Atlantic leatherbacks at risk from fisheries
5 January 2011, by Tamera Jones
Scientists have used satellites to track the world's largest nesting population of leatherback turtles across the South Atlantic for the first time.
Their results reveal the routes the critically endangered creatures take make them more vulnerable to commercial fishing in the South Atlantic than previously thought.
The turtles leave their hatching grounds in Gabon in western Africa and return to the open ocean to feed, following one of three routes. Some go straight to the equatorial region of the mid-Atlantic, while others journey across the Atlantic to the coast of South America, or to the South African coast. Some of these trips are up to 4,700 miles long.
They stay in these areas for two to five years to build up enough fat reserves to reproduce, before returning to Gabon to lay eggs once again.
The problem is their routes coincide with large coastal fisheries off South America and South Africa, and long-line fisheries in the mid-Atlantic.
While leatherback turtle populations in the North Atlantic appear stable, scientists are concerned that this could soon change. The pace of industrialisation of fisheries and the increasing numbers of turtles that have fallen victim to fisheries as bycatch are two reasons for this.
Not just that, but numbers of turtles at nesting sites vary hugely each year. Scientists don't yet know if this means they're in decline.
In the Pacific Ocean, population of leatherback turtles have plummeted by a huge 98 per cent over the past 30 years. One colony in Mexico fell from 70,000 in 1982 to just 250 by 1998-9. While it's hard to pinpoint one single cause, harvesting turtle eggs, coastal fishing and long-line fishing are most likely to blame.
Conservationists are keen to take action now to avoid a repeat of the Pacific story. 'We wanted to find out where the risks might be for the turtles to stop the same thing happening in the Atlantic before it's too late,' explains Matthew Witt from the University of Exeter, lead author of the report, published in Proceedings of the Royal Society B today.
Witt and colleagues from Gabon, the US and Italy fitted satellite trackers to 25 adult female leatherbacks nesting in Gabon to find out exactly where they go. They could only track females, because unlike males, they come back to the beach to lay eggs, giving the researchers the opportunity to attach miniature trackers to them.
As well as analysing where the turtles go, Witt and his colleagues looked at how their movements coincided with ocean productivity and the presence of commercial fishing boats. They found the turtles spend most of their time in the most productive parts of the ocean where there's a lot of fish or jellyfish – their favourite food. This is also exactly where fisheries concentrate their efforts.
'We were surprised the leatherbacks spend so much time in the mid-Atlantic. We didn't think these waters would be that productive. But when we looked at all the oceanographic data, we saw that this region is highly productive,' says Witt.
'No-one has tracked leatherbacks like this before. But the information it gives us puts us in a better position to influence current fishing practices,' he adds.
Witt and his colleagues have already identified 11 nations that could be more involved in conservation efforts to protect the leatherback.
There are already well-established mechanisms in long-line fishing to reduce marine turtle by-catch, but fisheries don't always implement them. 'We need to put legal conventions into practise to stop this species declining in the Atlantic,' says Witt.
The next thing Witt is keen to do is to follow the turtles over longer periods to see if they always stick to the same route. If they always use the same strategy, this could put them at greater risk from fisheries than if they are more flexible in the route they take.
'We need to learn the lessons from the Pacific,' Witt says.
Matthew J. Witt, Eric Augowet Bonguno, Annette C. Broderick, Michael S. Coyne, Angela ormia, Alain Gibudi, Gil Avery Mounguengui Mounguengui, Carine Moussounda, Monique NSafou, Solange Nougessono, Richard J. Parnell, Guy-Philippe Sounguet, Sebastian Verhage and Brendan J. Godley, Tracking leatherback turtles from the world's largest rookery: assessing threats across the South Atlantic, Proceedings of the Royal Society B , published 5 January 2011, doi:10.1098/rspb.2010.2467
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