Thermal heterogeneity, stream channel morphology, and salmonid abundance in northeastern Oregon streams

Abstract

Heterogeneity in stream water temperatures created by local influx of cooler subsurface waters into geomorphically complex stream channels was associated with increased abundance of rainbow trout (Oncorhynchus mykiss) and chinook salmon (Oncorhynchus tshawytscha) in northeastern Oregon. The addition of cold water patch frequency and area as explanatory variables in salmonid habitat models indicated that doubling of cold water patch frequency was associated with increases in rainbow trout and chinook salmon abundances of 31% and 59%, respectively. Doubling of cold water patch area was associated with changes of 10% in rainbow trout abundance but was not associated with chinook abundance after accounting for other habitat factors. The physiognomy, distribution, and connectivity of cold water patches, important attributes determining the effectiveness of these habitats as thermal refuges for stream fishes, were associated with channel bedform and riparian features. Monitoring of thermal heterogeneity and salmonid populations in response to ongoing habitat restoration efforts will provide additional insights into causal relationships among these factors.