Fig 1.
Map of the study area (inset) in the eastern Gulf of Alaska.
The division of Steller sea lion populations into the eastern and western distinct population segments at 144° west longitude, as well as other subpopulations is noted.
Fig 2.
Male and female survival parameters used in the life table matrices for estimates of Steller sea lion population trends in the eastern Gulf of Alaska.
Age 1 survival was specific to year, while survival to ages 2+ varied between the sexes but was the same across years based on published data (Maniscalco 2014, Maniscalco et al. 2014) and a beta distribution on age. See S1 Table for complete age-specific survival rates of males and females used in this analysis.
Table 1.
Life table population estimates for females (F) and the total age 1+ male and female population (MF).
Starting population in 2002 based on survey counts in the EGOA (DeMaster 2009, 2011).
Fig 3.
Population trend for Steller sea lions estimated from life tables (Table 4.2; black diamonds ±95% CI: r2 = 0.987, P < 0.001), census counts across the eastern Gulf of Alaska (open squares), and Chiswell Island census counts (open triangles).
Fig 4.
(a) Density-independent projections (95% C.I.) of the Steller sea lion population in the eastern Gulf of Alaska based on bootstrapped values of fecundity and survival observed over the years 2003–2012. (b) Projected population trend (95% C.I.) for Steller sea lions in the eastern Gulf of Alaska based on an intrinsic rate of increase of r = 0.059 and carrying capacity of K = 10,000 age 1+ males and females.
Fig 5.
Expected change in λ based on proportional changes to individual vital rates (λ less than 1 indicates a declining population).
Fig 6.
Population projections to 2040 based on multiple changes in vital rates.
Left to right represents reductions in adult survival from 100% to 95% to 90%, whereas top to bottom represents reductions in juvenile survival from 100% to 95% to 90%, of current estimates. The dark line within each graph represents no change in current rates of fecundity, whereas the lower 3 dotted lines represent change in fecundity to 90%, 80%, and 70% in decreasing fashion. Note different scales in the y-axes.