Big dams and salmon evolution: changes in thermal regimes and their potential evolutionary consequences

Area of Science:

• * Ecology and Evolutionary Biology
• * Fisheries Science
• * Environmental Science

Background:

• * Hydropower dams significantly alter aquatic environments, affecting fish species of economic importance.
• * Chinook salmon (Oncorhynchus tshawytscha) populations are particularly vulnerable to these environmental modifications.
• * Dams cause seasonal water temperature shifts, influencing fish physiology and life cycles.

Purpose of the Study:

• * To analyze the impact of dam-induced thermal changes on Chinook salmon.
• * To predict the evolutionary consequences of altered thermal regimes on salmon fitness.
• * To investigate the role of embryonic development sensitivity in dam impacts.

Main Methods:

• * Conducted a sensitivity analysis of fitness consequences.
• * Modeled the effects of thermal changes mediated by embryonic development.
• * Examined temperature alterations in the Rogue, Willamette, Cowlitz rivers, and Fall Creek.

Main Results:

• * Dams decreased summer temperatures and increased fall/winter temperatures.
• * Predicted a decrease in mean fitness for Chinook salmon post-dam construction on the Rogue River.
• * Identified potential selection for compensatory strategies like delayed spawning or slowed embryonic development.

Conclusions:

• * Dam-induced thermal changes pose significant fitness challenges for Chinook salmon.
• * Evolutionary pressures may favor adaptive strategies in salmon populations.
• * Dams disproportionately affect late-spawning salmon, highlighting the need for further research on environmental perturbation impacts.