Tracks of marine animals in the wild, now increasingly acquired by electronic tagging of individuals, are of prime interest not only to identify habitats and high-risk areas, but also to gain detailed information about the behaviour of these animals. Using recent satellite-derived current estimates and leatherback turtle (Dermochelys coriacea) tracking data, we demonstrate that oceanic currents, usually neglected when analysing tracking data, can substantially distort the observed trajectories. Consequently, this will affect several important results deduced from the analysis of tracking data, such as the evaluation of the orientation skills and the energy budget of animals or the identification of foraging areas. We conclude that currents should be systematically taken into account to ensure the unbiased interpretation of tracking data, which now play a major role in marine conservation biology.
The dramatic worldwide decline in populations of the leatherback turtle (Dermochelys coriacea) is largely due to the high mortality associated with their interaction with fisheries, so a reduction of this overlap is critical to their survival. The discovery of narrow migration corridors used by the leatherbacks in the Pacific Ocean raised the possibility of protecting the turtles by restricting fishing in these key areas. Here we use satellite tracking to show that there is no equivalent of these corridors in the North Atlantic Ocean, because the turtles disperse actively over the whole area. But we are able to identify a few 'hot spots' where leatherbacks meet fisheries and where conservation efforts should be focused.
Large oceanic migrants play important roles in ecosystems, yet many species are of conservation concern as a result of anthropogenic threats, of which incidental capture by fisheries is frequently identified. The last large populations of the leatherback turtle, Dermochelys coriacea, occur in the Atlantic Ocean, but interactions with industrial fisheries could jeopardize recent positive population trends, making bycatch mitigation a priority. Here, we perform the first pan-Atlantic analysis of spatio-temporal distribution of the leatherback turtle and ascertain overlap with longline fishing effort. Data suggest that the Atlantic probably consists of two regional management units: northern and southern (the latter including turtles breeding in South Africa). Although turtles and fisheries show highly diverse distributions, we highlight nine areas of high susceptibility to potential bycatch (four in the northern Atlantic and five in the southern/equatorial Atlantic) that are worthy of further targeted investigation and mitigation. These are reinforced by reports of leatherback bycatch at eight of these sites. International collaborative efforts are needed, especially from nations hosting regions where susceptibility to bycatch is likely to be high within their exclusive economic zone (northern Atlantic: Cape Verde, Gambia, Guinea Bissau, Mauritania, Senegal, Spain, USA and Western Sahara; southern Atlantic: Angola, Brazil, Namibia and UK) and from nations fishing in these high-susceptibility areas, including those located in international waters.
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