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And in a paper published recently in journal Fisheries Management and Ecology, researchers have proposed a series of measures
to prevent the situation turning into a costly and controversial issue.
''The sea lions will take several times more fish than what combined recreational and commercial fisheries take,'' researcher Amelie Auge, who took part in the study while at the University of Otago, said.
It was important preventive management measures were decided upon soon to limit costs to fishermen, she said.
The New Zealand sea lion population established on Otago Peninsula in 1994 was increasing slowly, with about 12 breeding adult females this year. It was estimated about 250 animals could live on the peninsula by 2031, increasing to 1000 by 2044.
Sea lions were critically endangered, and their being caught in the nets of commercial fishermen around Auckland Island breeding and fishing grounds had resulted in controversy and costs from trying to remedy the situation.
Management options needed to be progressively implemented by fishermen and conservationists to avoid conflict off Otago Peninsula, she said.
Options should include marine protected areas, local fishing quotas and management of sea lion numbers, although that was illegal under the Marine Mammal Protection Act, she said.
Additional information was needed on marine production areas, fish stocks and sea lion population dynamics around Otago Peninsula for some of those steps to be implemented.
''An MPA (marine protected area) or a network of MPAs with fishing restrictions or no-take zones would ensure bycatch, depredation and competition issues are avoided.''
These plans could also solve issues of bycatch of yellow-eyed penguins, she said.