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Together with their Australian cousins, the South African Fur Seals are the largest fur seals around. Unlike other fur seals their teeth are cusped behind the canines. They have small external ears which have evolved to keep out water. Their hind flippers have adapted for use on land and can be turned forward. As a result they are at home on the steep sided islands and rocky promenades which they inhabit and use as breeding colonies. Their colony at Blacks Rocks in the Bird Island group situated at the Eastern side of Algoa Bay has particularly steep and rocky sides.
Enormous numbers of seals were killed in South Africa and Namibia from as early as the 17th century when the Dutch arrived at the Cape. They were exploited for their blubber which was rendered down to make seal oil and in turn soap, rubber and calcium grease. Numbers crashed to around 100 000 by 1900 with 23 colonies being wiped out, so in 1893 controls were brought in that necessitated a government permit in order to harvest the seals. Thankfully the colony on Black Rocks would have been nearly impossible to reach on a regular basis to harvest seals.
Black Rocks near Bird Island is the only breeding colony in Algoa Bay and marks the furthest East of their distribution. It always looks overcrowded at any time of the year. The only reason why seals were not totally wiped out in Algoa Bay by the British Settlers was due to the nature of the rocks. The sides are really steep and slippery and it was not always possible for the sealers to access the rocks. All the seals had to do to escape was to roll off the edge.
South African Fur Seals display a very high degree of sexual dimorphism, with the chocolate brown adult bulls becoming 2,5m and 300kg while in contrast the diminutive cows only attain 1,6m and 75kg. Males have a greatly enlarged neck and shoulders and have a noticeable main of guard hairs. Pups are blackish at birth with silver streaks and are paler ventrally and are totally reliant on their mothers for the first 3 months until they can start venturing into the waters, start swimming and the hunt for food. Of all the seals, they look the most like sea lions, even in their barking vocalizations. The ear pinnae are fairly long and noticeable. The vibrissae (whiskers) are equally prominent and extend as far as the ears.
Seals are extremely efficient predators and have evolved numerous adaptions to extend their time beneath the waves. They have developed strong laryngeal muscles which prevent water entering the body while catching prey at depth. Their nostrils are closed when relaxed, so as pressure increases with depth, they become even more watertight. As unlikely as it seems, they exhale before diving and the rib cage flattens to get rid of any remaining air. The bronchi and trachea also reduce to half retaining only a small amount of air. Like cetaceans they do not take enough air down with them to get decompression sickness that is associated with breathing compressed air at depth.
The seals are lovely to come across while out on our tours. Often seeing them laying on their backs sunning themselves with just their front flippers extended up out of the water catching the sun rays to thermoregulate themselves. They are warm blooded and have a thick layer of fatty blubber underneath the skin which serves to insulate the animal, assist with buoyancy and as an energy reserve, but sometimes they need the warmth of the suns rays in chilly waters to help keep them warm.