Fishing problems: Destructive fishing practices

Many fishing practices are extremely destructive to delicate habitats - particularly vital fish breeding grounds like coral reefs and seagrass meadows.

For example:

  • Bottom trawling: Industrial trawlers once avoided coral reefs and other rocky regions of the ocean floor because their nets would snag and tear. But the introduction of rockhopper trawls in the 1980s changed this. These trawls are fitted with large rubber tires or rollers that allow the net to pass easily over any rough surface. The largest, with heavy rollers over 75cm in diameter, are very powerful, capable of moving boulders weighing 25 tonnes. Now, most of the ocean floor can be trawled down to a depth of 2,000m.

    These trawls - whose use is now widespread - are extremely damaging. In an experiment off Alaska, 55% of cold-water coral damaged by one pass of a trawl had not recovered a year later. Scars up to 4km long have been found in the reefs of the north-east Atlantic Ocean. And in heavily fished areas around coral seamounts off southern Australia, 90% of the surfaces where coral used to grow are now bare rock. When covered with marine life, these seabed areas provide habitat for juvenile fish and other species. Like removing forest, removing this cover decreases the area available for marine species to live and thrive in.
	© Institute of Marine Research, Norway
Smashed and dead cold-water coral fragments in a trawling ground on the Norwegian continental shelf.
© Institute of Marine Research, Norway
Cyanide fishing in a coral reef, the Philippines. The cyanide kills coral polyps and algae. 
	© WWF / Jurgen FREUND
Cyanide fishing in a coral reef, the Philippines. The cyanide kills coral polyps and algae.
© WWF / Jurgen FREUND
  • Cyanide fishing: In this technique, fishers squirt sodium cyanide into the water to stun fish without killing them, making them easy to catch. Cyanide fishing on coral reefs began in the 1960s to supply the international aquarium trade. But since the early 1980s, a much bigger, more profitable business has emerged: supplying live reef fish for the restaurants of Hong Kong, Singapore, and, increasingly, mainland China. Some 20,000 tonnes of live fish are eaten annually in the restaurants of Hong Kong - and for every live fish caught using cyanide, a square metre of their coral reef home is killed.
  • Dynamite fishing: In this technique, dynamite or other explosives are set off under water. The dead fish floating to the surface are then simply scooped up. The explosives completely destroy the underwater environment, leaving it as rubble. Dynamite fishing has contributed to massive destruction of, for example, Southeast Asian coral reefs over the past 20 years.

  • Ghost fishing: Ghost fishing occurs when fishing gear is lost or abandoned at sea. The gear can continue to catch fish, dolphins, whales, turtles, and other creatures as it drifts through the water and after it becomes snagged on the seabed. When driftnets were used on the High Seas, an estimated 1,000km of ghost nets were released each year into the North Pacific Ocean alone.

    Although the current contribution of ghost fishing to bycatch is unknown, it is likely to have a large impact. One survey estimated that a quarter of the rubbish on the bottom of the North Sea is fishing nets, while fishers speak of a dolphin and turtle graveyard among the nets that drape the cliffs of Cape Wessell, Northern Australia.

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