Bottom Trawlers Are Menacing the Fragile Deep Sea Coral Ecosystem

In a report made for UN, oceanographers warn that the use of heavy trawling gear in deep waters is now doing immense damage to the ecosystems around sea mounts (underwater mountains) and should be stopped immediately.

"At the very minimum we want an agreement this year to freeze any further expansion of bottom-trawl fisheries," said Matthew Gianni of the campaign group Deep Sea Conservation Coalition.

"We also want to see established a reverse burden of proof; that is, you cannot fish on the high seas using bottom gear unless you can prove you are not going to do damage to the ecosystems in which those fisheries will take place."

Huge trawl nets armed with steel weights or heavy rollers are dragged over the seafloor, crushing and ripping everything over zones which harbor particularly sensitive deep sea corals and sponges, destroying the habitat on which fish and diverse organisms depend.

Targeted fish species are, amongst others, orange roughy, oreos, alfonsino and roundnose grenadier.

This practice is used by roughly 200 boats worldwide, accounting for about 0.2% of the total world catch.

"This meant the scale of the destruction was out of all proportion to the gain in terms of the value of the fishery," said Dr Alex Rogers, a senior researcher at the Zoological Society of London, UK.

"It's the equivalent of clearing old-growth forest to collect squirrels. It's a practice on land that just wouldn't be acceptable," he added.

Around the world, there are around 100,000 underwater mountains, which attract aggregations of the plankton, the food base of marine ecosystems.

These sea floors are situated at 1,000-2,000m depths and are covered by large "forests" of slow-growing corals, the basic habitat of very high densities of fish, targeted now by industrial trawlers.

"But if there are species which you really shouldn't fish, these are the ones," said Dr Rogers.

"The orange roughy (photo above) lives for up to 150 years or more; they don't mature until they are 30 or 40 years old; their reproduction is very sporadic; they are very vulnerable to overfishing."

The team has compared the distributions of commercially trawled fish, fishing effort and coral habitat on seamounts.

These biological communities form a broad band of the southern Atlantic, Pacific and Indian Oceans between 20 degrees and 60 degrees south, where bottom-trawling fishing is concentrated.

As large areas in this zone are beyond the authority of national or regional fisheries' regulation, the fishing's result could be catastrophic.

Ironically, most bottom-trawlers belong to northern fleets from developed nations, the majority under Spanish flag.