GREY SEALS AS COMPETITORS WITH MAN FOR SALMON 319 



females : 21 males. Presumably males disperse further from the breeding 

 grounds than do female seals. 



However, the biased sex ratio does not affect the calculations at this stage 

 since these are based on recoveries and age differences. We may estimate the 

 number of immatures and young bull seals in the study area as follows : 



Twenty-four first-year seals are already estimated. From age determina- 

 tions of the seals captured in the study area, nine were < i year old and 

 twelve older but not mature : thus the number of immature seals older than 

 one year plus young bulls was 



12 



24 X — = 32. 



9 



This is probably an underestimate, because one would expect seals gradually 

 to become less prone to capture with increasing age, rather than for proneness 

 to capture to cease abruptly at the onset of maturity. As a minimum value, 

 then, there were fifty-six immature grey seals in the study area. 



Or, one may proceed differently and assume that the distribution of 

 marked yearlings is the same in relation to the study area as that for all 

 immature animals (including young bulls). The only support for such an 

 assertion is that rather few immature seals are seen on the breeding grounds 

 at any time of year (Hickling, 1957; Fames) and during the breeding season 

 (Hewer, 1957; Shillay; and others). 



The number of immature animals and young bulls in the study area 

 would then be : 



^ X 1,497 = 77. 

 78 



The average of these two estimates is 67. Consisting of twenty-nine 

 yearlings, thirty-five two to five year olds and three young bulls (proportions 

 from Table II). It is likely that the number of young bulls is underestimated. 



It is not possible at present to estimate the number of adult seals in the 

 study area. Nor can we say how many seals from other colonies, e.g. from 

 Orkney and North Rona may be present. Three hundred and fifty moulters 

 were ringed on North Rona in 1959 but, so far, there is only one recovery, 

 from Orkney. 



FOOD EATEN 



Nature of the food. Eight stomachs from seals (age groups one to four years) 

 taken at salmon nets in the study area are available for the months June, 

 July and August, 1956-7. But the study of the food of seals from stomachs 

 alone may be misleading because large fish are often skinned and beheaded. 



