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<br />further complicated because of limited life history information. Habitat use <br />of endangered fishes may only reflect temporary, seasonal, or marginal habitat <br />availability. Thus, caution must be exercised when determining habitat needs <br />and limiting factors for fishes in decline, and professional biological <br />judgement must be recognized as critical in data interpretation. We stress the <br />need for system-level cognizance and interpretation in evaluating factors that <br />are potentially limiting species in decline; e.g., a high number of an <br />endangered species in one restricted location may not justify its delisting. <br /> <br />Based on professional interpretation of the best available data, we <br />consider the following flow and non-flow related measures as important for <br />recovery of listed Colorado River fishes in the Green River basin. These are <br />presented by time of year and species. <br /> <br />Spring (March 21-June 21) <br /> <br />Colorado sauawfish <br /> <br />Adult Colorado squawfish utilize inundated shorelines and lowlands during <br />spring. This natural lowland inundation, and the increased availability of <br />food and habitat is viewed as important for physiological conditioning. Use of <br />these habitats may mitigate some of the affects of winter stress, and aid in <br />offsetting the large energy expenditure required for migration and spawning. <br />less-than-annual spawning observed in the fish may be associated with adverse <br />winter/spring conditions. <br /> <br />Migration is an important component in the reproductive cycle of Colorado <br />squawfish and migration routes must be protected and barriers discouraged. We <br />consider migration cues such as high spring flows, increasing river <br />temperatures, and possible chemical inputs from flooded lands and springs as <br />important to successful reproduction. The duration, magnitude, and timing of <br />spring runoff also affects spawning substrates,' and formation of eddy <br />habitats used by staging fish. High spring flows mobilize nutrients and <br />sediments, and aids in forming nursery habitat. Ground and surface water in <br />the spawning areas may provide orientation/piloting cues. High and/or erratic <br />flows in early spring (March-April) may adversely affect backwater habitats to <br />the detriment of young Colorado squawfish. <br /> <br />Reduced spring runoff may aid growth of the introduced sa1tcedar and other <br />plants which invade flood zones, trap sediments, and thereby increase bank <br />stabilization. This can decrease habitats of young Colorado squawfish and <br />other native fishes while increasing habitat and providing environmental <br />conditions that are more suitable for some introduced fishes. <br /> <br />Humoback chub <br /> <br />The availability and suitability of rocky, canyon-bound habitat used by <br />humpback chub may be adversely affected by the present alteration of spring <br />runoff in the Green River. Spawning of humpback chub occurs shortly after <br />highest spring discharge at river temperatures of about 200C in tKe Yampa <br />River, and presumably in Gray Canyon area of the Green River. Flow effects on <br />the availability of shoreline eddy habitat, bank stabilization due to exotic <br /> <br />28 <br />