But longlining is widely considered to be the main cause of mortality, Mast said.
Longlining is one of the most common forms of industrial fishing. It involves a single fishing line that can extend up to 60 miles (100 kilometers) and dangle thousands of hooks. It is the method of choice for catching swordfish and tuna in the Pacific, Indian, and Atlantic Oceans. But longlines attract many nontarget species that swallow the hooks or get entangled in the line. This unintended catchcalled bycatchis a major cause of mortality for turtles, seabirds, and many other marine mammals.
Two species frequently caught in the pelagic, or open-ocean, longlines are leatherbacks and loggerhead turtles.
Swordfish longlines, which snare turtles at a rate ten times that of tuna longlines, tend to be set at night and in shallower waterincreasing the chances of turtle encounters.
Four Million Hooks Per Day
A recent report published in Ecology Letters estimates that 1.4 billion hooks were set by longline fleets during 2000. That's 3.8 million hooks per day.
"Globally, more than 200,000 loggerheads and 50,000 leatherbacks were likely taken as pelagic longline bycatch in 2000," said Larry Crowder, a marine biologist at Duke University in Durham, North Carolina. Crowder led the research.
"There has been a 90 percent decline in Pacific leatherbacks over the last 20 years," Mast said. In 1980 more than 90,000 reproductive females could be found along the Pacific coast of North and South America. In 2002 that number had plummeted to fewer than 2,000. At the largest remaining nesting colony, in Costa Rica, numbers of nesting turtles have dropped from 1,400 in the late 1980s to 50 in recent years.
In the Pacific, where the population of both loggerheads and leatherbacks hovers around 200,000, Crowder estimates that in 2000 about 30,000 loggerhead turtles and 20,000 leatherbacks were caught as bycatch.
"Every year these turtles have about a fifty-fifty chance of running into longlines," Crowder said. Both the leatherback and loggerhead turtle could face extinction within 10 to 30 years if international fishing practices are not dramatically altered, he added.
Modified gear is part of the solution, say many scientists.
When the Hawaii swordfish fishery reopens, the fishermen will be required to use the new circle hook with a barb that is offset from the plane of the circle by 10 degrees. This will replace that J-hook that is traditionally used for swordfishing.
J-hooks are particularly dangerous for turtles because this style of hook tends to get caught in the throat, often causing life-threatening injuries. Nonoffset circle hooks, in which the barb is in the same plane as the circle, cause much less severe injuries, because the hook is "protected" and snagged animals tend to get caught in the jaw rather than the throat.
"I have data that proves that nonoffset circle hooks (flat circle hooks) reduced turtle bycatch," said Alan Bolton, a marine biologist at the Archie Carr Center for Turtle Research at the University of Florida, Gainesville. Bolton ran a four-year experiment in the Azores studying fishing gear modifications to reduce turtle bycatch.
"But I believe it is premature to recommend the offset circle hook," Bolton said. Intuitively, this hook appears to defeat the design advantage of the nonoffset circle hook.
Crowder agrees with Bolton. "My goal is to have turtles coexist with fisheries. And I'm not opposed to the Hawaii longline swordfish fishery, as long as the new technology is proven, but I'm not sure that this technology is ready for primetime. It needs further testing in the Atlantic, where there are more turtles left."
NMFS scientists, in collaboration with the New Jersey-based Bluewater Fisherman's Association, conducted experiments in the Atlantic testing both types of circle hooksoffset and nonoffset. They showed that both circle hooks significantly reduced the number of turtles caught, compared to the J-hooks.
Loggerhead and leatherback catches were reduced by 92 and 67 percent, respectively, said Tim Price, the acting assistant administrator with the Southwest branch of the NMFS. "Reopening of the Hawaii fishery will not cancel the benefits of the California fishery closing."
International Solution Required
The data from the Atlantic experiment is preliminary. It has not been reviewed by other scientists, it involves a small sample size, and the results are not published in a peer reviewed journal, Steiner said. "We are going to see an increase in the number of turtles killed."
U.S. longline fleets represent only about 6 percent of the global longline effort, Crowder said. Even if the entire U.S. longline fleet disappeared, the extinction trajectory for leatherbacks and loggerheads would be unchanged. The problem requires an international solution.
"Our view is that if we are not killing sea turtles, then we are in a much stronger position to convince other countries to do the same," Steiner said. "The problem is that the U.S. isn't in a position to have any moral authority right now."
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