Calving and early mortality in the western Mediterranean striped dolphin, Stenella coeruleoalba

Abstract

Foetal growth and associated calving parameters for the northwestern Mediterranean striped dolphin (Stenella coeruleoalba) population were studied using data from 437 strandings. Births occurred during autumn and length of calves was estimated as 92.5 cm, which corresponds to a weight of 11.3 kg. Calving was estimated to peak in mid-October according to the Huggett and Widdas model, and in mid-September according to the mean date of births for the population. In the western Mediterranean, calving in autumn coincides with the time of year when waters are warmest and precedes a peak of productivity, both of which provide optimum conditions for feeding and coping with the energetic demands of lactation. The frequency of strandings shows a clear peak in September–November, which suggests that mortality of neonates and of calves early in lactation is much higher than that of juveniles and calves during mid or late lactation. Consistent with previous studies on the genus Stenella, the sex ratio favoured males, falling from an initial value of 1.4 in foetuses to almost 1 postweaning.