Montana Fishery Project
Seasonal movements of rainbow trout, brown trout, and mountain whitefish in the Smith River, Montana
January 2015 - January 2019
- Montana Fish, Wildlife and Parks
Movements of stream-dwelling fishes can be obstructed or hindered by habitat alterations and in-stream barriers, and such fragmentation of habitats deleteriously affects many taxa worldwide. Conversely, diverse movement and life history patterns can optimize resource availability, increase genetic exchange, and promote population resilience to environmental disturbances. Fish that move can access food, favorable thermal conditions, and spawning substrates that may be unavailable or limited within local habitat patches. Along with our Montana Fish, Wildlife & Parks partners, we sought to comprehensively determine the factors affecting unconstrained fish movements (species, physical drivers, seasons, and landscapes) and how movements and vital rates (survival, site fidelity) interrelate in a large, inland watershed, while also avoiding some common limitations of movements studies (e.g., limited spatial or temporal scopes, species, and sample sizes). Specifically, we determined the movement patterns and vital rates of three abundant salmonids—brown trout (Salmo trutta), mountain whitefish (Prosopium williamsoni), and rainbow trout (Oncorhynchus mykiss)—in the Smith River watershed of central Montana, an unfragmented system with three distinct geomorphic regions. Watershed-scale movements were common, diverse, and overlapped, thereby connecting distant groups of fish. Volume of movements of each species peaked at specific locations and during specific seasons. Patterns of survival also varied among species and locations, and movements throughout the Smith River watershed connected fish populations in habitats with relatively high survival, where populations were probably most stable, to habitats where survival was lower but per capita resource availability was probably higher. Studies restricted in scope to single species or seasons of interest risk mischaracterizing vital rates and the diversity of movements expressed by a fish assemblage. Accounting for the diversity and spatial extent of movement patterns expressed by all species in a fish assemblage will promote life history and species diversity while helping to ensure the persistence of robust fish populations. Managers may perhaps best protect life history diversity of inland fishes by emulating management of highly migratory anadromous fishes, which seeks to facilitate unhindered movements.