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" " . . Area Manager DRAFT 16 that is resource limited. Charmel catfish (Ictalurns punctatus) has been identified as a um:allu sub adult ai1d adult pikeminnow in the San Juan River. Channel catfish were first introduced in the upper Colorado Basin in 1892 (Tyus and Nikirk 1990) and are now considered common to abundant throughout much of the upper Basin (Tyus et al. 1982, Nelson et al. 1995). The species is one of the most prolific predators in the upper Basin and, among the non-native fishes, is thought to have the greatest adverse effect on endangered fishes due to predation on juveniles and resource overlap with subadults and adults (Hawkins and Nesler 1991, Lentsch et al. 1996, Tyus and Saunders 1996). Adult pikeminnow that have preyed on channel catfish have died from choking on the pectoral spines (McAda 1980, Pimental et al. 1985). Data from a 7-year research period on the San Juan River where channel catfish were mechanically (electro fishing, seining) removed have not indicated a positive population response in pikeminnow (Service 2002a). Status and Distribution The pikeminnow was designated as endangered prior to the Act; therefore, a fonnallisting package identi fying threats was not prepared. Construction and operation of main stem dams, non-native fish, and local eradication of native minnow and suckers in the early 1960s were recognized as early threats (Miller 1961, Holden 1991). The pikeminnow recovery goals (Service 2002a) summarize threats to the species as follows: stream regulation, habitat modification, competition with and predation by non-native fish, and pesticides and pollutants. Major declines in pikeminnow populations occurred in the lower Colorado Basin during the dam-building era of the 1930s through the I 960s. Behnke and Benson (1983) summarized the decline of the natural ecosystem, pointing out that dams, impoundments, and water use practices drastically modified the river's natural hydrology and channel characteristics throughout the Colorado River Basin. Dams on the main stem fragmented the river ecosystem into a series of disjunct segments, blocked native fish migrations, reduced water temperatures downstream of dams, created lake habitat, and provided conditions that allow competitive and predatory non- native fishes to thrive both within the impounded reservoirs and in the modified river segments that connect them. The highly modified flow regime in the lower Basin coupled with the introduction of non-native fishes decimated populations of native fish. In the upper Colorado Basin, declines in pikeminnow populations occurred primarily after the I 960s, when the following dams were constructed: Glen Canyon Dam on the main stem Colorado River, Flaming Gorge Dam on the Green River, Navajo Dam on the San Juan River, and the Aspinall Unit dams on the Gunnison River. Some native fish populations in the upper Basin have managed to persist, while others have become nearly extirpated. River reaches where native fish have declined more slowly, more closely resemble pre-dam hydrologic regimes, where adequate habitat for all life phases still exists, and where migration corridors allow connectivity among habitats used during the various life phases. A factor not considered when the pikeminnow was listed was water quality. Surface and ground water quality in the Animas, La Plata, Mancos, and San Juan River drainages have become 001410