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.
"In these countries, the blue shark meat has historically been regarded as unpalatable due to its soft texture and strong odor of ammonia, so that targeted fisheries did not develop," explained Aires-da-Silva.
Two other factors have helped the shark. The first is that they are rather hearty fish and often survive after being caught on a long line. The second is that blue sharks are among the most productive shark species in the world, with females producing an average of 37 pups per litter, with some litters numbering 80 pups or more.
"These pups can nearly double their size over their first year of life to increase their chances of survival," Aires-da-Silva said, adding that it "is not a coincidence that the blue shark has often been described in the scientific literature as the most widespread and abundant of the pelagic sharks in the world's oceans."
Enric Cortes, a National Oceanic and Atmospheric Administration research fishery biologist in Florida, told Discovery News that the new report "is a good, serious study" that used data sources that "are generally regarded as being more reliable than fishery-dependent data," the basis of earlier research.
Cortes said the findings "generally confirm what those who work on sharks know for this species: that it is one of the most productive sharks and that despite heavy exploitation, mostly for the international shark fin trade, the Atlantic populations seem to be in a fairly good state."
Both Cortes and Aires-da-Silva, however, warn that blue sharks are still vulnerable.
Aires-da-Silva said new fisheries directed towards the sharks have just emerged within the last decade, due to swordfish quotas in the Atlantic leading to greater focus on other targeted species.
Improved "blast-freezing" technologies onboard fishing vessels have also improved the processing and quality of blue shark meat, reducing the nose-holding ammonia quality.
Aires-da-Silve said blue shark meat now represents "a dominant proportion of the landings" in Spain and Portugal, where consumers, along with those in Italy, are developing a taste for the traditionally unpalatable sharks.