Stream entry of many fishes is influenced by environmental factors including water temperature, stream discharge, and photoperiod (Leggett 1977; Jonsson 1991). Environmental factors influence stream entry differently depending on the species and life stage of fish, likely because of varying physiologies and life histories (Lucas and Baras 2008). Many spring-run migratory fishes occupy Laurentian Great Lakes Basin (e.g., lake sturgeon, Acipenser fulvescens; steelhead, Oncorhynchus mykiss; white sucker, Catostomus commersonii; coho salmon, Oncorhynchus kisutch; and sea lamprey, Petromyzon marinus), and the timing of when they enter a river system each year is likely influenced by different environmental variables. For example, water temperature and stream discharge seem to be two of the triggers to upstream movement for many migratory fishes in the Great Lakes region (Hamel et al. 1997; Workman et al. 2002; Binder et al. 2010). Although much is known about the environmental cues for upstream migration of many species in the Great Lakes, understanding fish migration at higher spatial and temporal resolutions is needed (Landsman et al. 2011), especially in and around fishways. Therefore, our goal was to determine what factors influence the timing of fish entry into a Lake Michigan tributary at a relatively high temporal resolution using a noninvasive and continuous monitoring technique.

Enhanced understanding of the environmental cues that trigger fish movement in Great Lakes tributaries is important because it can improve recreation, native fish restoration, and invasive species control. For example, fisheries managers need to know when and at which life stage fish are moving into the rivers to establish closed seasons and catch limits. Additionally, knowing when native or invasive species move upstream can inform the operation of selective fishways and hydropower facilities that protect native or economically valuable fishes (e.g., lake sturgeon, white sucker, steelhead, coho salmon) while blocking invasive species (e.g., sea lamprey).

Here, we evaluate the environmental triggers of stream entry for three size classes of migratory fishes in the Lower Boardman River. Located in northern Michigan, the Boardman River is an important system for improving knowledge of fish migration because of its high productivity and value to the local community. Many fishes would benefit from increased habitat connectivity in the Boardman River, which connects a productive and relatively pristine tributary with a large and productive bay. The Boardman River is valued by both recreational and tribal stakeholders and is the focus of a restoration project aimed at improving habitat connectivity by removing and modifying all existing dams. For these reasons, the Great Lakes Fishery Commission is leading a project to replace the Union Street Dam on the Boardman River with a facility that integrates various technologies to pass desirable fish up- and down-stream while blocking and removing undesirable fish (the FishPass project). Using Dual-frequency Identification Sonar (DIDSON) cameras, we characterized the sizes of fishes migrating into the Boardman River below the Union Street Dam as well as the timing of their movements. Our results provide fine-scale details on the timing of fish movements in the Boardman River and directly inform the FishPass project. We were specifically interested in the movement timing of sea lamprey, an undesirable invasive fish that must not be passed upstream at FishPass, and lake sturgeon, a highly desired native fish that should pass upstream.