Sharks Harmed by Long Line Fishing

Bycatch and Finning Jeopardize Ocean Ecosystem Stability

Oct 25, 2007

Declining shark populations worldwide are further strained by losses to long line fishing. Tighter rules on finning and bycatch may help prevent loss of biodiversity.

Long line fishing for tuna, swordfish, mahi mahi and billfish represents a multi-million dollar industry. Sharks are responsible for significant depredation on hooked fish. But they are also bycatch victims and taken for the shark fin market. Methods to reduce bycatch and finning are needed to protect these keystone predators.

The Impact of Long Line Fishing on Sharks

While many species of shark are taken, the blue shark (Prionace glauca), the species most heavily impacted by long line fishing for tuna and swordfish, is now thought to be taken at levels at or above maximum sustainable yield. Losses to long line fisheries is estimated at 10-20 million blue sharks per year. Many of them are alive when landed. But many are killed either for finning or to retrieve the fishing gear they become entangled in. One of the other species affected- the silky shark-rarely survives if bycaught.

As with all sharks, the blue is a long-lived, slow maturing species with low reproductive rates. This means that when the population falls it will take a long time to recover. The IUCN has expressed concern over removal of large numbers of an important keystone species.

Shark Bycatch and Depredation Study Findings

A study funded by the Western Pacific Regional Fishery Management Council, the Regional Seas Programme of the United Nations Environment Programme and the Moore Foundation reviewed the impacts of shark predation on long line fishing and the shark bycatch issue, with insight into the role that the finning industry plays in long line fishery and shark interaction.

A review of regulations and guidelines from various international organizations, including the Food and Agriculture Organization of the UN, the IUCN and various tuna industry groups, shows that most have banned or are in favor of banning finning. By requiring that anyone taking sharks bring in the entire carcass, total numbers that can be taken are limited and the rest of the shark can be utilized as a protein source locally.

In Australia, Italy, South Africa and the US, where finning is banned, 93% of the sharks from bycatch are released alive when nets are landed. It is believed that this is a result of the requirement to produce the body of the shark, which takes up valuable hold space, in order to legally keep the fins. In areas where finning is unregulated, blue sharks are often discarded if mako sharks are also caught as the mako is more valuable commercially.

Recommendations for Reducing Bycatch

Bycatch losses can be as high as several thousand US dollars per set based on damage to and loss of gear, decrease in the catch of marketable fish and time spent disentangling the sharks.

Of these, avoiding areas and times of shark abundance and reduction in chumming and bait and offal discharge seem likely to be accepted by most long line fishermen as useful. As does the use of magnets on hooks. Sharks have highly sensitive electromagnetic receptors, which may cause them to avoid magnetized hooks.

Eco-labeling, which would bring public pressure into play, would take more effort to implement. As consumers have become more environmentally aware this method of bringing the issues into the open and allowing customers to decide with their wallet is more and more valuable.

Self policing is likely to be of use if the long line fishing industry is faced with the possibility of a fishery closure. By publishing information on each boat’s bycatch, fellow fishermen can bring pressure to bear on colleagues who fail to fish responsibly.

Whatever methods are employed it is clear that efforts must be made to reduce shark losses to finning and the long line fishery to avoid areas of oceanic ecosystem collapse.

Gilman, E., Clarke, S., Brothers, N., Alfaro-Shigueto, J., Mandelman, J., Mangel, J., Petersen, S., Piovano, S., Thomson, N., Dalzell, P., Donoso, M., Goren, M., Werner, T.

The copyright of the article Sharks Harmed by Long Line Fishing in Ecosystem Preservation is owned by Dawn M. Smith. Permission to republish Sharks Harmed by Long Line Fishing in print or online must be granted by the author in writing.