Laserfiche WebLink
<br />I <br /> <br />I <br /> <br />I. INTRODUCTION <br /> <br />I <br /> <br />Human alteration of the main rivers and tributaries in the Upper Colorado <br />River Basin (Upper Basin) had a major negative impact on some native fishes <br />to the point where the razorback sucker (Xvrauchen texanus), bony tail (Gila <br />eleqans), Colorado squawfish (Ptvchocheilus lucius), and humpback chub (Gila <br />cvoha) are now listed as endangered under the Endangered Species Act. Other <br />native fish species (e.g., flannelmouth sucker, Catostomus latipinnis and <br />bluehead sucker, Catostomus discobolus) are still able to maintain self- <br />sustaining populations, despite the drastic altered condition of the historic <br />river environment. In less altered river reaches, native fish species still <br />dominate the fish fauna (Anderson 1997; Burdick 1995) while, in more altered <br />reaches, nonnative fish species are more abundant demonstrating that they are <br />highly adaptive and can quickly dominate a fish community (Miller et al. 1982; <br />Tyus et al. 1982). <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />Many riverine fish species exhibit seasonal movements into inundated <br />floodplain habitats for spawning, rearing, and foraging (Copp 1989; Finger and <br />Stewart 1987; Lambou 1963; Ross and Baker 1983). Seasonal flooding is <br />important in sustaining various fish species that are characteristic of river <br />channels (Baker and Killgore 1994). Baker and Killgore emphasize that the <br />pattern of flooding appears to be of paramount importance in structuring <br />wetland fish communities and that fish may spread over large areas of the <br />floodplain during high streamflows. The lateral movement of fish on the <br />floodplain decreases exponentially with reductions in streamflow (Kwak 1988) <br />and recruitment may not occur if water levels remain low (Starrett 1951). <br />Dramatic declines of Age 0+ fish, that were correlated to the loss of <br />floodplain habitat, were reported by Coop (1990). A higher riverine fish <br />standing stock was associated with high spring floods in the Atchafalaya <br />floodplain in the lower Mississippi River whereas the standing stock was lower <br />following low spring floods (Bryan and Sabins 1979). Because of floodplain <br />importance to fisheries, the American Fisheries Society adopted a position to <br />"encourage restoration of historic floodplain and upland wetlands to regain <br />stormwater retention, conveyance, and low-flow augmentation capabilities of <br />the watershed, focusing on efforts to restore large 'functioning' floodplain <br />wetlands" (Rasmussen 1996) . <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />Habitat alteration and nonnative fish introductions were considered to be the <br />two most important factors in the extinction of 40 native North American <br />fishes (27 species and 13 subspecies) during the past century (Miller et al. <br />1989). These two factors also appear to be extremely important in the decline <br />of razorback sucker stocks in the Upper Basin and are undoubtedly related to <br />the decline of the other three endangered Colorado River fishes. <br /> <br />I <br /> <br />One of five major elements that are being addressed through the "Recovery <br />Implementation Program for Endangered Fish Species in the Upper Colorado River <br />Basin" (Recovery Program) is habitat development and maintenance (U.S. Fish <br />and Wildlife Service 1987). The declining numbers of some endemic Colorado <br />River fishes is attributed to the lack of recruitment. Although the long- <br />lived endangered fishes spawn successfully and produce larvae, high mortality <br />during the early life stages limits recruitment. Most Recovery Program <br />participants believe that the lack of recruitment in the razorback sucker is <br />related to the lack of adequate nursery habitat and predation/competition by <br />nonnative fishes. <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />This report summarizes the published literature on the ecological value of <br />floodplains to riverine fish communities and relates this literature to <br />reports on the ecological requirements of razorback suckers that have been <br />developed through the Recovery Program and management endeavors of biologists <br />in the Lower Colorado River Basin. It emphasizes the need for concurrent <br />integration of Recovery Program elements, particularly streamflow management, <br />habitat development and maintenance, management of nonnative fishes, and <br /> <br />I <br /> <br />I <br /> <br />7 <br /> <br />I <br />