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Alaska Ecosystems Program

Steller Sea Lion Survival and Vital Rates Research, Summer 2009

figure 1 map, see caption
Figure 1.  Locations of NMML Steller sea lion field camps in Alaska.

The National Marine Mammal Laboratory's (NMML) Alaska Ecosystems Program (AEP) conducted Steller sea lion (Eumetopias jubatus) population and abundance research at remote Alaska field camps and from a chartered vessel during May–August 2009. This ongoing research is part of the AEP's Abundance Trend Monitoring and Vital Rates Investigations.

Vital rates (reproduction) and survival estimates are essential to understanding any potential cause of the decline of the Steller sea lion population in Alaska and provide a mechanism to monitor sea lion recovery. Mark-recapture (or resighting) studies are the best way to determine vital rates by sex, age, region, and cohort. The AEP conducted two field projects in summer 2009 that contributed significantly to these important research goals.

Marmot Island Beach 4 rookery
Figure 2.  Marmot Island Beach 4 rookery from the cliff-top observation site.  Photo by Cameron Hinman.

NMML has been branding pups in the central Gulf of Alaska near Kodiak Island (on Marmot and Sugarloaf Islands) since 2000 and in the eastern Aleutian Islands near Dutch Harbor (Ugamak Island) since summer 2001. In subsequent years, pups were also branded on two rookeries near Prince William Sound (Fish and Seal Rocks). Through 2009, 1,815 pups have been branded. No pups were branded in 2006 and 2007 due to a lawsuit filed by the Humane Society of the United States.

Remote field camps, staffed by a field team of two to three biologists, are located on Marmot Island (Beach 4 and Beach 7) and Ugamak Island (Fig. 1) from late May to early August. Weather permitting, counts by age group and sex, brand resights, and observations of reproductive status and behavior are conducted daily throughout the 2-month field season from the edge of high cliffs (400-1,000 ft), using high-powered spotting scopes and binoculars (Figs. 2, 3).

During the 2009 field season, Marmot Island field camp participants Jennifer Schmitt and Susannah Spock were stationed at the south end of Marmot Island (Beach 7), where they identified 59 individual, branded animals for survival analyses; 22 of these animals were adult females, which were also monitored for reproductive activity.

Kathryn Chumbley, Cameron Hinman, and Katie Luxa were stationed at the north end of Marmot Island (Beach 4), and they identified 55 individual, branded animals for survival analyses, 24 of which were adult females.

Kenady Reuland, Rebecca Scott, and Jessica Farrer were stationed on Ugamak Island, where they identified 322 individual, branded animals for survival analyses, 25 of which were adult females.

Biologists on Ugamak Island also monitored the recovery of the rookeries at the South and North beaches, following the research disturbance associated with pup branding on 24–25 June 2009.

  branded Steller sea lion
Figure 3.  Branded, female Steller sea lion, T13, with her pup on Marmot Island.  Photo by Naomi Worcester.

In addition to research conducted at the field camps, resightings of branded Steller sea lions were conducted from the chartered research vessel Norseman, 28 May–11 June 2009, in the eastern Aleutian Islands and western Gulf of Alaska: AEP personnel on this cruise included Sara Finneseth, Lowell Fritz, and Kathryn Sweeney.

Steller sea lions were observed at 40 rookery and haul-out sites in the eastern Aleutian Islands and the western Gulf of Alaska. In total, 57 individual, branded Steller sea lions were observed and positively identified; 52 of these were branded as pups within the range of the endangered western population (west of long. 144°W throughout Alaska and Russia), and 5 were branded as juveniles captured on land or at sea away from their natal rookeries. In addition, 111 food-habits samples (scats) were collected at five locations.

By Kathryn Chumbley

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