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Rainbow trout (Oncorhynchus mykiss) invasion in Hokkaido streams, northern Japan, in relation to flow variability and biotic interactions

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Abstract:

Factors controlling invasion success of rainbow trout (Oncorhynchus mykiss) and interactions with native masu salmon (Oncorhynchus masou) were examined by field investigations. The results suggested that flow regime has a major role in controlling rainbow trout invasion success. Although competitive relationships were found between the two species, masu salmon were not likely to prevent trout invasion. Analyses on the distributions and abundances of the two species indicated that the occurrence of rainbow trout was limited to streams with stable flows, and the density of each species was negatively related with that of the other. Habitat use and diet analyses revealed a pattern of their resource partitioning; rainbow trout occupy positions near the bottom or cover, foraging benthic prey, while masu salmon feed drifting prey at the middle layers of the water column. This resource partitioning was suggested to reflect a diet shift by rainbow trout. Our results also have a management implication that dams, which control flow regime, can be a key factor in managing rainbow trout invasion and its effects.

Des observations de terrain ont permis d’examiner les facteurs qui contrôlent le succès de l’invasion de la truite arc-en-ciel (Oncorhynchus mykiss) et ses interactions avec le saumon masou (Oncorhynchus masou) indigène. Les résultats font croire que le régime d’écoulement des eaux a un rôle majeur dans le contrôle du succès de l’invasion des truites. Bien qu’il existe des relations de compétition entre les deux espèces, il est peu probable que les saumons masou empêchent l’invasion des truites. Des analyses de la répartition et de l’abondance des deux espèces indiquent que la présence de la truite arc-en-ciel est restreinte aux cours d’eau à écoulement stable; il y a aussi une relation négative entre les densités des deux espèces. Des analyses de l’utilisation de l’habitat et du régime alimentaire montrent un patron de partage des ressources: les truites arc-en-ciel se tiennent près du fond ou des abris et se nourrissent de proies benthiques, alors que les saumons masou s’alimentent de proies en dérive dans les couches intermédiaires de la colonne d’eau. Ce partage des ressources semble refléter un changement de régime alimentaire chez la truite arc-en-ciel. Nos résultats ont aussi des conséquences sur la gestion, puisque les barrages, qui contrôlent le régime d’écoulement, peuvent être un facteur essentiel pour gérer l’invasion des truites arc-en-ciel et ses effets.

Document Type: Research Article

Publication date: September 1, 2009

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  • Published continuously since 1901 (under various titles), this monthly journal is the primary publishing vehicle for the multidisciplinary field of aquatic sciences. It publishes perspectives (syntheses, critiques, and re-evaluations), discussions (comments and replies), articles, and rapid communications, relating to current research on cells, organisms, populations, ecosystems, or processes that affect aquatic systems. The journal seeks to amplify, modify, question, or redirect accumulated knowledge in the field of fisheries and aquatic science. Occasional supplements are dedicated to single topics or to proceedings of international symposia.
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