DURHAM, N.C. – A study of the accidental by-catch of Pacific loggerhead turtles by local fishing fleets in Baja California is shedding new light on the previously overlooked role small fisheries may play in the decline of endangered migratory marine animals worldwide.   

“Our findings suggest that small-scale fisheries may be among the greatest current threats to non-target megafauna including turtles, sea birds and marine mammals,” says 91 marine biologist Larry T. Crowder, one of the study’s six authors.

Crowder is the Stephen Toth Professor of Marine Biology and director of the Center for Marine Conservation at Duke’s Nicholas School of the Environment and Earth Sciences.

The study was published today in the peer-reviewed, open-access Web-based science journal PLoS One. It is accessible online at .

Small-scale fisheries, which include artisanal, traditional and subsistence fisheries, employ more than 99 percent of the world’s fishermen, primarily in developing nations.

New telemetry data reveal that at some point in their migrations, many endangered marine species frequent coastal hotspots well within reach of these fisheries, Crowder says. But because documentation and management of the fisheries in developing countries is often limited or non-existent, few scientific studies have been able to quantify by-catch that occurs there.

Crowder and his colleagues’ study focused on a stretch of ocean off the coast of Baja California Sur frequented by 30 loggerhead turtles that the team satellite-tracked from 1996 to 2005. As adults, the turtles migrated through the North Pacific, but as juveniles they spent 70 percent of their time in a relatively small area of Baja coastal waters.

Working in partnership with fishermen, the scientists assessed loggerhead by-catch mortality in the area by putting trained observers aboard two small-scale fishing fleets that operated near the coastal hotspot.  One fleet, out of the village of Puerto Lopez Moreles, fished bottom-set gillnets; the other fleet, out of the port of Santa Rosa, fished bottom-set longlines.

Based on their observations over a three-month period, the scientists estimated that in 2005 a minimum of about 1,000 loggerheads died as a result of by-catch from the two small fleets, a number that rivaled mortality rates of much larger industrial-scale fleets in the open ocean.

The actual number of annual mortalities in the region was likely much higher than the estimate, because minimum values were used in the scientists’ calculations and their estimate covered losses from only two of 12 or more fishing fleets that were operating in or near the loggerhead hotspot.   

“It was a sobering realization,” Crowder says. According to research by the U.S. National Marine Fisheries Service, between 37 and 92 by-catch mortalities of large juvenile North Pacific loggerheads per year would appreciably increase the species’ extinction risk, he says, “and theminimum annual by-catch mortality rate we calculated for just these two fleets was a full magnitude of order greater.”

Further research is urgently needed to quantify small-scale fisheries by-catch in coastal hotspots around the globe, he says.

One positive outcome of the study is that as a result of the partnership between local  fishermen and the scientists, the fishermen have now mobilized with other area citizens and are working to establish a national loggerhead refuge in Baja California Sur’s waters.

Crowder’s co-authors on the paper are S. Hoyt Peckham and Andreas Walli from the University of California at Santa Cruz; David Maldanado Diaz and Georgita Ruiz from the Mexican NGO Grupo Tortuguero; and Nicholas School alumnus Wallace J. Nichols of the California Academy of Sciences. Peckham is the paper’s lead author.

 

Contacts: Larry Crowder, (252) 504-7637 or lcrowder@duke.edu; or Tim Lucas at (919) 613-8084 or tdlucas@duke.edu.