Wednesday, January 5, 2011

Turtles and Sharks: long migrations studied in the South Atlantic

Animal migration is one of nature's most mysterious presentations of animal behavior. What makes an animal travel great distances? How are they able to do it in a relatively straight path? Why do they use the same route year after year? Just how are they so good at it, while I can get lost in the local Costco?

One vast body of water where several marine species migrate but where mankind has not spent much time studying these movements is the South Atlantic, between South America and Africa. However, two recent studies have shed some interesting light on the long migration paths taken by leatherback turtles and blue sharks. Both of these species are threatened with possible extinction, so the more we know, the better we can manage our conservation efforts.

As reported in the Proceedings of the Royal Society B, researchers from England tagged and track the migratory routes of leatherback turtles for five years, from a breeding colony in Central Africa to feeding grounds in the southwestern Atlantic. Using satellite tracking tags on 25 females, the researchers found that the turtles followed three migratory paths, often traveling in remarkably straight lines.

One female turtle was tracked along a path that totaled just under 4,700 miles and took about 150 days of nonstop swimming to complete. The researchers are keen to know the "when and where" of these journeys to ensure that commercial fisheries do not take advantage of the turtle's singular purpose and place themselves right in the turtles' paths. The researchers are hoping to avoid a large decline in leatherback turtles in the South Atlantic as has happened to leatherbacks in the Pacific.

"All of the routes we've identified take the leatherbacks through areas of high risk from fisheries, so there's a very real danger to the Atlantic population," said University of Exeter professor Brendan Godley.

At the same time, researchers from the University of Florida were tracking the migratory routes of the blue shark. Working with a Brazilian team of researchers, Felipe Carvalho, under the supervision of renown shark expert Dr. George Burgess, Director of the Florida Program for Shark Research, began tagging blue sharks along the Brazilian coast. The question was whether the tracking results would show a migration that would link shark populations in both the southeastern and southwestern Atlantic.

Blue sharks are heavily fished in the South Atlantic and within coastal territorial waters some nations are trying to determine how to best manage the remaining populations. By showing a migratory link between these separate locations, it emphasizes the need for multinational cooperation. As it turned out, one of Carvalho's blue sharks, tagged off the coast of Brazil, was detected off Africa 87 days later.

“This is the first evidence of the transatlantic migration of a blue shark from the southwestern Atlantic Ocean to the southeastern Atlantic Ocean. We thought this migration might be happening, but we never had the data before to prove it,” Carvalho said.

More and more, we are finding species that travel along oceanic highways, making incredible journeys over and over again. Navigating by prevailing currents, or visual cues, or even by the Earth's magnetic fields - all have been suggested as possible theories that could account for the animal's amazing accuracy.

Whatever the method, it is important for us to understand these migrations and their purpose and use that knowledge to protect rather than take advantage of leatherback turtles, blue sharks, and so many other species that roam the seas.

Read about tracking leatherback turtles from the
Associated Press.
Read about tracking blue sharks from

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