A groundbreaking study by UCSC researchers finds that small-scale fisheries are the bane and the salvation, of endangered loggerhead turtles.
Posted on Oct 17th, 2007
By Traci Hukill
The picture is hideous and unspeakably sad: a half-dozen desiccated loggerhead turtle carcasses on the Baja beach in various agonized postures. The cause of death is drowning; these turtles were by-catch, unintentionally snared by nets or fishing lines set along the sea floor and tossed ashore after being hauled up with the catch.
The photographer is Hoyt Peckham, a doctoral candidate in ecology and evolutionary biology at UCSC who spent much of the last six years in Baja California studying the reason for the North Pacific loggerhead's plummeting numbers. The results of the study Peckham co-authored with a handful of other researchers, to be published online today in the open-access journal PloS ONE, are stunning: small-scale fisheries operated out of skiffs straight out of The Old Man and the Sea are accidentally killing as many loggerheads as industrial long-line fishing fleets in the North Pacific. In fact, on a per-hook or per-net basis, the low-tech, hand-operated fishing fleets are up to 1,000 times deadlier to the turtles than your average factory trawler.
"When I thought of by-catch, I always thought of huge factory ships pillaging the open ocean," says Peckham, who is back in Santa Cruz for the fall to write his dissertation. "I grew up around open boats, and you never think a couple of guys hauling up fish with simple gear could have that much impact."
One problem, explains study co-author Wallace J. Nichols, an Ocean Conservancy senior scientist who lives in Davenport, is that small-scale fishermen tend to drop bottom-set lines and bottom-set gill-nets and then leave. When they return a couple of days later, any ensnared turtles have already drowned. Some trawlers, by contrast, "are pulling the nets up to the deck in a couple of hours," he says, "so sometimes the turtles are still alive, though they can be in pretty bad shape."
If there's a species that can't afford to lose any more ground, it's the North Pacific loggerhead. In the last three generations, the nesting population in Japan has dropped 50 percent to 90 percent, for a total of fewer than 1,500 nesting North Pacific females. The loggerheads in the study are generally juveniles who travel to Mexico to feed and spend a three-decade-long "adolescence" before reaching reproductive maturity. The slow maturity rate leaves the species so vulnerable that the U.S. National Marine Fisheries Service has estimated that the loss of 37 to 92 large juveniles per year would "appreciably" increase the animal's risk of extinction. Peckham, Nichols and other researchers estimate that, at a minimum, the two small Mexican fleets they studied were accidentally killing 1,000 turtles per year.