New Zealand Sea Lions are large heavy-bodied sexually dimorphic animals. Adult males are 1.2-1.5 times longer and 3-4 times heavier than adult females. Adult males are 2.3-2.7 m long and may weigh from 320-450 kg, although these values might be high in the light of recent information that males are probably shorter than previously reported. Adult females are 1.8-2 m long and weigh 90-165 kg. Newborns are approximately 70-100 cm long and weigh 8-10 kg (Chilvers et al. 2006). Pups are born in a thick long dark brown lanugo with a lighter crown, nape, and mystacial area, and with a pale stripe on the top of the muzzle, originating on the crown. Female pups are lighter than male pups. Pups begin to molt their birth coat at 2 months and at the end of the molt look like adult females.

Males become sexually mature at the age of 5 years. The age of maturity for females is 3-4 years. Gestation lasts 12 months. Pup mortality at the end of one year is about 35%. Males live at least 23 years and females to at least 26 years (Reijnders et al 1993, Childerhouse 2007). The average age of reproductive females is 10.75 yrs (Childerhouse 2007).

The breeding season for the New Zealand Sea Lion begins in late November when adult males return and establish themselves on territories through displays, vocalizing, and fighting. Adult females arrive in early December and give birth on average within 2.1 days after returning to the rookery (Chilvers et al. 2006). Males may have as many as 25 females within their territories. The bulls are frequently challenged by newly arriving males and neighbors, and turn-over of males is a regular occurrence. Many territorial bulls depart in mid-January with the end of the pupping period (Robertson et al. 2005).

The onset of estrous occurs 7-10 days after a female gives birth. Prior to this, the mother continuously attends her newborn pup. Following mating, females begin a phase of short foraging trips followed by pup attendance, typical of many otariids. Foraging trips average 2.7 days and are followed by 1.5 days of pup attendance and feeding ashore (Chilvers et al 2005). Also typical of many otariids, pups gather into groups while their mothers are away. Females and pups recognize each other through vocalizations and scent, and a small percentage of females will allow additional pups to nurse along with their own pup, which is unusual behavior for a pinniped. Pups are weaned at approximately 10 months. The primary causes of pup deaths within their first two months of life are trauma (35%), bacterial infections (24%), hookworm infection (13%), starvation (13%), and stillbirth (4%) (Castinel et al. 2007). Adult males are a significant source of mortality to pups, occasionally killing them outright and also through incidents of cannibalism. Pups are also trampled and killed by adult males challenging other males during territorial disputes.

New Zealand Sea Lions do not appear to be migratory, although they disperse widely over their range during the non-breeding season (Robertson et al. 2005). Some animals can be found at the major rookeries and haul-outs year-round. At sea they are active divers that forage on both benthic and pelagic prey. Mean dives for female New Zealand Sea Lions are to 129 m and mean dive duration is 3.9 minutes. Maximum dive depths are over 600 m and dives have been recorded to last as long as 14.5 minutes (Chilvers et al. 2006a).

New Zealand Sea Lions take a wide variety of vertebrate and invertebrate prey. Frequently-taken species include: opalfish, octopus, munida, hoki, oblique-banded rattail fish, salps, squid and crustaceans. Prey is taken in both benthic and pelagic habitats. Antarctic, Subantarctic, and New Zealand Fur Seals are taken as prey by adult male sea lions. Penguins and sea lion pups are also occasionally taken.

Predators include sharks, Leopard Seals, and presumably Killer Whales. Pups are also cannibalized by adult males of their own species.

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Red List Category

Red List Criteria

Version

2008

Gales, N. (IUCN SSC Pinniped Specialist Group)

Kovacs, K. & Lowry, L. (Pinniped Red List Authority)

Justification

History

• 1996
  Vulnerable
  (Baillie and Groombridge 1996)
• 1994
  Vulnerable
  (Groombridge 1994)

New Zealand Sea Lions have a highly restricted distribution and a small population that numbers approximately 11,855 animals (Campbell et al. 2006). This equates to an adult population size of <10,000. Pup production has shown a decline of 30% in the last 10 years, but this was preceded by a few years of growth. Data from one of the main colonies shows no overall trend in pup production over the past 25 years (Chilvers et al. 2007).

Decreasing

New Zealand Sea Lions were once more abundant, with a much more extensive range that included the North and South islands of New Zealand. The Maori people of New Zealand have traditionally hunted sea lions, presumably since first contact, as did Europeans upon their arrival much later. Commercial sealing in the early 19th century decimated the population in the Auckland Islands, but despite this, continued until the mid-20th century, when it was halted. The population may not have fully recovered from this period of overexploitation, although estimates of pre-exploitation population size are difficult to derive.

New Zealand Sea Lions have a highly restricted distribution, a small population, and most of the breeding activity is concentrated in two island groups in New Zealand's sub-Antarctic. This combination makes them vulnerable to disease outbreaks, environmental change, and human activities.

Commercial squid fishing near the two largest rookeries reported their first sea lion bycatch mortalities in 1978. In 1982, the fishery was moved at least 12 nautical miles away from the islands. However, this did not end mortality which from 1988 to 2007 ranged from 17-132 seals taken annually (Wilkinson et al. 2003, Chilvers 2008). Apart from direct mortality there is also the potential for prey competition and habitat modification from the fishing industry in the habitat of the New Zealand Sea Lion's breeding areas. Tourism at mainland sites and remote subantarctic islands can cause disruption to haul-out patterns and breeding activities.

Epizootic disease outbreaks at the Auckland Islands in 1998, 2002 and 2003 led to more than 50%, 33% and 21% early pup mortality respectively, and also led to mortalities of an unknown number of animals from other age classes during 1998. The source of the suspected bacterial agent and cause of the outbreak and subsequent mortality for the 1998 outbreak is unknown, however, the 2002 and 2003 outbreaks have been identified as cause by Klebsiella pneumoniae (Castinel et al. 2007).

The New Zealand government has provided protection to New Zealand Sea Lions with laws that date back to 1881. The Marine Mammal Protection Act of 1978 provided additional measures. The squid fishery responsible for the by-catch of sea lions was moved away from the main colonies in 1982 when the government established a 12 nautical mile exclusion zone around the islands (Wilkinson et al. 2003) and later management plans set maximum levels of fishing related mortalities, which, when exceeded, led to the early withdrawal of the fishery. Sea Lion escape devices (SLEDs) have also been mandated in the fishery. Some concerns remain regarding the health of the sea lions expelled from these devices. The uninhabited Auckland Fauna Reserve forms part of the habitat of New Zealand Sea Lions (Reijnders et al 1993). Tourism is regulated on islands and at some mainland beaches on the South Island. Given the recent steady decrease in pup production at the Auckland Islands, and the uncertainty about the influence of human activities on this trend, it is unknown if the current conservation measures are sufficient to protect the species.