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F� <br />' requirements of other native fishes since studies were not designed to address these species <br />specifically. <br />' At this time sufficient information is known about habitat use of adult and YOY Colorado squawfish <br />and adult razorback sucker in the San Juan River that this task has been nearly completed by the <br />Program. <br />5.2.5.2. Identify Subreaches that Provide Habitats for the Different Life Stages. <br />' Contributing Investigations <br />' Two types of studies were conducted to identify important subreaches for the target fish species. <br />One type included fish sampling studies (Buntjer et al. 1993, 1994; Lashmett 1993, 1994; Ryden and <br />Pfeifer 1993, 1994, 1995a, 1996a; Miller 1994a, 1995; and others) that showed the areas of a raver <br />' that the fish used. The second type of study involved habitat characterization (Pucherelli and <br />Goettlicher 1992; Bliesner and Lamarra 1993, 1994, 1995, 1996) which identified the amount of <br />habitat in various parts of the river. When combined with information on habitat preferences of <br />' Colorado squawfish and razorback sucker, these studies can be used to understand why certain areas <br />of the San Juan River are used by fish as well as potentially identifying areas that appear to provide <br />suitable habitat, but are not currently occupied. <br />Findings <br />Fish Sampling Studies <br />Colorado Squawfish: Studies by Ryden and Pfeifer (1993, 1994, 1995a, 1996a) showed that <br />Colorado squawfish adults primarily use the San Juan River between RM 119 and RM 148. The <br />multi - threaded channel, habitat complexity, and mixture of substrate types in this area of the river <br />are somewhat unique and appear to provide a diversity of habitats favorable to Colorado squawfish <br />on a year -round basis. The Mixer (RM 129.8 to RM 133.4) was especially heavily used during the <br />purported spawning periods of 1992 -1994. Also, observations of radio - tagged adults indicate that, <br />within this reach, the mouth of the Mancos River and nearby habitats (RM 122 to RM 123) are used <br />during the prespawning period as possible staging areas. Another smaller area of use by adult <br />Colorado squawfish centers around RM 75. Figure 2 shows the locations of all adult Colorado <br />squawfish captures from 1987 to 1996. <br />Spawning habitats may also be identified to some degree by the capture of very young fish. Two <br />drift net locations have been sampled for young fish since 1991 (Buntjer et al. 1993, 1994; Platania <br />1996, 1997). One location is near Mexican Hat (RM 53) and another near Four Corners (RM 119) <br />which was moved upstream to RM 128 to be closer to the Mixer in 1995 (Platania 1996). Two larval <br />Colorado squawfish about 10 mm TL were caught at the Mexican Hat site in 1993, 24 hours apart <br />(Buntjer et al. 1994, Snyder and Platania 1995). During 1995, two more larval Colorado squawfish <br />were collected in drift nets at the Mexican Hat site. They were 9.0 and 9.5 mm TL and were caught <br />within 12 hours of each other. The collection of such young fish (only a few days old) at Mexican <br />Hat during 2 years suggests that perhaps another spawning area for Colorado squawfish exists <br />somewhere below the Mixer (Platania 1996) and that it may be related to the adult captures noted <br />San Juan River Recovery Implementation Program December 1997 <br />Summary Report 23 PR -602 -1 <br />