Chinook salmon emergence phenotypes: Describing the relationships between temperature,emergence timing and condition factor in a reaction norm framework

Water temperature can have a profound influence on development and distribution of aquatic species. Salmon are particularly vulnerable to temperature changes because their reproductive and early development life phases are spent in freshwater river systems where temperature fluctuates widely both daily and seasonally. Flow regulation downstream of dams can also cause temperature regime changes, which in turn may spur local adaptation of early life‐history traits. In a common garden laboratory incubation experiment, we exposed spring Chinook salmon (Oncorhynchus tshawytscha) embryos to four temperature regimes: warm stable, cold stable, daily variation and below dam. We found that fry from warmer thermal regimes emerged earlier than those from colder regimes both in terms of calendar date and temperature units and that warmer temperatures caused fry to emerge less developed. There was also a significant effect of family on both emergence timing and development level at emergence. By combining measurements of physiological and behavioural traits at emergence and interpreting them within a reaction norm framework, we can better understand which populations might be more vulnerable to altered thermal regimes.