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Duke scientists assess accidental turtle catching

A team of Duke scientists is pushing the boundaries of knowledge about sea turtles caught by commercial fishing processes.

The study compiled over 1,800 records of sea turtle bycatch, the unintentional snaring of sea animals by fishers, in all life stages from more than 230 sources globally and by three different fishing gears—longline, net and trawl. The study also tallied bycatch impact scores—bycatch rates, mortality, body size and regional fishing effort—rather than just sea turtle mortality and was published in the journal Ecosphere last month. The results may influence regional conservation and research efforts.

“What [we] really wanted to do was advance bycatch assessments… beyond the level of how many sea turtles are killed every year, and really try to do something that would be relevant on a population level, where we could actually compare impacts of bycatch in different gears,” said lead author Bryan Wallace, chief scientist at the Oceanic Society and adjunct assistant professor at the Duke University Marine Lab.

This study builds off of the goals of Project GloBAL—the Global Bycatch Assessment of Long-lived Species—a three-year project from 2005 to 2008. Hosted at Duke, this project helped establish Duke as a leader in the bycatch research field, Wallace said. The researchers, from both the Duke University Center for Marine Conservation and the Blue Ocean Institute, focused on researching bycatch of sea turtles as well as additional marine taxa, including marine mammals as well as seabirds.

Project GloBAL sought to compile bycatch data from around the world to get a better sense of the issue of bycatch globally, noted Rebecca Lewison, co-author of the study and researcher at the conservation ecology lab at San Diego State University.

“One of the goals of Project GloBAL was to say that we need to be looking large-scale,” she said. “We need to be able to look across ocean regions as well as gear types.”

While most bycatch information is regional and generally focuses on one gear type, this recent study is the first mapping effort globally across the three major commercial fishing gears, Lewison added.

The study found that the highest rates of bycatch occurred in the east Pacific Ocean, some Mediterranean regions and the northwest and southwest parts of the Atlantic Oceans, which were also the areas with the most accessible data. Although the researchers found that longline fishing bycatch impact scores were lower than those of trawling and net fishing, they urged further research at the more regional level to fill in data gaps.

“We have more information on longline gear from a commercial fishing standpoint,” said Connie Kot, associate researcher at the Duke Marine Geospatial Ecology Lab. “There may be a lot more net and trawl fishing that we are not capturing in this study that could affect sea turtle populations as well.”

Researchers hope that this data will inspire additional regional studies in areas with high bycatch rates.

Kot emphasized that solutions to the bycatch issue would vary by region, and that switching to one fishing gear would not be practical, as trawl, net and longline all target different fish. For example, in a region where the fishing industry is reliant on trawlers, implementing and maintaining turtle excluder devices would be more effective than switching to new equipment, she said.

The research team aims to conduct similar mapping studies in the future with other marine taxa, Lewison added.


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