Facts about fur seal

Description

Kekeno (Arctocephalus forsteri) are members of the Otariidae family of pinnipeds, fin-footed carnivorous marine mammals. They are distinguished by visible external ears and hind flippers which rotate forward.

This pointy-nosed seal has long pale whiskers and a body covered with two layers of fur. Their coat is dark grey-brown on the back, and lighter below; when wet kekeno look almost black. In some animals the longer upper hairs have white tips which give the animal a silvery appearance.

Adult females: maximum length 1.5 m, weight 30-50 kg.
Adult males: maximum length 2.5 m, weight 90-150 kg.

Range

Fur seal pup, Wellington

These are the most common seals in New Zealand waters and are found throughout the country and in western and southern Australia.

Kekeno are very good swimmers and weaned pups will turn up almost anywhere around New Zealand. A pup tagged on the west coast of South Island has even been recorded in Australia. On land they sometimes become disoriented and have been found in unusual places such as back-yards, drains and streets.

Population

In New Zealand, minimum estimates of the population are 50 - 60,000, but this is almost certainly an underestimate. Recent work in Otago has shown there was a population increase of 25% per year between 1982 and 1994 and surveys in 1995 indicated this was continuing.

A similar rate of increase has been noted in the Nelson/Marlborough region and also in the Sub-Antarctic Bounty Islands. Since 1991, fur seals have recommenced breeding on the North Island. In Australia latest estimates are 30 - 35,000 with an annual increase of 16 to 19%.

Although there are no estimates of population growth available for Southland, a nationwide survey in the 1970's showed fur seals in Southland accounted for over 40% of the total New Zealand population or 70% if the sub-Antarctic islands are included.

Diet and foraging

Kekeno feed mainly on squid and small mid-water fish but also take larger species such as conger eels, barracuda, jack mackerel and hoki mostly off the continental shelf in depths greater than 22 m.

The New Zealand fur seal dives deeper and longer than any other fur seal. Female fur seals on the West Coast are known to (occasionally) dive deeper than 238 m, and for as long as I I minutes. Off the Otago Peninsula in summer, they feed almost exclusively at night (88 - 97% of dives), as deep as 163m with a maximum recorded dive time of 6.2 minutes.

Most dives are however of 1-2 minutes. Most of their prey species follow a vertical migration, i.e. they come nearer the surface in the middle of the night, and sink back to deeper depths during the day. The seals appear to follow these migrations when they forage. Their summer foraging is concentrated over the continental shelf, or near the slope. They will dive continuously from sundown to sunrise. In autumn and winter, they dive much deeper with many dives deeper than 100m. At least some females dive deeper than 240m, and from satellite tracking they may forage up to 200km beyond the continental slope in water deeper than 1000m.

Life history

Kekeno spend a lot of their time on rocky shores, at sites called haul-outs. Every year, these sociable animals return to the same area for the breeding season.

Females reach sexual maturity between 4 and 6 years and will give birth to a single pup more or less every year until their death at on average 14 - 17 years. Females mate 6 - 8 days after the birth of their pup, even before their first foraging trip. Delayed implantation means the egg is fertilised, but does not implant in the uterine wall for another 3 months. Gestation is therefore about 9 months, even though the female is mated 360 days before she gives birth.

The breeding season is from mid-November to mid-January. Pups are suckled for about 300 days, though some will continue to suckle into their second year. Females alternate foraging trips (periods of 1 - 20 days at sea) to feed, with attendance periods (1 - 2 days), where they are at the rookery to suckle the pup.

Pups start to feed on solid food before weaning, and spend a large proportion of time playing with other pups and objects such as seaweed and reef fish. It is possible that they attain skills for later life (such as foraging, anti-predator behaviour and also social behaviour) during this period. After weaning pups disperse.

Juvenile fur seals have been found over a 1000 km from their place of birth. Males are sexually mature at 5 - 6 years, but are unlikely to be socially mature (able to hold a territory) for at least another 3 years. Dominant bulls put on displays of glaring and posturing and fighting with other males just prior to the breeding season to gain territories. Fur seals are polygamous breeders; this means that a male may mate with many females in a single breeding season.

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