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7/14/2009 5:02:35 PM
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UCREFRP
UCREFRP Catalog Number
9410
Author
Wydoski, R. S. and E. J. Wick.
Title
Ecological Value of Floodplain Habitats to Razorback Suckers in the Upper Colorado River Basin.
USFW Year
1998.
USFW - Doc Type
Denver.
Copyright Material
NO
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<br />predation by nonnative fishes because food organism availability is low in <br />the main channel and backwaters of Upper Basin rivers. <br /> <br />Nonnative red shiners and fathead minnows are often the most abundant fish <br />species in backwaters of the Upper Basin rivers. For example, Cranney <br />(1994) reported that red shiners constituted 66.5% and fathead minnows <br />31.9% of 3,599 fish collected in 13 seine hauls in the lower Duchesne <br />River, a tributary to the middle Green River. Only one native fish (a <br />bluehead sucker) was captured during that sampling effort. Red shiners <br />and fathead minnows constituted 90.4% of 149,489 fish collected between <br />1986 and 1994 from primary backwaters of the Colorado and Green rivers <br />during the Interagency Standardized Monitoring Program (McAda et al. <br />1994a, 1994b, 1995). In 1996, nonnative minnows (combined species) <br />comprised 92-99% of the total number of fish seined from backwaters of <br />Upper Basin rivers during standard monitoring (McAda et al. 1997). <br /> <br />Adult red shiners were found to be predators on fish larvae in the Yampa <br />and Green rivers (Ruppert et al. 1993). Adult red shiners (36.1 mm TL) <br />consumed all 100 razorback sucker larvae and terminated a cage experiment <br />in a wetland to determine competition between the two species (Modde and <br />Wick 1997). Fathead minnows have also been documented to be predators on <br />catostomid larvae (Dunsmoor 1993). Therefore, it is reasonable to assume <br />that nonnative minnows such as the red shiner and fathead minnow are <br />important predators on razorback sucker larvae. The razorback sucker <br />spawns on the ascending limb of the hydrograph and their larvae drift <br />downstream during May and June when zooplankton and benthic invertebrate <br />numbers are low in backwaters in the turbid waters of Upper Basin rivers. <br />Razorback sucker larvae would be highly susceptible to predation at that <br />time by abundant nonnative minnows. <br /> <br />The composition of fish species in existing backwaters along six reaches <br />in the middle Green River was made up primarily of nonnative minnows. <br />Fathead minnows composed between 37.7 and 88.1% of fyke net catches in <br />1997 and red shiners composed 6 to 48.5% of the catches at these six sites <br />(G. Birchell, 1998, personal communication). In backwaters that were <br />reconnected with the main channel along the same six river reaches, <br />fathead minnows composed over half (50.4 - 72.4%) of fyke net catches and <br />red shiners comprised between 3.1 and 18.3% of the catches in 1997. <br /> <br />Although successful natural spawning of razorback suckers occurs on wave- <br />swept rubble along the shoreline of Lake Mohave, survival of larvae only <br />occurs in habitats such as predator-free isolated coves (Minckley et al. <br />1991). However, in the absence of predaceous fish, large numbers of <br />odonate nymphs were produced in these coves and they replaced fish <br />predators (Mueller et al. 1993). Horn et al. (1994) reported that <br />odonate nymphs were very effective in capturing and consuming razorback <br />sucker larvae in the laboratory. Larger juvenile razorback suckers are <br />now stocked into the isolated coves to reduce or eliminate predation by <br />odonate nymphs. <br /> <br />Nonnative fishes quickly occupy floodplain habitats that are reconnected <br />to the main channels of Upper Basin rivers (G. Birchell, 1998, personal <br />communication; Burdick et al. 1997). For example, nonnative .fishes <br />invaded and colonized a gravel-pit pond in the floodplain of the upper <br />Colorado River within four months after the pond was drained, all <br />nonnative fishes removed, and the pond reconnected with the river (Burdick <br />et al. 1997) and, within eight months, five species of nonnative fishes <br />successfully reproduced in the pond. This pond had a irregular bottom <br />that was below the streambed of the main channel and did not drain as <br />streamflows from the spring runoff subsided. Burdick et. al. recommended <br />that deep gravel-pit ponds be rehabilitated by reshaping and sloping the <br /> <br />24 <br /> <br />I <br />I <br />I <br /> <br />I <br /> <br />I <br />I <br /> <br />J <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br />I <br /> <br />I <br />
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