Workshop on Role of Contaminants in Steller Sea Lion Decline
The Auke Bay Laboratory (ABL) sponsored a workshop in Anchorage, Alaska,
on 5-6 September 2001 to evaluate the possible role of contaminants in
the decline of the Steller sea lion population. Participants included
representatives from the Alaska Department of Fish and Game (ADF&G), National
Marine Mammal Laboratory (NMML), National Institute for Status and Trends,
Canada Department of Fisheries and Oceans, World Wildlife Federation, and
several universities. Presentations included 1) an evaluation of the nutritional
limitation hypothesis; 2) contaminant trends in murres, sea lions, seals,
and killer whales from the northern Gulf of Alaska, 3) impacts of contaminants
on immune function in marine mammals; and 4) discussion of other biomarkers
that may be useful indicators of exposure.
The meeting will produce a proceedings and provide NMFS with a basis for
developing a detailed science plan for a focused research effort. The
primary consensus was that low-level but widespread atmospheric pollution
is present in the North Pacific Ocean, and for those species with long
lives and fish as a major prey item, pollution may well be a contributing
cause of recruitment problems. Systematic data collections are rare, but
the few data points available for Steller sea lions indicate that they
have contaminant loads. Steller sea lions have a biology consistent with
this potential problem. There was consensus among the workshop participants
that pollutants should be seriously considered as a threat to these species
and that further research is warranted.
By Stan Rice.
Second Frederick Sound Cruise of Southeast Alaska Steller Sea Lion Prey
The second cruise in Frederick Sound for the Southeast Alaska Steller sea
lion prey study was completed during 4 - 17 September 2001 using the chartered
fishing vessel Solstice. The purpose of the Frederick Sound Steller sea
lion prey study is to test the hypothesis that juvenile sea lion prey diversity
and seasonality are related to Steller sea lion population trends and to
provide a comparison to a similar study conducted off Kodiak Island by
the University of Alaska. During the September cruise, prey abundance
was measured using echo-integration and a midwater trawl. Scat was collected
from sea lion haul-out areas for diet analysis. Fish also were collected
for proximate and free fatty acid analysis. Prior to the cruise, ADF&G
staff tagged sea lions in the area with radio tags. The location information
from these tagged animals was very helpful for conducting the cruise.
Mostly juvenile walleye pollock and Pacific herring were found at depths
less than 75 m, adult walleye pollock were found from 75 to 250 m, and
Pacific whiting were found deeper than 250 m.
Both day and night sampling were conducted to determine if fish available
at sea lion foraging depths were affected by time of day. Unlike the previous
cruise in May 2001, there was a substantial difference in the day-night
depth distribution found during the September 2001 cruise. During the
day in September, relatively few fish were found at depths less than 75
m, but during the night juvenile herring and pollock were found at these
depths. Sea lions were found at two haulouts in Frederick Sound near The
Brothers (Sail Island and Southwest Brothers Island); the number hauled
out totaled about 600 animals. The sea lions were at the haulouts during
day, leaving the haulouts at night to feed in near-surface waters (based
on two nights observation at Southwest Brothers Island). Quarterly sampling
is planned for the Frederick Sound study area; the next cruise is scheduled
for December 2001.
By Mike Sigler.
Sleeper Shark - Steller Sea Lion Predation Cruise Completed
A sleeper shark - Steller sea lion predation study is being conducted to
determine whether sleeper sharks prey on Steller sea lions and, if they
do, to estimate the predation rate. The first cruise was conducted by ABL
scientists from 30 July to 11 August 2001. The chartered fishing vessel Norska deployed longline gear to capture sleeper sharks adjacent to Steller
sea lion rookeries at Seal Rocks, Outer Island, Sugarloaf Island, and Marmot
Island in the central Gulf of Alaska (GOA). Samples were collected for
diet analysis, and archival tags were deployed to investigate sleeper shark
habitat utilization. One hundred eight sleeper sharks were caught and
ninety-nine sacrificed for samples during the August 2001 cruise. Archival
tags were attached to nine sharks; three were programmed to release from
the tagged sharks on 1 November 2001, three on 1 February 2002, and three
on 1 July 2002. The archival tags will provide time, depth, and temperature
data over several months and will detail the diurnal and seasonal behavior
of individual sharks of the GOA in a way never before possible. Stomach
contents and tissue samples were frozen for subsequent analysis. Preliminary
onboard stomach analysis revealed no sea lion tissue. Eleven percent of
the sleeper shark stomachs contained what appears to be cetacean tissue.
Unknown marine mammal tissue samples will be sent to the Southwest Fisheries
Science Center for micro-satellite DNA analysis for species determination.
Stomachs collected during the cruise will be processed during fall 2001.
The next cruise for this study is scheduled for May 2002.
By Lee Hulbert and Mike Sigler.
quarterly Jul-Sept 2001 sidebar
Auke Bay Lab