"Sharks are in trouble worldwide," says Dr. Ransom Myers the Killam Chair of Ocean Studies at Dalhousie University (Myers Lab website). "For these animals to survive, we need to reduce fishing effort by half and have a global ban on shark finning."
Dr. Myers and colleagues launched the Global Shark Assessment in October of 2003 to assess how global shark populations have changed since the beginning of industrial scale fishing, and to make predictions about how these populations will respond to global climate change and to different methods of fishing.
Sharks (and other elasmobranches) are vulnerable to fishing pressure because they are long-lived, slow to mature, and produce few offspring compared with most other fish. Hence, directed fishing can much more quickly decimate sharks than other fish species. Sharks are also often taken as bycatch in multi-species fisheries in which the target species are quick to replenish themselves while the sharks are not. This occurs in pelagic longline fisheries that target highly productive tuna species, but catch great numbers of sharks. It also occurs along southeastern U.S. coast where there is a bottom longline fishery that is targeted at sharks, but that catches many different shark species with different vulnerabilities to over-fishing. In these fisheries, the slow-to-reproduce shark species may be fished to extinction, while the more productive fishes continue to drive the industry.
Dr. Myers and colleagues have recently published three papers on the subject in prestigious scientific journals:
1) In Ecology Letters (2004), Baum and Myers estimate that less than 1% of oceanic whitetip sharks thought to have been the most common warm-water oceanic shark in the world just fifty years ago remain in the Gulf of Mexico today.
2) In Nature (2003), Myers and Worm described a global 90% decline in the world's predatory fish, including sharks in the Gulf of Thailand.
3) Finally, work by Baum and Myers in Science (2003) shows that pelagic sharks in the Northwest Atlantic are also in trouble with declines in recent years ranging from 40% in mako sharks up to almost 90% in hammerhead sharks.
The Global Shark Assessment
"We need to find out how general shark declines are across all the world's oceans," says Myers. As fishing pressure is intense everywhere, the situation he and researcher Julia Baum detected in the Gulf of Mexico may prove to be part of a general phenomena.
Currently, there exist both substantial amounts of unanalyzed data on sharks and a large number of dedicated shark biologists. However, these two key resources have not, as yet, been utilized to their full potential. The Global Shark Assessment will put the data and biological experts together with a team of modeling and statistical experts to produce a global assessment, with an emphasis on producing results in a form that is accessible to decision makers. Specifically, the Global Shark Assessment will:
1) Estimate the pre-exploitation population sizes.
2) Estimate current population parameters.
3) Predict the outcome of current management practices.
4) Effectively communicate the results.
5) Recommend the practices necessary to ensure shark survival.
The potential benefits of shark conservation are great. In protecting a host of large, charismatic, but particularly vulnerable species, shark conservation offers the opportunity to protect not just sharks, but the myriad other species and ecosystems with which and in which sharks interact. Hence, at stake are not merely sharks, but our still vastly misunderstood marine realm.
"It will be impossible to set management and restoration goals for these shark species without a clear understanding of how much we have lost. Our studies provide this missing baseline," says Baum.
