The Circumpolar Sea, what some call the Southern Ocean, has a long history of human over-exploitation. Fur seals, elephant seals, and the great whales were all hunted to the brink of extinction. Now scientists say increased Antarctic krill and fish catches could trigger a catastrophic collapse in the entire marine ecosystem.

The meeting was organized by the British Antarctic Survey (BAS), a UK government-funded organization responsible for scientific research in the region.

BAS Director Chris Ripley said: "Commercial exploitation of [Southern Ocean] fish stocks could result in major and potentially damaging changes."

The BAS provides scientific advice to the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR). Representing over 20 nations, the commission's main role is to balance commercial fishing with conservation in the seas around Antarctica.

"Krill" is Norwegian for "whale food"—an apt name for this essential building block for life in the Southern Ocean. Growing to six centimeters (a little more than an inch) long, and often living in dense swarms several miles wide, the shrimp-like crustacean is crucial to many birds and mammals.

John Croxall, principal research scientist at the BAS, said: "For many marine mammals and sea birds, particularly in the South Atlantic sector of the Southern Ocean, krill is by far the most important item of their diet. This is true for minke whale, Antarctic fur seal, Adelie, chinstrap, gentoo and macaroni penguins, black-browed albatross, and white-chinned and cape petrels."

Long-term monitoring by the BAS on South Georgia revealed these species are extremely sensitive to fluctuations in krill numbers. During the 1990s, when krill became less abundant, researchers found that seals, penguins, and albatrosses all struggled to raise their young.

The current Antarctic krill catch is around 120,000 tonnes (132,280 tons) a year, though this figure is well within sustainable levels for a species with an estimated total biomass greater than any multi-cellular animal on Earth, including man.

Scientists say fishing effort has so far been limited by practical problems associated with krill. It contains powerful digestive enzymes that can spoil its flesh after death, while the process of removing its unpalatable shell is relatively costly.

Shifting Fisheries Economics

Despite this, researchers say rapid shifts in global fisheries economics are outpacing efforts to predict future fishing pressure and conservation requirements.

"Antarctic krill remains the largest exploitable stock and its exploitation also poses the greatest threat to the ecosystem," said krill expert Stephen Nicol, from the Australian Antarctic Division in Tasmania.

"A challenge for CCAMLR will be to ensure this huge potential catch is distributed in a way that does not adversely affect populations of land-based krill-feeding seals and sea birds."

Nicol identifies rapid growth in the fish farming and biotechnology industries as two key threats to sustainable harvests.

He says fish farming is expanding at a rate of 11 percent each year. In a decade, output is expected to exceed catches from ocean fisheries and overtake global beef production within 20 years.

"Aquaculture is going to become a very hungry animal and will require very large quantities of marine-based protein and oil," Nicol added.

Fish farming currently consumes 70 percent of the world's fish oil supply and 34 percent of total fishmeal, according to the Worldwide Fund for Nature, with stocks in many Atlantic and Pacific fisheries already in danger of collapse. Fish feed producers are now looking at Antarctic krill to meet future demand.

Nicol says krill has particular value for salmon farmers as it contains astaxanthin—a carotenoid that turns salmon flesh an appetizing pink.

Incentives to use this natural pigment in salmon feed have risen recently due to consumer concerns over an artificially produced alternative. This year the European Union cut permitted levels of canthaxanthin (a coloring agent added to the feed of farmed salmon and trout to enhance the color of the flesh) by two-thirds after research revealed it could cause eye damage.

Nicol says the burgeoning biotechnology industry could place similar pressures on krill.

Drug companies claim it contains substances that can treat a range of human ailments, including heart disease, premenstrual tension, and skin cancer. Patents are pending for various krill-based medications.

While the Southern Ocean krill fishery is still in its infancy, scientists say Patagonian toothfish catches have already reached unsustainable levels.

Pressure on Toothfish

Economic factors elsewhere, including over-exploitation of North Atlantic cod stocks, have fueled a massive increase in fishing pressure.

A slow-maturing species that doesn't breed until ten years old, a single fish can fetch U.S $1,000.

Also known as "white gold," such prices have tempted "pirate" fishermen to follow legitimate vessels south in search of the fish.

Croxall said: "There's no doubt that in some places toothfish populations are on the point of collapse."

Last year's estimated illegal catch in CCAMLR waters was almost 11,000 tonnes (12,125 tons), with another 14,700 tonnes (16,205 tons) coming from adjacent high seas areas.

Nicol says policing pirate vessels is extremely difficult, adding, "The main problem is the vast area you've got to cover down there. Illegal fishing is a highly organized activity that involves multinationals."

Australian authorities have discovered illegal operators employ sophisticated techniques to avoid detection, including trans-shipment of fish and refuelling at sea.

The ecological damage caused by unregulated fishing isn't confined to toothfish. CCAMLR estimates pirate longlining vessels have killed up to 144,000 albatrosses and 400,000 petrels in Antarctic waters since 1996.

Longlining is a fishing method that uses thousands of baited hooks—hooks that can also catch feeding sea birds.

Croxall said : "10,000 to 20,000 hooks are set each day by these vessels on lines several kilometers long. In 20 to 30 years' time there's going to be an inexorable decline in albatross numbers."

Scientists now want the international community to act to safeguard krill and toothfish stocks throughout the Southern Ocean, otherwise its albatross, penguin, seal, and whale populations could all be left living on very thin ice.