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;,' ~k , 1j'i, the USFWS and other federal agencies, and has resulted in flow-related conservation mea- sures necessary to prevent loss of endangered species but not for recovery per see This is an important difference, because it is conceivable that protection under section 7 may ensure against further losses, but in doing so may limit options for recovery. The ecology and life cycles of fish are best studied where they remain abundant, in the least altered and most historic location, with the premise that conditions to which fish are best adapted are those in which they are most likely to maintain an advantage. Recovery needs may thus be formulated by comparing this "optimal" condition with habitats in areas where the species is in decline. In the following sections, protocols for habitat man- agement in the Green River, where the first condition obtains, will be compared where possible with those in the upper Colorado and San Juan rivers, where the species is rarer. Green River Many interagency studies since 1979 (re- viewed by Ferriole 1987; USFWS 1989a) have been concerned with determination of in- stream flow needs for endangered Colorado River fishes. Based on their results, the USBR and USFWS are cooperating to provide and evaluate the discharges from Flaming Gorge Dam necessary to form and maintain nursery habitats for young squawfish, an activity based on empirical verification of recom- mended flow scenarios. Associated with these efforts, the USBR and USFWS are completing studies of the requirements of rare and en- dangered fishes with respect to operations of Flaming Gorge, results of which will be pro- vided as part of a biological opinion and sup- porting documents under section 7 of the ESA. In 1984 the USFWS recommended interim flows to maintain nursery habitat for young (age-o) Colorado squawfish based on catch The Colorado Squawfish 393 records Oones and Tyus 1985). Survival of young was evaluated by analyzing catch data collected as part of an autumn sampling pro- gram. Recruitment was high in 1979 and 1980 when the August-September discharge varied from 44.8 to 53.2 m3 S-1 (1600-1900 ft3 S-I), and low in 1983 and 1984 when dis- charges were 84.9-n8.9 m3 S-1 (3000-4200 ft3 s - 1. A regression analysis of catches on means for August-September discharges at Jensen, Utah, demonstrated a high negative correlation (r = -0.89, P < 0.05). In addi- tion, a similar relationship appeared between larval growth and mean monthly discharge (r = -0.87, P < 0.05). The Green River is historically and predictably low in discharge in late summer, and field observations between 1979 and 1988 suggested thatlow abundance and slow growth of larvae were due to an ab- normally high summer discharge (releases of water stored during flood years of 1983 and 1984), which inundated prime nursery habi- tat (backwaters) for the species Oones and Tyus 1985; Tyus and Haines 1991). This hy- pothesis was supported by research conducted by the USBR in 1987 and 1988, in which aerial photography at different, controlled discharge levels indicated that the availability of back- water habitat was negatively correlated (r = - 0.91, P < 0.05) with late summer flows. Specifically, the surface area of backwater habitat was maximized at 47.4 m3 S-1 (1687 ft3 s - 1; average of Jensen, Ouray, and Sand Wash study areas), and numbers of backwa- ters were maximized at 39m3 s - 1 (138 I ft3 S-I; Pucherelli et al. 1988). Instream flow incremental methodology (IFlM), in association with physical habitat simulation modeling (PHABSIM; Bovee 1982), was also evaluated for use in determining habitat availability for young fish. Peaks and dips in model outputs made acceptable flows difficult to determine, and discharge levels at which recruitment, growth, and habitat were 1i lfi I 1 ',j