Laserfiche WebLink
<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />The acres and hectares of floodplain habitat necessary to support each combination of <br />input variables specified by the user, and the number of fish surviving to recruitment, as well as <br />recruitment rate, are plotted to facilitate visual interpretation of the model output. <br /> <br />This section describes pertinent life history variables of razorback sucker as used in the <br />floodplain model. A review ofliterature was done and is summarized is Appendix A. <br />3.1 Numbers of Adults <br />Historic numbers of adult razorback sucker in the Upper Colorado River Basin are <br />unknown. During 1979-81, 92 adult razorback sucker were captured in the Green River (Tyus et <br />al. 1982). Estimated number of adults in the middle Green River in J 988 was 948 (95% C.!. = <br />758-1,138; Lanigan and Tyus 1989), and estimates 8 years later were 524 adults (95% C.I. = <br />351-696; Modde et al. 1996). Although estimates showed the population declining, young fish <br />were captured that provided evidence of natural recruitment during 1983-86 (Modde et aI. 1996). <br />Numbers of wild adults in the Green River are too low for reliable estimates, and the current wild <br />population in the middle Green River is estimated at about 100 adults (Bestgen et al. 2002). <br />During 1979-81, 52 adult razorback sucker were captured in the Upper Colorado River <br />(Valdez et al. 1982). No estimates of abundance were made, and during 1984-90, only 12 adults <br />were captured with no evidence of reproduction or recruitment (Osmundson and Kaeding 1991). <br />The razorback sucker is considered to be extirpated from the Gunnison River (Burdick and Bonar <br />1997). Only two wild razorback sucker have been captured in the San Juan River; one in 1976 <br />and one and 1988 (Ryden 2000). No wild razorback sucker were found during a 7-year research <br />period (1991-97) in the San Juan River (Holden 1999). <br />These estimates of wild adults can be used in the model to illustrate survival necessary at <br />various life stages in order for the population to be self-sustaining. Recovery goals for razorback <br />sucker in ~.e Upper Colorado River Basin require self-sustaining populations that exceed 5,800 <br />adults each in the Green River subbasin and either the Upper Colorado River subbasin or the San <br /> <br />6 <br />