Long-term abundance dynamics of the South American sea lion (Otaria flavescens) in the most important breeding colony in central Chile

Long-term studies that monitor changes in the abundance of pinnipeds are particularly relevant given that these long-lived species are considered to be indicators of the quality of the ecosystems around them. We report a continuous record of the total abundance by sex and age-classes of the South American sea lion (Otaria flavescens) in Cobquecura, the most important breeding colony in central Chile over a twelve-year period (2008 to 2020). We also analysed the demographic trends in South American sea lion abundance at this location. A total of 110 and 43 sea/land based and aerial censuses were performed over the studied period, respectively. The number of sea lions on land was highest in the summer months, which corresponds to the breeding season of the species. The abundance ranged from a minimum of 870 to a maximum of 4,531 individuals from sea/land-based observations, and from 796 to 4,854 from aerial censuses. This variation was mainly influenced by the number of adult females, the most abundant age-class in the colony. On the contrary, adult and sub-adult males were least abundant in the population. The highest numbers of pups were registered in February of each year, ranging from 448 in February 2009 to 1,214 in February 2017. During the study period, we estimated a finite growth rate (lambda) of 1.031, suggesting an increase in the population size in the colony, especially in the number of pups. Considering Cobquecura is highly susceptible to anthropogenic disturbance, developing effective long-term protection through adequate management is critical to better conserve the South American sea lion in the most important breeding colony in central Chile.

Automated summary

The study conducted in the most important breeding colony of South American sea lions in central Chile over a twelve-year period revealed that these long-lived species are indicators of ecosystem quality, with the highest numbers observed during the breeding season and the most abundant age-class being adult females. The population size in the colony showed an increase over the study period, especially in the number of pups, highlighting the importance of developing effective long-term protection measures for the conservation of the South American sea lion in this location.