GPS Tracks Leatherback Turtle Hotspots To Prevent Fishing Deaths
January 9, 2014

GPS Tracks Leatherback Turtle Hotspots To Prevent Fishing Deaths

April Flowers for - Your Universe Online

One of the most endangered species in the world, the Pacific Ocean's leatherback sea turtle population has declined by more than 90 percent since 1980.

One of the greatest causes of this species' death is industrial longline fishing, which sets thousands of hooks in the ocean to catch fish, but sometimes catch turtles as well. Research teams use modern GPS technology to predict where fisheries and turtles will interact in order to reduce the unwanted capture of turtles by fishermen.

A new study led by Drexel University shows the use-intensity distributions for 135 satellite-tracked adult turtles and distributions of longline fishing efforts in the Pacific Ocean. The researchers are able to predict bycatch risk using the overlap of these distributions in space and time. Time and area closures for the fisheries are essential, the research team asserts, to protect these animals and maintain the health of the commercial fishery. The findings were published in the Proceedings of the Royal Society B.

Drexel scientists collaborated with several other universities, the NOAA/NMFS Southwest Fisheries Science Center and a US non-profit, The Leatherback Trust.

“Given the size of the Pacific Ocean and the number of fisheries from dozens of nations that use it, managing bycatch is a complex issue,” said John Roe, PhD, lead author of the paper and an assistant professor at the University of North Carolina at Pembroke. “To complicate things, fisheries authorities are not always forthcoming with information on when and where they capture turtles, so identifying problem areas, or hotspots, where bycatch likely occurs has proven elusive until now."

An unfortunate accident occurs when fisheries and turtles fish in the same place at the same time.

“Leatherback turtles get caught on longlines by both biting at the bait and getting entangled in the lines themselves,” said James Spotila, PhD, the Betz Chair Professor of Environmental Science in the College of Arts and Sciences at Drexel. “Fishermen do not want to catch the turtles but have had limited success in avoiding them. Now they will be able to set their lines in areas where the turtles are unlikely to occur, making the ocean safer for turtles and reducing the cost to the fishermen of having to deal with the giant turtles.”

Spotila has been studying sea turtles with Drexel students and colleagues for 25 years.

The team also found that areas of predicted bycatch risk did not overlap for nesting populations of leatherback turtles for the eastern and western Pacific Ocean. This suggests that these populations should be treated as distinct management units with respect to fishing bycatch.

There are key areas of high risk for western Pacific populations in the north and central Pacific Ocean. The greatest risk, however, is adjacent to the nesting beaches in tropical seas of Indo-Pacific islands such as Papua New Guinea and Irian Jaya and the Solomon Islands. These areas can readily be regulated as they are under the exclusive economic control of national authorities.

“Bycatch may be more easily avoided when areas of high risk occur predictably in space and time, allowing fisheries operators to adjust their efforts accordingly”, said Roe. “Because leatherbacks follow paths that persist from year to year as they revisit the same nesting beaches, these areas provide an especially good opportunity for flexible regulations that serve the needs of both turtles and fisheries alike.”

For the eastern Pacific nesting populations, migrations to nesting beaches are associated with moderate risk. A large and persistent risk exists, however, in the South Pacific Gyre -- a broad open ocean area outside national waters where management is currently lacking and might be difficult to implement.

The research team suggests that future efforts should focus on these predicted hotspots to develop more targeted management approaches that would alleviate leatherback bycatch.

“Now that we’ve scientifically homed in on where and when protections are needed, especially in the South Pacific Ocean the solutions to the turtle fishery problem will take international cooperation and innovative uses of technology to manage this wild west where regulations are few and enforcement is nil,” Spotila said.


Image Below: Maps show probable relative interactions between leatherback turtles and industrial longline fisheries in the Pacific, over four quarters of the year. (Top row: Q1-Q2. Bottom row: Q3-Q4.) Credit: Roe et al.