This study 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.
"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."
Sea turtles interact with a variety of fishing gears across their broad geographic distributions and ontogenetic habitat shifts. Cumulative assessments of multi-gear bycatch impacts on sea turtle populations are critical for coherent fisheries bycatch management, but such estimates are difficult to achieve, due to low fisheries observer effort, and a single-species, single-fishery management focus. We compiled the first cumulative estimates of sea turtle bycatch across fisheries of the United States between 1990 and 2007, before and after implementation of fisheries-specific bycatch mitigation measures. An annual mean of 346,500 turtle interactions was estimated to result in 71,000 annual deaths prior to establishment of bycatch mitigation measures in US fisheries. Current bycatch estimates (since implementation of mitigation measures) are ~60% lower (137,800 interactions) and mortality estimates are ~94% lower (4600 deaths) than pre-regulation estimates. The Southeast/Gulf of Mexico Shrimp Trawl fishery accounts for the overwhelming majority of sea turtle bycatch (up to 98%) in US fisheries, but estimates of bycatch in this fishery are fraught with high uncertainty due to lack of observer coverage. Our estimates represent minimum annual interactions and mortality because our methods were conservative and we could not analyze unobserved fisheries potentially interacting with sea turtles. Although considerable progress has been made in reducing sea turtle bycatch in US fisheries, management still needs improvement. We suggest that sea turtle bycatch limits be set across US fisheries, using an approach similar to the Potential Biological Removal algorithm mandated by the Marine Mammal Protection Act.
Citation: Finkbeiner, E.M., et al. Cumulative estimates of sea turtle bycatch and mortality in USA fisheries between 1990 and 2007. Biol. Conserv. (2011), doi:10.1016/j.biocon.2011.07.033
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