Insights into the reproductive strategies of crabeater seals Lobodon carcinophagus were obtained from satellite-linked dive recorders deployed during the breeding season. All of the three females and seven males on which instruments were deployed hauled out continuously for extended periods of up to 24 days. The duration of extended haulout is consistent with a lactation period of around 3 weeks. In two cases where dive recorders were deployed on a male and female in the same group, the two animals stayed together on the ice continuously and entered the water at exactly the same time when extended haulout ceased. In both cases the male and female became geographically separated within a short time after entering the water, indicating that the association did not last beyond the period on the ice. Some males had multiple periods of extended haulout, suggesting they may try to find more than one female with which to mate. An optimal reproductive strategy with regard to the time spent on the ice may balance the conflicting needs of a short time imposed by the availability of breeding habitat and a long time to increase the reproductive success of males and females by finding more, or choosing between, mates.

Growth in length and weight of a large sample of crabeater seals Lobodon carcinophagus collected over the period 1967–78 is reported. Growth in dorsal standard length of 1146 seals (490 males, 656 females) from 0.5 to 20 years of age was similar to the pattern seen in other phocid seals. Length was plotted against age and Gompertz curves fitted to the data. Growth rates were estimated from the derived equations: males, y = 231.9 − 58.7 e−0.55t; females, y = 236.8 − 63.6 e−0.44t. The asymptote is at approximate length 234 cm and age 10 years in both males and females. Body weights were recorded for 249 seals aged from 0.5 to 20 years, of which reliable age estimates for 230 (100 males, 130 females) were available. Rates of growth in body weight were estimated from the derived equations: males, y = 200.0 − 94.1 e−0.48t; females y = 212.4 − 116.2 e−0.40t. The best estimate of body weight from linear body measurements is obtainable from a predictive equation relating body weight, length and axillary girth, determined by maximum likelihood: W = 0.000046 LG2 (W, body weight; L, dorsal standard length; G, axillary girth). There was no significant difference between the sexes. Seasonal variations in body condition could not be determined because all animals were sampled in February and March. However, inter-year differences in recovery of body condition of adults, following the demands of breeding and moulting in the spring and summer, were observed. The data represent a unique time series covering the 1960s and 1970s. In terms of global climate change they should provide a valuable baseline for future studies.

The age of crabeater seals Lobodon carcinophagus was first estimated from the teeth by counting layers in the dentine in transverse sections of the canine teeth. Reliable estimation of age from canine teeth in animals older than c. 10 years is not possible because of root closure at a relatively early age. The present investigation compared various methods of estimating age by examination of tooth sections from a large sample of crabeater seals from Marguerite Bay, Antarctic Peninsula. The most reliable estimations were shown to be obtained by counting layers in the cementum of the third postcanine tooth. Ages of 1233 animals (58% female, 42% male) ranged from 0.5 to 39 years. It is suggested that time- and age-specific historical material is potentially relevant for contemporary growth and life-history studies as well as for trophic relations or concentrations of pollutants in animal tissues.