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23 May 06
Fishing 'major threat' to turtles
By Richard Black
EurekAlert 22 May 06
How satellite tracking revealed the migratory mysteries of endangered Atlantic loggerhead turtles
University of Exeter
Their journeys are among the longest in the animal kingdom and they have largely remained a mystery until now. An international team of scientists led by the University of Exeter have uncovered the migratory secrets of endangered loggerhead turtles in West Africa and the results could have huge implications for strategies to protect them.
In a paper in the journal Current Biology, Dr Brendan Godley and an international team describe how they used satellite tracking systems to follow the journeys of ten turtles from Cape Verde, West Africa, which is one of the world's largest nesting sites for loggerheads and a hotspot for industrial fishing.
What they found could turn current conservation strategies upside down, as the team discovered the turtles adopted two distinct approaches to finding food, linked to their size.
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, 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, 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 longline fishing effort that occurs in that region."
Dr Michael Coyne, of Duke University, 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 shows that in 2000 1.4 billion hooks were cast into the world's oceans through industrial fishing. It's thought that globally more than 200,000 loggerhead turtles were incidentally caught by fisherman scouring the waters for other species such as tuna and swordfish. Of these, tens of thousands are thought to die as a result.
37% of this fishing effort was in the Atlantic and a major hotspot for fishing is found off West Africa, 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 (e.g. 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.
For more information about tracking sea turtles, visit http://www.seaturtle.org/tracking
BBC 23 May 06
Fishing 'major threat' to turtles
By Richard Black Environment Correspondent, BBC News website
The endangered loggerhead turtle may face a greater threat than previously realised from longline fishing.
Researchers found that many turtles spend considerably longer in the open ocean, where longline boats operate, than earlier studies had indicated.
The boats aim to catch big predatory fish such as tuna and marlin, but accidentally snare other species including turtles and albatrosses.
The new research is published in the journal Current Biology.
Until now scientists have believed that young turtles live in the open ocean, but change to a coastal habitat when they reach a certain size.
But researchers working in Cape Verde found that most adults nesting there retain their open water behaviour, with the attendant risk posed by longline boats.
"The bottom line is that we thought juveniles experienced this risk out in the open ocean with longline fisheries," said Brendan Godley from the University of Exeter. "We thought that if you got them past that, then unless they're being taken by inshore fisheries, you're OK," he told the BBC News website.
"But now you've got adults exposed to longline fisheries, which is very worrying."
Longline boats trail fishing lines tens of kilometres long, with baited hooks at regular intervals to catch some of the biggest and most powerful fish in the oceans. Sea birds and turtles are among the other creatures caught accidentally.
With several thousand longline boats in operation, US scientist Larry Crowder has calculated that 1.8m hooks are set each night, and that a loggerhead turtle has about a 50% chance of encountering one each year.
Loggerheads (Caretta caretta) are categorised as Endangered on the internationally-recognised Red List of Threatened Species.
In theory, the turtles should be safe from longline vessels once they reach maturity, with research indicating that at an age of about 15 and a length of about 50cm they swap open water for a coastal environment.
"[The young ones] venture out into the open ocean, and that's thought to be because they hide in the open - the shore environment is the worst place to be for predatory fish," said Dr Godley.
"Then, we thought, they would grow to a size where if they come near to the shore they can deal with it, diving to 20 or 30 feet (six to 10 metres) [to hide from predators]. We always thought they moved into the inshore environment because the food supply is more reliable."
Using satellite transmitters placed on the turtles to follow their movements - a technique pioneered by the conservation group seaturtle.org, which co-funded the research - the team found that most of the adults did not make this switch.
Bigger individuals did, while smaller ones stayed away from the shore. This means, the researchers say, that attempts to conserve them will have to focus even more closely on longline boats.
Bird conservation groups have developed a set of simple measures which they say can substantially reduce the annual bycatch of albatross, thought to number about 100,000. These include trailing streamers behind the boats to scare birds away, weighting hooks so they stay below the surface, and fishing at night.
A similar set of measures to discourage loggerheads may not be so easy to develop, though keeping hooks deeper than the turtles usually dive may be one option, as may using blue-coloured bait, which they do not see as easily.
Related articles on Global issues: Biodiversity
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