Maternal strategies of the New Zeland fur seal: evidence for interannual variability in provisioning and pup growth strategies

Maternal attendance, nursing behaviour, pup growth and weaning age were investigated in the New Zealand fur seal (Arctocephalus forsteri) at Kangaroo Island, South Australia. Foraging trips to sea increased throughout lactation (5.9–9.8 days), while the duration of shore attendance bouts (1.7 ± 0.7 days) remained unchanged, resulting in time ashore declining from 24% to 14% throughout lactation. Mothers with sons made longer foraging trips than mothers with daughters throughout lactation and, as a consequence, maternal time ashore was less for sons (21%) than for daughters (28%). Pups maintained an overall sucking-rate of 1.4 h day–1 throughout their mothers’ lactation, by sucking more frequently and for longer periods as their mother became less available. Because mothers with daughters were ashore more frequently, the overall sucking-rate of females (1.7 h day–1) was greater than that of male pups (1.1 h day–1). The growth patterns of male and female pups from two cohorts were similar, but males grew faster and weaned heavier in one of the years. Age at weaning was ~285 days (9.4 months). This study indicates some significant differences in the nature of maternal expenditure in male and female pups, and the growth strategies used by pups both within and between years.