**1. Introduction**

The importance of multiscale habitat use by aquatic organisms is well recognized and central to the development of meaningful fisheries conservation actions. The distribution of fishes relies on natural features such as the appropriate climate and geology that comprise the physicochemical characteristics that are typically tolerated by species. These ultimate determinants constrain intermediate and proximate determinants on aquatic organisms (e.g., benthic algae, [1]). For example, the pH of a river is dictated, in part, by the underlying lithology of the region [2], and fishes have specific pH tolerances that regulate a variety of life-history attributes (e.g., egg hatching in salmonids [3]). A combination of other physicochemical factors at finer spatial and temporal scales contribute to a heterogeneous riverscape that shape species assemblages [4, 5], where fish use a set of variables that are assumed to maximize

fitness [6] or describe behavioral responses (e.g., changes in cover use, [7]). The habitat needs of fishes are often used as the foundation of conservation and recovery plans [8]. For example, priority use areas can be identified and restoration actions planned. As human pressures on fish populations increase, establishing multiscale relationships is more important than ever for guiding conservation actions.

### **1.1 Landscape change and anthropogenic pressures on fish populations**

Human pressures increase the threats on freshwater ecosystems and taxa. The modification of landscapes from historical land cover to agriculture and urban uses has resulted in significant physicochemical changes and water demands on rivers. Urban rivers, for example, are often associated with flashy hydrographs, increased contaminants, and degraded channel morphology [9] including channel incision and erosion [10]. Agriculture land use is also associated with higher sediment and nutrient loads [11, 12], more homogenous substrates and water depths [13], and bank instability [14, 15]. Pressure on water resources needed for human uses has resulted in rivers being dammed, leveed, and pumped thereby disrupting both flow and sediment regimes [16, 17]. The magnitude, duration, timing, frequency, and rate of change of stream discharge (hereafter flow regime) is considered a primary driver of ecosystem processes [18, 19] and biotic integrity [20, 21]. Flow regimes globally have been altered due to human activities [19, 22, 23]. Current and future changes to our climate and associated weather patterns will only exacerbate threats facing freshwater ecosystems.

North American freshwater fishes are experiencing the highest extinction rates among vertebrates [24]. Flow regime alteration and fragmentation due to dam construction (hereafter damming) are often cited as primary causes [22, 25, 26]. Dams alter fish-assemblage structure [27–29] and prey availability [30–32] by creating streamflow conditions and instream habitats favorable to lentic (i.e., lake and reservoir) species. The changes to flow magnitude, in particular, due to damming, have negatively affected many fishes leading to declines in diversity [22, 24, 26]. Altered flow regimes and fragmentation caused by damming are particularly detrimental to lotic (i.e., river and stream) fishes due to their mobility and requirement of multiple habitat types to complete a life cycle [4]. Dams disrupt spawning cues and block migration routes, prevent access to spawning and nursery habitats, and alter nutrient cycles [26, 27, 32]. Damming has largely ceased in North America, but the long-term effects of modified ecosystems result in numerous stream-fish conservation challenges [22, 33, 34]. Existing levels of flow regime alteration and fragmentation are also exacerbated due to climate change and additional anthropogenic pressures, particularly in arid and semiarid regions.
