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49p- 82 Environmental Enhancement of Water Projects netting. To improve fish collection, a benthic liner was installed in the deepest half acre (0.2 hectare) portion of Yuma Cove to prevent pondweed growth. Pondweed, which provides young fish cover, continues to grow in shallower areas of the backwater. A different spawning approach was attempted in 1993. Spawning suckers were again collected from the reservoir, but instead of allowing them to spawn naturally, their eggs were manually collected and fertilized. Approximately 250,000 fertilized eggs were then distributed in the shallows of the backwater where spawning would normally occur. Eggs did hatch and larval suckers were collected; however, the degree of success will not be known until later this fall when the fish are harvested. Davis Cove. Davis Cove is also located on Lake Mohave and represents a larger and deeper backwater isolated for the specific purpose of a grow-out area. The backwater is stocked with juvenile razorback suckers produced at Yuma Cove or Dexter National Fish Hatchery. A temporary net barrier was installed across the mouth of Davis Cove, isolating approximately 3 acres (1.2 hectares). A 3/8 inch (10 mm) bar mesh net was designed to conform to the cove's entrance. The opening is 150 feet (44 m) wide and 35 feet (11 m) deep. The net's borders were anchored with concrete block, supported with a flotation boom, and designed to accommodate the reservoir's 17 foot (5 m) fluctuation zone. The net barrier has worked well except along one shoreline where fine drift sand would accumulate on the net preventing it from following the rising reservoir. On two occasions, the barrier was compromised and sand had to be cleared from the net. The net worked well on the other shoreline, which was composed of large cobble and rock. The barrier net trapped resident fish found inside the cove. Instead of poisoning the fish, we attempted to remove non-native fish and release them unharmed into the reservoir. This procedure represented a test of whether a depleted non-native fish community would continue to exhibit high predation pressure. During the year, over 1,500 pounds (680 kg) were removed by electrofishing, gill netting, fyke netting, seining, and angling. Davis Cove received 10,000 juvenile razorback suckers from Dexter National Fish Hatchery and 150 larger suckers produced at Yuma Cove during June 1992. Razorback Sucker Program 83 Hatchery-produced fish averaged 25 inches (68 mm) in length upon stocking. Suckers produced at Yuma Cove averaged 6 inches (150 mm). Suckers collected during the following weeks showed the fish were growing. The collection also suggested that survival of the smaller hatchery produced suckers was substantially lower than the larger Yuma Cove fish. The ratio of Yuma Cove to hatchery produced fish recaptured by trammel nets or observed during scuba surveys was approximately 10:1. Many predators avoided capture using depth or concealment in pondweed beds or other types of cover. Although numbers of predators were depleted, those remaining continued to contribute to razorback sucker losses. This result suggests that even when numbers of exotic fish are greatly reduced, the depleted community can still cause severe predation pressure for small native suckers. It also suggests that survival is greatly enhanced as suckers reach lengths exceeding 6 inches (150 mm). Lake Mohave. Razorback suckers congregate along the shallow, wave washed shoreline each spring to spawn. Researchers take advantage of these concentrations to collect, tag, and monitor the population. These activities have been conducted during the past 15 years. one hundred and fifty three suckers exceeding 10 inches (25 cm) were released into Lake Mohave during the fall of 1992 from both Yuma and Davis Coves. Razorback suckers normally take 2-3 years to reach sexual maturity, and we anticipated a similar delay in detecting them in the reservoir population. To our delight, 5 of the 153 cove-reared fish released into the reservoir were recaptured during the 1993 spawning effort. Subadult suckers were collected in four different locations ranging from 3 to 21 miles (5-33 km) from their point of release. The fish had survived 6 months with the reservoir fish population and continued to reflect normal growth rates. The return of 5 of 153 fish from a reservoir of 28,500 surface acres (11,400 hectares) was remarkable. Although these numbers are extremely low, and we have yet to achieve our goal of introducing 10,000 juveniles, we remain optimistic that higher returns will result as more subadult suckers are released into the reservoir.