Kōrero: Seals

Whārangi 5. New Zealand fur seal

Ngā whakaahua

Distribution

New Zealand fur seals (Arctocephalus forsteri, or kekeno) are found around New Zealand and its offshore islands, and southern Australia. Excavation of midden sites shows that when Polynesians arrived about 1300 AD, fur seals became an important source of food. By the time Europeans arrived in the late 1700s the seals had been all but wiped out, save for colonies on the South Island’s sparsely inhabited south-western coast. The pale-faced sealers finished off the remaining few and severely depleted numbers on the Chatham Islands, Bounty Islands and subantarctic islands – all for their pelts and the oil rendered from their blubber.

On the tiny Bounty Islands, numbers went from 52,000 in 1800 down to five by 1831. There has been considerable recovery since: 16,000 were estimated there in 1980.

Food

Their prey is fish, cephalopods such as squid and octopus, and crustacea including krill. Most dives last one or two minutes. Fur seals will forage up to 200 kilometres beyond the continental slope, often diving as deep as 200 metres.

Breeding sites

The seals breed on steep boulder beaches with plenty of crevices and tidal pools. Their layer of fat and thick fur coats, which enable them to endure long periods in water, can cause overheating on land. Crevices provide shade, and tidal pools a place to cool off.

The dominant male mates with numerous females, so many males do not get a chance to breed in every season. They often have sites where they haul out (rest), away from the breeding colonies. These sites may become breeding colonies if females visit them.

Breeding

Adult males are the first to arrive at the breeding colonies, from late October to early November. They establish territories that they defend aggressively, and remain on land, fighting but not feeding, until mid-January. This inter-male competition has promoted the evolution of large males, weighing up to 185 kilograms (an average female weighs 40 kilograms).

Females arrive from foraging at sea in late November, and give birth to a single pup (conceived the year before) by early January. About eight days later she will mate – usually with the dominant male. The female does all the nurturing of the newborn. She stays with the pup constantly for about 12 days, then alternates between feeding at sea and suckling. As the pup grows, the mother needs more food to make enough milk. Pups are weaned in July or August, and the pregnant females go to sea to fatten once again. The young pups then head out to sea, coming ashore at times. Females start breeding at around four years.

Delayed implantation

After fertilisation, the embryo’s growth is suspended for two to four months. It then implants in the mother’s uterus, and development resumes. This enables females to give birth and then mate during the same episode ashore, while still allowing for a normal gestation of about nine months. The female can therefore recover from rearing one pup before developing the next. The pup’s birth is also synchronised with the female’s return to the breeding ground the next season.

Delayed development occurs in all New Zealand’s seals, and most likely in all seals. The longest known life span of a New Zealand fur seal is 15 years.

Me pēnei te tohu i te whārangi:

Lloyd Spencer Davis, 'Seals - New Zealand fur seal', Te Ara - the Encyclopedia of New Zealand, http://www.TeAra.govt.nz/mi/seals/page-5 (accessed 17 July 2019)

Story by Lloyd Spencer Davis, published 12 Jun 2006