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to 13.6 mm long) (tentatively identified as razorback sucker) in quiet river margins of the Green River downstream of areas where razorback suckers in breeding condition were previously sampled. Extensive collecting in Lake Mohave has not found larvae greater than about 12 mm total length (Minckley et al. 1991). The inability of larvae to recruit into young-of-year or juvenile life stages in wild populations has been recognized as a major limiting factor for the survival of the razorback sucker, and Minckley et al. (1991) identified three possible explanations: "(1) transport from the system, (2) nutritional constraints resulting in starvation, and (3) loss of early life-history stages to predation" with the last one thought the most probable. To examine all possible factors, however, food habitat investigations of larval razorback suckers have been initiated to determine whether food may be limiting such as availability of an appropriate size food items for larvae that have just consumed their yolk sack or have changed orientation of their mouth (Minckley et al. 1991, Papoulias and Mincldey 1992). An intensive study of larval razorback suckers spawned and raised in an isolated cove in Lake Mohave is the subject of an ongoing investigation (Paul Marsh, personal communication). BALD EAGLE The Colorado River corridor within the Grand Canyon has become an important winter .' concentration area for the bald eagle. Although not a separate subspecies, bald eagles in the southwestern United States and northern Mexico are considered a distinct population for purposes of recovery efforts and section 7 consultation (U.S. Fish and Wildlife Service 1982, 1986). Prior to 1984, Floyd Thompson (Service, retired) reported locating three possible bald eagle nests in the Grand Canyon region (Hunt et aI. 1992). However, whether the wintering bald eagles in the Grand Canyon are part of the southwestern breeding population or migrate from northern latitudes is not known. Bald eagles were not recorded in concentrations in the Grand Canyon until after the establishment of the mainstem rainbow trout (Oncorhynchus myldss) fishery following construction of Glen Canyon Dam. Prior to Glen Canyon Dam, low winter flows and the presence of large native fishes may have offered similar or even superior conditions to those that exist today for wintering bald eagles, but no documentation exists to support this premise. Wintering bald eagles were first documented in the winter of 1985-1986, four birds (Brown et al. 1989), and have increased to a high of 26 birds counted in a single day at Nankoweap Creek in late February 1990 (National Park Service 1992). Bald eagle use of the river corridor is opportunistic and currently concentrated around Nank'llweap Creek (RM 52) where the birds utilize an abundant food source in the form of winter-spawning trout. These trout have been found to comprise greater than 99% of eagle foraging attempts (Brown and Leibfried 1990, National Park Service 1992). The number of bald eagles at Nanlwweap Creek appears to be directly related to the abundance of spawning trout. The number of trout attempting to ascend and spawn is a function of the number of spawning trout in the river and conditions in Nankoweap Creek. More than 500 trout were recorded at 13 October 1993 Omit biological opinion 2-21-93-F-167 IS