Seasonal variation in the physiological ecology of the Galapagos (Zalophus wollebaeki) and California (Zalophus californianus) sea lions

Environmental seasonal change affects animal behavior and physiology. Pinnipeds living in lower latitudes where seasonal change is smaller and less predictable are less successful and have greater extinction risk than higher latitude species. Populations better adapted to change have greater foraging and survival success. Marine mammal foraging is constrained by diving duration, determined by their oxygen stores. To study how physiology limits behavior and the ecological role of seasonal change I studied diving behavior and physiology in a temperate and equatorial sea lion species during two contrasting seasons, warm and cold. I studied California sea lions (Zalophus californianus ) (CSL) from Granito Island, Gulf of California, Mexico, with increasing population and Galapagos sea lions (Zalophus wollebaeki) (GSL) from Caamatio Islet, Galapagos, Ecuador, with an endangered and declining population. I deployed time-depth recorders and satellite transmitters on females to study diving behavior. To study diving physiology, I collected blood and muscle samples to determine oxygen stores. I hypothesized a change in the sea lions diving behavior and physiology between seasons as a response to environmental change.GSL diving behavior did not change between seasons exhibiting three foraging strategies which suggest that intra-specific competition is maintained throughout seasons and that resources are limited in this area of the Galapagos. In contrast, CSL diving behavior changed between seasons, exhibiting greater variability, effort and infra-specific competition during the warm and less productive season.GSL exhibited physiological plasticity coupled with behavior within seasons. Oxygen stores of the three foraging strategies increased accordingly to dive durations showing that diving physiology is plastic and can be modified by behavior.As hypothesized, GSL and CSL diving physiology changed between seasons showing contrasting trends. During the warm season blood oxygen stores were significantly higher while muscle oxygen stores were significantly lower compared to the cold season. Physiological changes are attributed to pregnancy as females were in a late pregnancy status during the cold season.GSL exhibited greater dive and foraging effort than CSL suggesting that equatorial sea lions facing limited resources and unpredictable environments makes adjusting their behavior challenging. In contrast, higher latitude species -CSL facing productive and seasonal predictable environments adjust their behavior. GSL face greater nutritional stress than CSL, reflected in their contrasting population trends in which CSL are more successful.