The Marine Mammal Laboratory (MML) conducted aerial- and ship-based surveys to count Steller sea lion (Eumetopias jubatus) pups (approx. 1 month old) and non-pups (adults and juveniles ≥ 1 year old) on terrestrial rookery and haulout sites in Alaska in June to July 2018. The occupied aircraft survey team conducted their survey from June 23 to July 11 between the Shumagin Islands (161°W) in the western Gulf of Alaska (GULF) region and Tanaga Island (178°W) in the central Aleutian Islands (ALEU) region. The ship-based survey team conducted visual counts and used an unoccupied aircraft system (UAS or drone), to survey from June 21 to July 4 in the Aleutian Islands between Adak Island (176°W) and Attu Island (172°E). In addition, the Alaska Department of Fish and Game (ADFG) counted Steller sea lions from land on Round (Walrus) Island in Bristol Bay (eastern Bering Sea) on June 27, 2018.
Abundance surveys to count Steller sea lions are conducted in late June through mid-July starting approximately 10 days after the mean pup birth dates in the survey area (June 4–14 ) after approximately 95 percent of all pups are born (Pitcher et al. 2001; Kuhn et al. 2017). MML’s objectives for 2018 were to survey all terrestrial rookery and haulout sites in the Aleutian Islands and western Gulf of Alaska, as well as opportunistically in the eastern and central GULF regions (especially rookeries and major haulouts) because of the anomalous pup decline observed in these regions during the 2017 survey (Sweeney et al. 2017).
The occupied aircraft survey team operated from a NOAA Twin Otter fixed-wing aircraft equipped with three high-resolution digital cameras (as in 2009–2017; see Fritz et al. 2016). The team captured imagery or conducted visual counts (when less than 10 sea lions were present) from west of the Shumagin Islands to Tanaga Island, and two major haulouts in the central Gulf of Alaska (Fig. 1). The ship-based survey team worked off the U.S. Fish and Wildlife Service (U.S. FWS) R/V Tiĝlâx to survey the Aleutian Islands from the Delarof Islands to Attu Island. Observers conducted sea lion counts from the research vessel offshore (either a single counter or mean counts of 2–3 observers are reported); or from aerial images captured using the UAS (i.e., APH-22 hexacopter). MML analyzed aerial images captured with the UAS and Twin Otter camera array as in previous years (see Fritz et al. 2016).