i82 I. A. McLaren 



at present imposed by availability of seals must be replaced by limits imposed 

 by sustainable yields; this is a problem for technology. Such an increase of 

 yield must be considered in relation to the outlay of economic effort and to 

 the rest of the economy, and this is a problem for the economist. While 

 economical and technological improvements are not his concern, the 

 population ecologist cannot close without the cautionary remark that a 

 resultant over-production of people is a far more immediate danger in the 

 Arctic than its wide-open spaces suggest. 



SUMMARY 



(i) The ringed and bearded seals are important in the subsistence economies 

 of Eskimos. Study of them has benefited from absolute methods of age 

 determination. 



(2) Equilibrium populations of ringed seals are not determined trophically or 

 through compensatory mortality but through reproduction, by the amount 

 and quality of land-fast ice available for the construction of birth lairs in 

 the snow. 



(3) Local censuses of ringed seals can be combined with measurements of ice 

 areas from maps to give theoretical estimates of the size of under-exploited 

 populations. 



(4) More information is needed on the hmits of response of pupping success 

 and even pregnancy rates, but balanced tables based on known and estimated 

 mortality and birth rates in south-west Baffin Island suggest safe maximum 

 sustainable yields of 7-10 per cent of ringed seal populations. Biomass yields 

 are more complex, but can be estimated. 



(5) Bearded seals may be limited trophically by the availability of ice-free 

 feeding banks in winter, but no deductive population estimates can yet be 

 made. The analysis of numbers and yields of this species is based on its 

 numbers relative to the ringed seal in summer, from shipboard censuses. 



(6) Availabihty indices of seals can be calculated from their theoretical 

 numbers and the areas of water or ice in which the populations are dispersed. 

 These may be converted empirically to catches per unit of effort, giving the 

 expectations of a day's hunt in any region. The probabilities of suitable 

 weather and the loss of seals by sinking are major calculable modifications. 



(7) A preliminary economic analysis of a region can thus be formulated 

 firstly in terms of maximum sustainable yield of meat or other product per 

 native inhabitant, and secondly in terms of availability, to reflect the 

 economic effort presently required of the Eskimos. 



