The subantarctic fur seal Arctocephalus tropicalis is widely distributed north of the Antarctic convergence. We analysed data concerning vagrant individuals of A. tropicalis encountered on the beaches of Bahia and Sergipe, north-eastern Brazil, using the Instituto Mamíferos Aquáticos database of occurrences reported between 20 July 1990 and 18 August 2005. The information collected for each case included: date, location of the occurrence, condition of the individual, sex, and total length. Twelve occurrences of A. tropicalis were reported in the study area, with 42% corresponding to sub-adult specimens. All individuals were found alive, but only two were in good health. Most occurrences were reported during the months of July, August and September, a period in which south-eastern winds predominate. The importance of developing public educational campaigns as well as population dynamics studies of this species is discussed.

Growth in body mass in pups of the subantarctic fur seal Arctocephalus tropicalis was studied at Amsterdam Island, southern Indian Ocean during the rearing period between December 1995 and August 1996. We examined the change in the rates of mass gain and mass loss with pup age to explain the overall change in mass throughout the rearing period, when mothers alternate foraging trips at sea and attendance periods ashore. In the absence of their mothers, pups fast and lose mass. During the maternal attendance period ashore pups suck and gain mass. There was no significant difference in the rate of growth in mass between male and female pups. The rate of loss in mass during a fasting event was positively related to the initial body mass but negatively related to the age and duration of the fast of the pup. The rate of mass loss was best related to pup age by a quadratic relationship. The rate of mass loss increased until pups were 120 days old and then decreased until the end of the study period. The rate of gain in mass following a maternal foraging trip was positively related to the initial pup mass but negatively related to the foraging trip duration, and we found that the rate of mass gain decreased linearly with the age of the pup. The concomitant decrease in the rate of mass loss and mass gain for pups > 120 days old allowed pups to maintain a positive growth until they were 220 days old. After 220 days of age the rate of mass loss exceeded the rate of mass gain and the pups start to lose mass until weaning.

Early mortality and pup growth during the perinatal period were investigated in pups of the subantarctic fur seal Arctocephalus tropicalis on Amsterdam Island. Mothers that were shorter in body length and expected to be younger, gave birth earlier in the pupping season, compared with longer/older mothers. Pups born early were often still-born, suggesting that shorter/younger mothers that gave birth early in the season were not able to carry their foetuses to term. Pregnant females arrived ashore 1.4 days before giving birth, regardless of the date and their body condition. There was a positive relationship between maternal body length and pup birth mass. Consistently, birth mass increased throughout the pupping period. After parturition, mothers suckled their pups during an average 8.7-day postnatal period that was significantly shorter in mothers giving birth late in the season. However, the absolute gain in pup mass was 1.5 kg regardless of the birth date, suggesting that mothers did not leave their pups before they had transferred a given amount of body reserves to them. We propose that pups born late grew faster because they were bigger at birth and because their mothers were likely to be more experienced. Mothers in good condition, nursing male pups transferred more milk and therefore greater mass to their pup, whereas mothers in poor condition were unable to do so. Such differences did not occur in smaller female pups, suggesting that pup growth was limited by maternal resources in male pups but not in female pups. The lack of a relationship between birth mass and absolute gain during the perinatal period suggests that mass at birth determined pup body mass after the perinatal period. Body mass is an important factor in growth rate and survival during the period of pup dependence.