Figure 1.
Map of the Fraser River watershed.
Map of the Fraser River watershed, with Early Stuart sockeye salmon spawning grounds highlighted with an ellipse. The locations of Hell's Gate, Qualark, and Hope (lower river) are also shown.
Figure 2.
Inter-annual and intra-annual patterns in river temperatures and flows.
(A) Average July water temperature at Qualark as a function of year. Dark line indicates significant (P<0.01) linear trend towards increasing temperatures (slope = 0.04°C year−1). (B) Mean temperature and discharge (±2 SD, dotted lines) for the lower Fraser River for June–October from 1961–1990 (red lines) and from 1991–2009 (blue lines). The shaded area indicates a symmetric 31-day period around the historical median run timing date for Early Stuart sockeye (July 14).
Figure 3.
Survival functions used as inputs to simulations.
(A) Temperature-survival functions explored. Solid sigmoid curve was used to generate the main results reported in Figs. 4&5. Simulations were also run using the dotted sigmoid curves to explore the sensitivity of the results to the inflection point (T50) and slope (b) parameters of the sigmoid function (results presented in supplementary figure S1). (B) Sigmoid curves used to characterize the relationship between migration survival and maximum river flow. For the main results reported in Figs. 4&5, no effect of flow was modeled (dark line). The sensitivity of these results to including a flow effect was then tested using two alternative survival curves (dashed curves). Note that survival is necessarily zero when there is no river flow (0 m3/s), but summer flows close to zero are extremely unlikely to occur in our model.
Figure 4.
Projected evolutionary trajectories for each warming scenario.
Projected future evolutionary changes, averaged across 100 replicate model runs, in mean migration timing (days relative to the historic median Hell's Gate migration date of July 14) for different simulated river warming scenarios, assuming no flow effect on survival (i.e., PF = 1). Black curves: heritability (h2) of migration timing = 0; red curves: h2 = 0.25; green curves: h2 = 0.5; blue curves: h2 = 0.75.
Figure 5.
Effects of evolution on quasi-extinction risk.
Probability of quasi-extinction as a function of the rate of river warming, assuming no flow effect on survival. Data points show means of 100 replicates; curves are best sigmoid fits to data. Black curve: heritability (h2) of migration timing = 0; red curves: h2 = 0.25; green curves: h2 = 0.5; blue curves: h2 = 0.75.
Figure 6.
Sensitivity of main results to flow effects.
Sensitivity of results to including a flow effect on migration survival. Left panels show projected evolutionary changes in mean migration timing for a scenario where mean river temperature increases by 2°C by 2100, assuming either a steep flow effect (A) or a shallow flow effect (C) on migration survival. Right panels show probability of quasi-extinction across all river warming scenarios for the same steep (B) and shallow (D) flow effects on survival. The default sigmoid temperature-survival curve (dark curve in Fig. 3B) was used in all cases. Data points show means of 100 replicates; curves are best sigmoid fits to data. Black curves: heritability (h2) of migration timing = 0; red curves: h2 = 0.25; green curves: h2 = 0.5; blue curves: h2 = 0.75.
Figure 7.
Effect of phenotypic variance on evolutionary trajectories and population persistence.
Total change in mean migration timing by 2100 relative to the historic median (A) and probability of quasi-extinction by 2100 (B) as functions of the phenotypic standard deviation in migration timing. Currently, the phenotypic standard deviation in migration timing for Early Stuart sockeye salmon is approximately 7 days. Data points show means of 100 replicates; curves are best linear or quadratic fits to data. Black curves: heritability (h2) of migration timing = 0; red curves: heritability = 0.25; green curves: heritability = 0.5; blue curves: heritability = 0.75.