172 I. A. McLaren 



very great, one male at least 43 years old having been taken. Tooth wear is 

 possibly the most significant natural cause of death of the adults before 

 physiological maximum longevity. The teeth of very old seals are often 

 badly decayed, and this may accelerate their death because they can no 

 longer keep open holes in the ice. Immature seals, on the other hand, have to 

 suffer the rigours of the unstable pack ice in winter; it is believed that many 

 must meet accidental death by being crushed or trapped without access to 

 the air. 



It is apparent from the above qualitative considerations of their life 

 histories that populations of these seals are particularly amenable to quantita- 

 tive analysis. A very preliminary analysis of this kind has in fact been 

 pubhshed as a guide to the economics of seals in the Eastern Canadian Arctic 

 (McLaren, 1958c) and its essential points will be summarized here. This 

 paper was not intended for wide distribution, and the study is still considered 

 to be in a prehminary stage. A more up-to-date elaboration of some of the 

 techniques and formulae for the assessment of numbers and availabilities of 

 ringed seals will be published elsewhere (McLaren, in press), since detailed 

 methodology need not concern those interested in population ecology itself 



THE NUMBERS OF SEALS 

 A knowledge of population size is of course almost always of great import- 

 ance in the rational exploitation of animals. The direct approach, by counting 

 or marking, is generally necessary, but the student who is fortunate enough 

 to find simple environmental determinants of equilibrium populations may 

 be rescued from the demands of extensive or continuous counting. 



A method of census from shipboard has been developed by the author, 

 which allows for the variables of ship-speed, limits of visibility, and the 

 times spent by seals under water and on the surface. More information is 

 needed on the last two variables before the results can be considered more 

 than relative. 



The importance of fast ice to the ringed seal has been emphasized above, 

 and it can be shown to offer a deductive basis for the estimation of popula- 

 tions. In an under-utilized population of ringed seals pup production appears 

 to be limited by the amount and quahty of fast ice available for the repro- 

 ducing females. Possibly there is a hmited number of sites suitable for the 

 construction of birth lairs and reproduction is unsuccessful elsewhere. 

 Alternatively, each seal may require a territory of fixed size so that there is 

 an upper hmit to the number inhabiting a given area of fast ice. It is in fact 

 unHkely that any one such abrupt mode of hmitation, analagous to that 

 applying to hole-nesting species (such as the bee, Megachile, discussed by 



