Fishing Pressure Pushing Sharks Towards Extinction

The global status of large sharks has been assessed by the IUCN-World Conservation Union, which maintains the Red List of Threatened Species.

The assessment finds that many large shark species have declined by more than half due to increased demand for shark fins and meat, recreational shark fisheries, as well as tuna and swordfish fisheries, where millions of sharks are taken as bycatch each year.

"As a result of high and mostly unrestricted fishing pressure, many sharks are now considered to be at risk of extinction," said Julia Baum, a member of the IUCN's Shark Specialist Group and a postdoctoral fellow at Scripps Institution of Oceanography in San Diego.

"Of particular concern is the scalloped hammerhead shark, an iconic coastal species, which will be listed on the 2008 IUCN Red List as globally 'endangered' due to overfishing and high demand for its valuable fins in the shark fin trade," said Baum.

School of scalloped hammerhead sharks at Isla del Coco, a Costa Rican National Park and World Natural Heritage Site. (Photo courtesy USGS)

Research at Dalhousie University over the past five years, conducted by Baum and the late Ransom Myers, demonstrated the magnitude of shark declines in the northwest Atlantic Ocean.

All species the team looked at had declined by over 50 percent since the early 1970s. For many large coastal shark species, the declines were much greater - tiger, scalloped hammerhead, bull and dusky shark populations have all plummeted by more than 95 percent.

The first complete IUCN Red List assessment of the status of all Mediterranean sharks and rays has revealed that 42 percent of the species are threatened with extinction. Overfishing, including bycatch, was identified as the main cause of decline by the study, which was released in November 2007.

"From devil rays to angel sharks, Mediterranean populations of these vulnerable species are in serious trouble," said Claudine Gibson, Programme Officer for the IUCN Shark Specialist Group and co-author of the report.

"Our analyses reveal the Mediterranean Sea as one of the world's most dangerous places on Earth for sharks and rays," Gibson said. "Bottom dwelling species appear to be at greatest risk in this region, due mainly to intense fishing of the seabed."

New research unveiled at the AAAS conference suggests that sharks migrate along fixed routes between well-established gathering places.

Peter Klimley, director of the Biotelemetry Laboratory at the University of California-Davis, has used electronic tags to track scalloped hammerhead sharks along their migration routes in the tropical Eastern Pacific Ocean. Their results suggest that these sharks speed between a series of "stepping stone" sites, near coastal island groups ranging from Mexico to Ecuador.

Great white shark at Isla Guadalupe off Baja, Mexico. (Photo credit unknown)

"Hammerhead sharks are not evenly dispersed throughout the seas, but concentrated at seamounts and offshore islands," Klimley says. "Hence, enforcing reserves around these areas will go far to protecting to these species, and will provide the public with places for viewing sharks in their habitat."

The great white shark, perhaps the most universally recognizable species in the ocean, also appears to return to a limited number of sites as part of its seasonal migration.

Salvador Jorgensen, a researcher at Stanford University's Hopkins Marine Station, has teamed with his colleagues in the Tagging of Pacific Predators program to tag nearly 150 great whites found near the coast of central California. In the winter, these sharks leave the seal rookeries where they feed all summer, and set off for warmer waters near one of two tropical "hotspots." One site between Hawaii and Mexico attracts so many of these giants, it has become known as "the white shark café."

"We started calling it the café because that is where you might go to have a snack or maybe just to 'see and be seen.' We are not sure which." Jorgensen says. "Once they leave the café, they return year after year to the same exact spot along the coast, just as you might return to a favorite fishing hole."

Reef shark surrounded by fish in the waters of the Maldives Islands. (Photo by Peter Smithson)

Baum points out that no single conservation strategy can work for all shark species. For those that spend much of their lives on the high seas, Baum cites a recent United Nations General Assembly Fisheries Resolution that recommends science-based catch limits and bans on finning—the practice of removing only a shark's fins and discarding the carcass. Such bans would require sharks to be brought back to land with their fins attached.

For coastal species, a network of marine reserves also can be an effective strategy. In both cases, Baum sees consistent and tough enforcement as absolutely crucial.

"Many pelagic sharks are getting snuffed out from longliners that target tunas and swordfish, while deep sea sharks are caught in bottom trawls and gillnets," explains Lance Morgan, a marine scientist from the Marine Conservation Biology Institute and organizer of the AAAS session.

"Sharks have nowhere left to hide in an ocean subject to widespread fishing. Catch limits, finning bans and a network of enforced marine reserves are all necessary conservation strategies to protect them."

Copyright Environment News Service (ENS) 2008. All rights reserved.