Review of California sea lion (Zalophus californianus) abundance, and population dynamics in the Gulf of California

Abstract: The life history of California sea lion (Zalophus californianus) in the California Gulf is marked by a series of important events influencing and modifying its population growth, evolution and distribution. Despite the fact that the population has been studied since the 1950s, research has been have been rather punctual and fragmentary, before 2010, there are a very few censuses conducted simultaneously in all rookeries, which prevent obtaining information on key aspects of life cycle, population trend and potential threats. In the present work we conducted a thorough review encompassing the last 37 years of California sea lion life history and environment in the Gulf of California. This allowed an opportunity to focus on short- and long-term processes acting on the population and hopefully improve knowledge about the population trend and status and unveil some latent aspects hardly recognizable using a partial vision. We collected and analyzed data from different sources since the 1970s to 2018: published papers, master’s and doctoral thesis, in addition to technical reports. The data is organized in sections corresponding with crucial population life history events. Considering a long-time frame period the population could appear stable with zero growth due to the cyclic interannual fluctuation that could denote a certain dependence with climatic factors, not directly with El Niño event, but with sea surface temperature anomalies that determine a change in prey availability. However, many doubts persist about the incidence of different local environmental factors on gender and age, particularly related with juvenile recruitment and female survival rate. More information is required based on seasonal censuses, life cycle, regional environmental variation; statistical errors need to be assessed and monitoring methods should be standardized and must be considered to ascertain short- and long-term population and colony spatial-temporal patterns.