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Keywords:

  • Steller sea lion;
  • Eumetopias jubatus;
  • adult female;
  • behavior;
  • satellite telemetry

Abstract

During the 1990s, the Steller sea lion (Eumetopias jubatus Schreber) Western Alaska stock (WS) suffered steep population decline while the Eastern Alaska stock (ES) steadily increased. One bottom-up forcing hypothesis explaining this decline predicted lactating adult female foraging behavior would be different between stocks. To investigate this effect, we monitored 11 ES females at two breeding rookeries using satellite dive recorders (SDR) during the early breeding seasons of 1992–1993, examined their behavior with respect to prey, physiological limitations, and habitat, and made limited comparisons to observations of WS female behavior reported in the literature. ES females were not operating at the extremes of ability, with most diving within the limits of aerobic metabolism, less than one-quarter of possible foraging time during trips spent submerged and most foraging trips requiring less than one-half the lipid store fasting ability of dependent pups. Thus, females may have some capacity to alter behavior to accommodate future changes in foraging conditions, but the extent of this plasticity is unknown. Because recent work suggests WS recovery is impeded by low natality, future studies should test differences between reproductive and non-reproductive mature females in order to properly assess the contribution of foraging ecology to SSL population dynamics.