Deep sea: threats

A number of human activities threaten the deep sea:
  • Destructive fishing practices: Bottom trawling is currently the greatest threat to deep-sea biodiversity. First introduced in the 1980s, rockhopper trawls fitted with large rubber tires or rollers allow bottom trawling on virtually all of the ocean floor down to a depth of 2,000m.

    These trawls - whose use is now widespread - crush everything in their path. 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.

    These and other deep-sea trawlers also kill a large amount of unwanted deep-sea life as bycatch.

  • Overfishing: Deep-sea species are generally extremely slow growing and do not reach sexual maturity for many years. Some commercial deep-sea fish also congregate in large numbers around seamounts to feed and spawn. And many deep-sea fisheries are located on the High Seas where there is often little or no regulation. These factors make deep-sea fish extremely vulnerable to overfishing. Newly fished populations of deep-sea species like Patagonian toothfish and orange roughy, for example, have been fished to commercial extinction in just a few years. At present most deep-water species are likely to be over-exploited - and as many as 40% of the world’s fishing grounds are now in waters deeper than 200m.

  • Oil, gas, and mineral exploration: At present, most oceanic reserves of oil, gas, and minerals are extracted from the continental shelf, under shallow coastal waters. However, with valuable reserves also located under the deep ocean floor, the oil and mining industries are expected to venture further afield, and eventually explore down to 3,000m. Such activity could have devastating effects on fragile, slow growing deep-sea communities.

Find out what WWF is doing to protect the deep sea!
 / ©: 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

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