the aquarium from Taiwan. At the time, Taiwan fishery officials had said they were satisfied the aquarium provided the quality care the young whale sharks - named Yushan, which means "Jade Mountain" and Taroko, named after a national park in Taiwan - would need.

Aquarium officials planned a necropsy Wednesday afternoon for Norton. His death came five months after the death of Ralph, another whale shark that was among the aquarium's first stars after it opened in 2005.


More at the above link...

It's typical that pelagic sharks like whale sharks, makos, blues, etc. tend to do poorly in aquaria.

many pelagic fishes have problems in confined spaces; they simply aren't used to having vertical structures like walls around.

At the Monterey Aquarium, they tried to put blue sharks into their huge "pelagic" tank (35x40x30 - or thereabouts), but never got them to survive for long either.  Several experiments there and at other aquaria with white sharks have ended in similar failure.

also, tuna captured and placed in the tank sometimes had problems adjusting, and when excited, would run into the glass walls at full speed (around 35 miles an hour), essentially exploding on impact.  I don't remember the exact percentage, but the majority managed to adjust ok, unlike the sharks.

It's possible that given enough effort and enough animals, some individual sharks would be found that would adjust, just like with the tunas.

I'm a bit torn about that.  The educational value to the public of zoo exhibits can't be argued against, but when repeated attempts to keep an animal in captivity result in its demise, I gotta think that waiting until we learn more about them in the field is likely warranted.

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khan



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(Permalink) Posted: June 14 2007,13:01   

Quote
The critters these guys commonly feed on (elephant seals),


Interesting thought occurred to me:

Sharks swimming around essentially unchanged for many millions of years while their food supply slowly evolves.

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Stephen Elliott



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(Permalink) Posted: June 14 2007,13:08   

Quote (Ichthyic @ June 14 2007,12:15)
...The educational value to the public of zoo exhibits can't be argued against, but when repeated attempts to keep an animal in captivity result in its demise, I gotta think that waiting until we learn more about them in the field is likely warranted.

I feel similarly. In some ways it is a shame to see such creatures in captivity. OTOH the educational value is enormous and I feel almost certain that if done well, public interest in study and conservation can be increased.

It is bottle nosed dolphins that realy capture my atention. The Sea world parks are probably the most humane places I have seen them in captivity but it is nowhere near as magnificent as viewing them in their own natural habitat. However, if keeping a relative few in captivity raises awareness and persuades people that they are worth saving I supose it is worthwhile.

  
Ichthyic



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(Permalink) Posted: June 14 2007,13:22   

Quote
Sharks swimming around essentially unchanged for many millions of years while their food supply slowly evolves.


...and yet still plenty efficient.

yup. it's a puzzler, but there are several issues involved here.

If you are thinking in terms of co-evolution of predator/prey, you have to wonder just how strong of a selective pressure on mammalian prey items are large predators like sharks and crocs?

crocs are entirely ambush predators, and the only times they contact large mammals are when they are near water, which is very periodic and relatively rare for most of them, on a diurnal basis (you only need to go near the water to grab a drink).

so I would guess that crocs simply aren't a significant selection pressure for mammals to evolve in response to, as opposed to say, lions, in the same general area.

similarly for elephant seals, white sharks only can take advantage of them at certain times of the year, when they are concentrated on haul out spots, and pups are available. (the pups are the preferred food items, though they will occasionally go after adults)

so again, given the relative rarity of white sharks, and the limited effect they would have on elephant seal populations, it seems plausible that they might not be a major selective pressure source.

Ok, i grant, that's a very specific case scenario, so let's take a broader look at the two predators;

most sharks are NOT specialists; they are entirely opportunistic, and will often eat a variety of different protein sources.  white sharks will feed on fish when available, and mammals when available.  blue sharks fish and squid, for another example.

crocs are the same way.

so again, the co-evolutionary ties are weakened between these predators and any specific food source.

then we get into the idea of "evolutionary constraints", the application of which has been attempted in cases like sharks and crocs numerous times, but I haven't seen much conclusive yet.  

as i mentioned, the evolution of sharks isn't really my area of expertise; but I think reading the paper i referenced earlier wrt evolutionary stasis might be helpful.

heh.

now you know why it's still a hot topic.

thanks for the feeback, the questions and comments in this thread have rekindled my own interest in the topic.

oh, and a final note...

yes, it's true that generally, sharks haven't changed a lot in the last ~100 million years or so, but that doesn't mean they haven't developed some new tricks, either.

many of the pelagic sharks that rely on widely distributed and patchy food resources (like makos and white sharks, for example), have developed a heat exchange system that allows them to keep large sections of their swimming muscles considerably warmer than ambient water temperature; this allows them far more efficient use of energy (tuna and billfish have a very similar system).  IIRC, it has been proposed this is a "relatively" recent evolved trait, but since sharks are cartilaginous, a lot of that is inferred from phylogeny.

doug long would know a lot more about the evolution of that trait in sharks than I would, but I could go into gory detail about how the system works and the anatomy of it, if anybody is interested.

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Stephen Elliott



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(Permalink) Posted: June 14 2007,13:29   

Quote (Ichthyic @ June 13 2007,17:17)
well hell, let's go!

got any contacts left in that part of the world?

Unfortunately no I haven't. It is aproaching 15 years since I was last there. I did 6 months from Aug 87 and again from June 92. Thanks to google it is easy to get information "on t'internet".

The country was facing large changes on my 2nd time around. Drugs and related violence was on the increase run by gangs affiliated to your bloods and krips plus larger USA style hotels where begining to pop up. On the plus side the government where begining to take conservation seriously.

  
BWE



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(Permalink) Posted: June 15 2007,02:30   

we've had some pretty severe hypoxic zones off the central oregon coast over the last few years. Some of it might be due to currents shifting and upwellings but phosphorus is becoming the limiting factor in algal production rather than nitrogen which means that the trend may become more pronounced over time because typically there's a lot more phosphorus than nitrogen in the water. Fertilizer is one culprit but there are some complicated things going on down there. And yes, the fish die. Actually, the dungeness crabs were washing up into tidepools. F&W and OSU have some people studying it but I don't know if there are any real conclusions.

Sorry to hijack the thread there Icthyic, back to sharks.

BTW, sharks are fish. Did someone ask that or was that somewhere else?

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Ichthyic



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(Permalink) Posted: June 15 2007,02:42   

no worries.

yeah the fertilizer problem is ubiquitous and nasty.

don't see great changes occurring in a positive direction in the near future either.

another reason to move to NZ.

they've actually passed legislation to attempt to curtail the farming industry effluent into the local watersheds.

I was just looking into that a few months back.

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BWE



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(Permalink) Posted: June 15 2007,02:56   

I'd come with you if I could. It's a long way off though.

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Ichthyic



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(Permalink) Posted: June 15 2007,21:29   

yeah, about as far as one can get from the west coast of the US.

I'm just hoping it's far enough.

I'll scout it out for ya.

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Renier



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(Permalink) Posted: June 20 2007,01:40   

Ichthyic, thanks a million for this thread. I love sharks. I even have a collection of fossilised White's teeth Blue-grey colour).

I often do spear fishing here in the Western Cape (South Africa). I have been spear fishing all my life and have never ever ever seen a Great White (or other dangerous shark, such as the Zambezi and Tiger sharks in the warmer waters) while spear fishing.

About four years ago I went to Gansbaai for a cage dive. Conditions were bad, South Easter howling and the swell at about 4 to 5 meters. Visibility on the open sea at about 4.5 meters, less than 1.5 meters in the tidal zone. Since the cage was connected to the boat via ropes, it was shaking like mad, making photography very difficult. I did however get two acceptable underwater photos of a White. The average Whites we saw was between 3 and 4 meters. However, at one stage, a White passed under the boat. It looked like a friggin submarine. It was about 6 meters, maybe even 6.5.

The bloke who owned the boat (he was also the skipper) claimed that he did spear fishing even though there are Whites around. His reasoning was that if you see a White, you should be safe because he is in "scavenging" mode. If the White wanted to eat you, he would hit you at high speed without you even realising it was there. A while after my cage dive adventure I saw the nutcase in a diving/nature magazine. They had a photo of him touching a white on the nose, in open water, without a cage. He had is speargun in the other hand... and I thought the dude was lying.

  
Ichthyic



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(Permalink) Posted: June 20 2007,02:37   

3 m is very small (likely male), 6.5 is absofriggin' gigantor.

largest I ever saw was a 5.5 meter female, out of about 20 or so separate individual observations.

6.5 is right up there with some of the largest ever officially recorded.

I too had the same impression the first time I saw a really large white swim under our boat (which was smaller than the shark, btw):  it doens't look like a fish, damnit!  more like a whale, or yeah, a submarine.

 
Quote
His reasoning was that if you see a White, you should be safe because he is in "scavenging" mode.


that's some pretty poor reasoning based on false assumptions, IMO.  

I know some of the folks that work on white in SA, and, just like the ones we worked on in CA, these were rarely "scavengers" (as there is rarely large meat sources to scavenge on) and were far more often actively hunting large marine mammals.  However, he is right about the ambush thing, as that is what we sometimes have observed when they hunt elephant seals.

plus, given their apparent curiosity about unique things in their environment, I personally would always think it a risky thing to dive with one.  You simply never know when one might decide to take a bite to see what you are, like a baby sticking a rubber ball in its mouth.

of course, there is some evidence that if you show "awareness" of the shark's location, they tend to back off a bit.  Not an easy thing to do, though, unless you are specifically looking for them to begin with.  Also the thing where you touch them on the nose is a common observation as well.  You will often get them to raise their head out of the water with their mouth agape if you press the palm of you hand on the end of their snout (you being on a boat and the shark swimming by at the surface).  It's probably an automatic response.

most divers that are attacked in CA are urchin or abalone divers, who are completely preoccupied with their work (the friend i mentioned on the scooter is an uncommon exception).  Surfers are also occasionally attacked, but the silhouette of a surfer on the surface looks remarkably like that of a sea-lion or elephant seal.

of the sharks you mentioned, the Zambezi (actually is correctly known as the bull shark), is the one most known to attack humans.  Both the bull and the tiger sharks, when they attack, typically do more damage than a white shark, as they often come back for repeated attacks.  IOW, it looks like in cases of fatalities with these species, they indeed were feeding, and were not just cases of mistaken identity or investigatory behavior.

The problem with whites, is that they are just so damn big and strong, and their teeth concurrently big as well, that even when they are just investigating, they tend to do a lot of damage to soft fleshies like humans.

bottom line, I wouldn't worry too much about whites while spearfishing, simply because they really aren't all that common, and they typically wouldn't be much interested in the kinds of fish typically speared around reefs.

You can check with the SA shark research groups to find out what times and places the marine mammals in your area tend to haul out on the beaches for mating or pupping.  I would tend to avoid these areas to minimize your risk.

oh, btw, I would mention that there is a great difference in cage diving rules here off of CA vs. in SA, and the issue has been one of tremendous contention over the years here.

more on that story if you wish.

Quote
I even have a collection of fossilised White's teeth Blue-grey colour).


heh.  my collection of fossil shark's teeth contains mostly everything BUT Charcaradon spp.

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Renier



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(Permalink) Posted: June 20 2007,08:10   

Quote
largest I ever saw was a 5.5 meter female, out of about 20 or so separate individual observations.


We had about 8 individual sharks around the boat that day. I don’t have a source but I recall hearing that Gansbay has the world’s most concentrated Great White population. I will check on the details.

Quote
that's some pretty poor reasoning based on false assumptions, IMO.  

I know some of the folks that work on white in SA, and, just like the ones we worked on in CA, these were rarely "scavengers" (as there is rarely large meat sources to scavenge on) and were far more often actively hunting large marine mammals.  However, he is right about the ambush thing, as that is what we sometimes have observed when they hunt elephant seals.


I remember they chummed the water and had a cut-out rubber seal and a rope with half of a smaller shark (not a White!) in the water. The sharks would spot the fake seal and swim closer. The fake seal the got hauled in closer to the boat until the shark came close to the piece of meat (shark meat) in the water. At that stage the bait got hauled closer to the boat with the shark following the bait. At one stage, a White popped his head out of the water. The skipper touched his nose and the White went into a sort of trance and after about 5 seconds just slipped back into the water. I don’t know why this is but I suspect it is an over stimulation of those little organs on the nose that picks up electric signals. Hmmm… does this mean the shark pods are like drugs to them… Just kidding.

Quote
plus, given their apparent curiosity about unique things in their environment, I personally would always think it a risky thing to dive with one.  You simply never know when one might decide to take a bite to see what you are, like a baby sticking a rubber ball in its mouth.


Agreed. The whole “tasting” thing we call “mouthing”. For this reason we try and avoid dirty water (poor viz) like the plague. We were once diving at Rooi-els and got scared sh*tless by a Sea-otter. It was playing with a piece of kelp but made such a splash that we thought a White just got hold of a seal. Talk about paranoid.

Quote
of course, there is some evidence that if you show "awareness" of the shark's location, they tend to back off a bit.


Sounds interesting. A fellow diver told me a story of a shark attack that he witnessed. They were spear fishing of Wilderness area, around a huge rock peninsula when a diver spotted a White and raised alarm. I am not sure how many divers they were but I recall a figure of eight. They sort of grouped together in a circle and tried to locate the shark. The shark (White) came out of nowhere, really fast, and took a diver. He bit (mouthed) the poor bloke and then just left. The freaky thing is the shark swam past two other divers to get the bloke. The dude was injured but survived.

Quote
of the sharks you mentioned, the Zambezi (actually is correctly known as the bull shark), is the one most known to attack humans.


Bull shark. Yeah mate, if you’re an Aussie! Lol. Zambezi sharks are locally known as the bullies of the sea. Maybe they are territorial and that would explain their aggressive behaviour? I have an old book with Shark attacks recorded in South Africa. Most of them are Zambezi attacks. The freaky thing is that Zambezi sharks has a high tolerance of fresh water ( I know you know that, just info for lurkers). The record inland attack was 2000km inland (river) by a Zambezi Shark (Must double check on source).

Quote
Both the bull and the tiger sharks, when they attack, typically do more damage than a white shark, as they often come back for repeated attacks.


That also struck me. I know of only 2 White attacks where the shark returned and actually ate the victim. 1966, Theo Klein at Buffels Bay, close to Cape point and another one, about two years ago, at Fishhoek. We often dive Buffels Bay and Fishhoek looking for Yellowtail.

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The problem with whites, is that they are just so damn big and strong, and their teeth concurrently big as well, that even when they are just investigating, they tend to do a lot of damage to soft fleshies like humans.


Yes, being punctured by a razor sharp row of teeth of what, about 5cm each, is going to do some damage. Speaking of sharp. I have another little shark tooth I wear around my neck (not a fossil). Its small, about 1cm long, but it takes the hair off my forearm like a razor. I love demonstrating it to people.

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bottom line, I wouldn't worry too much about whites while spear fishing, simply because they really aren't all that common, and they typically wouldn't be much interested in the kinds of fish typically speared around reefs.


Agreed. The local fish thieves are Raggedtooth sharks that steals the captured fish off the stringers. I don’t really mind, it’s like paying hunting tax. Raggies look fierce and have long tearing (not cutting) teeth. Years ago people attributed attacks to Raggies when it was actually Mako sharks.

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You can check with the SA shark research groups to find out what times and places the marine mammals in your area tend to haul out on the beaches for mating or pupping.  I would tend to avoid these areas to minimize your risk.


Great idea. Thanks.

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oh, btw, I would mention that there is a great difference in cage diving rules here off of CA vs. in SA, and the issue has been one of tremendous contention over the years here.


I’d like to hear! I am aware of some debate over here about cage diving. Some people reckon that baiting the water is going to make Whites think we are food, since the chum and humans will be associated. I don’t know how accurate this is, but my opinion is that cage diving will do a lot for the conservation of Whites.

Now, a question for you. I cannot help but notice that a White and a Mako looks very very similer, but that their teeth differs radically, as sharks go. Any studies as to a common ancester link between the two you could refer me too?

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heh.  my collection of fossil shark's teeth contains mostly everything BUT Charcaradon spp.


I was walking down the road at Camps bay when I notice a hippie dude with an old brown vw combi. He had an array of shark fossils. I only had 40 Rand (8US$) so I bought two White’s fossils. However, he also had another fossil tooth on sale there, a Megalodon. As big as my hand. Pity, I did not have enough bucks on me to purchase it.

  
Louis



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(Permalink) Posted: June 20 2007,10:27   

I suppose I can relate my tiny shark experience here, just FYI. Even in the UK we get sharks, where I am from originally (Dorset coast) we get two species: Porbeagle sharks and Basking sharks.

I have never seen Porbeagles in the wild but I have snorked off a boat and come a lot closer to a young Basking shark than I ever thought I would. I know they are harmless filter feeders but I got out of the water in precisely the same way an ICMB gets out of a submarine (i.e vertically and "rocket" powered) when I saw at the edge of my underwater vision a huge shark with a massive mouth heading roughly in my direction (actually, it was diagonally off to my right hand side, but I could still see the mouth).

Coward when it comes to large cartilagenous fish? Yup!

Louis

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J-Dog



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(Permalink) Posted: June 20 2007,13:42   

Quote (Louis @ June 20 2007,10:27)
I suppose I can relate my tiny shark experience here, just FYI. Even in the UK we get sharks, where I am from originally (Dorset coast) we get two species: Porbeagle sharks and Basking sharks.

I have never seen Porbeagles in the wild but I have snorked off a boat and come a lot closer to a young Basking shark than I ever thought I would. I know they are harmless filter feeders but I got out of the water in precisely the same way an ICMB gets out of a submarine (i.e vertically and "rocket" powered) when I saw at the edge of my underwater vision a huge shark with a massive mouth heading roughly in my direction (actually, it was diagonally off to my right hand side, but I could still see the mouth).

Coward when it comes to large cartilagenous fish? Yup!

Louis

That's got to be tough for them, trying to sneak up on people... did the cello music give it away?

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Ichthyic



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(Permalink) Posted: June 20 2007,15:33   

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Bull shark. Yeah mate, if you’re an Aussie! Lol.


or US or South America.  I should more clearly have said a zambezi is a bull shark is:

Carcharhinus leucas  which is of course, a great example of why scientists use latin names to describe species.

:)

and yes, they not only are euryhaline in South Africa, they also are found in estuarine and riverine habitats in most locations they are found.  there's a nice wiki on them:

http://en.wikipedia.org/wiki/Bull_shark

 
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Maybe they are territorial and that would explain their aggressive behaviour?


hmm, I'm not sure I buy into that; most of the attacks in fresh water suggest they really are hunting for food.  Could be a case of mistaken identity, but again, a lot of those attacks involve multiple bites.  Some have suggested they are more aggressive in fresh water, but I also don't buy that, as it just seems more likely to me that where these attacks occur in freshwater, there are simply a lot higher concentration of people actually in the water, so you get a higher frequency of attack.


 
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I am not sure how many divers they were but I recall a figure of eight. They sort of grouped together in a circle and tried to locate the shark. The shark (White) came out of nowhere, really fast, and took a diver.


yeah, again, they didn't know where the shark was.  I've seen many videotapes of dives where when the divers could see where the shark was, and turned to face it, the shark would go into circling behavior instead of attack behavior, and often would move off.

sharks aren't invulnerable; especially ones that feed on large prey items like elephant seals.  We've seen whites with missing eyes and huge numbers of scars on occasion.  Even one missing eye can put a serious damper on prey location.  of course nothing is absolute, and while we often see whites hit once (hard) and then circle to allow for ensanguination, we also infrequently see them just going all out and chomping the prey to bits in rapid fashion.

lots to learn still.


 
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Years ago people attributed attacks to Raggies when it was actually Mako sharks.


Mako's typically feed on large pelagic fishes, but again, sharks being typically opportunistic, I've seen video of them feeding on marine mammals as large as full-grown bottlenose dolphins.  Amazing stuff - they would hit the tail of the dolphin full-speed to immobilize it and cause severe ensanguination, then come back to feed on it.

We know even less about mako behavior than we do about whites, mostly because they're pelagic, and large ones might be almost as rare these days as whites (they are a great food and sport fish, and so many have been taken by the longline and gill net fisheries that large ones have become quite rare).

A friend of mine has been studying a close relative, the Salmon Shark (Lamna ditropis) for some time now.

 
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I cannot help but notice that a White and a Mako looks very very similer, but that their teeth differs radically, as sharks go. Any studies as to a common ancester link between the two you could refer me too?


yes, there has been some work on this area, and I have those references, but not ready to hand.  give me a couple of days to dig them up for you.  They do belong to the same family:  Lamnidae.  However, I recall a tremendous amount of controversy surrounding whether the linneages are actually based on a common ancestor.  also a lot of controversy around whether megalodon is actually an ancestor of carcharias or not, which is related to the same issue.



 
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I’d like to hear! I am aware of some debate over here about cage diving. Some people reckon that baiting the water is going to make Whites think we are food, since the chum and humans will be associated. I don’t know how accurate this is, but my opinion is that cage diving will do a lot for the conservation of Whites.


The opinion of all the scientists around CA is that cage diving would only contribute to the observation of aberrant behavior, like feeding bears at Yellowstone park.  We were part of writing up and pushing legislation in CA protecting white sharks, and that included a provision for anybody wanting to get close to the sharks to apply for a special permit to do so.

Oh yeah, we had some knock-down drag-out fights with the  sport diving operations that wanted to have unlimited cage diving, but after MANY MANY meetings over a couple of years time, most of them realized that to begin to really understand these animals, we couldn't have thousands of cage diving operations in the only areas that existed to really study the animals.  Moreover, as I recall the state liability experts (read: lawyers), made the standard arguments about safety and cost issues, and managed to show the sportdivers that if they wanted to proceed to gain permits to cagedive, then the state would have to implement a strict liability insurance program.

can you guess how much liability insurance for cage diving in CA would cost?

let me put it this way:  not many sport diving operations figured they'd end up making money.

A general agreement was made that to do anything but observe the sharks from distance, a permit would have to be applied for, covered by the Monterey Bay Sanctuary program.

I don't know for sure, but if you are interested, I think there might be some copies of the original papers covering the "debates" available.  Sean Van Sommeran has a better memory on this kind of thing than I do; you can contact him  from the addy on the PSRF website I linked to in the first post.

personally, i think the data from the long term studies of the sharks based on the satellite tagging and behavioral ecology programs will yield better results for long-term conservation than cage dives ever would.

for example, we have learned how the sharks migrate between different locales withing the state, have observed how they move within their hunting grounds (we actually set up essentially a sonar net with a satellite transmitter to track movements over the areas they hunt in), and have learned through satellite/gps tags that they can, in fact, migrate all the way from CA to Hawaii.  Nobody suspected they migrate from temperate to tropical waters before that.

so, yes, we lose some potentially great pics of big sharks chomping on bait on a rope, and perhaps the opportunity to show humans and sharks in the same environment, but we have the chance to study their natural behavior, as undisturbed as possible, instead.

both can be valuable, but the research on their natural behavior is pretty much required, considering how little we actually know about them.

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Ichthyic



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(Permalink) Posted: June 20 2007,15:37   

Quote
I suppose I can relate my tiny shark experience here, just FYI. Even in the UK we get sharks, where I am from originally (Dorset coast) we get two species: Porbeagle sharks and Basking sharks.


There's a guy that's been studying Basking Sharks around the UK for decades now.

argghhhh, now what was his name...

he pioneered the study of basking sharks around the Isle of Man.

man my memory is going.  I'm sure it will click in a couple of hours.

ITMT, since that guy started, there have been a lot of groups in the UK that have picked up and expanded on research on baskers; there is a great satellite tagging program that started around 2001.  Not sure who is responsible for publishing the data from that at this point, but a quick google on something like "basking sharks UK" would likely turn it up.

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skeptic



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(Permalink) Posted: June 20 2007,17:23   

Quote (Renier @ June 20 2007,08:10)
Bull shark. Yeah mate, if you’re an Aussie! Lol. Zambezi sharks are locally known as the bullies of the sea. Maybe they are territorial and that would explain their aggressive behaviour? I have an old book with Shark attacks recorded in South Africa. Most of them are Zambezi attacks. The freaky thing is that Zambezi sharks has a high tolerance of fresh water ( I know you know that, just info for lurkers). The record inland attack was 2000km inland (river) by a Zambezi Shark (Must double check on source).

I'm not sure of the distance comparison, not brushed up on my metric system sad to say, but bulls have traveled up the Mississippi in the US as far as Illinios and I remember swimming in the Miss. and the Ohio many times during my younger days with never a thought that a shark may be cruising by.

  
"Rev Dr" Lenny Flank



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(Permalink) Posted: June 20 2007,18:14   

Quote (Ichthyic @ June 14 2007,13:22)
you have to wonder just how strong of a selective pressure on mammalian prey items are large predators like sharks and crocs?

crocs are entirely ambush predators, and the only times they contact large mammals are when they are near water, which is very periodic and relatively rare for most of them, on a diurnal basis (you only need to go near the water to grab a drink).

so I would guess that crocs simply aren't a significant selection pressure for mammals to evolve in response to, as opposed to say, lions, in the same general area.

Keep in mind too that endothermic predators need to eat every day or so, while ectothermic predators do just fine on one or two good meals a month, and can happily go half a year without eating anything at all.

So yes, I'd have to agree with you that selection would respond far more strongly to mammalian predators than to reptilian or, uh, fishilian ones.

Unless, of course, the ectothermic predator is your only one (the newts of the Pacific northwest aren't generally eaten by anything but garter snakes, who are the only predators that can deal with the newt's toxins, that newt-onian vulnerability therefore leading to even stronger toxins, which the snakes then adapt to overcome, and on and on and on -->  which is why Pacific newts have enough toxin to kill a horse, even though pretty much nothing eats them but garter snakes).

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Ichthyic



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(Permalink) Posted: June 20 2007,18:18   

Quote

Keep in mind too that endothermic predators need to eat every day or so, while ectothermic predators do just fine on one or two good meals a month, and can happily go half a year without eating anything at all.


It gets a little weirder with some of the shark species we are speaking of though, since they're kind of "half endotherm".

they do have large sections of musculature that operate endothermically due to heat-exchange systems.  white sharks have both swimming muscles and their stomachs warmed by counter-current exchange systems, for example.  (hmm, I seem to recall a discussion about this round these parts where you pointed out that sea-turtles also have a comparable heat-exchange system in their flippers)

However, as to the calculations wrt to energy expenditure based on that, since the endothermy is non metabolic in nature, you're probably right that energy calculations aren't particularly relevant.

I haven't seen it adopted in the literature as of yet, but I always thought non-metabolic endotherm was a good way to describe these critters actually.

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"Rev Dr" Lenny Flank



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(Permalink) Posted: June 20 2007,21:40   

Quote (Ichthyic @ June 20 2007,18:18)
I haven't seen it adopted in the literature as of yet, but I always thought non-metabolic endotherm was a good way to describe these critters actually.

The currently popular terms are poikilotherm ("various temperature") and homeotherm ("same temperature").

Those make no reference to the source of body heat, though, whether metabolic or environmental.

But they *should*, dammit.  It's a big difference.

And those terms are ugly anyway.   :)

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"Rev Dr" Lenny Flank



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(Permalink) Posted: June 20 2007,21:54   

Quote (Ichthyic @ June 20 2007,18:18)
However, as to the calculations wrt to energy expenditure based on that, since the endothermy is non metabolic in nature, you're probably right that energy calculations aren't particularly relevant.

Well, it would make a difference to the prey, I'd think, whether the *predator* is endothermic or ectothermic, and that would change the selection pressures . . .

If you're a small fish, say, and there's a big barracuda near you and a dolphin near you, you're far more likely to get eaten by the dolphin, since it eats a lot more (and a lot more often) than the barracuda does.  Ditto if you are a small furry critter on the African plains --- you've got a much better chance of being eaten by a lion or leopard (which have to eat, what, every two days or so?) than by a big python that only eats once or twice a month.

By the time you've adapted to selection pressure from the ectothermic predator, the endotherms have not only eaten you, but your entire family as well.  And all the neighbors.

So I'd think that the endothermic predators would put a far greater selection pressure on you than the ectotherms would.

So even if the shark is "sort of" endothermic, it still doesn't need the high level of food intake that a mammalian (or avian) predator does (since its body temp is still environmental rather than metabolic) -- so it'd still be, I'd think, rather lower on the list of selection pressures.

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"Rev Dr" Lenny Flank



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(Permalink) Posted: June 20 2007,21:58   

On the other hand, though, I'd guess that maybe the adaptive response to both dolphin/barracuda would be similar anyway --- (1) swim really fast away from it, or (2) stay hidden so it can't find you.

When something is trying to eat you, I guess it doesn't really make much difference WHAT it is -- the proper response is to run like hell away from it.   ;)

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Henry J



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(Permalink) Posted: June 20 2007,23:04   

Re "By the time you've adapted to selection pressure from the ectothermic predator,"

Unless the ectothermic predators are a lot more numerous than the endothermic ones. ;)

Henry

  
Ichthyic



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(Permalink) Posted: June 21 2007,00:25   

Quote
(2) stay hidden so it can't find you.


doesn't work so well with either dolphins or sharks.

sharks use "electrolocation" to nail prey items hiding in crevices or even under the sand, and dolphins do the same with echolocation.

running still works, schooling works...

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Louis



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(Permalink) Posted: June 21 2007,03:25   

Quote (Ichthyic @ June 21 2007,07:25)
Quote
(2) stay hidden so it can't find you.


doesn't work so well with either dolphins or sharks.

sharks use "electrolocation" to nail prey items hiding in crevices or even under the sand, and dolphins do the same with echolocation.

running still works, schooling works...

Lenny,

And having the underwater equivalent of an AK-47 also works.

("When you absolutely, positively have to kill every mother fisher in the room, accept no substitute")


Louis

P.S. J-Dog, to be honest it was the cello music that first alerted me! ;-)

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Renier



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(Permalink) Posted: June 21 2007,04:13   

Quote
... most of the attacks in fresh water suggest they really are hunting for food.  Could be a case of mistaken identity, but again, a lot of those attacks involve multiple bites.  Some have suggested they are more aggressive in fresh water, but I also don't buy that, as it just seems more likely to me that where these attacks occur in freshwater, there is simply a lot higher concentration of people actually in the water, so you get a higher frequency of attack.


I agree. Rural Africa, for instance, has a lot of villages next to the big rivers. These people don't have access to fresh water and thus bath and swim in the rivers very often. I don't know what the ratio is to say holiday makers (swim, surf etc.) along the warm water coasts.

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yeah, again, they didn't know where the shark was.  I've seen many videotapes of dives where when the divers could see where the shark was, and turned to face it, the shark would go into circling behavior instead of attack behavior, and often would move off.


I'll keep that in mind if ever I encounter one of the big Whites on a dive. All brave now, but I reckon I'll just crap myself an island and go sit on top of it :-) I do however carry a power head just in case. I suppose it won’t really help if a shark is bent on munching me, but it does at least give one a greater sense of ability to defend oneself.

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sharks aren't invulnerable; especially ones that feed on large prey items like elephant seals.  We've seen whites with missing eyes and huge numbers of scars on occasion.  Even one missing eye can put a serious damper on prey location.  of course nothing is absolute, and while we often see whites hit once (hard) and then circle to allow for ensanguination, we also infrequently see them just going all out and chomping the prey to bits in rapid fashion.


I noted that many sharks close their "eyelids" when they start to bite a pray. Obviously to protect the eyes from injury. Whites however don't close their eyes, but rolls them back. This seems a less effective way of protecting the eyes? Another fascinating thing. If you have bait in the water and a White closes in to munch it then it rolls it's eyes back just before it bites the bait. However, at the last moment before contact with the bait, the Whites often turn their heads away and bites a metal part of the boat. The conclusion was that at the last moment, when the eyes are rolled back, the White uses those electric sensors on the nose to guide it towards the prey, and thus confuses the metal parts of the boat as prey/bait. Is this correct?

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Mako's typically feed on large pelagic fishes, but again, sharks being typically opportunistic, I've seen video of them feeding on marine mammals as large as full-grown bottlenose dolphins.  Amazing stuff - they would hit the tail of the dolphin full-speed to immobilize it and cause severe ensanguination, then come back to feed on it.


My grandfather was a fulltime fisherman (boat) at an early stage of his life. One day they were catching fish when all of a sudden a big shark jumped out of the water and landed in the boat. It knocked two people clean out of the boat and got its head stuck under one of the wooden benches. Of course, the crew got a helluva fright and promptly proceeded to calm the shark down... with nice big wooden batons and some spicy fisherman words. It worked. They killed it thinking the shark tried to grab one of them clean out of the air. I had a newspaper clip that showed the jaw. From left to right it was about 40-50cm. The newspaper had it down as a "Blue shark" but it was clearly the jaw of a mako. They had strange names for different sharks and fish in those days. Why do makos do that? Why do they jump out of the water and often attack boats? I think Whites are also known for such behavior?

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We know even less about mako behavior than we do about whites, mostly because they're pelagic, and large ones might be almost as rare these days as whites (they are a great food and sport fish, and so many have been taken by the longline and gill net fisheries that large ones have become quite rare).


It’s a sad thing. This whole shark fin soup stuff just makes me really angry and sad. To cut off a beautiful creature like that's fins and just leave the innocent dying animal. For friggen soup! Wonder who the REAL "murder" machines are. Don't think it's the sharks.

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A friend of mine has been studying a close relative, the Salmon Shark (Lamna ditropis) for some time now.


Never heard of it, but thanks for the tip. I'll trace down some info on distribution, behavior etc.

Quote
yes, there has been some work on this area, and I have those references, but not ready to hand.  give me a couple of days to dig them up for you.  They do belong to the same family:  Lamnidae.  However, I recall a tremendous amount of controversy surrounding whether the linneages are actually based on a common ancestor.  also a lot of controversy around whether megalodon is actually an ancestor of carcharias or not, which is related to the same issue.


I would appreciate any info on this. It freaks me out. Makos look like Great Whites, but have teeth just like Raggies. Their type of teeth (grabbing teeth) forces them to catch smaller prey, yes? I assume that cutting teeth, like Whites, are useful when you are hungry and there is a nice juicy, pickled whale carcass floating around.

I don't believe them, but there were rumors about Megalodon not being extinct but alive and well in certain (human isolated) spots on Earth. Do you know anything about this and if there is any substance to these claims?

Did you ever encounter one of those "cookie-cutter" sharks? We don't have any over here, as far as I know. I saw a documentary that showed some seals with weird bite marks (think it might have sparked the Megalodon theory). Apparently, these cookie-cutter sharks swim up to a seal, bites a chunk out and then swims away (Drive-thru style). I would hate meeting one of those under water - wet suits are expensive!

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personally, i think the data from the long term studies of the sharks based on the satellite tagging and behavioral ecology programs will yield better results for long-term conservation than cage dives ever would.


You made some valid points. I'll read up on it, thanks for the info. "satellite/gps tags". Geez, I never knew that type of technology was being used. It's awesome. I should tag my kids with some...

Quote
I suppose I can relate my tiny shark experience here, just FYI. Even in the UK we get sharks, where I am from originally (Dorset coast) we get two species: Porbeagle sharks and Basking sharks.


The basking sharks scare the surfers over here. What, they grow up to 12 meters I think?

Quote
I'm not sure of the distance comparison, not brushed up on my metric system sad to say, but bulls have traveled up the Mississippi in the US as far as Illinios and I remember swimming in the Miss. and the Ohio many times during my younger days with never a thought that a shark may be cruising by.


Never even imagined the Mississippi had Zambezi/Bull sharks. Interesting.

Ichthyic, another question. Just to check up on a rumor. I heard that there are records of Whale Sharks hunting tuna somewhere in, I think, The Gulf of Mexico. Do you know anything about this offhand? I was under the impression that they are strictly filter feeders. Did any of you ever read Thor Heyrdahl's Kontiki expedition? There is some really freaky stuff in there, like the thing that munched the one bloke's sleeping bag.

  
"Rev Dr" Lenny Flank



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(Permalink) Posted: June 21 2007,07:17   

Quote (Henry J @ June 20 2007,23:04)
Re "By the time you've adapted to selection pressure from the ectothermic predator,"

Unless the ectothermic predators are a lot more numerous than the endothermic ones. ;)

Henry

That's actually a good point --- there does tend to be a greater number of ectothermic predators in a given area than endothermic, since each individual ectotherm requires less food than an endotherm would . . .

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Ichthyic



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(Permalink) Posted: June 21 2007,13:16   

Quote
All brave now, but I reckon I'll just crap myself an island and go sit on top of it :-)


so...

eat lots of roughage before diving in an area known to be frequented by large sharks.

*pulls out pad*

better add that one to my list.

:p

         
Quote
I noted that many sharks close their "eyelids" when they start to bite a pray


it's called a nictating membrane, and tends to protect the eye from abrasions when they get close to prey items.

not all sharks have that, BTW.  You might take a look at the various families and genera, and see if it makes any sense which have them and which don't.

         
Quote
However, at the last moment before contact with the bait, the Whites often turn their heads away and bites a metal part of the boat. The conclusion was that at the last moment, when the eyes are rolled back, the White uses those electric sensors on the nose to guide it towards the prey, and thus confuses the metal parts of the boat as prey/bait. Is this correct?


that's the current theory.  It makes a lot of sense given the large distribution of ampulae of lorenzini on the front of the shark's head.

I don't recall ever seeing this tested formally, however, so consider it anecdotal.

would be a nice tank experiment, as you should be able to test this with sharks much smaller and more manageable than whites.

       
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The newspaper had it down as a "Blue shark"


LOL

yeah, no way could a blue shark pull that feat off.  they aren't that quick or strong.  I've handled both, and a nine foot blue can quite easily be handled by one person.  a nine foot mako??  not gettin near that thing with FOUR people.

hell, I only tagged two makos the whole time I was working with sharks in Monterey, and the largest was only about 2m.

it took almost 30 min. to get that thing IN the boat, and it took two people to hold it down.

in contrast, a nine foot blue takes about 5 min to get in the boat, and one person can easily manage to hold it down.

btw, the only time we actually pulled the sharks in the boat was to take blood samples before release.

       
Quote
Why do they jump out of the water and often attack boats? I think Whites are also known for such behavior?


well, the actual answer is that they don't.  it just sticks in one's memory when they do.  Also, I personally have never heard of a white shark jumping INTO a boat, not saying it hasn't happened, but it's gotta be far rarer than the mako.

as to why?

why do billfish end up in boats sometimes?

My guess would be it's a simple matter of speed and miscalculation.  they are probably chasing a fast prey item, which darts under the boat to confuse the chasing predator, and succeeds.  the predator trys to jump over the interfering object, and fails.

thinking about the reverse situation, things like flying fish ending up in boats...

I've seen this situation in several different circumstances.  The most notable was a group of harbor seals that would round up schools of flying fish in a shallow harbor on Catalina Island, then launch themselves into the middle of the balled-up school, and the flying fish would "fly" onto the surrounding rocks and beach in the shallow cove.  The seals would then leisurely gather them up off of the rocks.

so since it was quite clear to me that a predator could use an obstacle to trap prey, it seems the converse might also work.

     
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This whole shark fin soup stuff just makes me really angry and sad.


yup. very bad mojo.

attitudes about shark fin soup and the cartilage industry (also a horrible bit of homeopathic idiocy) are changing far too slowly to stop the rampant depredation of shark populations they are causing.

     
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Their type of teeth (grabbing teeth) forces them to catch smaller prey, yes? I assume that cutting teeth, like Whites, are useful when you are hungry and there is a nice juicy, pickled whale carcass floating around.


"typically" yes, but see the note about makos taking out dolphins above.

even though the tooth shape is different, mako teeth are still extremely sharp.  you can cut stuff with the tip of a sharp knife if you draw it across fast enough, just as easily as you can with the serrated edge if you move slower.

though, yes, makos have more trouble ripping hunks out of large items than a white would, they can still do it.

Code Sample
I don't believe them, but there were rumors about Megalodon not being extinct but alive and well in certain (human isolated) spots on Earth. Do you know anything about this and if there is any substance to these claims?


don't know... next time I see bigfoot I'll ask him.

;)

   
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I would hate meeting one of those under water - wet suits are expensive!


IIRC, those suckers live pretty deep, so no worries.

 
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I should tag my kids with some...


people do.  no joke.  Of course, more typically people just buy gps locators for their kids to carry in their pockets or backpacks.

 
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What, they grow up to 12 meters I think?


yup, that's about right.  very docile, very tiny, not sharp teeth. never heard of anybody being hurt by one, though they could give you a nasty knock with their tails if they wanted to.  OTOH, we had lots of yahoos trying to hook them with giant treble hooks to get "towed" on their kayaks or canoes, and one idiot who decided to use one for archery practice once.  many used to be seen with bullet holes.

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I heard that there are records of Whale Sharks hunting tuna somewhere in, I think, The Gulf of Mexico. Do you know anything about this offhand? I was under the impression that they are strictly filter feeders.


nope, not entirely filter feeders, but the biggest things I've ever heard them feeding on are small squid and sardines.

they actually have very small (relatively) throat openings, so swallowing a large tuna would be a bit of a problem.

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J-Dog



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(Permalink) Posted: June 21 2007,13:30   

Quote (Ichthyic @ June 21 2007,13:16)
btw, the only time we actually pulled the sharks in the boat was to take blood samples before release.

Was that "bladder release"?

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Ichthyic



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(Permalink) Posted: June 21 2007,13:35   

heh.  only after a lot of beer.

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khan



Posts: 1525
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(Permalink) Posted: June 21 2007,21:33   

An interesting tangent on risk of death:
---------------------------------
http://www.msnbc.msn.com/id/19334698/

More deaths by sand than sharks
People naturally worry about splashier threats, like shark attacks. However, the Marons’ research found there were 16 sand hole or tunnel deaths in the U.S. from 1990-2006 compared with 12 fatal shark attacks for the same period, according to University of Florida statistics.

And Bradley Maron thinks the sand-related deaths are less well-documented than shark attacks.

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That's so fucking stupid it merits a wing in the museum of stupid. -midwifetoad

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Ichthyic



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(Permalink) Posted: June 21 2007,21:36   

the next horror thriller:

"Sand: The Gritty Killer!"

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Renier



Posts: 276
Joined: Jan. 2006

(Permalink) Posted: June 22 2007,04:26   

Quote
that's the current theory.  It makes a lot of sense given the large distribution of ampulae of lorenzini on the front of the shark's head.

I don't recall ever seeing this tested formally, however, so consider it anecdotal.


I have some footage somewhere on an old video where they demonstrated this “turning away from bait and bite metal” behaviour. However, help me out here. A piece of bait is a dead piece of flesh. What electric current could possibly be detected in a dead lump of flesh? Or, is it a question of whether the shark, in hunting live prey, does not make a distinction once the eyes are rolled back, but treats it as live prey?

Quote
yeah, no way could a blue shark pull that feat off.  They aren't that quick or strong.  I've handled both, and a nine foot blue can quite easily be handled by one person.  a nine foot mako??  not gettin near that thing with FOUR people.

hell, I only tagged two makos the whole time I was working with sharks in Monterey, and the largest was only about 2m.

it took almost 30 min. to get that thing IN the boat, and it took two people to hold it down.

in contrast, a nine foot blue takes about 5 min to get in the boat, and one person can easily manage to hold it down.


Some amazing footage I have on a video here was when they did some experiments on determining how much force a shark displays when biting down on something. They had a big piece of bait with some sort of measuring device inside the bait. Took a lot of effort to convince the sharks to bite it. Most sharks that bit it were impressive, however, and then a mako came along and showed them how it’s done. I also have footage of a White biting a motor vehicle tyre. It looked like the White was playing with a piece of soft sponge.

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btw, the only time we actually pulled the sharks in the boat was to take blood samples before release.


Hope you gave them a nice sucker and a pat on the head for their co-operation. Is there anything interesting about shark blood as compared to other fishes perhaps?

Quote
well, the actual answer is that they don't.  it just sticks in one's memory when they do.  Also, I personally have never heard of a white shark jumping INTO a boat, not saying it hasn't happened, but it's gotta be far rarer than the mako.



My guess would be it's a simple matter of speed and miscalculation.  they are probably chasing a fast prey item, which darts under the boat to confuse the chasing predator, and succeeds.  the predator trys to jump over the interfering object, and fails.



Sounds like a reasonable explanation to me. Thanks. I’ll see if I can trace a source for Whites jumping into boats. I know they are notorious for nibbling on outboard motors. Iron deficiency? Heh! I have seen pictures of ski-boats after a White took a bite out of some hulls. It is amazing when humans introduce themselves to an environment how strange some animals react to it.

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"typically" yes, but see the note about makos taking out dolphins above.


I once read a study about dolphins and sharks. They put some dolphins and some harmless sharks in a tank somewhere (perhaps Durban). They trained some dolphins to attack the sharks (hi-speed hit on the gill slits) when a certain signal (whistle) was given. The dolphins did just fine. Then they introduced some more heavy weight sharks (I think it was Bull/Zambezi sharks) into the test and gave the dolphins the signal. The dolphins went nuts. They swam around the tank making distressed noises. It was like they knew that some sharks are not to be played with.

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even though the tooth shape is different, mako teeth are still extremely sharp.  you can cut stuff with the tip of a sharp knife if you draw it across fast enough, just as easily as you can with the serrated edge if you move slower.


Good point.

Quote
don't know... next time I see bigfoot I'll ask him.


I thought so.

Quote
IIRC, those suckers live pretty deep, so no worries.


Hey. Don’t underestimate my apnea. They don’t call me “The Great Giant Squid Hunter” for nothing, y’know! Heh, I wish.

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OTOH, we had lots of yahoos trying to hook them with giant treble hooks to get "towed" on their kayaks or canoes, and one idiot who decided to use one for archery practice once.  many used to be seen with bullet holes.


That’s just sad man. Wtf is wrong with people anyway? I remember walking around some rock pools at spring tide and found some octopus heads lying around. They were still alive! Some people caught them and just cut of their tentacles (for bait), leaving the mutilated octopus on the dry rocks to die a slow and painful death. I have killed some octopus (in my younger days) for bait and food but made sure the critter had a quick death. Once, fishing on the deep sea I caught a nice big octopus. I wanted to keep it for seafood stew and took a knife to give it a quick stab between the eyes. As the blade came closer, the octopus saw what I was up to and tried to block the blade with its tentacles. And, it gave me a look! It KNEW what I wanted to do. I just threw it back overboard. They are strange creatures. OT, sorry.

Quote
they actually have very small (relatively) throat openings, so swallowing a large tuna would be a bit of a problem.


I thought the story might have been thickened a bit.

I have a question about Tiger Sharks. We don’t get them here in the cold Cape Town water, but the things I have read about them! They are like garbage collectors. An article (in a book somewhere in my garage) claims they have found the weirdest things in Tiger Shark bellies. Stuff like food tin cans, match boxes, shoes (hmm), monkey parts and some misc mechanical junk and assorted metal and plastic things. Hey, I am all for cleaning up pollution, but this goes a bit far. Do you perhaps know why they have such exotic tastes?

  
BWE



Posts: 1898
Joined: Jan. 2006

(Permalink) Posted: June 22 2007,07:39   

Not that I know anything specific about shark blood that you would study if you had a vial of it but, sharks, lacking bone and thus bone marrow, make their red blood cells in a funky little doohickey called a  Laedig's organ (sp?) and probably also in their spleen.  Their hemoglobin is weird for some reason I can't remember offhand. It is one of the most efficient oxygen diffusers in the ocean though I don't know about the white (but I assume it's probably among the best of the sharks because it needs a lot of power for a big body). The no bone, hence no marrow thing is actually a major issue in sharks. Their chemistry is often different in unexpected ways.

Icthy, do whites have spiracles?

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Somebody thought of that, and someone believed it
Look what it's done so far

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BWE



Posts: 1898
Joined: Jan. 2006

(Permalink) Posted: June 22 2007,09:30   

Quote
That’s just sad man. Wtf is wrong with people anyway? I remember walking around some rock pools at spring tide and found some octopus heads lying around. They were still alive! Some people caught them and just cut of their tentacles (for bait), leaving the mutilated octopus on the dry rocks to die a slow and painful death. I have killed some octopus (in my younger days) for bait and food but made sure the critter had a quick death. Once, fishing on the deep sea I caught a nice big octopus. I wanted to keep it for seafood stew and took a knife to give it a quick stab between the eyes. As the blade came closer, the octopus saw what I was up to and tried to block the blade with its tentacles. And, it gave me a look! It KNEW what I wanted to do. I just threw it back overboard. They are strange creatures. OT, sorry.


If you are into octopi, Puget sound has some a-f'ing-mazing cephalopods. They hang out in cracks so at first you don't see em when you're poking around looking for eels. Suddenly you see you're 3 feet away from a big one. It can be a bit scary. I guess most people don't have nightmares about an octopus but the have a sturdy tool to bite you with. I wouldn't want to get bitten.


This guy is pretty crazy. Incidentally, he is dressed appropriately. If you are used to warm water, it's best to use a dry suit.

--------------
Who said that ev'ry wish would be heard and answered
When wished on the morning star
Somebody thought of that, and someone believed it
Look what it's done so far

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BWE



Posts: 1898
Joined: Jan. 2006

(Permalink) Posted: June 22 2007,11:40   

Quote
yeah, no way could a blue shark pull that feat off.  They aren't that quick or strong.  I've handled both, and a nine foot blue can quite easily be handled by one person.  a nine foot mako??  not gettin near that thing with FOUR people.

hell, I only tagged two makos the whole time I was working with sharks in Monterey, and the largest was only about 2m.

it took almost 30 min. to get that thing IN the boat, and it took two people to hold it down.

in contrast, a nine foot blue takes about 5 min to get in the boat, and one person can easily manage to hold it down.


I pulled in a nine foot sturgeon once off the bank. She was a fattie too. I didn't take her out of the water but I would've needed a crane. I don't remember how long it took but it had to been at least an hour. I had to go up and down the bank and there were other people fishing but no one was mad.

--------------
Who said that ev'ry wish would be heard and answered
When wished on the morning star
Somebody thought of that, and someone believed it
Look what it's done so far

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Stephen Elliott



Posts: 1754
Joined: Oct. 2005

(Permalink) Posted: June 22 2007,11:46   

Quote (BWE @ June 22 2007,09:30)
...
This guy is pretty crazy. Incidentally, he is dressed appropriately. If you are used to warm water, it's best to use a dry suit.

Yeh,
Dry suits are one shed-load warmer than wets.
I was pretty damn warm in the water off Scotland in November wearing one.

  
Ichthyic



Posts: 3325
Joined: May 2006

(Permalink) Posted: June 22 2007,15:06   

Quote
This guy is pretty crazy.


naww. I'd do that in a flash.  you have bones, and can exert leverage the occy can't.  It's easy enough to keep their beak away from you.

what's a little harder is to keep those damn curious arms away from your facemask and regulator.  even a relatively small occy (say 5 feet) can cause a problem there, especially with novice divers prone to panic if they lose their mask or regulator.

the mask is the worst thing, actually, as they typically aren't attached to anything, so when the occy pulls it off it's easily lost.  then the dive's over, unless you have some miraculous ability to see clearly underwater without one.

the regulator is usually pretty easy to get back, since it's attached to the scuba tank.

I speak from experience.

:)

Octopus are very cool.

--------------
"And the sea will grant each man new hope..."

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BWE



Posts: 1898
Joined: Jan. 2006

(Permalink) Posted: June 22 2007,15:31   

I dunno. We got one in a dredge one time and he pulled up a rock that might have weighed 30 lbs. Losing your mask to one could be a bit disconcerting but if you didn't get your grip right away and one got you with its beak you'd be injured.

Tell us about shark's blood. All the sudden I'm interested. I couldn't find anything meaningful on the web. (admittedly a brief search) All sharks have Laedig's organs don't they? Do whites have spiracles? Can they rest on the bottom? Inquiring mind wants to know.

--------------
Who said that ev'ry wish would be heard and answered
When wished on the morning star
Somebody thought of that, and someone believed it
Look what it's done so far

The Daily Wingnut

   
Ichthyic



Posts: 3325
Joined: May 2006

(Permalink) Posted: June 22 2007,15:38   

Quote
What electric current could possibly be detected in a dead lump of flesh?


evidently, even dead muscle tissue still generates an electric field that can be detected by a shark.

metal objects generate a far larger field, so the idea is that this is what causes them confusion when both food and metal are in close proximity.

It might also be that it's not the "generation" of an electric field, exactly, but the interruption of a detectable general field the shark is working with.

Have you ever seen a visible representation of a magnetic field?  like with iron filings on a paper with a magnet underneath?  if you add a small magnet near the larger, it will disrupt the field generated by the larger magnet.

it could be that sharks are detecting "electrical field patterns" and detecting things that cause disruptions in them.  since things like flesh and metal conduct electricity, they can cause changes in the general "ambient" electrical fields.  

This has been demonstrated in many species of weakly electric fish, for example, though these fish also generate their own electrical fields to maximize their detection ability, and even to communicate.

Quote
Is there anything interesting about shark blood as compared to other fishes perhaps?


tons of things, actually.  In addition to the things BWE mentioned, for example,  sharks utilize nitrogenous waste compounds (urea) to help maintain osmolality with seawater.  however, the reason we specifically were taking samples was for measurement of organochlorine levels (DDT metabolites, PCB's, etc.), and for some genetics work.

here's an overview covering the general issue of osmotic regulation and nitrogenous waste compounds, fyi:

http://www.marietta.edu/~mcshaffd/aquatic/sextant/excrete.htm

Quote
It was like they knew that some sharks are not to be played with.


there was a video taken near the Farallon Islands (off of San Francisco) a few years back of a mother killer whale taking a full grown white apart when it got near her calf.

remarkable stuff.  It might still be floating around somewhere.  a google search might turn it up.

pods of dolphins have been observed to kill sharks by ramming them in the midsection with their rostrums, causing severe internal injury to the sharks.

Quote
Do you perhaps know why they have such exotic tastes?


well, it's fairly small percentage of the stuff they eat (one of their favorite foods appears to be sea turtle, and they can actually make it through the shells with those strong jaws and serrated teeth).  frankly, I can only speculate as to why they pick up junk.  Incidental?  smells good?

However, if you really want to know what they eat, there are several published studies of their diet out there which shouldn't be too hard for you to track down.  don't rely on pop-science books when you can go straight to the source, i always say.

you might also try these guys, who have a specific interest in those bad boys:

http://www.fiu.edu/~heithaus/SBERP/pages/Tiger.htm

also, there is a good deal of study on these guys conducted through the University of Hawaii.

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Ichthyic



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(Permalink) Posted: June 22 2007,15:45   

Quote
Icthy, do whites have spiracles?


nope.

not all sharks have spiracles.  They are an extension of the primary respiratory structures, and so usually appear in sharks/rays that spend most of their time on the bottom, especially in species with ventral mouths.

allows them to breathe kinda like a dolphin's blowhole.

I'll post examples...

here, compare this fella, with the obvious spiracles right behind the eyes:



with the picture of the white shark I posted on the first page.

interesting note... tiger sharks have spiracles.

--------------
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BWE



Posts: 1898
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(Permalink) Posted: June 22 2007,15:46   

Thanks. Those were the links I was looking for.

--------------
Who said that ev'ry wish would be heard and answered
When wished on the morning star
Somebody thought of that, and someone believed it
Look what it's done so far

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Ichthyic



Posts: 3325
Joined: May 2006

(Permalink) Posted: June 22 2007,15:53   

Quote (BWE @ June 22 2007,15:46)
Thanks. Those were the links I was looking for.

here's the classic paper on the subject:

http://ajplegacy.physiology.org/cgi/content/citation/215/6/1493

amazing that it STILL hasn't been released into public domain after 40 years.

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Lou FCD



Posts: 5402
Joined: Jan. 2006

(Permalink) Posted: Jan. 03 2008,19:59   

Interesting Shark Article at LiveScience

Quote
Whale sharks, which grow to weigh as much as two or three adult elephants, are thriving in waters off Western Australia, a new study of underwater images suggests.

Up to 65 feet long (20 meters), the whale shark, Rhincodon typus, is the world's largest living fish species — and also the largest shark. Though hefty, this shark is known as the "gentle giant" for its non-predatory behavior. Rather than tearing through meaty flesh of prey like many sharks, this fish, with its broad, flattened head and tiny teeth inside a giant mouth, eats tiny zooplankton, sieving them through a fine mesh of gill-rakers.

Relatively little is known about the health and migratory behaviors of whale sharks, which live in tropical and warm seas, including the western Atlantic and southern Pacific.

The new research combines computer-assisted photographic identification with data collected by ecotourists, among others, and suggests whale shark populations in Ningaloo, Western Australia, are healthy, although research at other locations, such as South Africa and Thailand, has reported declines in population size.


More at the link.

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