Sea lions monitored for decline

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SEA LION COUNT: Department of Conservation marine mammal scientist Louise Chilvers monitoring threatened New Zealand sea lions on a research expedition in the sub-Antarctic.

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A department of Conservation team returned from the sub-Antarctic this week after monitoring New Zealand sea lions, a species struggling to survive.

The sea lions' population has dropped by about 40 per cent during the past 10 years and there are now less than 10,000 of the endemic New Zealand mammals.

A team of six researchers lived on the Auckland Islands for three months and a team of three were on Campbell Island for 10 weeks where they monitored, tagged and performed necropsies on the sea lions to try to find the reasons for the dramatic population decline.

DOC head office marine mammal scientist Louise Chilvers said the reasons were still not clear, but human impact and naturally occurring bacterial outbreaks were among the causes.

The fishing season coincided with the sea lions' breeding season, with between 60 and 140 seal lions killed each year by fishing trawlers. Of these, between 60 and 80 per cent were females.

When a female was killed in breeding season it was likely to be pregnant, and if it had a pup on shore, which was also likely, this too would starve, she said.

The researchers were also working to find out if the fishing boats were depleting the sea lions' fish sources.

The expedition's research revealed an increase in the number of pups on the islands – for the first time in 10 years – but there were still not as many as there should be, she said.

"Sea lions are supposed to be in their hundreds of thousands."

The sea lion population was completely wiped out on the New Zealand mainland by sealers about 200 years ago, but the beach-dwelling mammals have since returned to Otago and Southland, including a few breeding females.

Ms Chilvers monitored them in the sub-Antarctic for the past nine years and it was always an adventure. "It's the most astounding place in the world," she said.

But the last trip back was "the worst I've ever had", with the boat ride taking 40 hours instead of the usual 30 because of bad weather, she said.

- © Fairfax NZ News