Figure 1.
Sampling sites within the Wood River Lakes, southwest Alaska, USA.
Table 1.
Some properties of the six streams and populations.
Table 2.
Factors potentially driving inter-population variation in senescence rates.
Figure 2.
Population-specific predator selectivity for fish of different in-stream ages.
Shown are proportions of the available fish of a given in-stream age (i.e., individuals that survived to day d) that are killed by bears in each creek. Our estimate of predator selectivity was the average of the predation rates on the first three days in the stream (i.e., the average of the first three points in each panel, see Electronic Supporting Information, Text S1). Note that the probability of being killed decreased within increasing in-stream age in Hansen and A creeks (i.e., bears killed salmon showing little senescence), but increased to varying degrees in Bear, Hansen, Pick, and Yako creeks (i.e., bears killed salmon showing more advanced senescence).
Table 3.
Candidate models explaining variation in senescence.
Figure 3.
Population-specific hazard functions (y-axis) plotted against in-stream age (x-axis). These functions are based on a mean day of entry and on population-specific day of entry parameters. The higher the hazard for a given in-stream age, the greater the senescence rate at that age. The slopes of these lines represent variation in the shape of the hazard function (α) and the elevation of the lines represent variation in their magnitude given the shape (λ).
Figure 4.
Senescence rates (ω±95% confidence intervals generated from likelihood profiles, [42]) plotted against (A) predator selectivity for salmon that show little senescence (± SE across the first three days in the stream) and (B) predation rate (± SE across years). For both plots, the line represents the predicted senescence rates from an ordinary-least squares regression.
Table 4.
Parameter estimates for the best model.
Table 5.
Candidate models for explaining inter-population variation in senescence.
Figure 5.
Photographs showing breeding sockeye salmon in various states.
Panel A shows newly arrived sockeye salmon that show little senescence. Note their bright red coloration. Panel B shows a bear-killed male salmon. Panel C shows a senescent male (top) and female (bottom) salmon. Note their frayed fins, drab coloration, and general emaciated appearance relative to the newly arrived fish. Panel D shows salmon that have stranded in an area of low water (bottom left corner of panel D). Photographs by Ranae Holland (A), Stephanie Carlson (B,C), and Neala Kendall (D).