Cooperative Fish and Wildlife Research Units Program: Utah
Education, Research and Technical Assistance for Managing Our Natural Resources

**McLaren, J. S., P. E. Budy, S. Brothers, R. W. Van Kirk. 2023. The scale-dependent role of submerged macrophytes on trout habitat. Canadian Journal of Fisheries and Aquatic Sciences 80:1533–1546. USGS FSP IP-139190.


Submerged macrophyte communities are prevalent in low-gradient rivers around the world and interact with rivers and their biota in complex ways; the net effect of these interactions on trout habitat provision remains poorly understood. We used snorkel surveys and bioenergetics to study trout habitat selection and potential mechanisms driving habitat selection in the submerged macrophyte-rich Henrys Fork, ID, USA. At smaller spatial scales (i.e., individual microhabitats), we hypothesized trout would select for locations with more submerged macrophytes that provide overhead cover from predators, drifting macroinvertebrates as food, and lower swimming costs. In contrast, we found individual trout selected for microhabitats without submerged macrophytes (, with deeper water ( and with greater bioenergetic potential (. At larger spatial scales (i.e., reach-scale), submerged macrophytes acted as a living substrate, indirectly creating a riverscape of complimentary microhabitats by increasing depth (), bioenergetic potential (), and by influencing reach-scale ecosystem dynamics which modulated trout habitat selection. Our study improves understanding of the complex relationship between submerged macrophytes and trout habitat, explaining conflicting results among previous studies and revealing potential management actions to improve trout productivity. Continued study of abiotic and biotic processes across multiple scales may continue to reveal unexpected scale-dependent effects and mechanisms controlling trout habitat quality, quantity, and preferences.