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2023 Results Of Steller Sea Lion Surveys In Alaska

December 20, 2023

The Alaska Fisheries Science Center’s Marine Mammal Laboratory (MML) conducts annual crewed aircraft and vessel surveys to known terrestrial Steller sea lion rookery and haulout sites in Alaska to collect visual counts and high-resolution imagery.

In 2023, MML survey teams collected counts from 82 sites in the Aleutian Islands, totaling 11,522 non-pups and 3,868 pups. We used agTrend (R package) to model all raw count data through 2023 to estimate modeled counts (as an index of abundance) and annual rates of change since 2008. Between 2008 and 2023, non-pups and pups in the western distinct population segment (DPS) of Alaska increased 1.09 and 0.64% y-1, respectively; however, there was high variability among regions. The estimated model count for non-pups and pups for the population in 2023 was 39,051 and 12,539, respectively. Non-pups and pups in the western Aleutian Islands region declined significantly (-5.69 and -3.98% y-1, respectively), along with pups in the neighboring central Aleutian Islands region (-1.97% y-1). Non-pups in the central Aleutian Islands region were stable (-0.11% y-1, confidence intervals -1.75-1.81% y-1) over the last 15 years; however, model uncertainty was high in the eastern portion of this region due to low survey coverage in recent years (due to inclement weather, survey logistics, and mechanical issues). In the eastern Aleutian Islands region, non-pups and pups increased significantly (2.14 and 1.48% y-1, respectively) between 2008 and 2023. For the Aleutian Islands regions combined, declines in the western and central Aleutian Islands regions were largely offset by the increasing eastern Aleutian Islands; non-pups increased 0.91% y-1 while pups were stable. It is evident that the status of the western Steller sea lion DPS in Alaska remains variable, and support for regular surveys of this challenging and large geographic area is critically important to the monitoring and recovery of this population.

Last updated by Alaska Fisheries Science Center on 12/20/2023