POPULATION DYNAMICS AND EXPLOITATION OF SEALS 179 



Indices of availability are of course abstractions and must be made more 

 meaningful by being converted to catches per unit of effort. This has been 

 done with the aid of observations on almost 100 hunting trips carried out in 

 favourable conditions, mostly from boats in summer. The results of such 

 trips have been found to agree quite well with the indices of availability, and 

 the resulting combination can claim with some reliability to give the actual 

 expectations of a day's hunting trip. 



While there are many minor conditions, apart from the obvious ones of 

 local or extensive over-utilization, which may render the theoretically 

 predicted catches per unit of effort vahd only over large areas and long 

 periods, there are two major modifications which affect the expectations of 

 the hunter. The figures on catch per unit of effort are in fact based on kill, 

 not catch for there is an important loss of seals by sinking, which may be 

 as high as 60 per cent in full sea water immediately after the ice breaks up. 

 Sinking loss varies seasonally, latitudinally, and with salinity, and a graph 

 giving the best present predictions of the loss is given elsewhere (McLaren, 

 in press). The other important factor is the wind, which has adverse effects 

 at all seasons, and when it is greater than a few knots makes hunting from 

 boats unprofitable in all but the most sheltered waters. The influence of the 

 wind should be readily predictable from the weather records. The importance 

 of the wind and surface salinity should not be under-estimated; their com- 

 bined effect may make some regions places of hunger in the midst of plenty. 



INTEGRATED ECONOMIC ANALYSIS 



Fromi what has been said thus far, how can we best compare the economies 

 of different regions where seals are almost the only subsistence resources for 

 the Eskimos, and what does our analysis have to say about the administra- 

 tion of such resources? While several products (meat, blubber, skins) have 

 been dealt Vv^ith, general conditions in terms of production of meat are most 

 illuminating. 



Considering first the maximum sustainable yield of meat, our best estimate 

 at present can be formulated as follows. The average weight of seals in a 

 population can be calculated from the age-specific lengths and from log- 

 length to log-weight relationships (which gives a slight under-estimate due 

 to the proportionately greater influence of longer seals). About 30 per cent 

 of each species is considered to be edible as human food. Then, in a delimited 

 region where Nr and iV& are the stocks respectively of ringed and bearded 

 seals, where Yr and Y^ are their respective levels of sustainable yield (ignoring 

 sinking loss), and Wr and Wt are the expected average weights of the catch 

 (geographically variable only in the ringed seal), we may predict the potential 



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