POPULATION DYNAMICS AND EXPLOITATION OF SEALS 171 



pack ice, but the adult female ringed seal needs land-fast ice, covered with 

 a good depth of snow, for the construction of a birth lair. These lairs may be 

 hollowed out in the overlying snow, particularly in drifts over rough ice or 

 along tide cracks, or the female may take advantage of a natural *tent' of 

 ice in the pressure ridges near shore. The pup is protected and fed here until 

 weaning, which may not occur until the ice breaks up. Irregular coasts with 

 skerries and inlets, which retain large amounts of stable, long lasting, fast ice, 

 thus provide most suitable conditions for long and uninterrupted suckling of 

 the pups. 



In winter, the ringed seals taken in the open water at the edge of the fast 

 ice are exclusively immature in most regions; seals killed in the peripheral 

 ice of complex coasts or in the fast ice of adjacent simple coasts are mostly 

 younger adults; those taken at the heads of bays, or well within island-filled 

 regions, and in general in thick, heavily snow-covered ice, are mostly older 

 adults. Increase of experience with age and possibly competition for more 

 suitable pupping sites may serve to explain this distribution of adults. 



The influence of ice conditions is also reflected in the higher proportion 

 of small pups and the common occurrence of starvehngs, the result of 

 premature separation from their mothers, among seals of simple coasts. The 

 offspring of younger, less experienced mothers dwelling on less stable, less 

 snow-covered ice seem generally to be weaned earlier. When it was found 

 that the seals of simple coasts of south-west Baffin Island were shorter on 

 average (by perhaps 10 per cent as adults) than seals of the same age from 

 nearby more complex coasts, it was presumed that the size of full-grown seals 

 was related directly to their size at weaning. Certainly the food available 

 along these coasts does not differ (if anything, the open coast is more pro- 

 ductive) and it is unlikely that populations only 200 miles apart will be 

 different genetically. A similar explanation is offered to account for size 

 differences throughout the ringed seal's wider range. Adult seals from high- 

 Arctic localities may average 15 per cent longer than adults from south-west 

 Baffin Island, while those from southern Hudson Bay may be 8-10 per cent 

 shorter. The longer suckling period permitted in the more northerly 

 locahties results in larger, more vigorous pups. These grow into larger 

 adults, which in their turn may produce large pups. Within hmits, then, 

 the effect may be self-sustaining. 



Adult bearded and ringed seals have no significant predators. The polar 

 bear is rare and local and the killer whale all but absent from the eastern 

 Canadian Arctic. Ringed seal pups may suffer quite heavy mortahty by 

 foxes {Alopex), and even be killed by gulls and ravens when in exposed 

 situations. Only a few seals have been found suffering from apparently 

 debihtating disease or parasites. The potential longevity of the ringed seal is 



