Leatherback turtles' newly discovered migration route may be roadmap to...(track was remaining the same. Not only w...)
track was remaining the same. Not only were the turtles heading in the same direction, they were actually trying to follow an even narrower path than the raw data showed. As Bograd put it, "They definitely had a place they wanted to go."
That place is the South Pacific Gyre, a vast region considered a relative desert among the world's oceans. So why go there if it's so barren?
"That's still a big puzzle as to why they choose to go to this region," Palacios said.
The only data available are satellite images showing the color of the sea. Researchers interpret greener water to be richer in chlorophyll, which is considered the foundation for the ocean food chain. Thus, the relative abundance of chlorophyll is inferred to indicate the relative richness of a fishery. Satellite images show very little green in the South Pacific Gyre.
But, satellites can only penetrate about 25 meters below the surface in the gyre. "Maybe the turtles are targeting something that is deeper in the water column," Palacios said.
"What are they doing there is a big question," Shillinger said. "Perhaps the tremendous water clarity may work to the advantage of these leatherbacks because they are visual predators," he said. "They can spot little specks of white out in the deep blue sea." Leatherbacks dine exclusively on gelatinous zooplankton, such as jellyfish.
Shillinger also said that there is a substantial longline fishery in that area, for bigeye and yellowfin tuna. "Obviously, the fish are eating something and it's something we're not picking up in chlorophyll signatures from satellite imagery," he said.
Given that leatherbacks have been recorded diving as deeply as 1,280 meters, they have ample choice as far as where in the water column they choose to feed. And considering that they can grow to over 6 feet in length and weigh up to 2,000 pounds, it seems like a safe bet that they're feeding on something.
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| Contact: Dan Stober dstober@stanford.edu 650-723-2558 Stanford University Source:Eurekalert |
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