Expert warns Government on wrong track with sea lions

A University of Otago zoologist is urging the Government to take another look at its proposal not to set a fishing industry limit on sea lion by-catch, saying MAF’s science behind its recommendation is flawed and could hasten the species towards extinction.

Otago Zoologist and sea lion expert Dr Bruce Robertson was responding to the Government’s making a “major departure from past policy” and proposing no by-catch limit be set, citing new evidence from MAF that by-catch of NZ sea lions in the squid fishery is no longer an issue contributing to the extinction risk of the species.

Dr Robertson says this conclusion is at odds with his own recently published study which concludes that by-catch, and also resource competition with the squid fishery, is resulting in the decline of the Auckland Island breeding colonies of the sea lion.

Dr Robertson’s study examined all possible causes for the 40 per cent decline since 1998 in the number of pups born at the Auckland Islands, where 71 per cent of this rare sea lion population is located. It is also a location for New Zealand’s sub-Antarctic squid fishery. By contrast, the sea lion pup population a considerable distance away from the Auckland Islands, on Campbell Island, is slowly increasing.

“The contradiction of the scientific evidence examined in my study is caused by the mathematical models used by MAF fisheries managers, and stems from unproven assumptions around the use of sea lion exclusion devices (SLEDs) and fuzzy logic,” he says.

He says that these sea lion exclusion devices are placed into trawl nets to, in theory, allow sea lions to escape and avoid drowning. But considerable uncertainty still exists about the condition of sea lions once they escape via SLEDs.

“MAF’s new data quantifies whether SLEDs in trawl nets are resulting in more deaths of sea lions and it seems that SLEDs only slightly increase the risk of mild traumatic brain injury to sea lions” he says.

MAF is also incorrectly equating low levels of mild traumatic brain injury caused by SLEDs as evidence that all sea lions will escape trawl nets alive, pointing to declining numbers of sea lion bycatch in their proposal.

“Unfortunately, there is no evidence to support this optimistic assumption. We know very little about the state of NZ sea lions leaving SLEDs. Only one sea lion has ever been seen to leave a net alive. Plus, it is important to note that MAF’s new evidence is not based on sea lions escaping SLEDs, instead it is based on Australian fur seals escaping trawl nets via a similar device.

Crucially, that Australian study showed that 12 known-drowned fur seals were never landed on the trawler deck as they fell out of the device when the nets were pulled up and hence were never counted in the official by-catch tally. There is no evidence to suggest that our SLED are behaving any differently,” Dr Robertson said.

New Zealand Government fisheries managers (MAF) have just produced a discussion document (initial position paper, IPP) with the purpose of setting a limit (fishing related mortality limit, FRML) on the number of New Zealand sea lions drowned in the deepwater trawl nets of the squid fishery around the sub-Antarctic Auckland Islands.