TRACKING DATA COULD CUT LONGLINE TURTLE KILLS

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By Jan Tenbruggencate

HONOLULU, Hawai‘i (August 21, 2000 – The Honolulu Advertiser)---Loggerhead turtles are seldom found in Hawai‘i, but they frequently swim by the islands on cross-Pacific voyages that pass north of us.

They also are occasionally caught on longline fishing gear by the Hawai‘i-based longline fleet, which makes their biology of interest in the islands.

A group of researchers worked with data gathered from radio tags placed on nine juvenile loggerheads accidentally caught by longliners in 1997 and 1998.

The radio signals, reported to satellites, tracked the turtles’ positions for months, generally until the batteries ran out or something happened to the turtles or transmitters.

Among their findings: The movements of these turtles can be predicted, because they tend to stay in water of a specific temperature. Thus, presumably, longliners that avoid waters of those temperatures are likely to avoid hooking the turtles.

Researchers Jeffrey Polovina, Donald Kobayashi, Michael Seki and George Balazs of the National Marine Fisheries Service and Denise Parker of the University of Hawai‘i Joint Institute of Marine and Atmospheric Research combined the turtles’ paths with other satellite data that measured water temperature, sea height and amount of chlorophyll in the water, which is determined from sea color.

"This study shows the power of combining data from instruments on animals that describe their movements, together with remotely sensed environmental data covering the region around the animal during its movement to describe its habitat and its movement relative to oceanic features," the scientists said.

Satellites, operating in different ways, provide both prices of the puzzle.

Contrary to popular belief, the young loggerheads were found to be swimming into the current rather than drifting with it. The scientists figured that they were likely to encounter drifting food more often.

The turtles also appeared to favor water temperatures of about 63 degrees and 68 degrees Fahrenheit. These temperatures seem to occur where higher quantities of chlorophyll are available, suggesting productive feeding areas.

The data could be useful in directing the longline fishery, the scientists said. They found that turtles prefer the lower temperature area, around 63 degrees, and suggested that turtle catches could be reduced by keeping longline boats – all of which carry water temperature sensors – away from areas where turtles are likely to be feeding.

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