Floodplain Wetland Suitability, Access, and Potential Use by Juvenile Razorback Suckers in the Middle Green River, Utah

In the upper Colorado River basin, razorback suckers Xyrauchen texanus primarily occur as adults in low‐gradient reaches of rivers or as juveniles or subadults in adjoining floodplain depressions. During the high‐water years of 1995 and 1996, a number of habitat variables—zooplankton density, water temperature, quality, and depth, and vegetative cover—in a Green River floodplain depression were favorable to age‐0 razorback suckers and other fishes. Conversely, main‐channel habitats were not suitable as rearing sites due to lower temperatures, less food, and ineffective cover. During the spring runoff in 1995 and 1996, larval razorback suckers were found in the river after floodplains were isolated from the Green River. Although favorable nursery sites are located off‐channel, the connectivity of the river and floodplain did not last long enough for all razorback sucker larvae to access these areas. Maintaining the connectivity of the floodplain to the river via levee removal and adequate flood duration will increase access to and the use of nursery habitat favorable to larval razorback suckers in the middle Green River. This study also suggests that larval razorback suckers are more likely to survive and grow in floodplain depression habitats than in main‐channel habitats. Although age‐0 razorback suckers grew and survived in an environment dominated by nonnative predators and competitors, the magnitude of nonnative fish impacts on razorback suckers in floodplain wetlands remains undefined.