Influence of water temperature on behavioural interactions between juvenile brook charr, Salvelinus fontinalis, and rainbow trout, Salmo gairdneri

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Abstract
Interspecific behavioural interactions between paired brook char (Salvelinus fontinalis) and rainbow trout (Salmo gairdneri) were compared at different water temperatures to test the hypothesis that a species realizes a competitive advantage within its optimal thermal range. Three test temperatures were used: 19 °C (optimal temperature for rainbow trout), 13 °C (optimal temperature for brook charr), and 8 °C (below the optima for both species). Brook charr dominated rainbow trout at both 8 and 13 °C. At 19 °C, neither species displayed an obvious competitive advantage. The time (days) to the establishment of a dominance hierarchy reflected specific optimal temperatures; it was shortest for rainbow trout and brook charr at 19 and 13 °C, respectively. The implications of optimal temperatures and competitive ability are discussed in relation to habitat partitioning in the stream environment.