Discovering no New Zealand sea lion pups were born on one of only five breeding colonies in the Auckland Islands is a concern despite an overall increase in pups on the islands, University of Otago zoologist Dr Bruce Robertson says.
The latest report on pup production in the Auckland Islands, completed by Department of Conservation contractor Blue Planet Marine, has been released and shows a 15.2% increase in pups, to 1931, on last year.
Any increase in pups was positive but the lack of pups born at South East Point, Enderby Island, one of the four island breeding colonies, was concerning, Dr Robertson said.
The researchers visited the colony on nine different days and failed find to any live or dead pups. No adult or juvenile sea lions were seen either.
Blue Planet Marine senior marine scientist Dr Simon Childerhouse, who was on the Auckland Islands' research team, said pup production hit rock bottom in the 2008-09 season at 1501 pups, compared with the 3021 recorded at their height in 1997-98.
While there had been increases in pup production in three of the past four years, pup production was still 36% below what it was in 1997-98, but that was an improvement over the big drop in 2008-09.
''I would say that the signs so far are promising and that if the increases continue, it will be good news for New Zealand sea lions.''
There was also some good evidence to suggest the number of pups born outside of the Auckland Islands was also increasing, including at Campbell Island and Stewart Island.
The reason for this season's increase was not clear, but it could be because of the lack of disease outbreaks over the past few years, which allowed the population to recover from three previous disease outbreaks, when many pups died, Dr Childerhouse said.
''A few more years will be required before we can have confidence in this positive upwards trend,'' he said.
It would not be until sea lions recolonised the mainland in reasonable numbers that ''we will we have some confidence in their safe future'', he said.
New Zealand sea lions used to occupy the whole coastline of the country and so they were still only a remnant population.
Both Doc and the Ministry for Primary Industries were investing ''significant resources'' in trying to understand the sea lion issue, including reviewing both the science that underpinned management and management systems, he said.
Dr Robertson presented his genetic research findings at the review of the sea lion modelling system and hoped this would lead to an adjustment in the modelling behind the management.