Maternal and birth colony effects on survival of Weddell seal offspring from McMurdo Sound, Antarctica

Abstract

1. Maternal and birth colony effects on offspring survival to weaning and to reproductive age were examined for Weddell seals using mark–recapture models and over 25 years of mark–resight data from McMurdo Sound, Antarctica. 2. Pre‐weaning mortality (proportion of the total pups found dead on the ice surface) varied significantly with maternal age and was significantly higher for primiparous mothers than for multiparous mothers. 3. Offspring survival to reproductive age also increased significantly with maternal age and experience. Survival of offspring from birth to 6 years of age increased significantly with maternal body length only for male offspring. 4. Increased survivorship of offspring with maternal age was only evident for offspring of multiparous (rather than primiparous) mothers. This suggests that the age when mothers have their first pup may not affect survival of offspring, although lack of effect of age on offspring survival for primiparous mothers may be due to insufficient variation in age of first reproduction in our sample for us to detect a trend. 5. Pre‐weaning survival of offspring also varied significantly among pupping colonies. In 1983, a year of low reproduction and low first‐year survival for the McMurdo population (Testa 1987b; Hastings 1996), first‐year survival was lower for offspring born in Outer Erebus Bay (west of 166·7°E) than for offspring born in Inner Erebus Bay (east of 166·7°E). 6. Maternal effects on offspring survival may be related to quality of breeding site. Maternal age and experience varied significantly among pupping colonies. That pup population size was stable at all colonies over the study period suggests non‐random age‐distribution of mothers may not be an artefact of population growth, but instead result from intraspecific competition for space in good pupping colonies. 7. Offspring survival, pup population size, and mean maternal age at colonies were significantly positively correlated. This suggests that favourable environmental conditions and high maternal or paternal quality may interact to enhance survival of offspring at larger colonies.