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Applying Fish Swimming Research to River Restoration Efforts by Christopher A. Myrick Assistant Professor, Department of Fishery and Wildlife Biology, Colorado State University D =ified throughout the United States have been to improve navigation or access, to pro- duce hydroelectric power, to serve as conduits for wa- ter deliveries, or to control flooding or erosion. These changes, while undoubtedly beneficial, have often had unintended negative effects on the aquatic ecosystems found in those rivers. One of the most common ef- fects is the loss of ecological connectivity that results from the installation of diversion dams, weirs, cul- verts, and various flood control structures in a river channel. These structures can impede the movement of fishes, particularly in the upstream direction, and when they form a barrier to upstream migrations, then the system's ecological connectivity has been severed, placing fish populations and aquatic communities at risk (Moyle et al. 1995; Schlosser and Angermeier 1995). In the most severe cases, the presence of an impassable impoundment or structure can lead to the local extirpation of one or more of the native fishes (Helfrich et al. 1999; Winston et al. 1991). Fishery biologists and other resource managers have long been aware of these problems, and in the case of high -value fisheries, such as the salmon in Pa- cific coast rivers, have expended considerable ef- fort designing and installing fish passage structures (fishways) to allow fish to successfully negotiate the instream obstacles (see Clay, 1995, for a comprehen- sive review). One class of these structures, the pool - and -weir fishways, take advantage of the tendency of salmon and trout to jump over obstacles during their upstream migration, and allow the fish to negotiate an ascending series, or ladder, of pools by jumping over the weirs. Other designs that do not require jumping were also developed, and these include Denil -type fishways, vertical slot fishways, and rock -ramp or na- ture -like fishways. These fishway classes rely on the manipulation of hydraulics to provide fish with water velocities that they can manage, and areas where they can rest between bouts of upstream movement. Un- fortunately, a similar level of effort has yet to be made on the vast majority of the inland rivers, or for the ma- jority of non - salmonid fish species that are not similar in performance to trout or salmon, such as minnows, darters, and suckers. Many of the small- bodied fishes endemic to inland rivers are fairly strong swimmers, but they may not rely on their jumping ability to surmount obstacles, as is the case for large- bodied salmon and trout. Ongoing studies in the Fish Physiological Ecology Laboratory at Colorado State University using an in- novative type of artificial waterfall (Kondratieff and Myrick 2005) have shed some light on the question of whether some of these small- bodied fishes will attempt to jump over a vertical obstacle. Theses stud- ies have demonstrated that while small- bodied fishes, such as brassy minnows (Hybognathus hankinsoni) and fathead minnows (Pimephales promelas), will try to jump over a vertical obstacle representing a low weir. However, their small size (commonly less than 6" long) means that even if they can jump three times their own body length, a relatively short vertical ob- stacle (e.g., a two -foot high weir), can still represent an impassable barrier. The studies have also shown that other small- bodied fishes, like the Arkansas darter (Etheostoma cragini), cannot negotiate a verti- cal weir, even one that is only one body - length high. Because of these performance limitations, the use of classic pool- and -weir fish passage structures is not recommended for most inland rivers systems. Doing so would impose an artificial selective pressure on the local fish community, and, from an engineering stand- point, it would be probably be impractical to incorpo- rate the number of small weir -steps needed to allow successful upstream passage of a fish that can only jump four or five inches high at a time. Fortunately, the extensive research on salmon and trout passage structures resulted in alternative designs that do not require the fish to jump (see above). Regardless of the type of fishway being considered, how does one adapt a structure developed for large, strong -swim- ming salmon and trout to successfully allow passage of these smaller, non jumping fish species? There are a number of biological factors that should be considered when designing a fish passage struc- ture. First, one needs to know what fish species are present in the river and what their size range is. Where possible, additional information on the fishes' life history is valuable because it may identify critical times or seasons when migrations or mass move- 17