New Report Available:
"Decline of the Steller Sea Lion in Alaskan Waters: Untangling Food Webs
and Fishing Nets"
For more information see:
http://www.nap.edu/catalog/10576.html
The National Research Council's Ocean Studies and Polar Research Boards
have just published the report of their study on the Alaska groundfish
fishery and Steller sea lions. The study was funded by the North Pacific
Fishery Management Council at the request of Congress. The report,
"Decline of the Steller Sea Lion in Alaskan Waters: Untangling Food Webs
and Fishing Nets" is now available from the National Academy Press
http://www.nap.edu/catalog/10576.html. A short description of the
report's contents is provided below.
If you have questions about the report or the study contact:
Susan Roberts (sroberts [at] nas.edu)
Decline of the Steller Sea Lion in Alaskan Waters: Untangling Food Webs
and Fishing Nets (NRC, 2003)
There used to be hundreds of thousands of Steller sea lions in Alaskan
waters. But over the past three decades, their numbers have dwindled to
just 30,000 -- an 80 percent decline. The rapid population loss
prompted the federal government to place sea lions, from the Gulf of
Alaska to the westernmost Aleutian Islands, on the endangered species
list. In 2001, the North Pacific Fishery Management Council
commissioned a report from the National Research Council to examine the
potential causes of decline and to assess the potential impact of the
groundfish fisheries on Steller sea lions. Many hypotheses have been
proposed to explain the dramatic decline in sea lion numbers, including
reduced food availability or quality due to large-scale fishery
removals, a change in the abundance or distribution of prey species
following a climate regime shift in the late 1970s, a disease epidemic,
pollution, illegal shooting, subsistence harvest, and predation by
killer whales or sharks.
The committee's report, Decline of the Steller Sea Lion in Alaskan
Waters: Untangling Food Webs and Fishing Nets, uses several methods to
evaluate these hypotheses based on the limited data available on the sea
lion's biology and habitat. First, the report employs population and
ecosystem models to identify causes of decline that are consistent with
demographic and ecological data. The modeling exercises indicate that
food availability alone is insufficient to account for the rapid
population decline and suggests that factors reducing the survival of
adult female sea lions would most readily explain the demographic
trends. The report then uses response variable analysis to examine
indicators of sea lion health and behavior relative to the response
expected under each proposed hypothesis. This analysis revealed that top
down causes such as predation, shooting (either illegal or for
subsistence), or incidental take in fishing gear were most consistent
with the available research on Steller sea lions over the past decade.
Additional factors, including food limitation, may have contributed to
the population losses observed in the 1970 and 1980s. There is not
enough evidence to conclusively support or rule out any of the
hypotheses that have been proposed to explain the decline. Fishing
activities may change the distribution of the sea lion's preferred prey,
disturb the normal activities of sea lions, or cause the injury or death
of sea lions that become entangled in fishing gear. To resolve the
potential effects of fisheries on sea lion survival, the committee
reviewed five management strategies that could help determine the impact
of fisheries on sea lion survival. Only one -- establishing open and
closed fishing areas around sea lion rookeries -- directly tests whether
the fisheries contribute to the decline. This strategy would allow
researchers to study sea lions in relatively controlled, contrasting
environments. Properly designed, experimental open and closed fishing
areas would help fill some of data gaps in five years or less, but
long-term monitoring would be required to assess sea lion demographics
and account for environmental variability.