All of these sharks have already been caught over the past five years, and sometimes by the thousands. For example, approximately 41,000 blue sharks were caught in the North Pacific over that period of time, with these figures not even taking into account catches that were not officially reported. The sharks found to be sustainably fished accounted for about 9 percent of the current global catch, or more than 200,000 tons in live weight.
The researchers have not yet established firm catch limits for these sharks. Those would have to be agreed upon and implemented by international management organizations, based on this and other scientific studies. The authors did, however, calculate a "Maximum Sustainable Yield" for each species, and then noted whether or not the current estimated population for these individual shark species was above or below that figure. Those estimated as being above were said to have met the criteria for sustainable fishing.
Where the Debate Begins
Many fished sharks are part of bycatch, referring to animals that are accidentally caught with target species, such as tuna. Shelley Clarke, technical coordinator of sharks and bycatch for the Western and Central Pacific Fisheries Commission, sees the problem firsthand every day as it applies to the commission's 33 member countries and territories.
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"There is technically no argument whatsoever that sharks can be sustainably fished. It is simply a question of limiting the mortalities to a sustainable level," Clarke told Seeker. "That is where the scientific argument ends and the judgment begins."
The three basic conservation options are: attempt to ban shark fishing altogether, ban the fishing of certain highly endangered species or establish catch limits for sharks, rays and chimaeras based on their sustainability.
"Strict enforcement is difficult no matter what the regulation [is], but I'm not convinced it is easier to enforce a ban than a catch limit," Clarke said. "A ban sounds more clear-cut and easy to spot, but we're still expecting to count the number of sharks on board whether the allowable number is zero or fifty. If we can't count, then neither a ban nor a catch limit will work."
Bans Can Work, But Not Without Problems
No-take zones are already in place in certain parts of the world, banning the fishing of sharks and other species. One such shark sanctuary exists along the coastal area of Raja Ampat, Indonesia.
Last year, scientists working for the Wildlife Conservation Society (WCS), The Nature Conservancy (TNC) and other groups investigated no-take zones within the sanctuary to see if the restrictions were really protecting sharks by increasing their numbers. The researchers confirmed that, as expected, sharks were more abundant in the areas with fishing restrictions.
The bad news is that local fishermen - often in poverty and finding few other work options - adapted to the closures by moving to other fishing grounds or by engaging in illegal activities, such as illegal transportation of gasoline via their vessels.
Sangeeta Mangubhai of the WCS and TNC, who worked on the study at Raja Ampat, said, "Protecting shark populations from overfishing is not merely a matter of establishing marine protected areas. Such measures also require considerations of increased fishing effort in unprotected areas and how to provide more livelihood opportunities for people who depend on marine resources."
Fishing bans clearly also impact consumers. Simpfendorfer points out that "shark and ray meat is often the cheapest form of animal protein" in certain areas, particularly in Asian countries. "Thus to replace it, people would either be able to buy less or increase their income, something that is unlikely."
Many are hoping that sharks can be viewed as being worth more alive than dead, such as through ecotourism, which provides career options and promotes the conservation of sharks and other marine life. As it stands, though, not enough of these work opportunities exist.
Effective Fisheries Management Needed
Sharks and their relatives tend to have slow growth rates and relatively few offspring. Other fish, such as rockfish, share similar life cycles so only a small fraction of their entire population can be harvested each year, according to Ray Hilborn, a fisheries specialist at the University of Washington's College of the Environment.
No matter the target species, however, Hilborn told Seeker, "Many countries do not have effective fisheries management, and you can't be optimistic about sustaining their shark fisheries. Because sharks take particularly effective regulation to keep exploitation rates low, they are likely [to be] the most at risk of severe overfishing in the absence of fisheries management."
Glenn Sant, fisheries trade program leader of the wildlife trade monitoring network TRAFFIC, agrees that effective fisheries management is critical. Sant told Seeker that "there needs to be management in place to ensure catches are sustainable, but also that there is in place traceability of products back to these legal and sustainable sources."
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"Any traceability needs to be designed around the array of different products in trade such as fins, meat, gill plates, skins and liver oil," said Sant, senior research fellow at the Australian National Center for Ocean Resources & Security. "Key to this working is engaging with local fishing communities right through the chain of custody to the consumers."
Simpfendorfer said that "the million-dollar question" now is how to make shark meat, fins and other shark products traceable from hook to plate, to make sure that products sold as from sustainable sources can be clearly identified.
Technology to the Rescue
DNA forensics can trace the geographic origin of any shark or other fish on the market. Mahmood Shivji, director of the Guy Harvey Research Institute, was among the first to develop this technology. He and his team used it to identify fins from endangered scalloped hammerhead sharks in a Hong Kong market. Fins are particularly difficult to identify by sight alone, since they are often sold off the shark and in a dried state.
Increased random DNA testing could help to enforce shark fishing regulations, but even that measure is not enough. Tom Letessier of the Zoological Society of London told Seeker that other technologies for monitoring fishing activities could include remote surveillance using Synthetic Aperture Radar on satellites, as well as video and acoustic systems mounted on ocean gliders or fixed on land.