Arctocephalus pusillus

Arctocephalus pusillus, commonly known as the Cape fur seal and the Afro-Australian fur seal, is a species of fur seal.

Description

thumb|Skull of male

Arctocephalus pusillus is the largest and most robust member of the fur seals. It has a broad, flat head with a pointed snout that may be slightly upturned. It has external ear flaps (pinnae) and its whiskers (vibrissae) are long, possibly extending past the pinnae, especially in adult males. The fore-flippers are covered with sparse hairs over about three-quarters of their length. The hind flippers are short relative to the large body, with short, fleshy tips on the digits. Females are smaller, averaging in length and typically weighing . Males of the Australian subspecies (A. p. doriferus) are in length and weigh . Females are length and weigh . Also eaten are other crustaceans, cephalopods, and sometimes seabirds. The Australian fur seal mostly eats squid, octopus, fish, and lobsters. The Australian subspecies generally feeds at lower depths, diving an average of 120 m African land-based predators, primarily of pups, include black-backed jackals, brown hyenas and occasionally lions on the Skeleton Coast in Namibia. In addition, seagulls and other seabirds are thought to peck the eyes out of baby seals, especially sick or injured individuals, to render them helpless and disabled, as they begin to feast on their flesh.

In False Bay, the seals employ several defensive strategies while in shark-infested waters, such as:

Swimming in large groups and harassing sharks in the vicinity.
Low porpoising, to increase subsurface vigilance.
Darting in different directions to confuse when attacked.
Using their agility to stay out of reach.
Swimming near the dorsal fin to stay clear of the shark's jaws, when pursued.

Behaviour

Acoustic behavior

Australian fur seals are social animals that use vocalizations in a broad range of contexts. These vocalizations have been shown to possess unique properties that enable individual recognition.

This is particularly important for the reunion of mothers and pups that experience repeated separations whilst mothers are out at sea foraging, sometimes for days at a time.

Upon their return, mothers need to locate their pups. This reunion process may also be facilitated through a combination of smell and spatial cues.

In males, increases in testosterone and calling rates are seen in conjunction with the onset of the breeding season. Males can also differentiate neighboring males from stranger males, responding more aggressively to the vocalizations of strangers. This difference in response is suspected because the threat posed by a stranger is unknown and potentially greater than their neighbor, which they would have previously encountered while establishing their territories.

Breeding behaviour

Brown fur seals often gather into colonies on rookeries in numbers ranging from 500 to 1500, at least for the Australian subspecies. They fast at this time and do not eat until after mating in November or December. When the females arrive, they fight among themselves for territories in which to give birth. Female territories are smaller than those of males and are always located within them. Females within a male's territory can be considered part of his harem. However, males do not herd the females, who are free to choose their mates and judge them based on the value of their territories. For the Australian fur seals, 82% of copulations are performed by males whose territories are located directly at the water's edge. Breeding and haul-out sites are protected by law. South African fur seals have a robust, healthy population. Seal hunting was outlawed in South Africa in 1990.

Brown fur seals are still harvested in Namibia. Permits are issued for the killing of pups for their luxurious fur and adult males for their genitalia, which are considered an aphrodisiac in some countries. It is also considered necessary to limit seal numbers in Namibia because of the supposed effect seals have on the country's fish harvest. Research by environmental groups disputes this.

Unexplained aggression

In January 2023, media reports indicated that seals have been attacking humans in South Africa, particularly in the Cape Town area. Scientists believed it was due to a brain-altering poison in the fish they consumed. The poison affects their behaviour making them more aggressive towards humans. Some attribute the aggressive behaviour to the surge of toxic red tide algae, fuelled by pollution and climate change. The incidents have increased recently, prompting concern and calls for further investigation.

In July 2024, it was confirmed that 17 seals along a 650-km stretch of coastline between Cape Town and Plettenberg Bay tested positive for rabies, and that could be the cause of the attacking behaviour in fur seals. The hypothesis is the rabies was acquired from black-backed jackals who prey on the seals; rabies is endemic among southern African jackals.

Threat by marine debris and industry

A 2021 study published in The Marine Pollution Bulletin found that the brown fur seal colonies in Namibia are vulnerable to extensive entanglement in marine debris as a result of extensive pollution in the oceans. The study overall found that juveniles are more prone to becoming entangled in marine debris, and that 53% of all entanglements discovered were caused by fishing line.

Ocean Conservation Namibia, a local animal conservation group based in Walvis Bay, was formed by volunteers who capture entangled seals and free them from discarded entanglement discarded by ships and the fishing industry. The organization monitors the coast regularly, but their founder, Naude Dreyer, told reporters of drastically declining numbers of seals as pollution continues to increase.

References

External links

Photos of brown fur seals at Cape Cross, Namibia – photographs and information
Pictures of fur seals at Geyser Rock, South Africa on jostimages.com
Animal Diversity Web – Arctocephalus pusillus
Skull of adult male