Adult bull, fremale, and juvenile Steller sea lions.
The western stock of Steller sea lion
(Eumetopias jubatus) and the northern fur seal (Callorhinus
ursinus) are sympatric over large portions of their ranges in Alaskan
waters, and both have declined substantially over the past 30 years. These
population declines have resulted in a listing of ‘endangered’ for
the western Steller sea lion under the Endangered Species Act, and of ‘depleted’ for
the northern fur seal under the Marine Mammal Protection Act.
Though
both share some common traits, significant differences exist in body size
(northern fur seals are much smaller than similarly aged Steller sea lions),
life history traits, and in how each utilizes the marine environment. Exploring
the interrelationship among these traits and environmental variables may
help elucidate underlying environmental or anthropogenic factors affecting
survival and reproductive rates, and hence population trends, of these two
species.
This article presents results of the most recently completed Steller sea
lion and northern fur seal abundance
surveys and examine their population trends from 1976 through 2005.
