Seals and Sea Lions (Families Phocidae and Otariidae)
New Zealand fur seal, Arctocephalus forsteri, hauled out at Cape Palliser. Photographer S. J. Baird
Suze Baird, Franz Smith, and Taoho Patuawa
General Description
The order Carnivora includes suborder Caniformia (previously Pinnipedia), with two families of carnivorous, semiaquatic marine mammals which represent seals and sea lions. These large mammals are truly adapted to life in the aquatic environment with a streamlined shape that contains major limb bones and organs, either reduced or absent ear flaps, paddle-like limbs, a small tail, and a layer of fat beneath the skin for insulation. Pinnipeds shed their hair (moult) once a year.
True or "earless" seals, of the family Phocidae, lack external ear flaps. They are unable to rotate their hind flippers forward to walk on land and instead must pull themselves along with their fore flippers. In water, they are proficient swimmers and use their flippers for propulsion and manoeuvring. They vary in size from about 2.4 m and 200 kg for the Ross seal to 5 m and 5 tonnes for the male southern elephant seal. All phocid seals in New Zealand waters are found in the Antarctic and on subantarctic islands. These seals live exclusively in the southern hemisphere and represent five of the thirteen phocid genera worldwide and five of the nineteen species. None are endemic and they are considered migrants or visitors within the region.
Sea lions and fur seals are members of the family Otariidae ("eared seals") which are characterised by the presence of external ear flaps and the ability to walk on land using both their fore and their hind flippers. Fur seals are distinguished from sea lions in having a short dense layer of hair close to the skin, which traps air and provides waterproof insulation. Sea lions and fur seals can reach a maximum size of 3.3 m in length, obtaining 400 kg or more. Worldwide, there are sixteen recognised otariid species in seven genera. Two genera and four otariid species are represented in the New Zealand region and only the New Zealand (Hooker's) sea lion is endemic, breeding almost exclusively on subantarctic islands. Most New Zealand fur seals breed on rocky shores of the South Island and offshore islands, including the Chatham Islands and most subantarctic islands, and at several isolated colonies around the lower half of the North Island. Healthy breeding populations of this fur seal also exist in southern Australia.
Pinnipeds must return to land (or ice) to give birth, usually in spring or summer. Female pinnipeds give birth once a year, and shortly after mate again. In a phenomenon known as "delayed implantation", the new embryo undergoes a short development and then is quiescent for several months before development continues. Gestation is usually 10-12 months. Otariid pups are weaned after about 7-10 months, during which time females undertake short feeding trips; whereas phocid pups are weaned quickly (at the most, after eight weeks for the Weddell seal) by their fasting mothers. Male otariids are significantly larger than females, strongly territorial, and mate with many females in a single breeding season. Male phocid southern elephant seals can be five times heavier than females. They use their enormous size to establish dominance hierarchies, which include many females, at the large breeding colonies on land. Other phocid males, such as the Weddell seal, are limited by the physical presence of ice in their access to females, and mate with one or more females in water or on ice.
Phocid seals are extreme divers and dive deeper and for longer than otariid species. They often dive continuously while foraging, spending little time at the surface. Southern elephant seals can dive to 1500 m, and a single dive can last 160 minutes. Phocid dives are used for foraging, travel, predator avoidance, and sleep; whereas foraging is the main activity of otariid dives. Fur seals and sea lions are also intensive divers, diving continuously along bottom contours in search of prey. Dives tend to be less than five minutes, with deepest dives recorded at about 500 m.
Pinnipeds are generalist predators, and most diets consist mainly of pelagic fish and squid which is supplemented from time to time by benthic prey, such as octopus. Some occasionally prey on penguins and other seabirds. Antarctic fur seals consume large amounts of krill when foraging during summer months, and take fish and squid in winter months. Males kill and eat some penguin species. Some phocid species feed either wholly or mainly on crustaceans. Crabeater seals have particularly specialised teeth to sieve krill. Leopard seals feed on krill, cephalopods, penguins, and other seals. New Zealand sea lions are also known to kill and eat fur seal pups.
Status
Most southern hemisphere species of seal and sea lion were exploited at some stage for their skins and meat. The intensive culling in the nineteenth century led to major population declines, and in some cases, eradication from sites. Since protection has been accorded to these mammals, numbers have increased for many species.
Historically, the distributions of both the New Zealand sea lion and the fur seal included the whole New Zealand coastline. Currently most fur seal populations are south of Cook Strait, but they are successfully expanding their range northwards. The sea lion range remains significantly contracted with few breeding sites and thus the conservation status of this species is "vulnerable". Between 10,400 and 13,800 New Zealand sea lions live at the Auckland Islands. Southern elephant seals showed substantial increases in numbers once accorded protection, but suffered sharp unexplained declines subsequently, from which some populations have recently begun to recover.
Key Locations
New Zealand fur seals breed around the South Island's coastline, on offshore and subantarctic islands, and in several isolated colonies on/off the lower half of the North Island. This species appears to be extending its range northwards. About 95% of New Zealand sea lions breed at three colonies at the Auckland Islands; the remainder breed at Campbell Island and occasionally at Otago Peninsula. Both these species use the continental shelf waters to forage. The Ross Sea is one of the summer breeding areas for crabeater, leopard, and Weddell seals.
Summary of Threats
Incidental capture in trawl-fishing nets is the main human-induced threat to individual fur seals, especially off the west and southern coasts of the South Island, at the Bounty Islands, and Campbell Island. These threats also apply to New Zealand sea lions, especially around the Auckland Islands and occasionally at Campbell Island. Human-induced threats could also include the effects of climate change on prey abundance and available habitat and overfishing of prey resources. Natural threats to these mammals include predation by killer whales, sharks, and other pinnipeds, and parasitic and bacterial disease. New Zealand sea lion populations at the Auckland Islands recently suffered large pup losses due to bacterial infection.
Typical Habitats
New Zealand sea lions prefer sandy beaches as breeding sites, whereas New Zealand fur seals prefer rocky coastlines and boulder beaches. At sea, most forage along shelf breaks. Southern elephant seals prefer sandy, gravel, and cobble beaches. Breeding Antarctic and subantarctic fur seals use rocky and cobble beaches, and non-breeders may haul out onto grassy meadow or tussock. Antarctic fur seals also use ice floes. Weddell seals require fast-ice habitats, including the Ross Sea, for breeding and offshore pack ice and open water areas are important foraging habitats. Crabeater and Ross seals prefer pack ice. Leopard seals use fast-ice and pack-ice habitats.
State of Information
Most aspects of the biology, ecology, reproduction, and behaviour of New Zealand fur seals are well-studied, but population estimates for many colonies and the entire New Zealand population have not yet been made. New Zealand sea lions are well studied and population numbers are estimated for the main colonies annually. Recently, work has focussed on the at-sea distribution and foraging behaviour of these species. Aspects of biology, ecology, abundance, and distribution are known for some phocid species, but are lacking for species such as the Ross seal and the leopard seal.
Significance for Maori
Maori hunted New Zealand fur seals and sea lions and used the skins for clothing and the meat for food. When Polynesians first arrived in New Zealand both species occurred around the entire coast of both main islands. When European sealers arrived in the late eighteenth century both species were found only around the southern tip of the South Island and the islands further south.
Key References
Folkens, P A, Reeves, R R, Stewart, B S, Clapham, P J, and J A Powell. 2002. Guide to Marine Mammals of the World. National Audubon Society. Alfred A. Knopf Inc. 528pp.
Gaskin, D E. 1972. Whales dolphins and seals with special reference to the New Zealand region. Heinemann Educational Books Ltd. 200pp.
Hoelzel, A R (ed). 2002. Marine Mammal Biology: An evolutionary approach. Blackwell Science Ltd., Oxford. 432pp.
Perrin, W F, Würsig, B, and Thewissen, J G M (eds). 2002. Encyclopedia of Marine Mammals. San Diego: Academic Press. 1414pp.
Shirihai, H. 2002. The Complete Guide to Antarctic Wildlife: Birds and marine mammals of the Antarctic Continent and the Southern Ocean. Princeton University Press, Princeton, New Jersey. 510pp.
Table 12: Seals and Sea Lions (Families Phocidae and Otariidae) in New Zealand
| Taxon | Common name | Status in New Zealand region | IUCN status | DoC status |
|---|---|---|---|---|
| Family Otariidae | ||||
| Arctocephalus forsteri | New Zealand fur seal | Breeder | Unlisted | Not threatened |
| Arctocephalus gazelle | Antarctic fur seal | Vagrant | Lower risk-least concern | Vagrant |
| Arctocephalus tropicalis | Subantarctic fur seal | Vagrant | Lower risk-least concern | Vagrant |
| Phocarctos hookeri | New Zealand (Hooker's) sea lion | Endemic | Vulnerable | Range restricted |
| 4 | ||||
| Family Phocidae | ||||
| Hydrurga leptonyx | Leopard seal | Migrant | Lower risk-least concern | Migrant |
| Leptonychotes weddelli | Weddell seal | Vagrant | Lower risk-least concern | Vagrant |
| Lobodon carcinophagus | Crabeater seal | Vagrant | Lower risk-least concern | Vagrant |
| Mirounga leonine | Southern elephant seal | Breeder | Lower risk-least concern | Nationally critical |
| Ommatophoca rossi | Ross seal | Vagrant | Lower risk-least concern | Vagrant |
| 5 | ||||
| Total | 9 |
Figure 30: Elephant seal Mirounga leonina breeding.
Figure 31: New Zealand fur seal Arctocephalus forsteri breeding.
Figure 32: New Zealand sea lion Phocarctos hookeri breeding.