Volumen 44 - Número 3: 685-689 | 2009
Article

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Seasonal variation in the abundance of South American sea lions Otaria flavescens (Shaw, 1800) in Chañaral Island, Reserva Nacional Pingüino de Humboldt, Chile

Maritza Sepúlveda^1,2*, Patricia Inostroza², M. José Pérez-Alvarez^2,3, Doris Oliva¹ and Rodrigo Moraga²

¹Departamento de Biología y Ciencias Ambientales, Facultad de Ciencias, Centro de Investigación y Gestión de los Recursos Naturales (CIGREN), Universidad de Valparaíso, Gran Bretaña 1111, Playa Ancha, Valparaíso, Chile
²Centro de Investigación Eutropia, Ahumada 131 Oficina 912, Santiago, Chile
³Departamento de Ciencias Ecológicas and Instituto Milenio de Ecología y Biodiversidad (IEB), Facultad de Ciencias, Universidad de Chile, Casilla 653, Santiago, Chile

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From January 2007 to March 2008, we examined variation in the abundance of the South American sea lion Otaria flavescens in Chañaral Island breeding colony by sex, age-class, and reproductive seasonality. The number of sea lions on land was highest during the breeding season. This variation was mainly influenced by the number of adult females, because this age class was the most important in the colony and showed an increase in abundance during this period. No seasonal variation in the number of adult males, subadult males, and juveniles was detected. The sex ratio during the breeding season was highly biased towards females, while it was close to 1:1 during the rest of the year. This study demonstrates that variation in the abundance and sex/age class composition of sea lions at Chañaral Island colony is largely influenced by reproductive activity.

Key words: Census, Chilean coast, sea lions, circannual rhythms, Otaria byronia

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