Daily and seasonal variation in the haul-out behavior of the South American sea lion

Abstract

a b s t r a c tIn the South American sea lion (Otaria flavescens), daily fluctuations in abundance have been analyzed based on sequential counts of the number of animals hauled-out. However, no studies have analyzed haul-out activity in relation to an annual cycle or according to different age/sex classes. The objective of this study was to determine the daily and seasonal haul-out patterns of each age/sex class of South American sea lions as a function of the time of the day. A total of 222 days were analyzed in a breeding colony of Chile, from May 2008 to December 2010. During the non-breeding season (March to December) males, females, and juveniles showed a unimodal pattern, in which few sea lions are hauled-out in the morning and maximum numbers are found in the rookery during the early afternoon (1330-1630). In contrast, during the breeding season (austral summer) the proportion of individuals hauled-out shifted from a unimodal to a bimodal pattern, especially in the case of juveniles. Our results indicate that there are fine scale differences in haul-out behavior among age/sex classes, as well as larger scale seasonal differences in the proportion of sea lions ashore. These differences appear to be related to reproductive activities, food availability and thermoregulatory requirements. These patterns of seasonal variability of South American sea lion haul-out should be taken into consideration when planning surveys to estimate population abundance.

Annual, seasonal and daily variation in the abundance of the South American sea lion Otaria flavescens in two breeding colonies in northern Chile

“…Previous studies have demonstrated a strong diurnal component to SASL haul-out abundance, with few hauledout sea lions in the morning and maximum numbers of hauled-out individuals in the afternoon (Sepúlveda et al 2001(Sepúlveda et al , 2012, mainly due to the effects of time of day and height of tides. In particular, time of day has typically been examined to determine daily trends in haul-out patterns, relating observed patterns to ambient temperature, intensity of solar radiation, and prey availability in the water column (Calkins et al 1999).…”

“…Females on the other hand remain with their pups in the colony, alternating their time between pup attendances on land and foraging trips to the ocean (Campagna & LeBoeuf 1988, Muñoz et al 2011. During the rest of the year (April to December), sea lions of all ages and sex classes can be seen in the rookeries, although the number of sea lions hauled-out vary considerably in different months (Sepúlveda et al 2009(Sepúlveda et al , 2012. Thus, breeding season constitutes a strong component influencing haul-out patterns on this species.…”

“…Besides long-term abundance trends, SASL exhibits marked seasonal abundance fluctuations, mainly explained by the notable breeding period that occurs in this species, extending from January to March (austral summer) (Acevedo et al 2003, Sepúlveda et al 2012. During this period, the abundance of sea lions in the rookeries arises due to the presence of newborn pups, and adult males and females also that remain on land defending their territories, and caring for and suckling their pups, respectively (Sepúlveda et al 2012).…”

“…During this period, the abundance of sea lions in the rookeries arises due to the presence of newborn pups, and adult males and females also that remain on land defending their territories, and caring for and suckling their pups, respectively (Sepúlveda et al 2012). At the end of this period, most males disperse out to feed and rest (Sepúlveda et al 2001, Acevedo et al 2003, Muñoz et al 2011.…”

“…In particular, time of day has typically been examined to determine daily trends in haul-out patterns, relating observed patterns to ambient temperature, intensity of solar radiation, and prey availability in the water column (Calkins et al 1999). Several studies, both in SASL (Sepúlveda et al 2001(Sepúlveda et al , 2012 and in other species of otariids (e.g., Stirling 1968) have documented a maximum peak of abundance on land during the early afternoon. This pattern could be in response to air temperature, with sea lions more likely to haul-out under conditions of high temperature (Carlens et al 2006, Andrews-Goff et al 2010.…”