Size and growth of the crabeater seal Lobodon carcinophagus (Mammalia: Carnivora)

Abstract

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.