Keyword: mamíferos marinos

Este estudio resume el conocimiento sobre la abundancia y distribución de la población del elefante marino del sur, Mirounga leonina, actualizando la información publicada hasta 1990 con datos demográficos para el período 1991–1997 durante las dos etapas terrestres del ciclo anual (reproducción: septiembre–octubre y muda: diciembre–febrero). La información se obtuvo mediante censos aéreos y terrestres de la Península Valdés (PV) y áreas adyacentes. La agrupación de elefantes marinos de PV es la única en el mundo que se encuentra en incremento. La producción de crías aumentó el 41% entre 1982 y 1997, y el incremento fue lineal entre 1969 y 1997. En 1982 se censaron 7416 adultos reproductores en su mayoría distribuidos en 477 harenes; en 1997 el número de adultos fue 12572 repartidos en 492 harenes. La mediana del tamaño de los harenes aumentó de 11 a 16 hembras en el mismo período. El incremento poblacional se asoció a una variación en la distribución espacial de los animales en la costa. En 1982, el 42% de las hembras reprodujo en el sector SE de PV mientras que en 1997 lo hizo el 73%. El número de hembras adultas que mudan en PV se estimó en 11200 individuos para 1994. La distribución de animales fue similar durante la reproducción y la muda. El incremento en la producción de crías indica un aumento en el tamaño poblacional posiblemente asociado a factores que operan durante la etapa pelágica del ciclo anual.

Population status and distribution of southern elephant seals at Península Valdés, Argentina. Southern elephant seals, Mirounga leonina, breed and molt in Península Valdés (PV) along a 200 km stretch of coast. We conducted one aerial survey (1992) and three terrestrial surveys (1995 to 1997) of the entire population at the peak of the breeding season (first week of October) and compared results with similar data published for the period 1982–1990. During aerial survey, we photographed all harems and recorded solitary individuals by sex and age categories (breeding females, harem bulls, bachelor males, pups and weanlings). Females were counted from photographs and pup production was estimated based on the number of females plus weanling. During terrestrial surveys, all recorded individuals were categorized by sex and age. Pup production increased 41%, from 7455 in 1982 to 12106 in 1997. Growth was linear from 1969 (counts made by other authors) to 1997. Based on reported pup production for the species in the world, PV is the fourth largest southern elephant seal colony. At the peak of the breeding season of 1997 there were 24726 animals of both sexes ashore, including pups. The size of the population 1 year of age was estimated in 42371 individuals. There were 477 harems in 1982 and 492 in 1997; 99% of the females bred in harems. The range of distribution of elephant seals in Patagonia did not change, but the spatial distribution of births along the coastline of PV varied with the increase in numbers. In 1982, 58% of the births occurred in 106 km in the NE portion of the peninsula, versus 27% in 1997. In 1997, 73% of the females gave birth in 77 km along the SE coast. Only 1% of the adult population bred outside PV. We estimated the number and distribution of adult females during the molt conducting two aerial surveys when the maximum number of animals were ashore (last weeks of December 1993 and January 1994). Females made 40% and 95% of the molting population in each census, respectively. PV is apparently the only southern elephant seal colony in the world that is expanding. The increase in pup production could be the result of factors operating while the animals are at sea, where abundant food resources may be a crucial determinant of population trends.