Abstract

In otariids the presence of circarhythms activity has been studied on the basis of population density changes in sea lion colonies. In this work, the circadian rhythm (24 h) and the circannual rhythm (a year) of the South American sea lion Otaria flavescens from Cochoa and Punta Curaumilla colonies in Central Chile were studied. The circadian rhythm was studied in both colonies. In each one, census were performed every 45 minute during three days (72 h) of continuous observation. The results show that the number of animals on land increases during day times and decreases in the night. Such fluctuations are associated to a 24 h cycle and show the existence of a circadian rhythm in these colonies. The circannual rhythm was studied at Cochoa colony. With this purpose 145 observations were performed during three consecutive years (1995-1998). The results show a population increase during Autumn and Spring and a sudden decrease in the Summer. These fluctuations are associated to a one year cycle showing the existence of a circannual rhythm in this species.