Blue Sharks Beat the Odds, by Tasting Bad

July 30, 2008 -- Although many sharks are experiencing population declines of up to 90 percent now, a new study on western North Atlantic blue sharks has found that numbers of the colorful species there are currently down, but not out.

Other reports had concluded that the region's blue sharks were declining by around 60 percent, but the new analysis reduced the estimate by half, finding that populations of the 12.5-foot-long sharks have dropped by only 30 percent since the mid 1950s, when large-scale fishing practices began in that part of the Atlantic.

Lead author Alexandre Aires-da-Silva told Discovery News that "the blue shark picture is not as 'catastrophic' as previously reported" for the western North Atlantic, bounded on the south by Cape Hatteras, N.C., and extending upwards to northern Newfoundland, Canada.

Aires-da-Silva conducted the study, published in this month's Fisheries Research journal, as part of his Ph.D. program at the School of Aquatic and Fishery Sciences at the University of Washington, Seattle. He and colleagues John Hoey and Vincent Gallucci used data on blue shark catch rates over five decades to develop an index of the shark's abundance.

Like archaeologists, the researchers dug through thousands of pages of vessel cruise reports that logged blue shark sightings. They also scoured field fishing logs, grant reports and many other historical sources, mostly from the historical archives of U.S. and Canadian fishery agencies.

Much of the documentation referred to sharks caught during long-line fishing for tuna and swordfish. The study concluded that blue sharks appear to be most vulnerable to swordfish fishing gear -- hundreds to thousands of baited hooks hanging from a single line. The lines are deployed at shallower depths at night after dusk, when the sharks feed.

Blue sharks sometime become by-catch, but since U.S. and Canadian consumers tend to not like the shark's taste, they haven't gone after the blue shark for its meat.