MEPS 667:207-217 (2021)  -  DOI: https://doi.org/10.3354/meps13702

ABSTRACT: The successful recruitment of juveniles into a population is often dependent on receiving sufficient nutrition pre- and post-parturition. Thus, variation in maternal foraging ecology during pregnancy, whether due to prey choice, prey availability or fluctuations in environmental conditions, can impact offspring fitness in the subsequent breeding season. As many pinnipeds spend the majority of the gestation period at sea, past studies have used the biogeochemical analysis of pup tissues to infer female diets during this critical period. The objective of our study was to examine the trophic niches of a population of pregnant female gray seals Halichoerus grypus over a 4 yr period in coastal Massachusetts, USA by analyzing the stable carbon (δ¹³C) and nitrogen (δ¹⁵N) values of pup lanugo. In addition, we sought to determine if individual and inter-annual variation in pup body condition could be explained by differences in female trophic niches, prey availability, or environmental conditions. Stable isotope-based metrics of trophic niche position, width, and overlap indicated little to no interannual variability in female foraging ecology at the population level despite variation in environmental conditions and prey availability in the fall on Georges Bank. Model selection indicated a positive relationship between pup body condition and δ¹³C values, which is indicative of pregnant females foraging on benthic, demersal, or nearshore prey species during the fall prior to parturition. This indicates that individual variation in female foraging ecology during pregnancy has a carry-over effect on offspring condition with possible implications for first-year survival, and ultimately recruitment to the adult population.

KEY WORDS: Foraging behavior · Isotopic niches · Maternal investment · Gray seal · Halichoerus grypus · Stable isotope analysis · Carry-over effect