VERNAL COITION OF THE SEAL PHOCA VITULINA IN SHETLAND
- 1A colony of Phoca vitulina was under regular observation from 23rd May to 10th June 1958. Outbursts of sexual rolling were common between subadult pairs. No yearlings and no pregnant females took part, and fully grown bulls did so rarely.
- 2Both sexes rolled enthusiastically. Changes of partner were rare. Many males appeared eager for coition but the females, by arching back their heads and necks, usually prevented them from getting far enough forward for insertion. Successful coition was witnessed on at least one, possibly six, occasion(s).
- 3Probably rolling females were maiden cows, approaching oestrus. Ovulation can occur in May and may well be stimulated by this prolonged riding behaviour.
- 4The main mating season (September-October in Shetland) follows lactation and moult. In our three years' experience of this colony all pups were born during the three weeks commencing 14th June. If successful fertilization occurs in May, the implantation of the blastocyst is probably delayed until the normal season.
- 5A recent decline in the size of this seal colony may be due to the increase in price offered for pups' pelts with a consequent increase in hunting.