Background

Chinook salmon Oncorhynchus tshawytsca span a huge latitudinal gradient with populations in the Yukon River in northern Alaska all the way to populations in the Central Valley of California. Across this range juvenile fish experience a variety of different environmental conditions (climate, weather patterns, temperature, river intensity etc.) At the southern end of this range, in the Central Valley, Chinook salmon are contending with both the impacts of climate change as well as more local threats associated with expansion of agricultural, industrial and municipal lands.

Salmonids are famous for their long migration in which returning adults swim all the way back to the local river system where they hatched out 2-5 years earlier. This migration behavior (natal homing) isolates populations form one another an may allow for different populations to adapt to local environmental conditions. Furthermore, California possesses the southernmost populations of fall-run Chinook salmon, and the critically endangered winter-run Chinook salmon.

Populations of Chinook Salmon

I gathered data from eight populations of Chinook salmon. Check out their locations on the map.

The populations represent three different migratory phenologiess named for the season of adult return to freshwater.

The fall-run (red) is typified by adults returning from the ocean in the late-summer and fall months.

The spring-run (green) is typified by adults returning form the ocean from March - May. Adults historically would migrate high-up into the watersheds where waters are kept cool from snow-melt or groundwater springs and spend the summer maturing and spawn in the early fall.

The winter-run (blue) is the only remaining winter-run population in the world. They return to freshwater from January to March and would have migrated into the headwaters of the Sacramento, Pit and McCloud rivers. They spawn in May-June and their delicate eggs incubated in the cold spring-fed systems of the southern cascades. The installation of Shasta Dam eliminated access to these cold headwaters, now winter-run must spawn near Redding, CA at the onset of summer.

Populations of Studied Chinook Salmon

Many Ways to Measure Performance

To assess how temperature influences the physiology of an organism, it is important to asses multiple traits. Different traits can reveal different responses and different limitations on thermal capacity. During this experiment I assess three physiological traits, temperature dependent growth rate, aerobic metabolism and critical thermal maximum.