Abstract
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.
Highlights
In recent years, there has been increasing effort to sustainably manage fish populations and reverse the collapse of many target species [1]
In the northern Atlantic, 53.0% of all daily locations were located in international waters and 47.0% in exclusive economic zones (EEZs) (n 1⁄4 6863 locations for 65 turtles), compared with 54.5% and 45.5%, respectively, in the southern Atlantic (n 1⁄4 5664 locations for 50 turtles)
In the northern Atlantic, despite all breeding being in the west, high-use areas mainly occurred in the central (25–508 N, 50–308 W) and eastern regions, and in particular in the waters offshore western Europe, around Cape Verde and around the Azores (October–March)
Summary
There has been increasing effort to sustainably manage fish populations and reverse the collapse of many target species [1]. This information is combined with data on the distribution of pelagic longline fishing effort obtained from the International Commission for the Conservation of Atlantic Tunas (ICCAT) across the same temporal period. The origin of leatherback turtles foraging in the northeast Atlantic has not yet been investigated, we arbitrarily, but conservatively, attributed both tracks to the French Guiana nesting assemblage and weighted them . In order to assess spatial and temporal variation of leatherback susceptibility to longline fisheries bycatch, we first selected areas having a high fishing-pressure index, both annually and for each quarter separately We categorized these areas based on the coincident annual and seasonal estimates of leatherback turtle density. Data were analysed and mapped using MATLAB (The MathWorks, MA), the R software package [28] and ArcGIS v. 10.1 and 10.5 (Environmental Systems Research Institute, Redlands, CA)
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