Millions of sea turtles are killed as ‘collateral damage’ in the race for fish

Trail of green sea turtles (Chelonia mydas) caught during longline fishing by artisanal fishing boat.© Projeto Tamar Brazil

April 2010. Millions of sea turtles have become the unintended victims of a failure to properly manage the worlds' fisheries, with more and more of their habitats clogged with hooks and nets, an important new report has revealed.

Gillnets, longlines, and trawls
The report - the first ever global assessment of sea turtle bycatch in the three major types of fishing gear - gillnets, longlines, and trawls - highlights vast ocean regions where little about bycatch rates is known, and where urgent conservation action to reduce bycatch is necessary to prevent the extinction of these ancient, endangered animals.

The report clearly shows the links between increased fishing gear in regions and the increase in accidental capture of sea turtles.

Hawksbill turtle (Eretmochelys imbricata) entangled in a gillnet. © Projeto Tamar Brazil.

Bycatch occurs when fisheries use indiscriminate gear such as longlines with thousands of baited hooks, or nets that inadvertently snag animals other than what they are intended to catch. Sea turtles, along with sharks, dolphins, and albatrosses, are among the most frequently accidentally captured. Air-breathing reptiles, sea turtles often perish as a result of drowning in nets or swallowing sharp J-shaped hooks which can become lodged in the soft tissue of turtles' throats and stomachs, causing severe and often grave injuries.

Global Patterns of Marine Turtle Bycatch
In their report titled: "Global Patterns of Marine Turtle Bycatch", Dr. Bryan Wallace of Conservation International (CI), and Dr. Rebecca Lewison of San Diego State University, investigated the impact of bycatch on sea turtles around the globe from 1990-2008. Their findings show that tens of thousands (~85,000) of marine turtles have been reported as bycatch in the past twenty years, but Wallace and colleagues stress that actual numbers are likely to be significantly higher.

Green sea turtles (Chelonia mydas) drowned in a gillnet. Turtles become entangled and are unable to surface to breathe. © Projeto Tamar Brazil

Dr. Wallace, the Science Advisor for CI's Sea Turtle Flagship Program said: "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." 

Six out of seven marine turtles are Endangered
Six of the seven marine turtle species are currently categorized as Vulnerable, Endangered, or Critically Endangered globally by the International Union of Conservation of Nature's (IUCN) Red List. They include loggerheads, leatherbacks, hawksbills, Olive Ridleys, Kemp's Ridleys and green sea turtles; the flatback, an endemic to Australia, is currently categorized as Data Deficient.

Bycatch is by far the major threat to marine turtles
Sea turtles are highly migratory animals that cover vast areas of ocean between nesting and feeding grounds, travelling thousands of miles each year and traversing international boundaries. Their broad distributions expose them to several threats, including direct capture for their meat and collection of eggs, destruction of nesting beaches, pollution of the ocean, and climate change. However, bycatch is the most serious, acute threat to sea turtle populations around the world.

Reported bycatch
The global data review revealed that 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.

Leatherback sea turtle (Dermochelys coriacea) caught as bycatch in gillnet. © Projeto Tamar Brazil

Worst zones for sea turtles
However, when bycatch rates and amounts of reported fishing activity for all three fishing gear types were combined and compared, four regions emerged as the overall most urgent conservation priorities: the Mediterranean, the Eastern Pacific, the Southwest Atlantic, and the Northwest Atlantic.

Mediterranean

In the Mediterranean Sea, where more than 20 countries fish in the same ocean basin for species like bluefin tuna and swordfish, a lack of integrated management has led to some of the highest concentrations of longline fishing and trawling around the globe, and consequently, some of the highest sea turtle bycatch rates in the world. 

Eastern Pacific
In the Eastern Pacific - which stretches from Baja California, to Patagonia, Chile and hosts critical nesting and breeding grounds for the leatherback and Olive ridley sea turtles - populations of leatherback and hawksbill have nearly collapsed, owing in part to bycatch in large and small-scale fisheries which deploy large numbers of longlines, gillnets and shrimp trawls in both the high-seas and near shore.

US Atlantic Coast
Other regions highlighted as urgent conservation priorities in the report include the Southwest Atlantic and Northwest off the eastern United States, home to one of the world's largest loggerhead turtle populations, but where high numbers of longline and trawl fisheries also contribute to high incidents of bycatch.

"We have only begun to scratch the surface about the realities of sea turtle bycatch," said study researcher 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." 

"Sea turtles are sentinel species of how oceans are functioning. The impacts that human activities have on them give us an idea as to how those same activities are affecting the oceans on which billions of people around the world depend for their own well-being." said Dr. Wallace. "Our hope is that this study gives governments and fisheries alike another impetus for bolstering on-going efforts to reduce sea turtle bycatch and to promote more sustainable fishing practices as soon as possible."

The report appears in the journal Conservation Letters was conducted by Conservation International (CI) in partnership with Duke University's Project GloBAL (Global By-catch Assessment of Long-lived Species).