Green turtles safer in protected seas

Green turtles safer in protected seas

19 March 2012, by Adele Rackley

An international team of researchers, led by the University of Exeter, looked at the movements of green turtle populations which had been tracked by satellite. They found that 35 per cent of them across the world's oceans spend most of their time in shallow seas protected by Marine Protected Areas (MPAs).

The study is the first to provide concrete evidence for the world-wide effectiveness of MPAs for large marine vertebrates.

Green turtles live in tropical and sub-tropical seas, and can travel hundreds of kilometres from their nesting sites to the foraging grounds where they spend most of their time.

These feeding grounds are generally quite small areas of shallow coastal seas, which are home to their favourite algae and sea grass.

The researchers combined satellite tracking data from a number of projects around the world, and mapped the movements of 145 turtles, from 28 nesting sites to their foraging areas.

They statistically adjusted their findings to 'even out' the differences in the amount of MPA's in shallow seas in the range of the species, and then mapped the turtles' foraging grounds against the protected areas.

The results showed that on average 35 per cent of the turtles were congregating in protected seas, rising to 67 per cent for the Atlantic. The researchers also noticed that the longer an MPA had existed and the larger it was, the more turtles congregated there.

'We were surprised at the magnitude of the effect,' says Professor Brendan Godley from Exeter's Centre for Ecology and Conservation. 'The turtles appear in MPAs far more than would be expected by chance.'

MPAs are intended to reduce biodiversity loss and protect important marine creatures and habitats but, compared to land, not much of the sea has any protection at all. Existing MPAs vary in size and the level of protection afforded, and there has been some debate about how effective they are at preserving marine ecosystems.

So the results of this study are encouraging.

International trade in green turtle products been curbed since 1982, after hundreds of years of industrial-scale harvesting for their meat. They have been protected since the 1970s but are still at risk from being caught in fishing nets, and increasingly from pollution and damage to their shallow-sea habitats as humans continue to move into coastal areas.

Turtles face other threats, including interference with their nesting areas and predation while at sea. But they are particularly at risk from human activities impinging on their foraging grounds, so focusing conservation efforts on these areas could be an effective way of both conserving single species and managing whole ecosystems.

Because of their sensitivity to habitat damage the turtles are known as a 'sentinel' species; their presence points to areas of healthy habitat which are likely to be worthy of protection if they aren't already. Godley believes sentinels like the green turtles have great potential to influence future conservation policy.

He also emphasises the importance of international collaboration.

'Through coordinated, collaborative research we can turn individual studies into larger policy-relevant pieces of work that should form the basis of discussions about how we protect the marine environment – especially because such a small proportion of our seas are currently protected.'

The research is published in Global Ecology and Biogeography.