Sharks that live in the open ocean are being forced to share large parts of their habitat with fisheries, an analysis has found.
Longline fishing operations encroach on almost one-quarter of the area that pelagic sharks roam each month, finds the study. In some regions, that overlap is even higher. The method uses lines that can reach 100 kilometres and include hundreds of hooks, and it is the fishing practice that catches the most pelagic sharks.
Pelagic sharks live in open waters and many species migrate long distances each year. To track their movement, David Sims from the Marine Biological Association of the United Kingdom, Plymouth, and colleagues tagged almost 1,700 pelagic sharks with satellite transmitters between 2002 and 20171.
The team also charted the movement of longline fishing vessels using data from the automatic identification systems fitted to many ships.
In an average month, 24% of the area of the ocean used by sharks overlapped with the area of longline fishing operations (see ‘Encroaching fisheries’). The extent of this overlap varied from 8% in the east Pacific to 38% in the southwest Indian Ocean, but fishing vessels tended to be present in most locations around the world with particularly high densities of sharks, such as the ‘white shark Café’ off the coast of California, and the southern Great Barrier Reef.
The results show that sharks don’t have many options when it comes to seeking refuge from fisheries, say the authors, who suggest creating protected areas around important shark hotspots.
This is particularly important because many species of pelagic shark are considered threatened — including several of those which had the highest spatial overlap with fishing operations. The porbeagle (Lamna nasus), for example, is listed as vulnerable and shared 47% of its space with fisheries, and the endangered shortfin mako shark (Isurus oxyrinchus) had a 37% overlap globally, rising to 62% in the North Atlantic. The vulnerable great white shark (Carcharodon carcharias) and the near-threatened blue shark (Prionace glauca) had overlaps of 35% and 49%, respectively.