The development of dive capacity in northern elephant seal pups during the post‐weaning fast (1100.14)

Abstract

The post‐weaning fast (PWF) in seals has been associated with development of the physiological and behavioral capacity to perform the breath‐hold dives which characterize at‐sea behavior in these species. Previous studies in juvenile northern elephant seals (Mirounga angustirostris) indicate that the duration of the PWF varies substantially with body reserves at weaning, and many suggest that the terrestrial PWF enables juveniles to develop the physiological capacity to dive before initiating independent foraging at sea. However, few studies have examined the effect of magnitude of body reserves at weaning on development of dive capacity. We measured energy reserves at weaning and made longitudinal measurements of components of blood and muscle oxygen stores, thyroid and glucocorticoid hormones, iron status markers, muscle metabolic enzyme activities, and field metabolic rate in northern elephant seal pups during the first 8 weeks of the PWF. Our objective was to assess the impacts of body reserves at weaning on the rate of development during the first 8 weeks of the PWF. Although myoglobin concentration, a critical determinant of the muscle oxygen store, increases during the first eight weeks of the PWF, other key components of aerobic diving capacity do not increase during this same time period. When the magnitude of body reserves at weaning impacted the measured parameters of aerobic dive capacity, pups with smaller body reserves at weaning tended to exhibit greater cumulative increases across the PWF. Pups with smaller body reserves at weaning develop greater mass specific oxygen storage capacity during the first 8 weeks of the PWF. However, the greatest changes in dive capacity may occur near the end of the fast or after juveniles have left the natal rookery to initiate independent foraging.Grant Funding Source: Supported by NSF