New Zealand Sea Lion
(Phocarctos hookeri)
| Distribution and Numbers One of the rarest and most endangered sea lions, the New Zealand sea lion (also known as the Hooker's sea lion) is found only in New Zealand and breeds almost exclusively on New Zealand's subantarctic islands, the main breeding colony being located on Dundas Island in the Auckland Islands. Over 95% of the total pup production for the species occurs in three colonies in the Auckland Islands, within a very localised area (less than 7km apart). New Zealand sea lions haul out in an area ranging from the Australian subantarctic Macquarie Island to the southeast coast of South Island, New Zealand. Individuals are also occasionally seen on New Zealand's North Island. The total population was estimated at 12,000 - 14,000 before a mass mortality event of unknown cause resulted in the deaths of a large number of the species in January 1998. |
 Photo: Nathan McNally, University of Otago |
| Status Although the New Zealand sea lion was extensively killed for its hide and oil in the 19th century and, to a much lesser extent, the early 20th century, commercial killing of the species has been illegal in New Zealand since 1893. The New Zealand sea lion was designated as a Threatened Species under New Zealand's Marine Mammals Protection Act in August 1997. The species is also listed as Vulnerable on the IUCN Red List. There is a 20km Marine Mammal Sanctuary around the Auckland Islands which conservation groups would like to see extended to 100km. New Zealand's subantarctic islands were granted UNESCO "World Heritage" status in 1998. |
 Photo: Nathan McNally, University of Otago |
A major threat to the species is from entanglement and drowning in the nets of the squid trawl fishery which has operated within the sea lions' range since the late 1970s. In recent years vessels have withdrawn from the squid fishery, either voluntarily or due to government closure of the fishery, when the estimated trawl-related sea lion mortality has exceeded agreed limits, an annual measure first implemented by the government in consultation with the fishery in 1994. These limits were regularly exceeded between 1995-97 however and the estimated number of sea lions drowned in squid trawl nets was greater than 100 per year during this period. Stricter compliance has been enforced since 1998 and in the year 2000 the fishery ended early when the estimated number of sea lions caught and killed in the trawl nets reached 65, the maximum permitted. The final estimated number of sea lions killed by the squid trawl fishery in 2000 was 71. Marine mammal escape devices are being tested and conservation groups are also urging the industry to develop alternative methods for catching squid such as the use of jiggers instead of trawling. The New Zealand Department of Conservation is developing a Population Management Plan for the species due to its status as a protected species at risk from fisheries. |
| The species is particularly vulnerable because of its
restricted breeding sites. In 1998 an unknown illness during the breeding season killed at
least 1,600, over 53%, of the year's pups and an unknown proportion, but perhaps somewhere
in the order of 20%, of the adult population. The exact mortality figures will perhaps
never be known. There was previously a high juvenile mortality caused by the presence on
some of the breeding islands of rabbit burrows in which the pups got stuck while
exploring. Eradication of the rabbits by the Department of Conservation and the subsequent
collapsing of the burrows has reduced this problem significantly. |
| Lifestyle New Zealand sea lions prefer sandy beaches for both hauling out and breeding, often wandering quite far inland, sometimes over 2km, while on shore. They breed in colonies between November and January, the pups being born from early December until late January. In November each year the bulls arrive at the rookeries and fight, in a largely ritualistic manner, for territory before the females come ashore a few weeks later. The bulls who establish territory, the "beach masters", eventually have about 8 to 25 females on their territory. The females give birth shortly after arrival at the breeding site and mate a week to ten days later. The pups are born with a thick coat of light or chocolate brown fur that becomes buff to creamy-grey for adult females and dark brown to black for adult males. About 10 to 14 days after a pup is born, its mother starts leaving to feed at sea and returning every 2 - 3 days to nurse the pup, these feeding trips lengthening as the pup gets older. The pup starts swimming by about 2-3 weeks of age and the mother continues to nurse her pup for at least 8 months, sometimes for a year or more. The adult males remain ashore and do not normally feed during the entire breeding season. Moulting occurs in late February through to early May. |
| No regular migration of the species has been documented. New Zealand
sea lions are opportunistic feeders and the majority of their diet consists of cephalopods
(such as squid and octopus), crabs, crayfish and many species of fish. The occasional
penguin and fur seal are also eaten. Evidence has shown that although they start feeding
close inshore, New Zealand sea lions travel up to 130km offshore during feeding trips.
White pointer sharks and killer whales prey on adults and pups. Adult male New Zealand sea
lions have also been observed killing and eating sea lion pups. |
| Statistics Adult males measure between 2.0-3.25m in length and weigh 300-450kg, while adult females measure 1.6-2.0m in length and weigh up to 160kg. Pups are born measuring 70-100cm in length, male pups slightly heavier than female pups at an average 7.9kg compared to 7.2kg. Adult sea lions are able to dive repeatedly to 300m and have been known to dive to over 600m. Most females become sexually mature at 3-4 years of age, males at 5 years. Males do not reach social maturity however until they are at least 8 years of age. Evidence suggests that males may live as long as 23 years, females as long as 18 years. |
 Photo: Michael Bryden, University of Sydney |
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