GREY SEALS AS COMPETITORS WITH MAN FOR SALMON 317 



that cow grey seals do not become sexually mature until they are four or 

 five years of age. Kenyon & SchefFer (1954) show that only 7 per cent of 

 four-year fur-seal cows and 57 per cent of five-year cows have pups. The 

 basic facts of reproduction in the two species are thus perhaps even more 

 similar than was previously thought. Be that as it may, the fur seal hfe-table 

 appUed to grey seals is a useful first approximation. 



Hickling (1957) has pubhshed figures of the number of pup seals on the 

 Fame Islands in 1956, when there were 747 pups; she has now (1959) given 

 the sex ratio of the pups marked on the Fames with Monel Metal rings from 

 1952-7. The ratio of males to females varied somewhat from year to year, 

 even when the numbers of pups involved was large: in 1956 it was i : i-oi. 



Table I. Possible life-table applied to Fame Islands grey seal population as at 



June, 1957 



Fames seals 



N° 

 230 

 120 

 100 



93 



89 



82 



76 



75 



70 



67 



63 

 395 J 



Female class N^ 



Male class 



Immatures 

 = 632 



Mature 

 females 

 = 828 



230 

 120 

 100 



93 



89 ^ 



82 1 Young 



76 



75 

 70 

 67 



63 I 

 395 J 



Immatures 

 = 632 



bulls 

 = 233 



Mature 

 bulls 

 = 595 



Notes: 



(i) The survival figures are adapted from Kenyon & SchefFer, 1954, p. 40. 



(2) The percentage suriving each year refers to the number of seals aUve at the beginning of 

 each year. 



(3) The number of mature females is greater than the number of pups born and is based on an 

 82 per cent pregnancy rate (Kenyon & SchefFer, 1954)- 



For the purposes of this paper I have taken the sex ratio as unity and the 

 number of pups as 750, and from the information available have drawn up 

 a hfe-table adapting Kenyon & Scheffer's survival figures as did Hewer for 

 the Shillay colony. The estimates were then plotted against age in years and 

 values for half years were extrapolated to give an estimate of the numbers 

 of each age-group alive in June (i.e. half-way through the 1957 salmon- 

 fishing season). These figures (Table I), give a grand total of 2,920 animals 

 of all age-groups associated with the Fame Islands in June, 1957. 



Not all the animals were present at the Fames at the same time and it is 

 necessary to enquire how the various age groups were distributed. 



