A simple method for in situ monitoring of water temperature in substrates used by spawning salmonids

Interstitial water temperature within spawning habitats of salmonids may differ from surface-water temperature depending on intragravel flow paths, geomorphic setting, or presence of groundwater. Because survival and developmental timing of salmon are partly controlled by temperature, monitoring temperature within gravels used by spawning salmonids is required to adequately describe the environment experienced by incubating eggs and embryos. Here we describe a simple method of deploying electronic data loggers within gravel substrates with minimal alteration of the natural gravel structure and composition. Using data collected in spawning sites used by summer and fall chum salmon Oncorhynchus keta from two streams within the Yukon River watershed, we compare contrasting thermal regimes to demonstrate the utility of this method.