Bycatch is widely recognised as one of the most serious environmental impacts of the destructive fishing methods used by modern commercial fisheries. In Taiwan, Greenpeace is campaigning against fish aggregating devices and long-line fishing.
Many ships inadvertently catch enormous quantities of other fish and animals besides the one they are going for. Most of the time, these extra fish, or bycatch, are simply thrown dead or dying back into the sea.
Loggerhead turtle swimming around a fish aggregation device belonging to the Ecuadorean purse seiner 'Ingalapagos', which was documented by Greenpeace in the vicinity of the northern Galapagos Islands.
According to reports, in some trawl fisheries for shrimp, 90 percent of the catch may be thrown back. Other fisheries kill mammals, seabirds, sea turtles, sharks and dolphins, sometimes in huge numbers. In some fisheries, bycatch kills wildlife at such s scale that it may affect the structure and function of marine systems at the population, community and ecosystem levels.
Bycatch can also include juveniles of the fish the ship is trying to catch – they are too young or undersized to be sold. The bycatch of juvenile bluefin and yellowfin tuna is worsening the population pressure for these already over-fished species.
Destructive fishing practices
Different types of fishing practices affect different species: Nets kill dolphins, porpoises and whales; long-line fishing kills birds; bottom trawling devastates marine ecosystems.
Crew members on board the Taiwanese fishing vessel Kai Jie 1 set longlines.
Long-lines consist of short lines (called snoods) carrying baited hooks, attached at regular intervals to a longer main line. Main lines can be over 150 km long and can carry several thousand hooks.
Long-lines catch many endangered sharks, turtles, marine mammals and seabirds. Birds dive for the bait planted on long fishing lines, swallow it (hook included), and are pulled underwater and drowned. Around 100,000 albatrosses are killed by long-line fisheries every year – because of this, many species are facing extinction.
Fish aggregating devices (FADs)
FADs are like deadly magnets for fish. They float in the ocean and are used to attract tuna. Unfortunately, many other animals come to the FADs as well – endangered sharks, turtles, skates and rays, immature tuna and other fish. After the FAD attracts enough fish, the tuna and all other accumulated marine life is scooped up in a huge net, in one fell swoop.
Almost three quarters of the world’s tuna fisheries use FADs. Not only do these FADs kill thousands of turtles and sharks each year, they also further endanger the critically overfished bluefin, yellowfin and bigeye tuna. That’s because purse-seine fisheries for skipjack tuna – commonly used in canned tuna – frequently use FADs, which attract lots of juvenile yellowfin, bluefin and bigeye tuna as well. As a result, many young tuna are killed before they have a chance to reproduce.
A turtle caught in the net of the Ecuadorean purse seiner 'Ingalapagos', which was documented fishing on a fish aggregation device (FAD) by Greenpeace in the vicinity of the northern Galapagos Islands.
Tens of millions of sharks and rays are caught and discarded each year. Tuna fisheries, which in the past had high dolphin bycatch levels, are still responsible for the death of many sharks. Hundreds of thousands of cetaceans (whales, dolphins and porpoises) also die as bycatch each year, because they are unable to escape when caught in nets.
Bottom trawling is a destructive way of ‘strip-mining’ the ocean floor, harvesting the species that live there. This not only picks up target fish species but also many other creatures – just one pass of a trawler removes up to one fifth of the seafloor fauna and flora. Shrimp fisheries have the highest levels of bycatch: over 80% of a catch may consist of marine species other than shrimp.
Is there a solution?
Many technical fixes exist to reduce bycatch. Turtle exclusion devices are used in some shrimp fisheries to avoid killing turtles. Long-line fisheries can change the process of setting the hooks and employ bird-scaring devices, which radically cut the numbers of birds killed. Dolphin-deterring devices can also be attached to nets, but they are not always effective. Escape hatches (a widely spaced metal grid, which forces cetaceans up and out of the net) have also been used.
But these devices cannot address the whole problem. Such devices need continual monitoring to check for effectiveness and potential negative effects. Realistically, fishing ships will probably only them in areas with well-developed fishery management and enforcement agencies.
On a global level, perhaps the most effective solutions are to control fishing efforts and ban the most destructive fishing methods. In Taiwan, Greenpeace is calling for a ban on FADs. The creation of marine reserves can protect key ecological areas, but only discontinuing the worst fishing practices will protect highly mobile species such as seabirds and cetaceans.
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