The development of diving behavior and physiology in juvenile Weddell seals (Leptonychotes weddellii) in McMurdo Sound, Antarctica

Abstract

The development of diving behavior and physiology in juvenile Weddell seals (Leptonychotes weddellii) in McMurdo Sound, Antarctica was studied in order to determine the effects of age, body size, and condition on diving ability. During the austral summers of 1992, 1993, and 1994, the diving behavior of 39 pups and 15 yearlings was monitored using time depth recorders (TDRs). In addition, 26 pups were equipped with satellite-linked time depth recorders (SLTDRs) to track fall and winter diving behavior. Blood samples and morphological measurements were taken at each handling. Pups began to dive within two weeks of birth, and the mean dive depth, duration, and number of dives per day increased significantly over the next 10 weeks. During this period, the ability of pups to regulate physiological processes related to diving increased, as did their aerobic dive limit (ADL). Whereas diving behavior was determined primarily by age rather than mass in young pups, age had little effect on the diving behavior of pups older than 2 months (as determined from SLTDR records). Because seals were not handled after SLTDR deployment, the effects of mass could not be directly modeled in these pups. However, in yearlings, the ADL, and approximately 50% of the variation in dive behavior could be explained by differences in body size. Most dive parameters differed by time of day, and deeper and longer dives were more frequent in the afternoon period. The diel pattern was consistent with the hypothesis that pups were foraging throughout the day on vertically migrating prey species. In yearlings, dive patterns suggested that large individuals foraged primarily on shallow water prey, while smaller animals concentrated on deeper prey such as Antarctic silverfish. Tracking studies revealed that juveniles were capable of long distance movements, but suggested that they remained closer to the coastline than adults. The absence of obvious differences in dive behavior between regions suggested that juveniles were foraging on similar prey throughout the Ross Sea. While scat analyses confirmed this hypothesis, tissue stable isotope ratios suggested that some juveniles were feeding on different prey, or in different areas than adults.