Millions of Sea Turtles Killed Accidentally?

雪儿 · 发表于: 2011-7-8 12:49:32

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Sea Turtles Netted

Photograph courtesy Projeto Tamar Brazil, Image Bank

Entangled and drowned in a fishing net off the coast of Brazil, these green sea turtles in an undated picture are just a few of the millions of sea turtles that have been unintentionally killed by fishing operations over the past 20 years, according to a study released today by the journal Conservation Letters.
"Of all the threats sea turtles face right now, bycatch is the most serious," said Bryan Wallace, a marine biologist with Conservation International and lead author of the study. (Read a commentary by Wallace on how he thinks changing your eating habits can help sea turtles.)

The study pulls together data from around the world on sea turtle deaths from nets, hooks, and trawlsóand questions the estimates of previous reports.

"Because the reports we reviewed typically covered less than one percent of all fleets, with little or no information from small-scale fisheries around the world, we conservatively estimate that the true total is probably not in tens of thousands, but in the millions of turtles taken as bycatch in the past two decades," the authors write.

Six of the seven sea turtle species are listed as vulnerable, endangered, or critically endangered on the International Union for Conservation of Nature's Red List of threatened species.

雪儿 · 发表于: 2011-7-8 12:56:08

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Small Fishers = Big Sea Turtle Toll?

Photograph courtesy Projeto Tamar Brazil, Image Bank

Entangled green sea turtles trail from a fishing boat off Brazil (file photo).

More than 90 percent of the world’s fishers operate in local, small-scale operations, but researchers have no idea what proportion of the total sea turtle bycatch occurs in small-scale fisheries.

The new study tallied sea turtle bycatch from published reports, which are primarily from observers aboard industrial fleets. All told, about 85,000 turtles were reported accidentally taken between 1990 and 2008.

雪儿 · 发表于: 2011-7-8 12:56:29

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Sea Turtle Scavenger

Photograph courtesy Projeto Tamar Brazil, Image Bank

Fish still firmly in its jaws, this hawksbill sea turtle got entangled while scavenging from a gillnet off Brazil (file photo). Gillnets are nearly invisible mesh curtains with holes that are sized according to the intended catch.

"For turtles, just like the fish, if they can't easily perceive it visually, then they can easily run into it," said study leader Wallace. "And sea turtles don't have a reverse gear, so when they hit it and they try to evade it, all that means is they paddle harder into it."

雪儿 · 发表于: 2011-7-8 12:56:48

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Gillnet Offers No Way Out

Photograph courtesy Projeto Tamar Brazil, Image Bank

Gillnets–such as the one entangling this green sea turtle in a file photo taken off Brazil–tend to have higher sea turtle mortality rates than longlines or trawls, Wallace said. Longlines are floating lines that can stretch for miles, with thousands of baited hooks, while trawls are seafloor-dragging, bag-shaped nets.

Sea turtles need to breathe air, but with gillnets, "there's less chance of turtles getting to the surface when entangled and below the surface."

Many trawls, by contrast, have "turtle excluder devices," or TEDs, which have trap doors that allow turtles and large marine mammals to escape. And because longlines are at the surface, they at least allow trapped turtles to breathe.

雪儿 · 发表于: 2011-7-8 12:57:03

Cut Loose and Dead

Photograph courtesy Projeto Tamar Brazil, Image Bank

Many sea turtles that are drowned in fishing nets are cut loose and wash ashore, such as this turtle in a file photo taken in Brazil. Small-scale fishers, in particular, tend not to have room on their boats–or time–for entangled turtles, according to Wallace.

"It is really tricky," he said. "You can imagine if you are a small-scale fisherman and your gillnet is your meal ticket and you've got a big leatherback that's stuck and entangled in this thing–you are risking your own life trying to free the turtle."

雪儿 · 发表于: 2011-7-8 12:58:05

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Cut Loose and Dead

Photograph courtesy Projeto Tamar Brazil, Image Bank

Many sea turtles that are drowned in fishing nets are cut loose and wash ashore, such as this turtle in a file photo taken in Brazil. Small-scale fishers, in particular, tend not to have room on their boats–or time–for entangled turtles, according to Wallace.

"It is really tricky," he said. "You can imagine if you are a small-scale fisherman and your gillnet is your meal ticket and you've got a big leatherback that's stuck and entangled in this thing–you are risking your own life trying to free the turtle."

雪儿 · 发表于: 2011-7-8 12:58:21

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Freed Sea Turtle

Photograph courtesy Projeto Tamar Brazil, Image Bank

Freed from a net, a beached green sea turtle in Brazil heads for the ocean in an undated picture.

Sea turtle researcher Hoyt Peckham in Baja California, Mexico, (map) encourages local fishers to trade in their gillnets–typically used to snare such prey as salmon, cod, and sardines–for hook-and-line gear.

"Hook-and-line is way more selective than gillnets," said Peckham, director of the Proyecto Caguama with Grupo Tortugero, a sea turtle conservation organization, a sea turtle conservation organization, who was not involved with the new study.

The switch also allows fishers to capitalize on market demand for high-value species suited to hook-and-line fishing, such as tuna and swordfish, he said.

"Unfortunately," study leader Wallace said, "those kinds of programs are few and far between. ... "

雪儿 · 发表于: 2011-7-8 12:59:12

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End of the Line?

Photograph courtesy Projeto Tamar Brazil, Image Bank

Leashed by a stray hook in its flipper, a leatherback sea turtle struggles to break free of a longline off Brazil in an undated photo.

"Leatherbacks don't very frequently get hooked in the mouth," study leader Wallace said. Tending to selectively prey on jellyfish, leatherbacks "don't usually go after the bait" on longline hooks.

Other species, such as loggerhead sea turtles off the U.S. Southeast, are lured by longline bait. "It goes up to take a chomp out of it," he said, "and you can imagine what happens next."

雪儿 · 发表于: 2011-7-8 12:59:25

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No Turtles Allowed

Photograph courtesy Calen Offield

Turtle excluder devices, or TEDs–such as the circular white grate shown here on a net about to be deployed–are among the sea turtle bycatch prevention success stories, according to Wallace.

The bars prevent large creatures from swimming to the bottom of the net and funnel them toward a trap door in the netting.

"When TEDs are put in nets the way they should be, and when they are allowed to work," Wallace said, "sea turtle bycatch is reduced dramatically."

雪儿 · 发表于: 2011-7-8 12:59:43

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Playing Hooky

Photograph courtesy Calen Offield

Longliners primarily use two different types of hooks, the J hook (left) and the circle hook. Easier to swallow, J hooks tend to cause more serious injury to sea turtles, so many fishers are switching to circle hooks, according to study leader Wallace.

All longliners registered in Hawaii, for example, are now required to use circle hooks. The Hawaii fishery also has a sea turtle bycatch quota. Observers on all longline boats keep track of the sea turtle take. Despite the government regulations, Hawaii remains a stable, productive fishery, Wallace said.

"It shows that taking the right steps ... can lead to a holistic gear- and region- and fisher-appropriate response to sea turtle bycatch."

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