Scientists Estimate 90% Reduction in Accidental Sea Turtle Deaths in U.S. Fisheries

A loggerhead turtle escapes from a trawl net equipped with a turtle excluder device (TED). Image courtesy of NOAA.

A study published this month (PDF available here) estimates that the number of sea turtles accidentally caught and killed in United States coastal waters has declined by an estimated 90-percent since 1990, a dramatic reduction achieved in fisheries where specific regulations have been implemented to reduce bycatch. The report, published in the scientific journal Biological Conservation, is the first attempt to make a cumulative estimate of sea turtle bycatch and mortality from interactions with U.S. fisheries.

Researchers at Duke University’s Project GloBAL (Global By-catch Assessment of Long-lived Species) and Conservation International (CI) compiled available information reported by the National Marine Fisheries Service (NMFS), the agency responsible for managing US fisheries, to estimate how many sea turtles were taken as bycatch by U.S. fishermen between 1990 and 2007. Bycatch is the accidental capture and injury of marine animals in fishing gear that are not the target catch species.

The researchers estimated that 4,600 sea turtles currently perish each year in U.S. coastal waters, but nevertheless represents a 90-percent reduction in previous death rates. The scientists credit the reduced impact on sea turtles to bycatch reduction measures implemented in many fisheries over the past 20 years, in addition to critical declines in domestic fishing effort.  Overall turtle bycatch, including all fatal and non-fatal interactions, has been reduced by roughly 60-percent.

Before measures to reduce bycatch were put in place, total sea turtle takes surpassed 300,000 annually, killing more than 70,000 of these unintended captures across more than 20 fisheries that fish in U.S. waters in the Atlantic Ocean (from the Gulf of Mexico to the border with Canada) and Pacific Ocean (along the West coast and around Hawaii). Shrimp trawls in the Gulf of Mexico and Southeastern U.S. alone accounted for up to 98% of all takes and deaths during the past two decades.

To accomplish this reduction, NMFS instituted a series of regulations and mitigation strategies in individual fisheries, which included: the use of circle hooks in longlines as well as dehooking equipment to reduce the severity of injuries to turtles; the implementation of turtle excluder devices (TEDs) in shrimp trawl nets to allow captured sea turtles the chance to escape; and time-area closures that keep fishing activities and turtles separate in places and during times that turtles are most likely to be present in highest numbers.

All six marine turtle species that occur in U.S. waters are currently categorized as Threatened or Endangered on the U.S. Endangered Species List. They include loggerheads, leatherbacks, hawksbills, olive ridleys, Kemp’s ridleys and green sea turtles. Bycatch is the most serious, acute threat to sea turtle populations around the world, and high bycatch can be indicative of unsustainable fishing practices that negatively impact the health of marine ecosystems.

“The reduction of bycatch and mortality shows important progress by NMFS, which serves as a model for reducing sea turtle bycatch in other parts of the world,” said Elena Finkbeiner, a PhD student at Duke and lead author of the paper. “Our findings show that there are effective tools available for policy makers and fishing industries to reduce sea turtle bycatch, as long as they are implemented properly and consistently.”

While these trends are encouraging, the researchers also highlighted a crucial issue still in need of improvement. Currently, sea turtles are managed on a fishery-by-fishery basis, which means that bycatch limits are set for each fishery without accounting for the overall population impacts of all the takes added together. This piecemeal view and fragmented approach leads to total allowed takes that far exceed what sea turtle populations can sustain, in part because they are affected by multiple fisheries. So although these reductions in sea turtle bycatch are important, it is still unclear whether bycatch has been reduced enough to help sea turtles recover.

“We commend the successful efforts of fishers and NMFS managers to reduce sea turtle bycatch, but there is still important work to be done,” said Dr. Bryan Wallace, a co-author on the study and Director of Science for the Marine Flagship Species Program at Conservation International and Adjunct Faculty member at Duke University. “Bycatch limits must be set unilaterally across all U.S. fisheries with overall impacts to populations in mind, much as it’s done for marine mammals. This would ensure that these bycatch reductions are successful in recovering sea turtle populations.”

The report relied on NMFS data generated largely through an on-board observer program, which places non-fishermen aboard fishing vessels to independently monitor and document fishing activities, particularly bycatch. The observer program and mitigation efforts place NMFS among the best national fisheries management agencies in the world, but researchers stress that bycatch estimates in some fisheries are highly uncertain because observer coverage is too low relative to the sheer volume of fishing taking place.

In particular, the researchers noted high uncertainty in shrimp trawl bycatch estimates due to a lack of observer coverage and inconsistent compliance with TED regulations in these fisheries. This means that actual bycatch is likely higher than what the study reported, because researchers assumed full compliance by fisheries governed by bycatch regulations.

“This paper provides a baseline to examine what is working and what can be improved in preventing sea turtle bycatch,” Finkbeiner said. “It certainly does make a strong case for the need for increased observer coverage and bycatch reporting across US fisheries.”

“The bottom line is, we have the tools and the knowledge to save these iconic but threatened animals,” Wallace said. “We just have to commit to consistently implementing these tools in fisheries in U.S. waters and around the world to promote sustainable fisheries with reduced bycatch.”

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