Individual condition indicators of thermal habitat quality in field populations of redband trout (Oncorhynchus mykiss gairdneri)

We monitored redband trout (Oncorhynchus mykiss gairdneri) physiological status in multiple streams across eastern Oregon, USA that exhibit various summer thermal profiles. Summer river temperatures were higher overall in 2009 than in 2010. Heat shock protein 70 (hsp70) levels in both liver and fin tissue from redband trout increased with temperature regardless of location. Lipid levels were lower in fish from waters above 23 A degrees C (in terms of degree-day exposure), and lipids were also related to food availability in 2010. Overall, fish ate more in 2009 than in 2010. Fish size increased more rapidly, and lipids were higher and hsp70 was lower in the cooler Crooked River relative to streams in the John Day River system, though the Crooked River did not have the highest food available. While food availability plays a role in physiological health, our data suggest that temperature is the most influential factor driving growth and energy reserves in stream salmonids during high temperature months; we argue that monitoring physiological indicators in individual fish can serve as a useful proxy for overall thermal habitat quality and population status.