2013 Results of Steller Sea Lion Surveys in Alaska

Aerial and ship-based surveys to count Steller sea lion (Eumetopias jubatus) pups and non-pups (adults and juveniles) on land in Alaska were conducted by the National Marine Mammal Laboratory in June to July 2013. The aerial photographic survey was conducted from 22 June to 9 July, and targeted all known haul-out and rookery sites in the eastern distinct population segment (DPS) in southeast Alaska from Dixon Entrance to 144°W as well as the eastern portion of the western DPS from 144–163°W. Ship-based survey effort was conducted from June 21 to July 8 at selected sites in the Aleutian Islands between 165°W and 172°E.

Aerial surveys to count Steller sea lions are conducted in late June through mid-July starting at least 10 days after the mean birth dates of pups in the survey area (June 4–14; Pitcher et al. 2001). The primary objective in 2013 was to survey all terrestrial rookery and haul-out sites from southeast Alaska (eastern DPS) into the western DPS from the eastern Gulf of Alaska to the western Gulf of Alaska (Figure 1). A NOAA twin Otter aircraft equipped with three high resolution digital cameras was used as in 2009–2012 (Fritz et al. 2013). In 2013, 178 of the 196 targeted sites were successfully surveyed: 65 of 66 sites in southeast Alaska (one site missed due to fog), all 89 sites in the eastern and central Gulf of Alaska, and 24 of 41 sites in the western Gulf of Alaska. In the western Gulf, six sites were avoided due to close proximity (within 50 nm) to the active volcano at Mt. Veniaminof and 11 sites with recent histories of no sea lion presence during the summer breeding season were skipped due to restricted flight hours. The rookery at Atkins Island in the western Gulf of Alaska was only partially surveyed in 2013, with the cobble beach area missed. Counts of sea lions on the cobble beach area from 2011 (116 pup and 245 non-pups) were added to the 2013 count to yield a total Atkins estimate that was used in the trend analyses. Aerial photographs were analyzed as in previous years (see Fritz et al. 2013). Two researchers conducted aerial survey counts and means are reported. Ship-based surveys utilized the USFWS RV Tiĝlâx, and consisted of direct counts (means of 2–3 observers reported) from land-based overlooks, skiffs or the research vessel at 28 sites (Figure 2). Trends in pup and non-pup counts were estimated using agTrend (Fritz et al. 2013; Johnson and Fritz in review) which utilizes data from all sites with at least two non-zero counts between 1990 and 2012.