With the numbers of New Zealand's critically-endangered sea lions dropping fast, a research team is setting sail to investigate their main prey -- the yellow octopus.
The shifty sea creatures are abundant but tricky to catch, says NIWA fisheries scientist Dr Jim Roberts.
Despite sea lions eating around one million octopodes a year, he says scientists have only managed to catch around 50 to study.
"Somehow [the octopodes] evade trawl nets. They either squeeze out of nets, or avoid going into them at all. I think they're cleverer than the average fish."
Over the past 15 years, the main breeding population of New Zealand's sea lions located in the Auckland Islands has plummeted by half.
(Supplied / Darren Stevens)
Dr Roberts, who has been studying the dramatic decline for several years, saying while it's not likely there's a single cause to the drop, it is likely there's something going wrong with the sea lions' diets.
"We can say with a high degree of probability that sea lions are suffering nutritional stress," Dr Roberts says. "This is affecting their reproduction and may be contributing to low survival of both pups and adults."
Tomorrow, NIWA's flagship research vessel Tagaroa will head to the waters around the Auckland Islands and Stuart Islands to conduct the New Zealand sea lions' first prey survey.
They'll be travelling equipped with 100 purpose-built "yellow octopus pots" to help them catch the slippery creatures.
The pots are designed to lure in the octopodes by resembling a cosy den on the sea floor, with room for up to four octopodes at a time.
(Supplied / Darren Stevens)
While the scientists aren't sure if the traps will work, Dr Roberts says they hope to capture at least 10 yellow octopodes. They would be "delighted" with 50 captures, which would double the amount of yellow octopodes currently available for study.
Although the survey will be focused on yellow octopodes, as the sea lions' main prey, the team will also be mapping the mammal's other prey, which includes arrow squid, red cod and hoki, with underwater cameras.
New Zealand's sea lions had a bumper breeding season in Otago this year, with a record nine pups being born across seven beaches.
But they're still at risk -- it's been estimated there are less than 150 sea lions on the mainland.
By mapping out the critically-endangered mammals' prey, the research team hope to develop a greater understanding of the difficulties the creatures face.
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