Laserfiche WebLink
<br />averaged 67%, whereas survival in backwater sites averaged 40%. Both growth and <br />survival was low in Old Charley Wash. A net loss in weight occurred among all fish in <br />backwater cages. Conversely, gains in weight occurred in two of the three wetland <br />sites, with a loss in weight occurring in fish in one of the Old Charley Wash cages (no <br />fish survived in the other cage in Old Charley Wash). <br /> <br />Competition experiments in 1993 resulted in extremely low razorback sucker <br />survival in both larval and juvenile comparisons. Larval razorback sucker and red <br />shiners were counted into buckets for transfer to cages already in place at Old Charley <br />Wash. In the buckets containing a mixture of red shiners and razorback sucker larvae, <br />100% of the larvae were consumed by the red shiner. No additional larval razorback <br />sucker were available for experimentation so this portion of the study was discontinued. <br />The juvenile razorback sucker experiment was initiated 29 July and terminated 26 <br />August, 1993. Similarly, low survival of juvenile razorback sucker occurred in cages in <br />Old Charley Wash (Table 4). Only one juvenile razorback sucker survived the length of <br />the experiment representing 0.33% treatment survival. Conversely, red shiners survival <br />was high in two of the three cages averaging 66.7%. The single razorback sucker was <br />7 mm greater than the average size stocked and average red shiner total length was <br />7.6 mm greater than the average size stocked. <br /> <br />DISCUSSION <br /> <br />Growth experiments in this study provided limited information on the relationship <br />of wetlands to the growth and survival of early life stages of razorback sucker. Growth <br />and survival in two of three wetlands were much higher than all backwater sites tested <br />in 1991. Mortality of fish in Old Charley Wash was determined to be caused by <br />bacterial septicemia (USFWS, Fort Morgan Fish Health Laboratory). Field observations <br />noted that fish in Old Charley Wash had the heaviest infestation of Lemea sp. among <br />all wetland or backwater replicates. Tyus and Karp (1989, 1990) suggested that <br />emergence of razorback sucker larvae from spawning sites during peak runoff indicated <br />a link between floodplain habitat and nursery habitat. Modde et al. (1996) supported <br />the linkage of floodplain habitat with recruitment by correlating the number of small <br />adult razorback sucker collected in the middle Green River with previous high flow <br />events. Successful recruitment of many species occupying floodplain habitat has been <br />linked to high flow events in both tropical and temperate river systems (Welcomme <br />1985). Since the completion of this study, Fish and Wildlife Service personnel collected <br />eleven wild yearling razorback sucker (250-370 mm total length) in the Leota Pond <br />complex in 1994 (U.S. Fish and Wildlife Service, Vernal, unpublished data), and 73 <br />age-O juvenile razorback sucker in Old Charley Wash in 1995 and 1996 (Modde 1996, <br />USFWS unpublished data). These fish were spawned during high water years of 1993, <br />1995, and 1996 (peak flows at Jensen exceeding 566 m3/s). The occurrence of age-O <br />and subadult life stages in wetland habitat, together with high invertebrate production <br />(Mabey 1993) and rapid growth capabilities reported by Osmundson and Kaeding <br />(1989), supports the contention~of Tyus and Karp (1990), Modde et al. (1995), and <br />Modde et al. (1996) that floodplain habitat is important nursery environment for <br />razorback sucker. <br /> <br />26 <br />