Mass changes during their annual cycle in females of southern elephant seals at King George Island

Mass changes in female southern elephant seals. sampled sequentially at dif ferent points through their annual cycle, were measured at King George Isla nd, South Shetland Islands. during the 1995/1996 and 1996/1997 field season s. Females weighed after they had given birth showed an increase of 37 +/- 36 kg (mean +/- SD), which represented 6.2 +/- 6.4% in relation to their ma ss in the first breeding season. During the first aquatic phase, between th e end of lactation and the beginning of moult, females gained a mean of 128 +/- 35 kg. (n = 18) (2.19 +/- 0.65 kg day(-1)). which represented between 27 and 83% of the mass they had lost during lactation. Nine females followe d during moulting showed a mass loss rate of 5.0 +/- 0.4 kg day(-1). which was half the rate during lactation. Total mass loss during moulting (129 +/ - 22 kg) was not significantly different from mass gain for the same female s between lactation and moult (135 +/- 37 kg). Furthermore, at the end of m oulting, female mass was not significantly different from the mass at the e nd of lactation. These masses represented 65 +/- 5% and 63 +/- 5%, respecti vely, of their initial mass after parturition. During the second period at sea, from the end of the moult until females hauled out to give birth in th e following breeding season, the estimated mass gain was 1.45 +/- 0.24 kg d ay(-1) (n = 5), which was not significantly different to the rate of mass g ain shown by the same females during the first period at sea (2.26 +/- 0.70 kg day(-1)). Total mass during the second aquatic phase (364 +/- 63 kg) wa s not correlated with the mass at the end of moulting, but it was positivel y related to the mass loss experienced by females from parturition until th e end of the moulting period in the first breeding season.