Results of Steller Sea Lion Surveys in Alaska, June-July 2018

December 04, 2018

The Marine Mammal Laboratory (MML) conducted aerial- and ship-based surveys to count Steller sea lion (Eumetopias jubatus) pups (~1 mo old) and non-pups (adults and juveniles ≥ 1 year old) on terrestrial rookery and haulout sites in Alaska in June-July 2018. The occupied aircraft survey team conducted their survey from 23 June to 11 July 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 21 June to 4 July 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 27 June 2018.

Abundance surveys to count Steller sea lions are conducted in late June through mid-July starting ~10 days after the mean pup birth dates in the survey area (4-14 June) after ~95% 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 (USFWS) 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).

Last updated by Alaska Fisheries Science Center on 12/04/2018

Steller Sea Lion Alaska Ecosystems Program Steller Sea Lion Research