1. A joint live-recapture/live-resighting/dead-recovery mark–recapture model was used to investigate the effect of serum gammaglobulin (IgG) levels, sex, mass and condition (mass/length as a surrogate for total body fat) at weaning on the probability of survival from weaning to age 1, in Grey Seal (Halichoerus grypus Fabricius 1791) pups born at two different breeding colonies (Isle of May and Farne Islands) in two different years (1997 and 1998).
2. It was found that increased mass or condition at weaning had a positive effect on the first year survival of Grey Seal pups born at both colonies. Males had a lower probability of survival than females.
3. Higher postweaning circulating IgG concentrations also decreased the probability of survival. It is not known if those pups with high IgG were individuals with naturally higher circulating concentrations or because titres were elevated due to antigenic challenge.