A recognition system is required between pinniped mothers and pups. For otariids this is especially important since females frequently leave their pups for foraging and must reunite on return. Pups must deal with these fasting periods during maternal absence and consequently may attempt to obtain allomaternal care from unrelated females. This research on the New Zealand fur seal (Arctocephalus forsteri) at Ohau Point, Kaikoura, New Zealand, quantified mother-pup recognition behaviour during reunions, individuality of pup calls used by mothers to recognise their pup, and the occurrence of allosuckling as a possible recognition error by females and as a strategy employed by pups to gain allomaternal care during their mothers' absence. A combination of behavioural observations, morphometry, VHF radio telemetry, acoustics and DNA genotyping were employed to study these topics. Postpartum interaction behaviours between mothers and pups appeared to facilitate development of an efficient mother-pup recognition system, involving mainly vocal and olfactory cues that were utilised during reunions. Greater selective pressure on pups to reunite resulted in an asymmetry of searching behaviour between females and pups during reunions. The vocalisations of pups were stereotypic, especially those features of the fundamental frequency and frequency of the lowest harmonic, which are likely to facilitate recognition of a pup by their mother. Pups attempted to steal milk from unrelated females more often during maternal absence and appeared to modify the intra-individual variation pattern of a feature of their vocal signatures over this period, which may assist attempts at allosuckling under nutritional stress. Fostering was demonstrated to occur despite costs to filial pups and possible costs to female reproductive success and may be attributed to development of erroneous recognition between females and non filial pups, or kin selection. This study provides a valuable contribution to the knowledge of recognition systems between pinniped mothers and pups, of alternative pup strategies under nutritional stress and of the rare occurrence of fostering in otariid pinnipeds.