Female attendance and neonatal pup growth in Stellar sea lions (Eumetopias jubatus)
R.W. Davis, E.A.A. Brandon, D.G. Calkins, and T.R. Loughlin
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We studied attendance behavior of lactating Steller sea lions (SSL) and the growth rates of pups in Southeast Alaska, the Gulf of Alaska, and the Aleutian Islands from 1990 to 1997. These rookeries included one (Lowrie Island in Southeast Alaska) in an area of stable population and three (Chirikof and Marmot islands in the Gulf of Alaska and Seguam and Yunaska islands in the Aleutian Islands) in areas where the population of SSL has declined significantly over the past 30 years. Radio transmitters were glued to the fur of lactating SSL and their presence on the rookeries monitored for the first four to six weeks postpartum. Newborn pups were weighed and measured every two weeks over the same period. The time spent onshore (22.5 h ± 8.26 SD) by females did not differ significantly among rookeries. Average foraging trip duration was significantly different among rookeries and ranged from 25.6 h ± 11.64 SD in the area of stable population to 9.4 h ± 3.32 SD in the area of declining population. The average percentage of time spent at sea was significantly different among rookeries and ranged from 51% ± 8.9 SD in the area of stable population to 31% ± 9.99 SD in the area of declining population. Male pups (22.6 kg ± 2.21 SD) were significantly heavier than female pups (19.6 kg ± 1.80 SD) at 1-5 days of age, but there were no significant differences among rookeries at that age. Male and female pups on the same rookery grew at the same rate during the first four to six weeks. Body mass and standard length increased at a faster rate for pups in the Aleutian Islands and the western Gulf of Alaska (0.45-0.48 kg day–1 and 0.47-0.53 cm day–1 respectively) than in Southeast Alaska (0.23 kg day–1 and 0.20 cm day–1). Overall, average foraging trip duration among rookeries decreased and pup growth rate increased in an east-to-west direction from the area of stable to declining population. There was no evidence that female sea lions and pups were nutritionally stressed during the first six weeks postpartum in the area of population decline.
- Item number: AK-SG-06-01b
- Year: 2006
- DOI: https://doi.org/10.4027/slw.2006.02