afrol News, 23 May - The endangered loggerhead turtles of West Africa, mainly nesting in Cape Verde, have proven difficult to protect as fisheries grow in the region. Satellite tracking of the marine reptiles was to ease conservation efforts, but the scientists found that the turtles' migratory routes were surprisingly extensive and complicated.
Their journeys are among the longest in the animal kingdom and they have largely remained a mystery until now. Now, however, an international team of scientists - including researchers from Cape Verde, Canary Islands, the UK and the US - has uncovered many migratory secrets of West Africa's loggerhead turtles. "The results could have huge implications for strategies to protect them," the researchers foresee.
In a paper in the journal 'Current Biology', the international team describes how they used satellite tracking systems to follow the journeys of ten turtles from Cape Verde - an archipelago off West Africa, which is one of the world's largest nesting sites for loggerheads and a hotspot for industrial fishing. They basically found that the turtles adopted two distinct approaches to finding food, linked to their size.
The satellite tracking showed that the larger and thus older turtles foraged in coastal waters, whereas smaller, younger individuals foraged in the open ocean and in waters closer to the West African mainland. This is "in direct contrast with the accepted life-history model for this species," the researchers write.
Previously it was thought that hatchlings left the coastal region to forage far out at sea before returning, later in life, to find food closer to shore. However the new findings show that the oceanic habitats contained far larger animals than was previously thought. The team tracked the turtles as they left nesting sites in Cape Verde, following them for up to two years over ranges that covered more than half a million square kilometres.
Dr Brendan Godley, of the University of Exeter (UK), said: "We were surprised to find such large turtles looking for food out in the open ocean, as it was previously thought that animals of this size would have moved back to forage in coastal zones. This means there are much greater numbers of the breeding population out at sea and far more that are vulnerable to the intensive long-line fishing effort that occurs in that region."
Dr Michael Coyne, Director of Seaturtle.org added: "From the information collected, we have been able to determine how much time these animals are spending within the sovereign boundaries of each country in the region. This research highlights how complicated the migration of marine vertebrates really is and how sophisticated our conservation efforts must be to safeguard these animals. Given the range these reptiles can cover an international cooperative effort in seven African states is needed to create a strategy that would protect them."
Research indicates that, in 2000, 1.4 billion hooks were cast into the world's oceans through industrial fishing. It is thought that more than 200,000 loggerhead turtles were incidentally caught by fisherman around the world scouring the waters for other species such as tuna and swordfish. Of these, tens of thousands are thought to die as a result. 37 percent of this fishing effort was in the Atlantic Ocean and a major hotspot for fishing is found in the region where the Cape Verdean turtles reside.
In recent years marine turtle researchers have been using satellite telemetry to track turtle migrations. Satellite transmitter tags are attached to the shell of the turtle so that every time the turtle surfaces to breathe, the tag transmits the turtle's position, as well as other information - such as depth and duration of dives - to satellites orbiting above, which then relay the data by e-mail to the computer of the scientist who attached the tag.
The sea turtles were captured while nesting at the beaches of the island of Boa Vista, the third largest island in Cape Verde. Here, the satellite tag was glued on to them before they were released into the ocean. The works on Boa Vista were done in cooperation with the Cape Verdean National Institute for the Development of the Fisheries (São Vicente).
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