Vessels fishing for toothfish continue to get into trouble in the Southern Ocean, but scientists warn they are endangering more than human life.

The fire on board the Korean vessel Jung Woo 2 follows the rescue of the Sparta and last year's sinking of the In Sung No1. All were licensed to fish for toothfish.

Auckland University Associate Professor Clive Evans, who has returned to New Zealand after spending the summer at Scott Base researching antifreeze capabilities of Antarctic fish, said the toothfish population had declined rapidly.

Professor Evans said numbers started dropping off in 2001, five years after the Ross Sea was opened to commercial toothfishing.

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He said previous to that year as many 500 fish were caught for scientific research every summer season.

"This year we made a concerted effort to go to sites that we know have been successful in the past. And what did we get? 490 hours of fishing, and one fish. And that was the smallest fish we had ever caught.

"It is a warning that something is going wrong."

Toothfish (Dissoctichus mawsoni) is a long-living, slow-maturing species that grows as long as two metres. Professor Evans, who fishes through the sea ice to catch specimens from the southern fringe of the toothfish population, said not enough was known about the species to accurately model its behaviour.

"You're trying to work out the effects of fishing at a certain level. You need to know how many fish there are, how often they breed, how many eggs are laid. We simply don't have that life history information."

What little was known, he said, indicated the importance of the toothfish to the local ecosystem.

"It is the top fish predator, and taking it out of the equation is going to screw things up."

The University of Illinois' Professor Art DeVries, who has been coming to Antarctica since 1961, said the past couple of years were the worst he had seen.

"We aren't able to catch them any more. It used to be at this time of the year I'd be able to get at least four or five in 24 hours. There is just nothing around."

The Hobart-based Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR) is responsible for maintaining the sustainability of the Ross Sea fishery.

Executive secretary Andrew Wright said "almost all" of their information came from the fishing vessels themselves.

"CCAMLR prides itself on having a detailed and demanding process for analysis of available scientific information to suggest the sustainable allowable catch for a geographic area."

CCAMLR data manager David Ramm said a drop-off in numbers under the ice shelf did not necessarily mean a drop in numbers at the main, more northern, fishery.

Professor DeVries disagreed. "It is correlated with the commercial fishing in the Ross Sea. In a couple of years we'll know, because the catches out in the Ross Sea will drop off," he said.