Miscellaneous Mammals 6: The Southern Fur Seal

Southern Fur Seal at Bristol

 The last of the miscellaneous mammals in this series is our group of Southern Fur Seals, Arctocephalus australis, which is the only marine mammal species we have. Considering the number of species of pinniped alive today, comparatively few are to be seen in captivity, which reflects the expense of providing suitable feeding and accommodation for them compared to terrestrial mammals. Ours live in the section called Seal and Penguin Coasts, which is one of the newer sets of accommodation constructed in recent years.

Southern Fur seals, and other species of Arctocephalus, are much less commonly seen than Californian Sea Lions, which have over 550 listed on ISIS, and many more held privately or in non-WAZA zoos. There are only 47 A.australis listed worldwide in ISIS, with a further 122 South Africa Fur Seals A.pusillus. The only Arctocephalus listed for the US is a solitary female A.pusillus at Louisville zoo.

Californian Sea Lion at Fisherman's Wharf

The reason for the difference probably lies in the trainability and personality differences between sea lions and fur seals, which in turn reflect their different ecologies. In most places where fur seals are found, there is also a local species of sea lion, and they manage to overlap by having different hunting grounds and methods, different diets, and different societies. Typically sea lions live in fairly shallow water, mostly hunting over the continental shelf and even entering rivers. They spend long periods at the breeding rookeries and make fairly short hunting trips. Fur seals are far more pelagic, making long trips to the open ocean and only visiting the rookeries for comparatively short periods.

The preferred habitat for a breeding rookery also differs. Probably because of their size, sea lions are not as agile as fur seals on land and prefer to use sandy beaches, Fur seals mostly prefer much steeper rocky coasts, which they can climb more easily than sea lions can.

When breeding, male fur seals fight viciously for breeding space in order to maximise their chances of attracting females. As a result, fur seals in captivity are often more aggressive with both keepers and each other. Our group at Bristol gets on OK at present, but we have only a single adult bull with 2 adult females with 3 juveniles. Unfortunately, the juveniles are all male and will have to be moved on in a few years as they mature.

There has been comparatively little work done on the diet of fur seals in the wild, as at the breeding beaches where they are easiest to study the males in particular do not feed for the up to 60 days they can defend a territory, and such studies as have been done are mostly anecdotal records. However, fish and squid, mostly pelagic species as you would expect, with some shrimp and sea birds (especially penguins) are likely to form the basis of the diet.

With the plight of the world’s fisheries, it is important that Bristol encourages better fisheries practise wherever possible. For this reason, Bristol has managed to obtain certification from the Marine Stewardship Council for both the restaurant and also the fish we feed to our seals, which I believe is a world first. We have several displays around the aquarium and Seal coasts giving information and encouragement to visitors on sustainable fisheries practises. For further information, follow this link to the report to BIAZA on their website at http://www.biaza.org.uk/public/pages/research/detail.asp?uid=191

In addition to the right kind of fish, it is important that captive seals receive proper vitamin supplementation of their diet. The process of defrosting frozen fish destroys vitamins, and in order to keep them in good condition it is necessary that they receive specially formulated vitamin tablets, which are given to them hidden inside the fish they are fed.

They also need water of the correct salinity. Kept in fresh water, fur seals and others develop eye problems or even go blind, so although the water in their pool is not natural sea water it is kept saline with just rock salt, which is cheaper than artificial sea water but just as effective. The water in the pool cycles through a series of filters, finishing with a UV steriliser, to ensure that the bacterial content of the water is also as low as possible.

With all the work involved, the question naturally arises why keep them at all. Despite the heavy hunting pressure all pinnipeds experienced in the past, which resulted in the extinction of the Japanese sea lion, most species are now recovering, and the Southern Fur seal is expanding back to its former population size quite well. However, fur seals and other marine mammals are quite vulnerable to El Nino events, which drastically reduce food supplies, so any increase in these could have negative consequences quite quickly, especially for the rarest of all the fur seals, the Guadalupe Fur seal A.townsendi, which has a population of around 10,000 at the most. The key reason for keeping many animals in zoos is to provide research information which can then be fed back to those concerned with the front line conservation of wild populations. In the case of seals, veterinary information, gestation periods, drug reactions etc are the key knowledge required.

Guadalupe Fur Seal

This brings me to the end of my second year of blogging – I hope all readers have been entertained and informed. Next week, I will be running a quiz (results next year). Also in the New Year I will be covering fish, invertebrates, passerines, waterfowl, lemurs and whatever seems a good idea at the time, plus our 175th anniversary celebrations, which should generate a good few posts.

(images from wikipedia)