Threats: Bycatch

Publication - April 8, 2008
Industrial size nets measuring up to two kilometres in diameter (such as gillnets, bottom trawls, or purse seines) catch anything that is larger than the size of their mesh, while longlines dangle thousands of baited hooks in the water, attracting any hungry passerby including diving seabirds. An estimated 3.3 million sharks die every year on longlines, while entanglement is the leading cause of death for small cetaceans (such as porpoises, dolphins and whales) with one dying every two minutes. Hundreds of thousands of sea turtles and sea birds are also killed on longlines and caught in nets, landing many species on endangered and critically endangered lists. The Pacific loggerhead turtles, which have lived in the ocean for millions of years, are estimated to become extinct within the next five to 30 years if current trends continue.

Smaller organisms are suffering too. Bottom trawling is decimating deep sea cold-water corals, and invertebrates such as starfish, crab, sea urchins and sponges are scooped up by the tonne in fisheries that target bottom dwellers such as lobster, plaice and halibut. Once corals are torn out of the ground they won’t recover, and delicate species such as sponges and sea urchins often don’t survive the crush of fish in nets.

Even targeted species are negatively affected by bycatch, as young fish are hauled up along with old, then discarded because they do not meet size and length guidelines designed to protect the next generation of the stock. Sadly, once they are ripped from the nets and thrown back into the water to waiting predators, dazed and often injured, most do not survive.

Bycatch also undermines the recovery of protected species. In the North Atlantic trawling is netting huge numbers of juvenile cod, undermining efforts at rebuilding decimated Atlantic cod stocks. For example on the Grand Banks, cod fishing is banned but in 2003 an estimated 90 per cent of the biomass was caught as bycatch in other groundfish fisheries. Our wild king salmon populations in the northeast Pacific are also suffering with about 160,000 fish being caught as bycatch in the Alaskan pollock fishery last year. This mass incidental catch resulted in a collapse of a subsistence fishery because not enough fish returned from the ocean to spawn.

While there are methods to reduce bycatch (turtle exclusion devices, special types of bait, certain types of mesh that allow non-targeted species to escape and special hooks and sonar devices that can prevent them from being caught in the first place), a lack of education, adoption and enforcement on the part of both fishers and fisheries management is leaving tonnes and tonnes of marine life tossed overboard for dead.