ABSTRACT: This review presents a comparative analysis of the behaviour and energetics of the ice-breeding phocid seals of the North Atlantic in relation to their habitat(s). In very broad terms, it suggests that the term 'ice-breeding' is too simplistic and may lead to misconceptions about the actual degree of variability that exists in the breeding habitats of seals that do not give birth on land. The variation that exists within ice habitats is quite remarkable in terms of: temporal and structural stability of the pupping platform; the degree to which animals have access to the water; the risk of predation; and perhaps also the local availability of food. These factors all appear to influence the behaviour of mothers and pups and the allocation of energy during the lactation period of the species studied. Two basically different nursing strategies can be identified that may have evolved, at least in part, as a consequence of variation in these variables. The pattern displayed by grey (Halichoerus grypus), harp (Phoca groenlandica) and hooded (Cystophora cristata) seals involves a short lactation period, during which a large amount of energy is transferred from the mother to the pup through extremely-energy-rich milk. Pups of these species are very inactive and consequently a very high proportion of the received energy can be stored as body tissue, mainly in the form of subcutaneous blubber. The mothers generally feed little or not at all during the nursing period and the pups are weaned abruptly, having not yet entered the water in most cases. The other strategy, found in bearded (Erignathus barbatus) and ringed (Phoca hispida) seals, involves a longer lactation period, where less-energy-rich milk is transferred to very active pups. These pups learn to swim and dive during the nursing period, and are weaned with body compositions that are similar to those of adults. The mothers feed during lactation and weaning is less abrupt, with pups feeding independently, while still receiving milk from their mothers.

KEY WORDS: Behaviour · Diving · Lactation · Maternal investment · Ice-breeding seals

Published in MEPS Vol. 187 (1999) on October 14
ISSN: 0171-8630. Copyright © Inter-Research, Oldendorf/Luhe, 1999