It's easy to resist the rows of canned tuna in the supermarket, what with concerns about mercury, accidentally caught dolphins, and highly endangered species such as bluefin tuna. A new analysis, reported in this week's Science, may allay at least one of those worries. The study found that four major species of tuna in the Pacific have not collapsed, as feared; all told, fishing has removed just 26% of their biomass.
John Sibert at University of Hawaii in Honolulu and his colleagues examined 54 years of fisheries data from the Pacific, stretching back to 1950. They looked at catch records from the fishing industry and used standard models to estimate the size of the population still underwater. Of the eight major populations they examined, yellowfin tuna has been hardest hit with 64% of its biomass removed by fishing. North Pacific blue shark is faring the best with just 9% caught. Pacific fishing has removed between 21% and 26% of skipjack, a common tuna in grocery stores. "What is surprising is that some stocks show little impact," Sibert says. Managers usually aim to conserve about 40% of what the natural fish population used to be.
That's not to ignore the devastating impact that industrialized fishing has had on some species, especially the largest. Tuna that measure at least 175 centimeters from snout to the fork of their tail, for example, used to comprise 5% of the tuna biomass in the Pacific. Now they make up just 1%.
The removal of these top predators could help explain why the smaller fish populations are still robust, points out Boris Worm of Dalhousie University in Halifax, Canada. "I'm totally prepared to believe skipjack are doing well," he says. Sibert says that several other species, such as yellowfin, would be more sustainable if fishing were reduced by about 20%. "It's not at a crisis point yet, but if it continues for another 5 years, we could be in for some serious grief," he says.