The decline and fall of seals and sea
lions in Alaska: Is the carrying capacity of the
North Pacific Ocean decreasing?
Andrew W. Trites, Ph.D.
Marine Mammal Research Unit
University of British Columbia
Vancouver, B. C.
Wednesday, February 25, 1998
3:30 p.m.Pacific Forum
Significant declines have occurred in the numbers of harbor seals, northern fur seals,
and Steller sea lions in Alaska. These declines have been so abrupt that the Steller sea
lions were declared an endangered species, while northern fur seals were classified as
My talk will focus primarily on northern fur seals that breed on the Pribilof Islands
(in the Bering Sea) and migrate as far south as California. I will also briefly present
some of the recent insights we have gained from an ecosystem model of the Bering Sea, as
well as discuss some aspects of our ongoing captive and field-research program into
Steller sea lions.
A leading hypothesis in the decline of the Alaskan pinnipeds is that they are
nutritionally stressed. If this is true, there should be noticeable changes in their
I examined the standard body lengths of subadult males harvested on St. Paul Island
that have been measured sporadically since 1911. I also collected three years of
measurements (1995-1997) from subsistence-killed animals to test whether animals are
physically smaller today than in the past.
The relationship I found between body length and population size suggests that the
current fur seal population may be the maximum sustainable in today's Bering Sea/Gulf of
Alaska ecosystem, which is half of what it was 50 years ago. Concurrent declines in
numbers of harbour seals and Steller sea lions in these regions, as well as reduced body
growth of Steller sea lions, all suggest that pinniped carrying capacity is significantly
lower now than it was in the past.
evolution of single-cell eukaryotes
Last updated: December 19, 2000