Otago key to saving sea lion numbers

Wednesday, 8 July 2015

New Zealand's sea lion numbers are 'nationally critical' but scientists hope a small Otago colony will help arrest the drastic decline.

Only 10,000 sea lions are thought to be left and the main breeding population in the Auckland Islands has halved since the 1990s. Those numbers put sea lions as 'nationally critical' - the highest level in New Zealand's threat classification system.

A small sea lion colony on the Otago Peninsula has bucked the trend, however, growing while the Auckland Islands population declined.

National Institute of Atmospheric and Water Science (Niwa) researchers have been studying both populations to learn more about why one is succeeding while the other flounders.

Marine scientist Dr Jim Roberts said the Otago sea lions reproduced at a higher rate. Fewer of them died in the first years of life and female started having pups at a younger age.

There were several likely factors behind the Auckland Islands population decline, he said.

'Normally if pup survival is low it suggests their mothers aren't getting enough food.

'There are a number of clues that point to nutritional stress and disease is also affecting the number of pups who survive to adulthood.'

Several bacterial disease epidemics have knocked back the Auckland Islands population, including outbreaks of Klebsiella pneumonia  in 2002 and 2003. It was unknown what caused another epidemic in 1998.

Work by Massey University scientists suggested the Klebsiella bacteria could be responsible for killing hundreds of pups each year but developing a vaccine would be costly.

Further research would investigate the availability of key prey species for the sea lions, Roberts said.

'I feel we are beginning to solve some aspects of this puzzle. It looks very much like the sea lions are suffering nutritional stress as a result of changes in prey availability around the Auckland Islands, and some years it might be quite extreme.

'If we continue to think critically about changes occurring in sea lion populations and to compare growing and declining colonies we will continue to uncover the main threats.'

Another group of sea lions has recolonised Stewart Island. Roberts said that was a positive sign because it was rare for females to give birth away from the place they were born.