Fish movement and assemblage dynamics in a Pacific Northwest riverscape

Graduation date: 2002This study examined fish movements and assemblage dynamics in the Wenaha,\ud Grande Ronde, Snake river system of northeast Oregon and southeast Washington. I\ud investigated the role of fish movement in the dynamics of stream fish assemblages and\ud evaluated relationships between species movement, assemblage structure, and the\ud heterogeneity of habitat at multiple scales within the river network. In doing so, I\ud employed a landscape approach, visualizing the heterogeneity and dynamics of the\ud system as a "riverscape" that sets the stage for the ecology of stream fishes. I quantified\ud fish assemblage dynamics, characterized the nature and extent of movement by\ud representative fish species, and assessed spatial and temporal heterogeneity of stream\ud habitat within the river network. I applied multiple methods, including underwater fish\ud surveys and radio telemetry, and used multiple sampling approaches that allowed me to\ud detect patterns at nested spatial and temporal scales.\ud I found that spatial patterns in fish assemblage structure were highly dynamic over\ud seasonal to diel temporal scales. Seasonal changes in fish assemblage patterns along the\ud length of the river system were primarily driven by the migration of native fishes such as\ud mountain whitefish, bull trout, and largescale suckers. These highly migratory species\ud exhibited a diverse array of movement strategies and often had annual ranges of hundreds\ud of kilometers. The movement of fishes at smaller spatial scales influenced diel dynamics\ud of fish assemblage patterns. Important habitat features at stream, valley\ud segment and channel unit scales were separated spatially, and fish species exhibited a\ud variety of migratory strategies that reflected the complementary use of habitats\ud distributed throughout the riverscape. The importance of fish migration and the dynamic\ud nature of stream fish assemblages and fish habitat relationships should be taken into\ud account in research and conservation of stream fishes. Current conceptual frameworks\ud for stream fish assemblages do not fully reflect the temporal complexity of stream fish\ud life histories or the spatial heterogeneity of stream habitat. I introduce an alternative\ud framework by integrating fish movement into a dynamic perspective of assemblages set\ud within the context of the riverscape, and raise questions regarding the nature of ecological\ud communities