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 which juvenile fall Chinook salmon that were exposed to a constant 10°C added more weight over the 14-d exposure period (1% of body weight per day [WT/d]) than fish exposed to temperatures that fluctuated from 10°C to 19.0°C (0.3% WT/d) and from 10°C to 22°C daily (0% WT/d). We conclude that the lack of difference in growth rates between the fluctuating and constant temperature regimes at daily ration levels of at least 4% stems from the facts that the rate of temperature change in this study was within the acclimation range for growth, the daily average temperatures were less than thermal optimum values, and the temperature amplitudes were within lethal limits.

Received January 16, 2010; accepted November 22, 2010

ACKNOWLEDGMENTS

The authors thank Phil Groves and Brad Alcorn (Idaho Power Company) for catching the fish used in this study. Greg Gaulke and Chris Vernon (Battelle Memorial Institute) and Jennifer Monroe (Cascade Aquatics) were responsible for fish care. Chuck Coutant provided consultation on the study design and reviewed early versions of the manuscript. Andrea Currie (Battelle) was the technical editor and made substantial improvements to the document. Numerous other Battelle staff assisted on the study; we thank all of them very much for their support. Billy Connor and two anonymous reviewers improved the quality of this paper. This study was funded by Idaho Power Company under contract 56697A. The Pacific Northwest National Laboratory is owned by the U.S. Department of Energy and operated by Battelle Memorial Institute under contract DE-AC05-76RL01830.

Notes

^a C = constant, F = fluctuating; the subscripted numerals are temperatures or temperature ranges. See text for additional details.