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The practice of hot-iron branding New Zealand sea lions ended in controversy 13 years ago, but research has found it has not affected their survival.
The branding was part of an experiment by Department of Conservation staff, who anaesthetised the animals for the procedure, but it was stopped in 2000 by then Conservation Minister Sandra Lee, who said she was horrified by the ''unfortunate experiment''.
While it had been approved by Doc's animal ethics committee, some questioned the animal health and welfare effects.
Thirteen years on, Doc scientists, while acknowledging people had a problem with the practice, say it provided a wealth of information on the critically endangered sea lions.
In 2000, Doc branded 300 sea lion pups, aged between 5 and 10 weeks, and 134 adult females.
Doc marine scientist Dr Louise Chilvers said all of the sea lions' movements had been followed in the years since and the branding had not affected their survival or their reproductive rate.
''For a nationally critical species, we need to understand what is happening to them.''
Ten years on, a study of the branded females showed all of the animals were still alive and could be identified by their brands, even if they had been scarred by shark bites or bites from other sea lions.
Compared with female sea lions which had only been tagged, data suggested their survival rates were similar, if not better, she said.
The study found hot-iron branding could be an effective method of permanently identifying sea lions, providing robust parameter estimates and low disturbance in the resighting process and did not compromise survival.
''We can collect so much better information from them, which is why it was done in the first place.''
The number on the mature male sea lion photographed by the Otago Daily Times at the weekend meant it could be identified as one which travelled to and from Otago's coast to the Auckland Islands to breed every year.
Two years ago, he had a ''harem'' in the Auckland Islands, indicating he bred, she said.
The reason for trying different forms of identification was that plastic flipper tags had a high loss rate, especially for adult males, which outgrew the tags, she said.
Doc Catlins partnership ranger Cheryl Pullar said seeing about 30 sea lions at Cannibal Bay was normal at this time of year, when many of the males came back to Otago after breeding.