The Galapagos Sea Lion: Adaptation to Spatial and Temporal Diversity of Marine Resources Within the Archipelago

Abstract

Galapagos sea lions are the smallest sea lion species worldwide. The population consists of about 20,000 individuals, is endemic to the Galapagos Islands and has been separated for about 2.5 million years from the California sea lion. The equatorial environment differs from that of other pinnipeds by terrestrial heat and reduced marine productivity. Growth and development is strongly influenced by marine variability, particularly El Niño events, which also decrease juvenile and adult survival. Large males establish aquatic territories, but smaller non-territorial males also achieve reproductive success. Time at the colony proves the best predictor of reproductive success, which reflects the long drawn-out reproductive season often lasting 6 months. Females mature relatively late at about 5 years and reproduce often only every other year. Juveniles need exceptionally long to become nutritionally independent. The long period of lactation (2–5 years) often leads to competition between offspring born in different years. Adult females dive to great depths (max. 580 m) and mostly forage on shelf areas as well as along the shelf edge. Juveniles need many years to reach adult diving abilities. Increased human-sea lion contact in fast growing settlements and through boat traffic and fishery poses new and potentially highly dangerous threats to the population.