Shark Conservation Gone Wrong

To conserve an animal, one must have the scientific evidence to develop and support the policies needed to establish the necessary protection. It’s why I love scientific research. Having the potential to influence something that I am so passionate about really gives me the drive to pursue a career in conservation biology. However it is often tempting to accept scientific papers on face value and because they are published it must be true……it wouldn’t have been published otherwise would it….right? Wrong! Although I am relatively new to scientific research, I have already discovered that not all “science” is correct, scientific ideas and results evolve.

I recently read a presentation hosted by Nature Conservancy given by Dr Chip Cotton from Virginia Institute of Marine Science titled: Shark Conservation: global threats, local concerns. It is a really nice presentation that I would recommend you give a read, even if it is just for the amazing pictures from the VIMS shark survey work that  Cotton is involved in. One section of his presentation was of particular interest to me though, a case study of when shark conservation goes wrong.

In 2007, Myers et al published a paper in Science title: Cascading Effects of the Loss of Apex Predatory Sharks from a Coastal Ocean. Its a well cited paper (318 as of 28/05/12), and is a seminal paper for those studying sharks and their conservation. The paper provides evidence that declines in top apex predatory sharks such as tigers, black tips and bulls released mesopredatory elasmobranchs such as cownose rays, chain catsharks and little skates from top down control, causing them to increase in abundance. It was reported that increases in smaller elasmobranchs increased the predation of commercially important bivalve molluscs (such as Bay Scallop).  In some cases the subsequent decline in bivalves was so severe that fisheries collapsed for some taxa.

What more could a shark conservationist want. Direct evidence that the declines in large sharks can have ecological influences throughout a food web. Evidence had been given for a top down control of marine ecosystems. The oysters, scallops and other bivalves are commercially harvested, surely the public would listen now. The killing of sharks is now reducing the amount of oysters on the middle class dining table. CHRIST ALMIGHTY…..SAVE THE SHARK!!!

But this is where things take a turn for the worse. This proposed trophic cascade has now been heavy cited in both scientific literature and in the media. It was used as justification for the market development and harvesting of cownose rays in an effort to protect the bay scallop fishery in areas such as Chesapeake Bay, USA. The consumption of cownose ray was now marketed as “enviornmental-friendly” and a “green food source”. The slogan “Save the Bay, Eat a Ray” was adopted by media campaigns. This is something I had not heard of until reading Cottons presentation. I was shocked that the media were actively promoting the consumption of an elasmobranch species (below). Cownose rays are highly sensitive to fishing pressures due to a slow growth, late sexual maturity and production of very few pups, yet all of a sudden the harvesting of these sensitive rays was now being promoted!

What Cottons presentation brought to my attention was the potential flaws in Myers original 2007 research paper. The marine food web along the East Coast of the USA is very complex and it is suggested that the use of simplistic three level trophic model has lead to inaccurate conclusion concerning the ecosystem dynamics.

First up, evidence is provided that the diet of these apex sharks presented in the paper does not contain significant amounts of cownose ray (Cortes 1999). Similarly, diet studies of cownose ray do not support the notion that cownose rays significantly prey on commercial bivalves such as oysters and clams. Stomach content analysis suggest that east coast cownose ray diet, comprises only a small amount on commercial bivalves. In addition the life history of cownose rays does not support the population “explosion” suggested by Myers and closer inspection of some of the figures may be interpreted as unrepresentative.

Bullshark: A 6-foot bullshark in Spidercrab Bay, Eastern Shore VA. Note the juvenile sandbark shark in the bullshark’s mouth.

The Myers et al 2007 paper had the unintentional  consequences of developing an unregulated fishery on a highly vulnerable ray species. This fishery will no doubt be unsustainable. The evidence from this paper has been used at the detriment of the cownose ray that has  been tagged with this criminal bivalve snatching reputation so therefore its increased capture can be justified. I’m sure there are some very wealthy fisherman off the back of this misinterpretation of data.

There is no doubt that the declines in sharks will have cascading effects throughout an ecosystem. Instead of us humans stepping in and acting as the top down control, these local authorities and fisheries should concentrate their efforts on conserving the sharks that could potentially control mesopredators in a more natural way. They should increase the protection of commercial bivalves with improved aquaculture techniques and repellents if they are worried about cownose ray consuming them. Not go all out guns blazing, fighting fire with fire because that just isn’t going to work!

If you are interested in any of the work above, please give the presentation a read. It both highlights the need to challenge evidence given to use and also demonstrates that the conservation of sharks and rays is in no way a simple process…… It also has some pretty cool images of chimeras and sharks eating other sharks :D)

Shark Conservation: global threats, local concerns.

…..Accept nothing, question everything!

Christopher Bird


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