Rakiura sea lion colony could help boost Otago numbers

A small but thriving colony of New Zealand sea lions recently discovered in a remote harbour on Stewart Island could eventually help boost the sea lion population along Otago coasts.

That's the opinion of Massey University professor Lousie Chilvers, who said several of the pups born on southern Stewart Island/Rakiura are visiting beaches around Otago.

Prior to 2010, Prof Chilvers had received reports of sea lions on Stewart Island but did not know there were females with pups present.

After giving out questionnaires to hunters on Stewart Island, she came up trumps with a sighting in Port Pegasus.

"Someone sent back a photo with three females and five pups in it, so it was like "OK!".

"So the next year I arranged to go down and have a look and see if I could find these pups".

Sea lions on Stewart Island/ Rakiura. Photo: Supplied
Sea lions on Stewart Island/ Rakiura. Photo: Supplied

The newly-discovered colony is located on a wild and remote part of Stewart Island and she said it proved much harder to count the pups than on Otago's open beaches.

"It took us so long to find them and every single year they're in different places, and we spend ten days working really hard just to find as many pups as we do."

With more than 35 pups being born every year on Stewart Island, they are considered a viable colony.

Prof Chilvers said there's hope the species will reclaim the New Zealand-wide coastline where they lived in pre-human times.

"It's the first colony away from the subantarctic in 200 years, so it's quite a big thing for New Zealand sea lions.

"They used to breed all the way up to Cape Reinga, all through Nelson and even the Chatham Islands".

Researchers have recorded a number visits to the Otago coastline by sea lions born on Stewart Island.

Prof Lousie Chilvers. Photo: Supplied
Prof Lousie Chilvers. Photo: Supplied

While most females choose to give birth where they themselves were born, some could eventually join the other breeding females on Otago beaches.

Prof Chilvers said both Stewart Island and Otago seem to suit the sea lions well.

"Adult females are on average at least 15 kilos heavier up here than they are on sub-antarctic islands.

"And that's really a sign that they are foraging easier, and they're just doing better all round."

Unfortunately it's not all good news, with the base population of New Zealand sea lions on the Auckland and Campbell Islands still in decline.

Over the past twenty years, the number of pups produced on these subantarctic islands has almost halved from around 3000 to well under 2000 per year.

Research by University of Otago associate professor Bruce Robertson suggests a reason for the decline of sea lions on the Auckland and Campbell Islands.

His research indicates the population is being harmed when they are caught up as bycatch on New Zealand's deepwater trawlers.

"Fisheries bycatch is a likely to be a key player in the decline of sea lions", he said.

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