The development of efficient foraging skills is an essential part of the transition from dependent suckling to independent feeding. For most phocid seals this transition is abrupt and no parental help is provided beyond weaning. Pups are abandoned at weaning with what is termed an “insurance policy” in the form of stored fat. Body fat at weaning may increase the likelihood of pup survival. Insofar as body stores scale proportionally to body mass large, fat pups may survive the transition to independence better than small pups. Harbour seal (Phoca vitulina) pups have low energy densities at weaning and consequently a lower insurance policy. In the present study, I investigate how pup size and body composition at weaning affect the transition to nutritional independence. I monitored changes in haul-out patterns, blood chemistry, body composition, water fluxes, and the development of diving and foraging behaviour of recently weaned harbour seal pups in 1993 and 1994 on Sable Island, Canada. There were no significant differences in blood chemistry or body composition between small and large pups at weaning. However, longitudinal observations of pups showed that during the post-weaning period, there were significant differences in blood chemistry, body composition, energy utilization, water fluxes and diving behaviour between small and large pups. Large pups seem to have greater choice between fasting or initiating diving and foraging activities soon after weaning. Once they started diving, large pups dove longer and deeper than small pups. Small pups on the other hand appear to be forced to start diving and foraging almost immediately after being weaned. Thus, small pups start the transition to independence sooner than large pups but they are not as well equipped to make this transition as large pups. At least for weaned harbour seal pups from Sable Island, being bigger may confer a better chance at making the transition to nutritional independence.