Can Survival of Razorback Sucker be Improved by Stocking Them into Reservoirs with Manipulated Water Levels?
Stocking native Southwestern fishes into waters already containing fishes typically results in low survival of the stocked fish. From 1981-1990, 11 million razorback sucker Xyrauchen texanus and 750,000 Colorado pikeminnow Ptychocheilus lucius were stocked in the Verde and Salt Rivers Arizona, but only 519 and 444 of the fish from each species respectively were captured during electrofishing and netting surveys in the years following stocking. To improve survival of native fish stocked into Arizona rivers, nonnative fish populations must be depressed. Reservoir drawdown has been traditionally used as a means used to benefit sport fishes. Reservoirs are drawn down in late summer or fall to allow establishment of vegetative seedlings that will benefit spawning fish with nutrients and cover when water levels are raised in the spring. With water levels kept as high as possible in the spring, spring spawning is usually successful, and large numbers of fish are produced. Reservoir drawdowns are also used to reduce standing crops of some fishes, with associated increase in growth, condition, and other characteristics of desirable species. In a study of 11 reservoir drawdowns for fish control purposes, 45% were deemed successful. Native fish, such as Razorback Sucker, may benefit by stocking them into reservoirs subject to water level manipulations at appropriate times. Horseshoe Reservoir, on the Verde River, provides a location where combined reservoir water level management techniques and native fish stockings might be tried. Unlike most reservoirs, Horseshoe Reservoir water elevation is managed to benefit of native aquatic species. We are investigating the ability to improve survival of Razorback Sucker by stocking them into Horseshoe Reservoir, using an upstream site as a reference area. Our objectives are to provide information to management agencies on survival of Razorback Sucker stocked into a fluctuating reservoir compared to the river, identify water level manipulations associated with any increased survival, and compare movement and growth of Razorback Sucker stocked into both sites. Razorback Sucker stocked into the system were reared at Southwestern Native Aquatic Resources Recovery Center to appropriate sizes (200-350 mm TL) and implanted with both radio tags and pit tags so their movements and survival could be tracked following stocking. The first stocking of fish occurred in March 2022. Movement and survival of fishes was monitored through use of radiotracking towers placed on the shoreline of the reservoir and along the river. This project will result in a Ph.D. dissertation and several publications.