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35 hydrologic regime required fora particular life stage of the endangered fishes. Physical habitats include areas of the Upper Basin that are inhabited or are potentially habitable by the endangered fishes for use in spawning, nursery, feeding, rearing, or corridors between these areas. In addition to river channels, these areas also include bottom lands, side channels, secondary channels, oxbows, backwaters, and other areas within the 100-year floodplain, which when inundated provide habitat for the above uses. Food supply, predation, and competition are important elements of the biological environment. Food supply is a function of nutrient supply and productivity. which could be limited by reduction of high spring flows brought about by water depletions. Predation and competition from nonnative fish species have been identified as factors in the decline of the endangered fishes. .Water depletions contribute to alterations in flow regimes that favor nonnative fishes. The Service concludes that water depletions impact the primary constituent elements of water, physical habitat, and the biological environment. Because water depletions from the Upper Basin are a major factor in the decline of the endangered fishes, the Service has determined that any depletion will jeopardize their continued existence and will likely contribute to the destruction or adverse modification of their critical habitat. The effects of depletions by Federal projects (447 KAF) under consideration in this opinion further reduces the environmental baseline (648 KAF) of the Duchesne River by approximately 69 percent. Federal projects plus private uses (totaling 567 KAF), have reduced pre-development flows of the Duchesne River by nearly 74 percent. Flow reductions of this magnitude significantly limits the flexibility of Federal agencies and the RIP, both of which are charged with protecting listed species and their critical habitats, to meet final flow recommendations for the endangered fishes within the Duchesne River. Soecies Response to a Proposed Action The Service believes that historically the Duchesne River and its natural flow regime were important to the Colorado River endangered fishes. Adult and young-of-the-year Colorado squawfish and razorback sucker are known to, have occurred in the Duchesne River (Cranney, UDWR 1994). Cranney (1994) reported that documentation of the presence of Colorado squawfish in the Duchesne River was first noted in unpublished stream survey reports of the Utah Division of Wildlife Resources in 1956. Eight squawfish were collected in electrofishing surveys August 7-8, 1956 from Bridgeland (upstream of the town of Myton, UT at RM 49) to the Green River confluence. Sizes of captured fish ranged from 1-5"