Natures wonders:Sea turtle migration; new study (Introduction)

by David Turell , Sunday, December 06, 2020, 21:17 (1236 days ago) @ David Turell

Not always back to the same spot it is now known:

http://oceans.nautil.us/feature/644/how-sea-turtles-find-their-way?mc_cid=e6cd2fa557&am...

"Other than the moments after they hatch and crawl into the surf, sea turtles spend their entire lives in the ocean. Only when females return to lay eggs on the same beaches where they hatched do they leave the water—just briefly, for a few hours, before slipping back into the sea. They may lay several clutches of eggs during the mating season before setting off for their foraging territories. There they stay for several years, regaining energy by feasting on seagrass, before returning to their natal beach, mating just offshore, and beginning the cycle anew.

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"And so on that moonlit night in October of 2017 volunteers from the U.S. military facility on Diego Garcia helped Nicole Esteban, a marine biologist and sea turtle conservationist at Swansea University, fasten a GPS transmitter to the top of the turtle's shell while she laid her eggs. The volunteers nicknamed the turtle Serenity and watched as she and the computer on her back crept back into the waves and disappeared.

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"Their destinations underscored the extraordinary nature of sea turtle migration. It’s astonishing enough that a sea turtle can navigate across thousands of miles of open ocean, with no discernible landmarks, and wind up in the correct place. Even more astonishing is when the correct place is a dot of sand with nothing but blue until the horizon in every direction.

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"'We used turtles that had never been in the ocean before," Lohmann emphasizes. They had only hatched a few hours earlier, "and we just exposed them to these faraway locations." Sea turtles are born not just with a magnetic compass, but also with a magnetic map.

"Despite these sophisticated systems, however, adult turtles like Serenity do make mistakes. "They have these amazing feats of navigation but they're not perfect at it," says Rattray. From the ocean north of Madagascar, she would travel almost 600 kilometers further west before apparently realizing she was off course.

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"If turtles are born with a map of their natal ocean basin, I ask him, how can they wind up so many hundreds of kilometers off course? Even the few turtles whose foraging territories are located not in faraway waters but on the Great Chagos Bank, just a few dozen kilometers from Diego Garcia, didn't swim in anything resembling a straight path.

"'Turtles may sometimes choose not to go the most direct route," Lohmann offers. "There may be foraging areas along the way, they may wish to detour to areas that are rich in food. There may also be areas that have predators in them. And there sometimes are oceanographic reasons that they may not go on the most direct route."

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"A more likely explanation is that the turtles' inherited magnetic map is simply so crude that deviations of dozens or even hundreds of kilometers are to be expected. That evolution endowed them with a fairly coarse-grained map isn't very surprising, given the imperfections of Earth's magnetic field.

"The field is formed by movements of liquified iron and nickel within the planet’s core, a phenomenon called magneto-hydro-dynamics that geophysicists are still working to fully understand. Because those metals swirl around somewhat erratically, the resulting magnetic field winds up being somewhat uneven as well.

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"If sea turtles were sensitive to just one of these parameters—strength or inclination—then they could derive their position along a roughly north-south axis. Because sea turtles can detect both features, they can also derive their position on an east-west axis. The bi-coordinate grid utilized by sea turtles is not exactly the same as latitude and longitude, but it works in a similar way. "And that seems to be pre-programmed, that's the software that comes with the computer," says Putman. "Which is kind of wild."

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"'The real redeeming thing about that is they always manage to work out where they are and how to get to where they're going,” says Rattray. “It reinforces their reputation as these amazing marine navigators.'”

Comment: Great navigators but they make mistakes. Amazing migration that I think God designed as part of an oceanic ecosystem..