Interannual variation in the post-weaning and juvenile survival of subantarctic fur seals: influence of pup sex, growth rate and oceanographic conditions
Résumé
1. A major hypothesis of life history theory is that early development conditions affect future survival and reproductive success. However, although a growing number of studies have addressed this question, many of them are taxonomically biased, thereby impeding the generalization of this hypothesis. 2. This study examines the factors influencing post-weaning survival in five weaned cohorts of subantarctic fur seal pups from Amsterdam Island, southern Indian Ocean. It used mark–recapture data from 7 consecutive years of different environmental conditions. 3. The cohort return rate varied from 45% to 74% of weaned pups, depending on the year of weaning. In each cohort, 96% of weaned pups returned between 3 and 6 years of age, and none of the factors examined seemed to influence this timing pattern. The probability of survival to this first return was negatively related to sea-surface temperature anomalies (SSTa) of the 6 months following the weaning process. It increased with pup preweaning growth rate and differed between the sexes. Females' survival rate was significantly higher than males', except during years of extreme SSTa, where no difference was detected. 4. The juvenile state represented young individuals after their first return on their native island. Annual juvenile tag loss rate was constant at 0·217 (SE = 0·027), whereas temporary emigration rate varied over cohorts and was higher in males 0·423 (SE = 0·035) than in females 0·170 (SE = 0·012). This dispersion pattern may be prolonged in some cases, as the yearly immigration probability was constant at 0·290 (SE = 0·065). 5. Taking into account tag loss and temporary emigration, the estimated yearly survival probability of juveniles was 0·964 (SE = 0·022). This value was unrelated to any tested oceanographic or individual parameter including sex. 6. Results support the hypothesis that early development traits affect short-term post-weaning survival. However, no long-term effect of maternal postnatal investment was detected after the first return to the native island. Results also indicate that the effect of early development traits on survival interacts with environmental conditions encountered shortly after independence of individuals.