A team of international researchers lead by the university analysed the ancient DNA of a previously undiscovered sea lion on the Chatham Islands which was decimated in 1650AD.
The research determined the sea lion population of 50,000 was eradicated within 200 years of human settlement.
University of Otago department of zoology scientist Dr Nic Rawlence said the findings had important implications for the survival of the critically endangered modern day New Zealand sea lion. Using the same computer modelling approach used to measure the rapid decline of the Chatham Island sea lion, the researchers found if 410 New Zealand sea lions died every year for the next 50 years, the species would be extinct.
Dr Rawlence said the biggest threat to the species was death by bycatch.
Bycatch deaths were believed to make up 30-75% of sea lion deaths each year, he said.
There were about 150 reported bycatch deaths a year, but it was believed only half of all bycatch deaths were reported.
This amounted to 300 deaths a year and it was "alarming'' when deaths as a result of drowning or bacterial infection were added on top of bycatch casualties, he said.
"It is not too late to save the sea lion.
"What this research shows, though, is humans and sea lions just do not mix.
Dr Rawlence said a threat management plan for New Zealand sea lions which the Department of Conservation and the Ministry for Primary Industries was seeking public feedback on did not adequately address the risks to sea lions.
The management plan suggested death by bacterial infection and drowning were more of a risk to the species than the fishing, he said.
"Bacterial infections and drownings are periodic events which only impact one generation.
"If a female sea lion is caught because of squid trawling it kills her, her pup and any unborn pups.''
Unless measures were taken to minimise bycatch deaths, the outlook for sea lions was bleak, he said.
"There will always be people in the fishing industry who are not happy about the changes but they are necessary.''
The researchers were working with Niwa and the Ministry for Primary Industries to prevent further decline of the species, Dr Rawlence said.
