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.............-...-........ ...............,..-.... ................ - -.. ...-.---.. ...- . ....'...-......................_....... ................... .................. .............. ,..... ................... ................... ........................,'............. . . . . . . . . . . . . . . . . . . , ....-.............. ..... ................... ..............,...-. ....... ,........... ................. . I I I I I I I I I I I I I I I I I I I bays such as the outlet of Gypsum Canyon (Photos A-25 and A-26). For about the first year that these silt/sand bars were exposed, and while they were periodically inundated by fluctuating reservoir levels, they were soft mugmires (Photo A-27). As these dried, they were invaded by thick stands of tamarisk (Photo A-28). By 1987, most tamarisk st.ands were 3 to 5 feet tall, and had stabilized the silt/sand bars (Photo A-29 through A-32), much as this plant has done in the upper basin. Fish habitat in this region changed dramatically over a period of about 5 years (1983-1988). The region was transformed from a slow flowing riverine environment lined with talus slopes to a riverine channel constricted in width by tamarisk-covered silt/sand bars. The few backwaters that formed as the silt/sand bars were developing were short-lived for only 1 or 2 years, and were largely eliminated by the st.abilizing and const.ricting effect of the tamarisk invasion. The only backwaters in the region in 1988 were located between Rapids 25 and 26 (Photo A-30). These backwaters provided habitat for YOY Colorado squawfish and chubs as well as other native and non-native fishes (See Section 5.2.3). The low lake level of 1988 revealed that many sand bars in upper Lake Powell had been overgrown by tamarisk (Photos A-31 and A-32). 2.6 River Flows and Water Temperatures Flow and temperature of the Green River, Colorado River, and Cataract Canyon for 1985-1988 are presented in Figure 8. It should be noted that the flows in Cataract Canyon in 1983 and 1984 were record highs of about 100,000 and 120,000 cfs, respectively. These two record wet years were followed by two more normal flow years (1985 and 1986), but peak and base flows remained high from high soil moisture content. Flows in Cataract Canyon in 1985 peaked at about 62,000 cfs, although base flows generally remained above 10,000 cfs. In 1986, flows peaked at about 70,000 cfs and base flows also remained around 10,000 cfs. The 2 years that followed -1987 and 1988 - were relatively dry years with peak flows of about 40,000 and 28,000 cfs, and base flows of about 5,000 and 4,000 cfs, respectively. These flow scenarios had a marked impact on water temperatures. During the higher water years of 1985 and 1986, water temperatures did not reach 250C until mid-July and early August., respectively. In 1987 and 1988, this temperature was recorded by late June. Since fish are poikilotherms, these different temperature regimes manifested dramatic differences in spawning, growth and perhaps overwinter survival of many species, including the endangered forms (See Section 5.1.1.3.4). ..............'.'...............'........ ..................... ....... . ............................................................ ..::.S10.::j::.MSTHSD0I10GM::.iU: . . . , . . . . . . . . . . . . . . ................... .................. ................. . .....,........... . ................... .......,......... . .................. . .................. .................. .....,........... . ............,..... . . . . . . . . . . . . . . . . . . . ...................... ............................. ..............,...,........................--.-................ .... ........'...'.....'...................-............,........-................................. ..........--............. ....................... . .................... . . .. .. . ..............................................-................ ..........................................-..-.....-.... . ..... -................................... -.......... ... ................ .--....... . ............ ,.... ................. ................. ................. .' ...... . . . . . . . . . . . . . . . . . . . . . . . . . . . ................ -.......... ........................... .............. .. .. 3.1 Basic Study Design The four basic elements of the Cataract Canyon Studies are presented in Figure 9. These st.udies were conducted for 4 years, from 1985 through 1988. Five study regions were est.ablished to stratify sampling by morphologically similar reaches of river. Four basic gear types were used in eight different habitat types. Since a complete analyses of all data partitions of this st.udy design were too numerous and largely meaningless, data analyses were performed'to address hypotheses directed at the specific st.udy objectives. The methodology used in the Cataract Canyon Studies was basically the same for all 4 years. Generally, a team of four biologist.s (2 Reclamation and 2 BIO/WESl) participated in either of two types of sample trips: (1) canyon trips or (2) confluence trips. Canyon trips were generally 7 days afield, and extended for about 100 miles from Potash or Mineral Bottom to Hite Marina on Lake Powell. 14