Thursday, April 16, 2015
Baby sea turtle mystery partly solved: they're independent swimmers not drifters
A great mystery of the marine world—what green sea turtles
do as keiki—has partly been solved.
Researchers caught yearling turtles and attached tags that
would slough off after a couple of months.
They found the young turtles aren’t
just drifting around—they’re actively swimming. Which is interesting, because nobody's been able to prove this before, and it contradicts conventional wisdom.
(Image: When buoys and tagged turtles were placed in the water
together, they went different ways. Here, two blue lines track the buoys, and
the green is the track of one of the turtles followed in this study. Credit:
NOAA Fisheries.)
Nathan Putman and Katherine Mansfield published their results in the journal Current Biology. Their tagging included the green sea
turtle, Chelonia mydas, which is the dominant nearshore turtle found in the
Hawaiian Islands, as well as Kemp's ridley turtles.
The first couple of years of most turtle species' lives are
sometimes called the “lost years.” The keiki hatch on beaches, scramble into
the sea, and then disappear until they come back to they show up again as much
larger animals.
“It has been widely assumed that turtles simply drift with
ocean current,” says a NOAA press release on the study.
Putman, a sea turtle biologist with NOAA's Southeast
Fisheries Science Center, and Mansfield, director of the University of Central
Florida's Marine Turtle Research Group, set out to find out for sure.
Mansfield put solar-powered satellite tags on 44 wild-caught
young turtles, and at the same time deployed drifting satellite buoys that
would follow the currents. If the turtles and the buoys went the same places,
then it would suggest the turtles simply followed the currents.
But they didn’t.
Within the first few days, some of the turtles were already
125 miles from the buoys. The young turtles were actively swimming and navigating
independent of current flow.
Anyone who has seen freshly hatched green sea turtles flap
and clamber up out of the sand and then down the beach can appreciate how
animated they are. Their single-mindedness and independence seems to continue in the ocean.
“The results of our study have huge implications for better
understanding early sea turtle survival and behavior, which may ultimately lead
to new and innovative ways to further protect these imperiled animals," Mansfield
said.
In the past, young turtles have sometimes been found
downstream from nesting sites, suggesting they might move passively with
currents. They’ve also been found collected in association with drifting organisms,
like Sargassum seaweed, also suggesting they’re mainly drifters.
“Our data show that one hypothesis doesn't, and shouldn't,
fit all, and that even a small degree of swimming or active orientation can
make a huge difference in the dispersal of these young animals,” Mansfield said.
“We conclusively demonstrate that these turtles do not
behave as passive drifters. In nearly all cases, drifter trajectories were
uncharacteristic of turtle trajectories,” the paper said.
© Jan TenBruggencate 2015
Posted by Jan T at 9:27 AM
Labels: Conservation, Fisheries, Marine Debris, Marine Issues, Oceanography, Weather, Zoology
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