The Effect of Fluctuating Temperatures and Ration Levels on the Growth of Juvenile Snake River Fall Chinook Salmon

Abstract Determining the fate of juvenile fish that are exposed to elevated temperatures is complicated by the fact that the optimum temperature for the growth and survival of salmonids decreases as the amount of food becomes restricted. In this study, naturally produced juvenile Snake River fall Chinook salmon Oncorhynchus tshawytscha were fed daily ration levels of 1, 4, or 8% of their body weight and exposed to either constant temperatures (10–14°C) or fluctuating temperatures that mimicked the heating rate (1.5°C/h) and maximum daily temperatures (19–23°C) of entrapment pools that form along the shoreline downstream of Hells Canyon Dam when river flows are altered to meet electric power demand. The survival rate for all groups was 99.9%, and there was no evidence that juvenile fall Chinook salmon fed reduced rations and exposed to constant temperatures grew to a greater extent than juvenile fall Chinook salmon exposed to fluctuating temperatures. The only exception was with the 1% ration level in whic...