Huge deep-sea fishing nets which can be cut loose and left to keep catching fish as they float may be banished from South Pacific high seas.

Efforts led by New Zealand and Australia to ban gillnet fishing were close to succeeding last night after revelations that an illegal 130km-long gillnet bulging with Antarctic toothfish was spotted in the deep ocean off Antarctica.

New Zealand officials have been concerned about gillnets since two Spanish vessels were reported fishing with long, deep versions between Australia and New Zealand this year.

The nets, about 100km long, are indiscriminate fishers and are used to target deep-sea sharks and other species.

The Antarctic discovery was revealed as 150 representatives from Latin America, Asia, Europe and North America met in Auckland to negotiate the final stages of a fishing treaty to apply outside South Pacific countries' exclusive economic zones.

The head of the New Zealand delegation, Gerard Van Bohemen, said he was hopeful nations would adopt a voluntary ban on gillnets today or tomorrow.

Greenpeace and Environment and Conservation Organisations (Eco) representatives at the talks said the ban was essentially a "done deal".

The negotiations are the last in a series of talks to fill a gap in the protection of high seas fish (apart from tuna) by setting up a Pacific Regional Fisheries Management Organisation.

The new body will watch over a vast area of ocean, from the far eastern part of the South Indian Ocean through the Pacific towards South America - high seas where fish are vulnerable to illegal and over-fishing because of a lack of governance.

Speaking from the talks at Auckland's Crowne Plaza hotel, Eco's Cath Wallace said the gillnet ban was good news for New Zealand.

The huge nets were cheap, so fishing boats could easily afford to cut them loose and leave them floating around snaring fish as they went, she said.

Gillnets are banned in the northeast Atlantic at depths of more than 200m and in Antarctic seas managed by the Commission for the Conservation of Antarctic Marine Living Resources - where the illegal 130km net was found - but vessels still carry them for fishing in the high seas.

ABC News reported the Antarctic net was set at a depth of more than 1500m and had captured 29 tonnes of Antarctic toothfish by the time it was spotted by Australian authorities.

As well as setting up the new organisation and talking about gillnets, delegates have been debating new interim catch limits for jack mackerel fisheries off the coast of South America.

A science working group chaired by New Zealand Ministry of Fisheries scientist Andrew Penney told negotiators jack mackerel catches were well down on past years.

Ms Wallace said that unless interim limits - which were opposed by several countries - were set there would be a "race to fish" and stocks would be gone by the time yet-to-be-signed limits took effect.

Mr Van Bohemen said nations were likely to agree on the basic operating criteria for the new organisation today. A fishing treaty would come into effect in two to four years, as soon as enough countries had signed it.