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Alaska Ecosystems Program

Steller Sea Lion Research, Summer 2008

Figure 1, see caption
Figure 1.  The Alaska Ecosystems Program's (AEP) Steller sea lion research area in Alaska, July–September 2008.  Outlined area shows the extent of the aerial survey for adult and juvenile Steller sea lions.  Rookeries visited during the pup capture, condition, and branding cruise are shown, along with the locations of the two field camps on Marmot and Ugamak Islands.  Click image to enlarge.

The National Marine Mammal Laboratory's (NMML) Alaska Ecosystems Program (AEP) conducted fieldwork in July–September 2008 in support of the following Steller sea lion (Eumetopias jubatus) research projects (see Fig. 1 for geographic extent of field work in summer 2008): 1) Abundance Trend Monitoring of Steller Sea Lions in Alaska, 2) Steller Sea Lion Vital Rates, 3) Steller Sea Lion Stock Structure Investigations, 4) Steller Sea Lion Foraging Ecology and Health Studies, and 5) Food Habits of Steller Sea Lions and Northern Fur Seals.

The primary field activity associated with the Abundance Trend Monitoring of Steller Sea Lions in Alaska project was an aerial survey of more than 350 terrestrial rookery and haul-out sites in Alaska, conducted 7 June–6 July, from Dixon Entrance in Southeast Alaska to Attu Island at the western end of the Aleutian Islands. The main objective of the survey was to photograph and count adult and juvenile Steller sea lions for population status and trend determination. The survey was conducted using a deHavilland Twin Otter aircraft piloted by LCDR Mark Nelson and LCDR Nicole Cabana, with assistance from mechanic Michael Merek, from the NOAA Aircraft Operations Center, in Tampa, Florida. Scientific personnel on the survey were Kathryn Sweeney (AEP) and Morgan Lynn and Jim Gilpatrick (Southwest Fisheries Science Center).

Digital images were captured with a Canon EOS-1Ds Mark III digital camera (22 megapixels), with a 50-mm f1.2 lens, using a computer-controlled mount with forward-motion compensation. Location, time, altitude (from a radar altimeter), frame number, and mount settings were automatically logged for each image. The camera was oriented vertically and images were shot through the plane's belly port, which was open to the outside. This was the first use of this camera for the survey as well as the first survey in which only digital photography was used. The 2008 nonpup survey was the most complete adult and juvenile survey since 2004. During over 90 hr of flight time, covering approximately 8,000 miles of Alaska's southern coast, 341 of the 356 known rookery and haul-out sites were surveyed, along with 167 of the 173 sites used to monitor population trends. Results from the survey will be available in November 2008.

Estimation of survival and reproduction (vital rates) is fundamental to understanding any potential cause of the decline of the Steller sea lion population in Alaska and provides a mechanism to monitor their recovery. Mark-recapture (or resighting) studies are the best way to determine vital rates by sex, age, region, and cohort. The AEP reinitiated marking studies in 2000 by hot-branding pups born on two rookeries (Marmot and Sugarloaf) in the central Gulf of Alaska near Kodiak. In subsequent years, pups were branded on two rookeries near Prince William Sound (Fish and Seal Rocks) and another in the eastern Aleutian Islands (Ugamak). Through 2005, a total of 1,449 pups had been branded. No pups were branded in 2006 and 2007, pending the completion of an Environmental Impact Statement on Steller sea lion research activities written in response to a lawsuit filed by the Humane Society of the United States.

The AEP conducted three field projects in summer 2008 that contributed significantly to the Steller Sea Lion Vital Rates research project:

Pup capture, branding, and condition cruise aboard the U.S. Fish and Wildlife Service research vessel Tiglax, 24 June–7 July 2008, between Dutch Harbor and Homer, Alaska: AEP personnel on the cruise included Kate Call, Brian Fadely, Tom Gelatt, Carey Kuhn, Michelle Lander, Jeremy Sterling, Jim Thomason, and Rod Towell. Other participants included Eric Boerner and Bob Caruso (both of NMML), Kimberlee Beckman (DVM, Alaska Department of Fish and Game), and Heather Harris (DVM, The Marine Mammal Center). As part of the vital rates project, 178 pups were hot-branded with individual marks at Sugarloaf Island (5 July; N = 93) and at Marmot Island (6 July at Beach 4; N = 85). Each pup was also weighed, measured, and sexed, and skin and blood samples were taken from a subsample as part of the Steller Sea Lion Stock Structure Investigations and Steller Sea Lion Foraging Ecology and Health Studies projects, respectively. Approximately 50 pups were also weighed, measured, and sexed at each of six rookeries in the eastern Aleutian Islands, western Gulf of Alaska, and central Gulf of Alaska (Akutan/Cape Morgan, Sea Lion Rocks, Clubbing Rocks, Pinnacle Rock, Jude, and Chowiet); in addition, skin and blood samples were taken from approximately 25 of these pups. Scat samples were also collected at rookeries as part of the Food Habits of Steller Sea Lions and Northern Fur Seals research project.

Resightings of branded sea lions from the chartered research vessel Norseman, 17 June–11 July 2008, between Dutch Harbor and Seward, Alaska: AEP personnel on this cruise included Sara Finneseth, Lowell Fritz, and Carolyn Gudmundson. Steller sea lions were observed at more than 100 rookery and haul-out sites between the eastern Aleutian Islands and Prince William Sound. A total of 207 individual branded sea lions were observed and positively identified; 160 were branded as pups within the range of the endangered western population (west of 144°W through Alaska and Russia), 14 were branded as pups within the range of the threatened eastern population (east of 144°W through Southeast Alaska, British Columbia, Washington, Oregon, and California), and 33 were branded as juveniles captured on land or at sea away from their natal rookery. In addition, particular attention was paid to the observation of 72 marked adult females to determine whether they had given birth in 2008 or in a previous year (if they were observed nursing a juvenile). Cruise participants assisted with branding operations at Sugarloaf and returned to the site the following day to monitor post-disturbance recovery at the rookery.

Resightings of branded sea lions by observers based at field camps on Marmot and Ugamak Islands, late May–early August 2008: Jason Jones and Paula von Weller were stationed at the south end of Marmot Island from 28 May to 28 July 2008, where they identified 138 individual, branded animals for survival analyses; 28 of these animals were adult females, which were also monitored for reproductive activity. Kathryn Chumbley (AEP), Naomi Worcester, and Alyse Forrest were stationed at the north end of Marmot Island from 28 May to 28 July 2008. They identified 110 individual, branded animals for survival analyses, 16 of which were adult females. Perry Comolli, Mary Malley, and Rebecca Scott were stationed on Ugamak Island from 2 June to 31 July 2008, where they identified 141 individual, branded animals (including 42 adult females) for survival analyses. In addition to looking for branded animals, field camp scientists also counted animals on each haulout and rookery beach as frequently as weather permitted and conducted behavior scans. Personnel on Marmot Island also monitored the recovery of the rookery at Beach 4 following the research disturbance associated with pup branding on 6 July.

By Lowell Fritz

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