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. The New Zealand sea lion numbers around 10,000 and is perhaps the world’s rarest sea lion species. They are the only species of the genus Phocarctos.
Physiology & Behaviour
New Zealand sea lions are one of the largest New Zealand animals. Like all otariids, they 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 grey 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. New Zealand sea lions are strongly philopatric.
The main breeding populations are at the Auckland and Campbell Islands in the NZ Subantarctic, where approximately 99% of the species‘ annual pup production occurs. There are currently three functioning breeding rookeries on the Auckland Islands. 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. For the first time in 150 years, sea lions began breeding again on the South Island coast in 1994, on the Otago Peninsula. 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.
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 was wiped out by the first Maori settlers, and the subantarctic lineage has since then gradually filled the ecological niche. It has been inferred from middens and ancient DNA that a third lineage was made extinct at the Chatham Islands due to predation by the Moriori people.
Diet & Predation
New Zealand sea lions are known to predate on a wide range of prey species including fish (e.g. hoki and red cod), cephalopods (e.g. New Zealand arrow squid and yellow octopus), crustaceans, seabirds and other marine mammals. Studies indicate a strong location effect on diet, with almost no overlap in prey species comparing sea lions at Otago Peninsula and Campbell Island, at the north and south extents of the species‘ breeding range. New Zealand sea lions are in turn predated on by great white sharks, with 27% showing evidence of scarring from near-miss shark attacks in an opportunistic study of adult NZ sea lions at Sandy Bay, Enderby Island.
New Zealand sea lions are considered the most threatened sea lion in the world. The species‘ status is largely driven by the main breeding population at the Auckland Islands, which declined by ~50% between 2000 and 2015. The 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 (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 2013 number was the highest in five years. The Campbell Island population ‚appears to be increasing slowly‘ and births here comprise ~30% of the species‘ total. The Otago and Stewart Island sea lion populations are currently small, though increasing. Population estimates for the whole species declined from ~15,000 in the mid-1990s to 9,000 in 2008 (based on the number of pups born).
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’. In 2015, the International Union for Conservation of Nature (IUCN) changed the classification of this species to „Endangered“, based on low overall population size, the small number of breeding populations and the projected trend of the Auckland Islands breeding population.