PNNL

Abstract

Determining the fate of juvenile fish that are exposed to elevated temperatures is complicated by the fact that the optimum temperature for growth and survival of salmonids declines 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°C to 14°C) representative of the main river channel or exposed to fluctuating temperatures that mimicked the heating rate (1.5°C/h) and maximum daily temperatures (19°C to 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 fluctuating temperatures did not affect survival within any ration level relative to the constant temperature control group. 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 in the 1% ration level in the 10°C series in which juvenile fall Chinook salmon that were exposed to a constant 10°C added more weight over the 14-d exposure period (1% WT/d) than those fish exposed to temperatures that fluctuated from 10°C to 22°C daily (0% WT/d). Assuming ration levels are equal in the two habitats and that temperatures in the entrapment areas do not fluctuate outside the range of 10-14°C to 19-23°C, then our results show that juvenile Snake River fall Chinook salmon caught for up to 14 d in entrapment pools downstream of Hells Canyon Dam would survive and grow as well as juvenile fall Chinook salmon that remained in the main Snake River.