Humankind’s appetite for seafood has had a bigger impact on the world’s marine turtles than long thought. A new report by Conservation International (CI) in partnership with Duke University’s Project GloBAL (Global By-catch Assessment of Long-lived Species) finds that in the past eighteen years it is likely millions of marine turtles have been killed as bycatch by the world’s fisheries.
Revealing the true extent of fisheries’ role in collapsing marine turtle populations, the first ever global survey of sea turtle bycatch found that from 1990-2008 approximately 85,000 marine turtles were officially reported killed as bycatch, yet a staggering amount of unreported mortalities likely raise that total into the millions.
“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,” explains Dr. Bryan Wallace, the Science Advisor for CI’s Sea Turtle Flagship Program and one of the reports lead authors, in a press release.
 Leatherback sea turtle (Dermochelys coriacea) caught as bycatch in gillnet. Photo by: © Projeto Tamar Brazil – Image Bank. |
‘Bycatch’ is a term for species killed unintentionally by fisheries. Marine turtles are especially susceptible to bycatch since like all reptiles, they breathe air. Therefore they must frequently reach the surface of the ocean in order to breathe. If caught in a fisherman’s net or on a hook the marine turtle quickly drowns. In addition, marine turtles frequently swallow hooks which can become lodged in their throats or stomachs, leading to severe injuries. The most dangerous fishing equipment for marine turtles includes gillnets, longlines, and trawls.
Marine turtle populations worldwide have suffered gravely over the past century with some regional populations collapsing entirely. Currently the IUCN Red List classifies six of the seven marine turtles as threatened with extinction, while the flatback marine turtle, endemic to Australia, is considered Data Deficient. Three of the world’s marine turtles are classified Critically Endangered: the world’s largest, the leatherback; the hawksbill; and Kemp’s ridley. Despite a barrage of threats, including plastic garbage, pollution, beach development, light pollution, egg poaching, and climate change, the report highlights that the most pressing threat remains bycatch.
The report identified four areas where urgent conservation measures are necessary due to fishery bycatch: the Mediterranean, the Eastern Pacific, the Southwest Atlantic, and the Northwest Atlantic. The crowded, heavily-fished Mediterranean Sea has some of the highest bycatch rate in the world due to the concentrated use of longline fishing and trawling. The Eastern Pacific—from Baja California to Chile—possesses critical nesting sites for marine turtles, but bycatch rates are also high from both artisanal and industrial fisheries. In addition, off the coast of the eastern United States, the Southwest and Northwest Atlantic has high numbers of longline and trawling bycatch.
“We have only begun to scratch the surface about the realities of sea turtle bycatch,” said 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.”
 Dead sea turtle entagled in fishing net washed up onto a beach. Photo by: © Projeto Tamar Brazil – Image Bank. |
The report stresses that better management and changes in the way fisheries operate—both large and small—could prevent many marine turtle mortalities due to bycatch. In addition, mitigating the threat of bycatch would not only help marine turtles, but other bycatch victims, including sea birds, dolphins, sharks, and even whales.
Simple changes in gear, such as the use of circle hooks instead of J-shaped hooks have a big impact on turtle mortality. For trawling fishing—often used for shrimp—Turtle Excluder Devices (TEDs) allows marine turtles to escape drowning through a hatch in the trawl.
On-board observer programs are also needed for small-scale fisheries to document marine turtle mortalities and enforce regulations. CI is currently supporting such observers in Ecuador.
The report also recommends implementing seasonal and time-area closures, which halts fishing during peak-marine turtle presence. Most marine turtles migrate and therefore are only present in certain regions at particular times of the year.
Finally, the implementation of catch-shares programs and increasing Marine Protected Areas (MPAs) would not only aid endangered species like the world’s marine turtles, but would help sustain populations of the world’s targeted fish species for future generations.
“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.”
Of course, saving sea turtles is also the responsibility of seafood consumers. The report encourages consumers to use sustainable seafood guides and resources like FishPhone to make marine turtle-friendly choices at the supermarket and in restaurants.
Trail of green sea turtles (Chelonia mydas) caught during longline fishing by artisanal fishing boat. Photo by: © Projeto Tamar Brazil – Image Bank.
Green sea turtle (Chelonia mydas) entangled in gillnet. Photo by: © Projeto Tamar Brazil – Image Bank.
Leatherback sea turtle (Dermochelys coriacea) snagged by a hook in a longline. Photo by: © Projeto Tamar Brazil – Image Bank.
Longline hooks stored aboard fishing boat prior to deployment. Photo by: © Projeto Tamar Brazil – Image Bank.
Hawksbill turtle (Eretmochelys imbricata) entangled in a gillnet. Note the fish in the turtle’s mouth. Sea turtles become entangled when opportunistically feeding on fish caught in fishing gear. Photo by: © Projeto Tamar Brazil – Image Bank.
Green sea turtles (Chelonia mydas) drowned in a gillnet. Turtles become entangled and are unable to surface to breathe. Photo by: © Projeto Tamar Brazil – Image Bank.
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