Habitat utilization and behavioural ecology of Rainbow trout, Salmo gairdneri Richardson and Brook char, Salvelinus fontinalis (Mitchill) in Avalon Peninsula streams

Cunjak, Richard Anthony (1982) Habitat utilization and behavioural ecology of Rainbow trout, Salmo gairdneri Richardson and Brook char, Salvelinus fontinalis (Mitchill) in Avalon Peninsula streams. Masters thesis, Memorial University of Newfoundland.

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Abstract

Recent range extension of introduced salmonid species in insular Newfoundland has caused concern over their effects on native fish species. The present study was designed to investigate the habitat utilization of the exotic rainbow trout and the native brook char in streams of the Avalon Peninsula. Underwater field observations were carried out in a stream where the two species coexisted. Brook char occupied positions with significantly lower water velocities greater depth, and more cover than similar sized rainbow trout. Char showed similar microhabitat preferences regardless of the presence of trout. Behavioural observations of inter-specific pairs of fish at an in-stream viewing facility (Benthobservatory) showed that brook char were able to dominate rainbow trout in a slow flow (pool) environment. No species advantage was observed in a fast flow (riffle) environment. Subsequent experiments at the Benthobservatory provided evidence that trout preferred mid-stream stations in the main flow whereas char most often held station in slow flow areas usually associated with cover. Laboratory experiments designed to investigate the ability of one species, within its optimal temperature regime, to dominate another species indicated that brook char were most active, showed best growth, and were dominant over rainbow trout at 13ﾟC. Trout showed their best growth and achieved dominance most often at 19ﾟC. The results suggest that rainbow trout may realize a metabolic and behavioural advantage over char at high stream temperatures. -- The data indicate that microhabitat preferences of rainbow trout and brook char in the stream environment are sufficiently different to permit cohabitation with minimal interaction. This habitat segregation likely resulted from interactions with other salmonids in their indigenous ranges.

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