Variation in the secondary sex-ratio of the grey seal Halichoerus grypus (Fab.) during the breeding Season

Abstract

HEWER1 has suggested that the secondary sex-ratio (that is, the sex-ratio at birth) of the grey seal is probably close to equality. Since this publication, considerably more data have been collected on the grey seal colony on the Fame Islands, Northumberland, by members of the Natural History Society of Northumberland, Durham and Newcastle upon Tyne. Of 1,433 calves which were tagged, sexed and aged between 1952 and 1959 inclusive, 731 were males and the remaining 702 females ; a result which does not differ significantly from a 1: 1 sex-ratio and which confirms Hewer's findings. © 1961 Nature Publishing Group.