"What often happens with longliners is that it is just inconvenient to hassle with a turtle and they don't want to lose the hook, either, so what people will do is just cut the flipper off with a machete and just send the turtle away to die," he said. "A turtle without a front flipper is a dead turtle."
Shillinger said there may also be another reason for the leatherbacks' population crash, one not so obvious from their data.
There was one turtle that didn't follow the migration route to the South Pacific Gyre. Instead, it swam south along the coast of Central America, where it stayed for the entire time the tag was working, 588 days.
"It seems logical that turtles would want to move along the coast, because these are highly productive regions, where they don't have to work as hard to find food," Shillinger said. Even though only one of the 46 subjects of the study cruised the coastal areas, he said it might be a rare survivor of a larger population that used to swim in the coastal area, but could have been hit hard by human fishing pressure in the near shore areas. Gillnets and longlines are major threats to turtles in these areas.
Shillinger says they won't be able to answer that question until they have gathered more data, since very little current data exists about bycatch in these coastal fisheries. As the tags are designed to degrade and fall off, the researchers haven't been able to capture the turtles' movements beyond about two years. He suggests that turtles returning to Costa Rica from the South Pacific Gyre may turn out to be using the near shore habitats on their return.
Some progress in helping the leatherback population on the beache
|Contact: Dan Stober|