Shark Research - Fisheries analysis reveals high shark bycatch in longline fisheries

A recent paper published in Marine Policy has carried out the first analysis of global elasmobranch bycatch patterns in commercial fisheries.

Bycatch - where species other than the intended target species are caught in a fishery - is a global problem. Many of today's commercial fishing methods, such as trawling or long lining, have few ways to ensure that only the intended species is caught.

By examining current fisheries data, the researchers assessed the quantity of elasmobranch bycatch across 4 commercial fishing methods: longlines, trawlers, purse-seines and gillnets. Of these 4 fishing methods, they found that pelagic longlines are responsible for the largest amount of shark bycatch - in fact in some instances the quantity of sharks caught in pelagic longline fisheries may exceed the intended catch. The majority of the shark bycatch was made up of blue shark (Prinace glauca) which is classified as Near Threatened in the IUCN Red List.

Long line fishing is a type of commercial fishing whereby a main line is laid out with hooks hanging off the line at intervals. Whilst longlines are intended to catch a target species - such as swordfish - the baited hooks also attract other species such as seabirds, turtles, other fish and sharks. Worse still, if fishing gear is discarded at sea the equipment can continue to catch and kill marine life - something known as ghost fishing.

This paper does not draw conclusions about the direct threat to sharks from these high levels of bycatch, but instead emphasises that the large numbers of sharks unintentionally caught and discarded by the commercial fishing industry is concerning and more research is required to understand if it is sustainable. The authors also highlight a need to implement management plans for elasmobranchs on a global scale.