海龜 ──漁業競爭下的犧牲者

Millions of sea turtles are thought to have died over the past 20 years because they were caught accidentally in fishing nets or snagged on longlines, according to the first ever global study of unintended capture on marine turtle populations.

Unintended capture of non-target species, called bycatch, happens when fisheries use gear such as longlines with thousands of baited hooks, or nets that kill animals other than those they are intended to catch.

As a result, six of the world's seven species of marine turtles now are categorized as Vulnerable, Endangered, or Critically Endangered on the authoritative Red List of Threatened Species complied by the International Union for the Conservation of Nature, IUCN.

They are loggerheads, leatherbacks, hawksbills, olive ridleys, Kemp's Ridleys and green sea turtles. The conservation status of the seventh marine turtle species, the flatback, endemic to Australia, is currently unclear due to lack of data.

These ancient species, believed to have become distinct from all other turtles at least 110 million years ago, are now being wiped out by irresponsible fishing practices, the study shows.

Published this week in the journal "Conservation Letters," the research was conducted by Conservation International in partnership with Duke University's Project GloBAL, which stands for Global By-catch Assessment of Long-lived Species.

It documents what happens to marine turtles when they encounter the three major types of fishing gear - gillnets, longlines, and trawls. Air-breathing reptiles, sea turtles often perish as a result of drowning in nets or swallowing sharp J-shaped hooks, while their natural life spans range from 50 to more than 100 years, depending on species.

In their report titled "Global Patterns of Marine Turtle Bycatch," Dr. Bryan Wallace of Conservation International and Dr. Rebecca Lewison of San Diego State University, with several co-authors from Duke University's Center for Marine Conservation, investigated the impact of bycatch on sea turtles around the globe from 1990-2008.

Their global data review shows that some 85,000 marine turtles have been reported as bycatch in the past 20 years, but Wallace and colleagues stress that the actual numbers of sea turtles killed as bycatch are "likely to be significantly higher."

Sea turtles migrate across vast areas of ocean between nesting and feeding grounds, traveling thousands of miles each year. Their survival is threatened by capture for their meat and collection of eggs, destruction of nesting beaches, pollution of the ocean, and climate change. Yet the researchers found that bycatch is the most serious, acute threat to all sea turtle populations.

The highest reported bycatch rates for longline fisheries occurred off Mexico's Baja California peninsula, the highest rates for gillnet fishing took place in the North Adriatic region of the Mediterranean and the highest rates for trawls were found off the coast of Uruguay.
When bycatch rates and fishing activity for all three fishing gear types were combined and compared, four regions emerged as the most urgent conservation priorities - the Mediterranean, the Eastern Pacific, the Southwest Atlantic, and the Northwest Atlantic.

In the Mediterranean Sea, where more than 20 countries fish for lucrative species like bluefin tuna and swordfish, a lack of integrated management has led to some of the world's highest concentrations of longline fishing and trawling, and some of the highest sea turtle bycatch rates.

In the Eastern Pacific, from Baja California to Patagonia, Chile populations of leatherback and hawksbill turtles have nearly collapsed. Wallace and his team say the collapse is due in part to bycatch in large and small-scale fisheries which deploy large numbers of longlines, gillnets and shrimp trawls on the high seas and also near shore.

"We have only begun to scratch the surface about the realities of sea turtle bycatch," said Dr. Wallace. "Our review revealed important data gaps in areas where small-scale fisheries operate, especially Africa, the eastern Indian Ocean and Southeast Asia. These regions and fisheries are urgent priorities for enhanced monitoring and reporting effort so that we can fill in some blanks about turtle bycatch."

To lower sea turtle bycatch rates, and improve overall ocean health, Conservation International's Global Marine Division recommends establishing Marine Protected Areas, a vessel monitoring system and on-board observer programs.

Conservation International also recommends sustainable fisheries reform, including seasonal and time-area closures to control fishing activity in turtle migration areas as well as catch-shares, which place quotas on fishing efforts and reduce the race for fish.

Gear modification to replace damaging J-hooks with the expanded use of circle hooks, as well as the widespread implementation of Turtle Excluder Devices, which serve as escape hatches for sea turtles caught in shrimp trawls. These guidelines are also recommended by the UN Food and Agriculture Organization.