Marine researchers say commercial fishing could be killing off New Zealand's largest population of native sea lions.

From Radio New Zealand News: Marine researchers say commercial fishing could be killing off New Zealand's largest population of native sea lions.

In a study, the researchers discount non-human factors such as disease and say by-catch incidents and competition for food are the most likely cause of the population decline.

Report author, senior lecturer at Otago University Bruce Robertson, says about 70% of the species breeds on the Auckland Islands and the rest on Campbell Island.

Dr Robertson says breeding at the Auckland Islands has declined by 40% since 1988, with only 1500 pups born in 2009. However, breeding on Campbell Island is slowly increasing.

By comparing the two populations, he says, the team found two human factors could be the reason the Auckland Islands population is in decline.

The first is competition for fish between the marine mammals and humans and the second is the death of sea lions caught in nets.

Dr Roberston says the sea lions may be having to compete with fishermen for the squid around the Auckland Islands.

However Ministry of Fisheries deepwater manager Aoife Martin says there is no information to suggest the sea lion population decline is due to fishing activity.

Ms Martin says the number of reported sea lion captures is falling, with none at all reported at this year's squid fishing season.

She says the industry takes wildlife issues very seriously, and all vessels have devices on their nets to allow any sea lions that enter them accidentally to escape.

Dr Robertson says the researchers were not seeking to apportion blame, but to find out what is going on and identify areas where knowledge is lacking.

He says fewer than 10,000 native sea lions remain, so such information is very important.