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Electrofishing is commonly used when renovating small streams to remove nuisance fishes but the likelihood of complete eradication of unwanted species, particularly warm-water fishes, is unknown. In October of 2008, we electrofished Bonita Creek, a small stream with base flows (<0.56 m3/s) in southern Arizona, and then treated the stream with rotenone to kill all of the remaining fish and quantify the effectiveness of single and multiple-pass electro fishing. Six, 100-m transects were electro fished on three consecutive days followed by a single treatment with rotenone. Fish caught using electrofishing were identified, counted and removed from each transect daily and then compared to numbers of dead fish collected during the subsequent rotenone application. Electrofishing effectiveness was highly variable among transects. Single-pass electrofishing caught an average of 23% (95% CI=5 to 40%) of the fish present, and three-pass electrofishing on consecutive days caught on average 55% (95% CI=28 to 83%) of the fish in each transect. Native Arizona fishes were more susceptible to electrofishing (77 % captured) than non-native species (54% captured), though native fish were rare. Transects in Bonita Creek averaged 3.6±1.5 m wide and 0.25±0.20 m deep (max depth 1.2 m). Bonita Creek is a small first-order stream which exhibits ideal conditions for backpack electrofishing, yet we captured a relatively small percentage of the fish present. This suggests that complete removal of non-native warm-water fishes using backpack electrofishing is not likely to be successful, especially in larger more complex streams.
We report on Asilidae collected in southern Nevada from 2004–2012 across an elevation gradient from 170 m along the Colorado River to 3350 m in Spring Mountains National Recreation Area (SMNRA), with particular emphasis in Ash Meadows National Wildlife Refuge (AMNWR) and SMNRA. Collections were made opportunistically during extensive expeditions throughout the region. We detected 42 species in 25 genera among at least 116 specimens, including 18 new state records for Nevada. Our data increase the Nevada asilid species list to at least 151 species in 52 genera. Robber flies were relatively common in specific locations, but varied in abundance and composition among species and across the region. We detected 20 robber fly species among 13 genera in AMNWR, and 23 species in 17 genera in SMNRA. Despite the proximity of AMNWR and SMNRA, only 3 of 42 (7.1%) documented species co-occurred in the two primary study areas. The paucity of robber fly species in Ash Meadows may be attributable to the abundance of evaporitic alkaline precipitates and the absence of organic soils there. At upper elevations in SMNRA, the low abundance of robber flies may similarly be related to limited habitat area, as well as a shorter growing season. The large number of species new to Nevada among this relatively small number of specimens indicates that further robber fly collections are needed across elevation in Nevada to improve understanding of the biogeography of this family in this region.
We examined survival of bullfrog (Rana catesbeiana) eggs and tadpoles at 3 ppt and 6 ppt salinity in the laboratory to determine if low-level salinity could be used to eradicate bullfrogs from small ponds that contain native fishes. Bullfrog eggs and tadpoles <10 days old experienced 100% mortality when held at 6 ppt salinity for 10 days. Bullfrog tadpoles 10–15 days old experienced significantly reduced survival when exposed to salinity of 6 ppt for 10 days. Older bullfrog tadpoles (>9 months old) appeared unaffected by 14 days of 6 ppt salinity. Salinity of 3 ppt did not impact survival of bullfrog tadpole eggs or tadpoles at any of the life stages we tested. Adding salt to ponds in the early spring to increase salinity to 6 ppt may be a cost effective way to eradicate bullfrogs from small ponds without harming native fishes.
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