The Effect of Elevated Holding Temperatures on Adult Spring Chinook Salmon Reproductive Success

Abstract

A three-pronged study was designed to investigate the possible link between timber harvest-related temperature elevations and spring chinook salmon (Oncorhynchus tshawytscha) reproductive success. The study had three objectives: a) to determine if temperature experienced by adult spring chinook salmon prior to spawning influenced reproductive success, b) to determine if adult spring chinook salmon behaviorally regulate internal temperature through selection of cold-water refuges, and c) to characterize the thermal regimes historically tolerated by spring chinook salmon and to model the likely effects of forest practices on their success. To synthesize experimental results, TEMPEST, a stream reach temperature model, and stream temperature records were used to characterize the thermal regimes historically tolerated by spring chinook salmon and to predict the likely effects of forest practices on their success. Input parameters (view factor, mean annual air temperature, groundwater temperature, and stream depth) were selected based on historical distribution of spring chinook salmon and on heat transfer processes. Although spring chinook salmon residing within cool-water refuges may be capable of mitigating sub-lethal temperature effects, thermal refuge areas need to be abundant and available to the fish. Subsurface seepage may play a large role in stream temperature modification and thermal refuge formation. However, previous studies indicated that subsurface water temperatures may become elevated due to land use alterations. The availability of suitable thermal refuges and appropriate holding habitat within mainstem rivers may determine long-term population survival.