New Zealand sea lion
|New Zealand sea lion|
|New Zealand (Hooker's) sea lion|
|New Zealand sea lion range|
The New Zealand sea lion (Phocarctos hookeri), also known as Hooker's sea lion, and whakahao in Māori, is a species of sea lion that primarily breeds on New Zealand's subantarctic Auckland and Campbell Islands and to some extent around the coast of New Zealand's South and Stewart Islands.
Recent DNA information indicates the New Zealand sea lion is a lineage previously restricted to subantarctic regions. Somewhere between 1300 and 1500 AD, a genetically distinct mainland lineage did not survive hunting by the first human settlers, and the subantarctic lineage has since then gradually filled the ecological niche.
The New Zealand sea lion is probably the world's rarest sea lion and numbers around 10,000.
On the Auckland Islands, three functioning rookeries are found. Most sea lions are born on Dundas Island. A smaller rookery exists at Sandy Bay on Enderby Island and the smallest rookery is on Figure of Eight Island. An even smaller rookery at South East Point on Auckland Island appears to now have been abandoned. The other major breeding area is the Campbell Islands.
Characteristics and taxonomy
New Zealand sea 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.
The population was thought to be 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.
The Department of Conservation estimates that Auckland Islands' sea lions, nearly 80% of the total, could be functionally extinct by 2035. However, the New Zealand Ministry for Primary Industries considers research on which this prediction is based is low quality and ‘should not be used in management decisions’.
The January 2013, sea lion pup production count on the Auckland Islands showed the number of pups born on the islands has risen to 1931, from the 2012 figure of 1684. The 2013 number is the highest in five years. Dead pups are also counted, since the annual pup count is used to assess the population of breeding females, but not future births when the counted pups mature.
The Campbell Islands population 'appears to be increasing slowly' and births here comprise about 20% of the national total. In August 2013, the seasonal southern blue whiting fleet captured 21 male sea lions in fishing grounds more than 100 km off the Campbell Islands. Four were released alive. No captures were reported by government observers the year before. The government responded to the captures by requesting the vessels try sea lion exclusion devices (SLEDs) to reduce this bycatch.
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’.
Other small populations of breeding sea lions have recently begun to establish in various parts of the Stewart Island coastline and have been observed on the Catlins coast south of the Clutha River.
In the 1990s, as the volume of squid fishing around the Auckland Islands increased, numbers of sea lions were captured as bycatch and drowned in the squid trawl nets. The government uses a modeling system to set a fishing-related mortality limit (FRML) each year. If the limit is predicted to be exceeded, the Minister of Primary Industries may close the fishery. The last time the FRML was exceeded was in 2000, though a number of closures occurred in the 1990s.
The estimated (as different from reported) captures in the 2014 season were 11.58% of the FRML.
In late February 2013, the first observed sea lion mortalities in the Auckland Island squid fleet in three years occurred. Juvenile sea lions slipped through the grid at the opening of the net into its cod end. The 23-cm grid aperture is designed to hold adult sea lions in the SLED and yet still allow squid to pass into the net. In 2013, one adult female was taken as incidental bycatch. In the concluded 2014 season, two sea lions were reportedly captured in the fishery.
The proportion of vessels in the Auckland Island squid fishery with government observers has increased over the years, providing independent reports of bycatch based on observation rather than computer model estimates. In the 2014 season, the observers' coverage was of 84% of tows.
Sea lion escape devices
In 2001, the sea lion exclusion device (SLED) was introduced into the Auckland Island squid fishery to reduce sea lion bycatch. Since 2007, all vessels in the Auckland Islands fishery have been equipped with SLEDs.
Some scientists still do not believe sea lions survive the interaction with a SLED, though the Ministry for Primary Industries (MPI) believes the direct effect of fishing-related mortality on the sea lion population is minimal. MPI has concluded that a sea lion has an 85% chance of escaping the SLED and a 97 per cent probability of surviving a SLED escape, though it says this estimate may be 'mildly pessimistic'.
Though the Auckland Island sea lion pup production is highly variable, a decline trend for some years followed the outbreak of an introduced bacterial disease caused by a Campylobacter species in 1998 which killed an estimated 53% of newborn pups and 20% of adult females. In 2002, another probably introduced bacterial disease caused by Klebsiella pneumoniae killed 32% of pups, and in 2003 another 21% of the pups. Since 2002, K. pneumoniae bacteria have caused significant mortality in the sea lion pups at Enderby Island. Infected pups have meningitis, as well as septicemia.
On 12 March 2014, the Conservation Minister Nick Smith was quoted as saying an "excessive focus on fishing bycatch" existed and 300 pups had died this summer from an as yet unidentified disease.
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|Wikimedia Commons has media related to Phocarctos hookeri.|
- New Zealand sea lion at the Department of Conservation
- Encyclopedia of New Zealand - New Zealand sea lion
- ARKive - images and movies of the Hooker's sea lion (Phocarctos hookeri)