Understanding Stream-Resident Salmonid Movements in Groundwater-Fed Streams of the Driftless Area (USA)

Fish movements have been extensively studied and variously described for many years and several conceptual frameworks have since been proposed to help organize and understand these movements. Frameworks include ecological scale, the restricted movement paradigm, partial migration, dynamic landscape model, and riverscape approach. We blended reviews of selected frameworks and past studies in the Driftless Area of the upper Midwestern United States to advance an understanding of stream-resident salmonid movements. Past studies examined feeding and exploratory, seasonal migration and dispersal movements using underwater videography, radiotelemetry, capture–recapture method, and genetics method at various spatiotemporal and ontogenetic scales. Movements were complex and changed over the course of ontogeny. Most movement was at the youngest ages and smallest sizes and again at very large sizes as a result of exploratory behavior and feeding movements to seek better physical habitat conditions (e.g., deeper pool habitat) or to avoid competitive or predatory interactions with other salmonids. In between, adult-sized salmonids were mostly sedentary as suggested by the restricted movement paradigm. Restricted movement was likely due to ideal environmental conditions provided by a combination of groundwater-fed springs supporting good baseflow and cold temperatures, productive streams with abundant invertebrate prey, and diverse physical habitat conditions in a small spatial area. Thus, there was little evidence of seasonal migration to fulfill seasonal resource needs as predicted by the dynamic landscape model. Rather, a more general riverscape model best describes the partial migration of Driftless Area salmonid populations. In this model, stream reaches provide adequate seasonal habitat facilitating mostly sedentary adults, but with some inter-reach dispersal at juvenile ages and at the largest adult sizes.