Influence of Foraging Effort and Diet on Maternal Energy Stores and Offspring Weaning Mass in Gray Seals ( Halichoerus grypus )

ABSTRACT Understanding how foraging behavior and diet influence individual reproductive success is a key interest in evolutionary ecology. This is particularly true for capital breeding species where the accumulation and storage of energy to support offspring is critical, often following the “bigger‐is‐better” hypothesis. Using data collected from female gray seals ( Halichoerus grypus ) at Sable Island, Canada, between 1995 and 2018, we tested the hypothesis that differences in foraging effort and diet prior to the breeding season, estimated through satellite telemetry, stable isotope (SI) signatures, and quantitative fatty acid signature analysis (QFASA), respectively, affect reproductive success. There was no relationship between dominant prey type, the energy density of estimated diets, and maternal postpartum mass (MPPM). Females consuming a diet of lower diversity and with more positive δ 13 C estimates, possibly indicating more benthic foraging, had higher MPPM. MPPM was the best predictor of offspring mass at weaning. However, metrics of maternal foraging effort and diet alone did not influence pup weaning mass when MPPM was included in the model. These results suggest that different foraging strategies and diets can lead to sufficient body energy storage that enables reproductive success in a capital breeder. Considering this colony was increasing rapidly during the study period, the influence of foraging effort and diet might differ in a stable or declining population where intraspecific competition may be more evident.