Studies of pinniped reproductive strategies have concentrated on those species which mate on land. These are primarily otariids, but include a few phocids such as elephant seals, Mirounga leonina and M. angustirostris (Le Boeuf 1974; McCann 1981) and land-breeding grey seals, Halichoerus grypus, (Anderson, Burton & Summers 1975) which fast throughout the lactation period. In contrast, most phocids spend part of the lactation period in the water, during which time they may feed (Andersen & Fedak 1987). These species also tend to form more dispersed breeding groups, particularly on ice (e.g. Crabeater seals, Lobodon carcinophagus) and several species appear to mate in the water [e.g. Weddell seals, Leptonychotes weddelli (Cline, Siniff & Erickson 1971)]. The resulting differences in female dispersion would be expected to result in a wider range of mating patterns than those seen amongst land-breeding pinnipeds (Stirling 1975; Boness 1991; Le Beouf 1991), but few data exist to examine this hypothesis.