Deep sea: threats
(www.panda.org)
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.
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