Great Basin Naturalist


Redband trout (Oncorhynchus mykiss gairdneri) were observed approximately every 2 weeks in an intermittent southwest Idaho stream between August and December 1991. Instantaneous daytime dissolved oxygen concentration and water temperature declined from 4.0 to <2 mg/L and 17 to 2 °C, respectively, during this period. Redband trout declined from a maximum captured of 48 on 28 August to 1 on 8 November in one series of polls. As conditions approached hypoxia, trout exhibited little movement and positioned themselves in water just deep enough to cover their dorsal fin. High densities of speckled dace (Rhinichthys osculus) were also present in each pool until drying. The response of these fish to such extreme habitat conditions is probably a primary factor accounting for their distribution within arid landscapes.