Many marine species are currently under threat from commercial fishing due to their unintentional capture by fleets as ‘bycatch’. Animals that migrate vast distances across oceans are particularly vulnerable to bycatch as they naturally encounter many fisheries in different parts of the world. One such species is the leatherback turtle, Dermochelys coriacea, which has suffered catastrophic declines in the Pacific in recent years, to the extent that this subpopulation is now considered “critically endangered” by the IUCN.
The last large populations of the leatherback now survive in the Atlantic Ocean, but face a major threat from industrial fisheries there, especially those that use longlines. Pelagic longlines can stretch for tens of kilometres near the surface of the water and carry thousands of sharp hooks. Usually intending to catch tuna or swordfish, they often catch far more, including sharks and turtles. Turtles that swallow a hook can fatally gash their digestive tract or become tangled in the lines and drown.
Now for the first time a study has mapped the locations in the Atlantic Ocean where leatherback turtles are most likely to come into contact with these longline fisheries. This follows on from a similar study of the Pacific which successfully identified several hotspots in the western and eastern parts of the ocean.
The researchers gathered information on leatherback movement by attaching satellite tags to over 100 individuals between 1995 and 2010. They then compared areas of leatherback habitat-use with zones of highest fishing-pressure. This produced a total of nine zones where turtles are likely to face greatest danger from longlines. Four of these sites were in the North Atlantic and five in the South, and included areas within the exclusive economic zones of 12 different countries, among them Spain, USA, Brazil and the UK.
The wide distribution of these high-risk zones and the number of different nations involved means that it will require a huge international effort to implement conservation measures for leatherbacks. The first step will be to limit the potential for bycatch from fisheries in these locations, either by modifying current fishing gear or by establishing marine protected areas. Hopefully, these findings will be rapidly brought into policy for the fishing industry so that fishermen throughout the Atlantic can make more informed decisions on when and where to fish.
Reference: Fossette S, Witt MJ, Miller P, Nalovic MA, Albareda D, Almeida AP, Broderick AC, Chacón-Chaverri D, Coyne MS, Domingo A, Eckert S, Evans D, Fallabrino A, Ferraroli S, Formia A, Giffoni B, Hays GC, Hughes G, Kelle L, Leslie A, López-Mendilaharsu M, Luschi P, Prosdocimi L, Rodriguez-Heredia S, Turny A, Verhage S, & Godley BJ (2014). Pan-Atlantic analysis of the overlap of a highly migratory species, the leatherback turtle, with pelagic longline fisheries. Proc. R. Soc. B, 281 (1780) PMID: 24523271