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<br />, <br />'., <br /> <br />Kanab Ambersnail <br /> <br />Information on the population size of the Kanab ambersnail in Arizona is limited. Anecdotal <br />information on population size ranges from a couple dozen to over a hundred thousand <br />individuals. During 1995, a cooperative interagency effort was made to estimate population <br />size. Using a replicated, small-plot sampling technique, population estimates were made in <br />March, June, and September 1995. Density estimates were made in patches that were not <br />accessible due to sampling difficulties. <br /> <br />When Glen Canyon Dam closed in 1963, the high spring time floods of the pre-dam era ended. <br />Typically, high spring time flows were in excess of 2260 cms and in some years exceeded 2800 <br />cms (U.S. Bureau of Reclamation 1995b). Flows of this magnitude probably restricted habitat <br />for the Kanab ambersnail at Vaseys Paradise. How much habitat existed before the closure of <br />Glen Canyon Dam or whether the Kanab ambersnail even existed at Vaseys is not known. <br /> <br />During the interim flow period (1991 to present), maximum flows have been limited to 560 cms <br />and have rarely exceeded that level. This change in dam releases has allowed the vegetation to <br />expand down to the 560 cms level resulting in approximately 895 m2 of primary habitat where <br />most individuals are found in September 1995 (Stevens et aI. 1995a). The primary habitat is" <br />dominated by the native MimuIus and non-native Nasturtium. This primary habitat is <br />interspersed with other marginal or secondary habitat. The marginal habitat is dominated by <br />poison ivy, grasses, maidenhair fern (Adiantum capillus-veneris), or other species. Only one <br />individual was found in the marginal habitat during the 1995 field season (Larry Stevens. <br />personal communication). <br /> <br />Data estimates suggest that only a small percent of the actual Kanab ambersnai1 individuals will <br />be lost during a March flood, about 3.3 percent. However, information on population densities <br />is limited and estimates are cursory. Many of the habitat areas were not measured. For <br />example, population estimates were not performed on some 290 m2 of the 85 I m2 total area of <br />primary habitat calculated for March. If those 290 m2 in fact did not contain snails, then the <br />total primary habitat would not be 851 nt, but rather 561 nt. Mean densities likewise are not <br />known for those unsampled areas, but as primary habitat, these areas are assumed to contain lhe <br />same densities as the measured areas. <br /> <br />Southwestern WlUow Flycatcher <br /> <br />The southwestern willow flycatcher is one of the most rare birds in the Grand Canyon corridtlr <br />Historic records report the species near Lees Ferry and the Little Colorado River conllucra;c <br />(Phillips, personal communication, cited in Unitt 1987). Nesting southwestern WIll"", <br />flycatchers were reported to be common in the Glen Canyon area in the 1950s (later inund.1lc:.l <br />by Lake Powell) and two pairs with nests were located in Grand Canyon (RM 50.7 and R~t <br />71.1) (Behle and Higgins 1959). Carothers and Brown (1991) believe that nesting pairs tn (he <br />Grand Canyon may have increased following closure of Glen Canyon Dam and attribule: lh" <br /> <br />Biological and Conference Opinions Glen Caoyon BcachlHabitat-Building flows 2116196 <br /> <br />1.& <br />