Ecology: Sharks under threat from fisheries

A new study published in Nature, International Journal of Science revealed that around one quarter of the habitats of oceanic sharks fall within active fishing zones, which may threaten these iconic ocean predators. The study spearheaded by David Sims and colleagues, brought together 1500+ satellite tracks globally from 150 scientists, including LAMAVE, and demonstrates an urgent need for conservation efforts to protect pelagic sharks, which reported to be in decline.

Pelagic (or oceanic) sharks are highly migratory, covering vast areas of the ocean—including areas targeted by fisheries. Large pelagic sharks account for around half of all identified shark catches from fisheries. The extent of habitat overlap with industrial fisheries has been difficult to determine, as data from fisheries about catch numbers can be incomplete.

By combining satellite-tracked movements of pelagic sharks and global fishing fleets, David Sims and colleagues provide a global estimate of space-use overlap. A total of 1,681 large pelagic sharks (23 species) tagged with satellite transmitters were followed, and fishing vessel movements were monitored by a safety and anti-collision system. Their results reveal that 24% of the space used by sharks in an average month falls under the footprint of pelagic longline fisheries, which are responsible for catching most sharks from the open ocean. Areas of ocean that are frequented by protected species, such as great white sharks and porbeagle sharks, had higher overlap with longline fleets (around 64%).

Satellite tracks from whale sharks tagged by LAMAVE and the Marine Megafauna Foundation (MMF) where included in the study. One limitation in SouthEast Asia is many fishing vessels do not possess an Automatic Identification System (AIS), which is a problem in terms of large scale monitoring of fisheries and shark interactions. The pressure may appear low in SouthEast Asia, but in reality this is largely due to the small uptake of AIS on vessels. In reality the overlap with sharks would be much larger.

These findings indicate that pelagic sharks have limited places in which they can take refuge from fisheries. The authors suggest that conservation efforts are needed to protect these sharks, and that designated large-scale marine protected areas around regions of shark activity could be one solution.

Adapted from a Press Release by David Sims.

For further information please contact: David Sims (Marine Biological Association of the United Kingdom, Plymouth, UK), dws[@]mba.ac.uk Tel: +44 (0)1752 426487  

Tracks of different shark species.

Tracks of different shark species.

A whale shark fitted with a satellite tag by LAMAVE and MMF.

A whale shark fitted with a satellite tag by LAMAVE and MMF.