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I I I I I I I I I I I I I I I I I I I BIOLOGICAL OPINION Status of the Species the floodplain and the associated riparian areas, marshes, and backwaters upstream. Riverine main channel habitats are also lost. Spawning and nursery habitats may be compromised or lost completely. For fish species accustomed to small backwaters, reservoirs the size of Lake Mead represent new habitats and individuals must adapt to the new conditions in order to survive. Waters released from deep within the reservoir are cold year round; these releases create water temperatures that are generally too cold to support the native fish fauna of the Lower Colorado. However, cold water is conducive to trout reintroduction and establishment, thus these releases result in loss of habitat available to native fish and in maintenance of a non-native predator. Dam operators release water primarily in response to entitlements and contract orders and to prevent flood damage. Changes in flows from dams have effects to natural channel migrations, creation, maintenance and destruction of marshes, backwaters and stands of riparian vegetation, spawning or migratory cues based on flow levels, and water quality parameters. When water is diverted from the river, flow reductions are apparent below each diversion. Flu ctuations in daily, weekly and monthly releases and diversions have significant adverse effects to shallow water areas. For the native fish species, effects to local migration, spawning and nursery areas, and alteration in habitat patterns and distribution occur. Control of the released water is also necessary. Rapid transport of water from the dam to the diversion point minimizes loss to evaporation and seepage into the groundwater. Straight, stabilized channels achieve this, but with a resultant loss of meanders, often cutting backwaters and marshes off from the mainstem river. Even if not cut off, higher velocity water in the channel cut s a deeper bed, permitting water to drain from wetland areas. The fish species in this consultation depend considerably on backwater type habitats or main channel habitats with lower velocities. Because flows and velocities will vary over a day or week depending upon release, entrapment and stranding become threats to individuals. Non-native fish introductions have resulted in the establishment of a much more diverse fis h fauna than existed in the past. Many of these fish species are potentially predators or competitors with the native fish. Survival strategies that worked successfully before the non-natives arrived have not appeared to work since. While specific evidence for predation or competition between native and non-native fish is often not available, sufficient evidence exists to indicate that these effects occur (Bestgen 1990, Minckley et al. 1991), The effects range from predation on eggs, larvae and juveniles to contemporaneous use of the same habitats resulting in some level of competition for food, space, and protection. The adaptability of the non-native fish is evident even in relatively undisturbed river reaches such as those found in portions of the Upper Basin, where non-native fis h have established populations and native fish populations have declined. Almost all areas of designated critical habitat for native fish were degraded by past actions and have been kept in that condition by the presence of non-native fish, development activities, and maintenance and operation of dams in the Colorado River Basin. Add itional actions that continue 46