"Clearly we are in the midst of one of the great extinction spasms of geological history" E.O. Wilson
"We know that seamounts support large pools of undiscovered species, but we cannot yet predict what is on the unstudied ones. The tragedy is that we may never know how many species become extinct before they are even identified" Dr. Frederick Grassle, Rutgers University (1)
The deep ocean has, throughout human history, often inspired wonder and fear - the home of legendary leviathans of the deep which struck fear in the hearts of ancient mariners, or the source of the so-called "primordial ooze", at one time believed to be the origin of life itself.
Recent scientific investigations have served to confirm and reveal the truly remarkable extent of the mystery and diversity of life in the deep-sea. Among other things, scientists have discovered that there are more species of corals found in the deep ocean than in shallow-water tropical seas. Some of these coral species form reefs many thousands of years old, which support rich and highly endemic ecosystems. Many new and 'relic' species (species previously known only from fossil records) have been discovered on seamounts — the peaks of underwater mountains and mountain chains found throughout the Atlantic, Pacific and Indian Oceans. Most seamounts and other deep-water habitats have not yet been studied but many of the estimated 100,000 or more seamounts worldwide may well be unique 'islands' of biodiversity in the deep-sea.
Scientists estimate that the number of species inhabiting the oceans at depths below 200 meters could be as high as 1-10 million species. Research expeditions to the deep-sea routinely discover new species or ecosystems, often in unexpected places. For example, two cruises over the past several years south of Australia found 274 new species of corals, starfish, sponges, shrimps, and crabs 1.2 miles (2 kilometers) beneath the surface of the ocean around Antarctica. They also discovered 145 undersea canyons and 80 new seamounts. (2)
Unfortunately, the ability to reach deep into the ocean in search of new forms of life is not restricted to scientific research alone. As coastal and open ocean species of fish such as cod and tunas are overexploited, large-scale fishing vessels have increasingly turned to developing new fisheries and markets for species such as orange roughy, grenadiers and deep-water prawns found in the deep ocean. The fishing industry has developed the technology to fish the ocean bottom as deep as 2000 meters or more.
The preferred method of deep-sea fishing is 'bottom trawling' which drags heavy steel plates, cables and nets across the ocean floor destroying corals and other species that form the basic structure of deep-sea ecosystems. The scale of the threat to the marine biodiversity of the deep-sea as result of bottom trawling as well as other methods of deep-sea fishing is yet unknown, but potentially comparable to the threat to terrestrial biodiversity associated with the loss of tropical rainforests. Many thousands of species may be at risk, most of which are still unknown to science.
Today's trawlers are capable of fishing seamounts, deep-sea canyons and rough seafloor that was once avoided for fear of damaging nets. To capture one or two target commercial species, deep-sea bottom trawl fishing vessels drag huge nets armed with steel plates and heavy rollers across the seabed, pulverizing everything in their path. In order to catch a few 'target' fish species of commercial value, biologically rich and diverse deep-sea ecosystems are plowed through and often huge quantities of unwanted fish are caught as 'bycatch' and thrown dead back into the water. In a matter of a few weeks or months, bottom trawl fishing can destroy what took many thousands of years to create.
The mouth of the trawl net is held open by two steel plate doors that help to keep the net on the seafloor. One company markets what it calls 'Canyonbusters', trawl doors that weigh up to five tons each and undoubtedly live up to their name. To protect the net from snagging on rugged seafloors, heavy chafing gear is attached to the bottom of the trawl net. A heavy cable is then strung through steel balls or rubber bobbins — known as roller gear or rockhoppers — that can measure a meter or more in diameter.
Fragile deep-water ecosystems, coral systems in particular, stand no chance against these ruthlessly effective underwater bulldozers. Deep-sea structures are not merely damaged, they are obliterated in a manner akin to clear-cutting a rainforest. After heavy trawling, the surfaces of seamounts are reduced to mostly sand and bare rock or coral rubble.
Once destroyed, slow-growing deep-sea species are either lost forever or unlikely to recover for decades or centuries. Stable, living habitats such as coral and sponge communities in particular tend to be both the most heavily damaged and the slowest to regenerate. To make matters worse, the deep sea's remarkable array of coral, sponge, fish, crustacean and other species are, to an unusually high degree, undiscovered and endemic. The risk of extinguishing whole species never before seen is, therefore, very high when bottom trawling strips the surface of seamounts of their coral and sponge habitat.
Considerable damage to deep-water coral communities has been recorded off both coasts of North America, off Europe from Scandinavia to northern Spain, and on seamounts near Australia and New Zealand. In Norwegian waters, for example, the Institute of Marine Research in Bergen, Norway estimates that one-third to one-half of the cold-water coral reefs have been damaged or destroyed by trawling. Photographs document giant trawl scars along the seabed up to 4 kilometers (2.5 miles) long.
On the high seas south of Australia, in an area known as the South Tasman Rise, observers recorded trawlers bringing up an average of 1.6 tons of coral per hour in their nets in 1997 — the first year of the area's orange roughy seamount fishery. Up to several thousand tons of coral were estimated to have been brought up in the nets of the 20 or so deep-sea trawlers working in the area. This figure does not include coral that was damaged but not brought up in the nets. By contrast, the catch of orange roughy — the target species in this fishery — in the first year of the fishery was reported to be less than 4,000 tons.
A study in the Gulf of Alaska observed a trawl path that had pulled up one ton of corals. Thirty-one red tree coral colonies had been in the 700-meter trawl path observed. Seven years after the damage, some of the larger colonies that survived the initial trawl tow were still missing 95—99 percent of their branches. No young corals had replaced the dead ones in the damaged colonies.
(1) Dr Frederick Grassle of Rutgers University quoted in "Lost worlds of the ocean threatened by trawlers" by Roger Highfield, Science Editor. UK Telegraph 23/8/2003.
(2) National Geographic News 9 Oct 2008.