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Southeast Alaska Steller Sea Lion
Prey Study
Michael F. Sigler
(907) 789-6037
Mike.Sigler@NOAA.GOV
Note: This project is a cooperative project with the Alaska
Fisheries Science Center's Auke Bay Laboratory and the National Marine
Mammal Laboratory, the University of Alaska, the University of British Columbia, and the Alaska Department of Fish And
Game.
Steller sea lion abundance is decreasing in central and
western Alaska, but is increasing in southeast Alaska. This study
conducts seasonal measurements of prey abundance and nutritional quality
in southeast Alaska and is designed as a comparison to similar studies
from around the Kodiak Archipelago and a study proposed for the Krenitzin Islands (Unimak
Pass area).
Objectives:
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Seasonally measure prey abundance
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Nutritional energy and nutritional
quality
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Compare prey characteristics between
sea lion foraging regions
Methods:
The methods employed include acoustic and mid-water trawl
surveys, jigging, Remotely Operated Vehicle surveys and beach seine surveys, chemical analyses of prey energy
density and nutritional quality, scat collections (UBC & UA), aerial
surveys of sea lion haulouts (UA), and satellite tagging of sea lions (ADF&G,
NMML).
VIEW:
Nutritional Analyses Diagram
Mid-water trawl
surveys
Principal fish species
ROV and beach seine
surveys
Scat
collection
Aerial survey map
Map of satellite
tagging
Study Sites:
View Map of Alaska
Map of Southeast Alaska
Results and Conclusions
Some preliminary conclusions are:
1. Prey abundance is concentrated: 45-75% of prey
was concentrated in 10% of Frederick Sound during May, September, and
December 2001.
View
prey abundance
2. Overwintering herring aggregations in Frederick
Sound and lower Lynn Canal may be important energy sources for Steller
sea lions during winter. Herring were concentrated and found
throughout winter 2001/2002 at certain, known locations (e.g. on the
east side of Benjamin Island- a seasonal Steller sea lion haulout
located on the west side) and were at their highest energy density of
the year.
View herring
concentrations
3. Spawning aggregations of eulachon appear to be
important energy sources for Steller sea lions during spring. Peak
sea lion abundance at Berners Bay, the site of a eulachon pre-spawning
aggregation, was 949 animals. Sea lion abundance increased as
eulachon began concentrating in Berners Bay, peaked as eulachon
abundance peaked, and decreased as the eulachon moved up river.
Eulachon energy density was greatest during the period of highest sea
lion abundance.
View eulachon and
sea lion abundance
4. Steller sea lions eat 16 fish species that were
captured in nearshore waters. In summer, some of the most abundant
species that were captured also had the highest frequency of occurrence
in Steller sea lion scat (overall, 37 fish species were available in
summer and 25 species in winter). Of the total fish captured, 99% were
caught in summer. The nearshore provides important habitat for Steller
sea lion prey, especially in summer. Lower available prey in winter may
force Steller sea lions to travel farther from haulouts to forage.
View jig catch
data
View seine
catch data
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