Interactions Between the Redside Shiner (Richardsonius balteatus) and the Steelhead Trout (Salmo gairdneri) in Western Oregon: The Influence of Water Temperature

Water temperature influenced interactions between redside shiner (Richardsonius balteatus) and juvenile steelhead trout (Salmo gairdneri) (≥1 +) in the field and laboratory. Trout in cool water when shiner were absent and at intermediate water temperatures with shiner present occupied a similar range of habitats. Shiner alone in warm water occupied habitats similar to trout, but in the presence of trout occupied slower, deeper areas than when alone. In laboratory streams, production by trout was the same in the presence and absence of shiner in cool water (12–15 °C). In warm water (19–22 °C), production by trout decreased by 54% in the presence of shiner compared with when shiner were absent. Production of shiner in cool water decreased in the presence of trout, −0.3 g∙m−2∙d−1 together compared with 0.5 g∙m−2∙d−1 alone, but was not affected by the presence of trout in warm water. Trout distribution was not influenced by shiner in cool waters, but was influenced at warm temperatures. Shiner occupied all areas of the laboratory channels in the absence of trout in cool waters but were restricted to a few pools in the presence of trout. Distribution of shiner was not influenced by trout at warm temperatures.