Determinants of agonistic interactions in California sea lions

California sea lions aggregate in high density colonies during the breeding season. Competition for space and mates results in agonistic interactions that may have long-term population consequences. We explored how demographic, behavioral, and environmental variables influence the rate of agonistic interactions in male and female California sea lions at three breeding colonies with varying population trends and distributed across a wide latitudinal gradient within the Gulf of California, Mexico. Our results indicate that male agonistic interactions are related to environmental and spatial parameters, whereas female interactions are related to male interactions, operational sex ratio (OSR) and environmental parameters. Most demographic and environmental parameters were inversely related to rates of agonistic interactions, with the exception of positive relationships between agonistic interactions and territory size for males and OSR for females. In addition, the highest overall rates of aggression were associated with a declining population. Our findings suggest agonistic interactions may be useful in assessing population dynamics, but additional research is needed to identify mechanistic relationships.