Salmonid abundances in the Smith River are relatively low and believed to be limited by high summer water temperatures and low discharges. Pilot studies have suggested that the extent and complexity of salmonid movement may be greater than once perceived, underscoring the importance of understanding tributary use and salmonid movement in regard to potential management strategies.
Research began in 2010 on a major tributary of the Smith River, Tenderfoot Creek, with the primary goal of evaluating the tributary?s importance to salmonids of the Smith River system. Investigating the role of Tenderfoot Creek as a spawning and nursery area and thermal refuge revealed its importance as a spawning ground, especially for mountain whitefish (Prosopium williamsoni) and rainbow trout. However, contrary to expectations, Tenderfoot Creek was not used as a thermal refuge during periods of high water temperature. Instead, salmonids were suspected to be using the outflow of Tenderfoot Creek within the Smith River to escape thermally stressful conditions.
Salmonid movements and thermal hydrodynamics at the confluence of Tenderfoot Creek and the Smith River were therefore investigated in 2014 to specifically determine if the outflow of Tenderfoot Creek was being used as a thermal refuge instead of the tributary itself. Thermal mapping and modeling of the confluence area showed that the outflow of Tenderfoot Creek provided an accessible thermal gradient that was cooler than the Smith River by up to 6?C. Indeed, salmonids used the outflow more than otherwise would be expected for similar-sized areas elsewhere in the Smith River. A network of passive integrated transponder (PIT) antenna arrays showed that tagged fish preferred the outflow over other areas of the confluence and that use of the outflow increased when conditions in the main stem Smith River became stressful. Accordingly, other tributary confluences throughout the basin may be critical areas of thermal refuge for salmonids as well. Insight into Tenderfoot Creek?s role in the Smith River system prompted an expanded study, and research into fish movement throughout the entire Smith River watershed subsequently began in 2014. The movements of about 6,000 PIT-tagged fish, including seven native species and three introduced species, have been monitored since the study?s expansion.
The researchers have used a collaborative approach to problem solving in Smith River studies and have worked closely with students and professionals in completely different disciplines to accomplish their goals. For example, the movement of tagged fish throughout the system is monitored using fixed and mobile PIT antenna arrays, but the remoteness and size of the Smith River basin and antiquated nature of available PIT technology have presented logistical obstacles. Collaboration with Montana State University electrical engineering students and an outside engineering consultant has resulted in the development of more sophisticated PIT tag readers and a remote monitoring platform that allows control, access, and uploading of data by satellite and website interface. Agency biologists and researchers can now monitor fish movement in remote locations from the office or smart phone in near real-time, saving time and resources and avoiding dangerous field trips in inclement conditions.
Although movement is common among fish of the Smith River, migratory patterns vary in magnitude and timing. Peaks in migratory activity occur in spring and fall and some migrations are extensive, with some fish occasionally migrating more than 100 miles. Brown trout show the least propensity to migrate, whereas mountain whitefish are the most likely to migrate. Rainbow trout movements are mostly associated with spawning migrations into tributaries or juvenile outmigrations. Suckers (Catostomus spp.) migrate more than 30 miles within the main stem Smith River but rarely move into tributaries.
Movement of fish in rivers such as the Smith has created the distribution and structure of fish assemblages we observe today. Although in certain circumstances fish can complete their entire life cycle without substantial migration, many fish rely on migratory behaviors to move among various habitats across watershed landscapes. Migratory life history patterns can improve individual fitness and can make populations of fish more resilient to environmental disturbances. The variety of migratory patterns expressed among the Smith River fish assemblage adds strength and resilience to fish populations and can help fish cope with seasonally unfavorable environmental conditions. As climate change continues to alter the temperature and discharge regimes of inland streams such as the Smith River, migration will be an increasingly important way for fishes to persist. Proper management that accounts for migratory life histories is needed to ensure that fish can maintain these important migratory life histories.
The ONB features articles from Cooperative Fish and Wildlife Research Units across the country. Working with key cooperators, including WMI, Units are leading exciting, new fish and wildlife research projects that we believe our readers will appreciate reading about. This article was written by Mike Lance, Graduate Research Assistant working with Alexander Zale, Unit Leader, USGS Montana Cooperative Fishery Research Unit at Montana State University and T. David Ritter, Masters Student, at Montana State University.
