New research shows urgent action is needed to protect sharks from commercial longline fishing.
White shark researcher Oliver Jewell from Murdoch University’s Harry Butler Institute was among the international co-authors of a study, recently published in Nature, which found about a quarter of shark habitats fall within active fishing zones, putting these iconic predators under threat.
“Interactions with fisheries (commercial or recreational) are considered to be the greatest threat to white sharks as the species has few natural predators,” Mr Jewell said.
“As commercial fishing occurs worldwide, and it takes many years for a white shark to mature, it highlights just how tough it is for them to grow up.
We know they are caught at higher rates when they are younger, and this is a concern as it means they will not have had a chance to reproduce and add to their population.
Mr Jewell was part of a team that contributed data from 42 satellite tagged white sharks in South African waters to the study. Analysing the movements of this highly migratory species across several years, researchers found that several of the white sharks tracked moved to the edge of the continental shelf, where longline fishing was most prevalent.
Longline fishing vessels contain the type of fishing gear that catches most oceanic sharks, with each vessel capable of deploying 100 km long lines bearing 1200 baited hooks on a daily basis.
Habitat overlap
Large oceanic sharks, including species like white, tiger, bull and blue shark, account for around half of all identified shark catches from fisheries. The extent of habitat overlap with industrial fisheries had been difficult to determine, as data from fisheries about catch numbers can be incomplete.
Combining the satellite-tracked movements of 1,681 oceanic sharks across 23 different species with the movements of global fishing fleets, the researchers were able to estimate that 24 per cent of the space used by sharks in an average month falls under the footprint of oceanic longline fisheries.
For several protected species, such as white sharks and porbeagle sharks, the overlap with longline fleets was considerably higher (more than 50 per cent for these two species). The most commercially exploited species (the North Atlantic blue shark) shared an average 76 per cent of its space use with longlines a month.
The study’s 150 authors from 26 countries said the results could be used as a blue print for deciding where to place large scale marine protected areas around the world, protecting shark hotspots.
Their findings will be provided to policy makers at the United Nations High Seas Treaty and CITES (Convention on International Trade in Endangered Species of Wild Fauna and Flora) meetings in August.
The paper has been published by Nature.