A ban on the use of massive deep-sea fishing nets in South Pacific waters is about to be announced.

Gillnets, which can be 100 kilometres long, are banned in European waters but are allowed in the South Pacific.

Australia and New Zealand proposed the ban after two Spanish boats were spotted fishing with gillnets between the two countries.

A meeting is underway in New Zealand and it is expected the ban will be announced tonight or tomorrow, and will be in force by February.

Duncan Currie from Greenpeace says the ban must be total and long-lasting.

"Unfortunately the history of fishing shows that if boats think a buck can be made then they will try to use whatever sort of loophole to come down here," he said.

"There was a deep-sea gillnet found in Antarctic waters which measured in total 130 kilometres long; these things do have to be watched very carefully."

Deadly nets

A week ago the ABC reported that gillnet was bulging with 29 tonnes of Antarctic toothfish and a significant bycatch of skates.

Toothfish stocks in the Southern Ocean are under threat and the two species of toothfish - antarctic and patagonian - are seriously depleted.

Australian authorities found the illegal net in the Southern Ocean, in an area managed by the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR).

Gillnets target fish species that live on the bottom of the ocean such as the beleaguered deepwater dogfish.

Australia's deepwater migratory sharks and other fish species are likely to be caught in the nets, including harrison's dogfish, which is considered to be critically endangered due to overfishing.

The gillnet fleets are targeting sharks for their meat and for liver oil which is used around the world in cosmetics. The oil from the deepwater dogfish is highly prized.

Gillnets are a particularly lethal form of fishing. If the fishing net gets lost, it acts like a "ghost net" and continues to catch fish as it bobs about in the ocean.