Joined: May 2006
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:
...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!):
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:
However, at the same time, I would rather recommend its inevitable replacement:
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:
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.
"And the sea will grant each man new hope..."