The New Zealand sea lion (Phocarctos hookeri) also known as Hooker's sea lion or whakahao in Māori is a species of sea lion that breeds around the coast of New Zealand's South Island and Stewart Island/Rakiura to some extent, and to a greater extent around the New Zealand Sub-Antarctic Islands, especially the Auckland Islands. It is monotypic of its genus.

Characteristics and taxonomy

New Zealand lions, like all otariids, have marked sexual dimorphism. Adult males are 240-350 cm long and weigh 320-450 kg and adult females are 180-200 cm long and weigh 90-165 kg. At birth, pups are 70-100 cm long and weigh 7-8 kg; the natal pelage is a thick coat of dark brown hair that becomes dark gray with cream markings on the top of the head, nose, tail and at the base of the flippers. Adult females' coats vary from buff to creamy gray with darker pigmentation around the muzzle and the flippers. Adult males are blackish-brown with a well-developed black mane of coarse hair reaching the shoulders.^[2]

Endangered

As one of the larger New Zealand animals, it has been a protected species since the 1890s, is in decline^[3] and is considered the most threatened sea lion in the world.^[4]

It has been inferred from middens that the Hooker's sea lion was made locally extinct in the Chatham Islands due to predation by the Moriori.^[5]

There was thought to be a population of around 15,000 in the mid-1990s. Estimates (based on the number of pups born) were about 9,000 for 2008.

In 2010 the Department of Conservation - responsible for marine mammal conservation - changed the New Zealand Threat Classification System ranking from Nationally Endangered to Nationally Critical.^[6]

Though the Auckland Island sea lion pup production is highly variable, a longer decline is evident following the outbreak of the introduced bacterial disease Camylobacter in 1998 which killed 53 per cent of newborn pups and 20 per cent of adult females. In 2002, another introduced bacterial disease Klebsiella pneumonae killed 32 per cent of pups, and in 2003 another 21 per cent of the pups.^[7] Both Campylobacter and Klebsiella are known to reduce fertility in livestock and persist in populations.^{[8] [9]}

The Department of Conservation estimates that Auckland Island pup production has halved since 1998,^[10] and the species could be functionally extinct in the Aucklands by 2035.^[11] However the New Zealand Ministry for Primary Industries considers the research on which this prediction is based is ‘low quality’ and ‘should not be used in management decisions.’^[12]

For the first time in 150 years sea lions began breeding again on the South Island coast in 1994, on the Otago Peninsula. The Otago sea lion population is currently small but estimated to reach 1000 animals by 2044, leading to issues of ‘marine protected areas, local fishing quotas and numbers management.’ ^[13]

Bycatch

A Court of Appeal of New Zealand judgement of 7 April 2004, (with the reasons issued separately on 13 July 2004 (CA39/04)), overturned a decision by the Minister of Fisheries that only 62 sea lions could be taken as bycatch by squid fishers, based on advice from the New Zealand Ministry of Fisheries. The Court increased the bycatch to 124 sea lions in the 2004 season, saying the Minister's imposition of the lower figure (one of the lowest ever imposed in the 20-year history of such restrictions) was going beyond what the law required.

In January 2009 the Fisheries Minister allowed a kill of 113 sea lions by the squid fishery, an increase in 40 percent over the previous season. This was condemned by the Forest and Bird conservation organisation since the sea lion population is under threat and in decline.^[3] The Ministry for Primary Industries has set a limit of fishing related mortality of 68 for the 2012 - 2013 season.^[14]

Increasing refinement of the Sea Lion Escape Devices (SLEDs) which are now universally used in the Auckland Island squid fishery, has resulted in no sea lion mortalities from fishing reported by government observers in the past two southern summer fishing seasons, 2010-2011 and 2011-2012, with observers on board for 1100 trawl tows. The New Zealand Ministry for Primary Industries (MPI) attributes the use of SLEDs , “adequately manages the risk of fishing to the sea lion population. The most recent research strongly suggests that the direct effect of fishing-related mortality on the sea lion population is minimal…” MPI identifies ‘epizootic events’ (oubreaks of diseases) as an alternative possible cause for population decline.^[15]

A New Zealand sea lion nursing at Enderby Island, New Zealand

References

Further reading

• Randall R. Reeves, Brent S. Stewart, Phillip J. Clapham and James A. Powell (2002). National Audubon Society Guide to Marine Mammals of the World. Alfred A. Knopf, Inc. ISBN 0375411410.