Abstract
Abstract Variation in foetal and postnatal sex ratios was examined jointly with the 1986-1988 Faroese international research programme on the ecology and status of the long-finned pilot whale (Globicephala melas). Data were obtained from 58 schools of whales landed in the Faroe Islands from 1958 to 1992. The sample includes 505 embryos and foetuses. Variation in foetal sex ratios was analysed according to gestational age, mother's age and years. Foetal and postnatal sex ratios from pilot whales off the Faroe Islands also were compared with those obtained off Newfoundland by Sergeant (1962). The overall foetal sex ratio was biased significantly towards more females than males. The proportion of male foetuses declined as the size of foetuses increased. Females older than 25 yrs of age in comparison to younger females bore more female than male foetuses. From birth, through the three first years oflife, selection acted mainly against females and parity was observed again in the age group 3 and maintained until the age group 10. Annual variation may occur. For similar season, at a 30-year interval, foetal sex ratio differed significantly between the Faroes and Newfoundland (46.9% and 58.8%, respectively, more male foetuses). The relative higher mortality of male than female foetuses suggest that a significant overall foetal mortality occurs, which has to be taken into account when estimating fecundity.
Published Version
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