We evaluated the influence of drought conditions on the biomass of brown trout Salmo trutta in Spearfish Creek, upper Rapid Creek, and lower Rapid Creek in the Black Hills of western South Dakota. Stream discharge, mean summer water temperature, the biomass of juvenile and adult brown trout, and brown trout size structure were compared between two time periods: early (2000)(2001)(2002) and late drought (2005)(2006)(2007). Mean summer water temperatures were similar between the early-and late-drought periods in Spearfish Creek (12.48C versus 11.58C), lower Rapid Creek (19.28C versus 19.38C), and upper Rapid Creek (9.88C in both periods). In contrast, mean annual discharge differed significantly between the two time periods in Spearfish Creek (1.95 versus 1.50 m 3 /s), lower Rapid Creek (2.01 versus 0.94 m 3 /s), and upper Rapid Creek (1.41 versus 0.84 m 3 /s). The mean biomass of adult brown trout in all three stream sections was significantly higher in the early-drought than in the late-drought period (238 versus 69 kg/ha in Spearfish Creek, 272 versus 91 kg/ha in lower Rapid Creek, and 159 versus 32 kg/ha in upper Rapid Creek). The biomass of juvenile brown trout was similar (43 versus 23 kg/ha) in Spearfish Creek in the two periods, declined from 136 to 45 kg/ha in lower Rapid Creek, and increased from 14 to 73 kg/ha in upper Rapid Creek. Size structure did not differ between the early-and late-drought periods in lower Rapid and Spearfish creeks, but it did in upper Rapid Creek. In addition to drought conditions, factors such as angler harvest, fish movements, and the nuisance algal species Didymosphenia geminata are discussed as possible contributors to the observed changes in brown trout biomass and size structure in Black Hills streams.
This study evaluated the efficacy of two potential zero‐withdrawal anesthetics, Benzoak (20% benzocaine; 50, 60, and 75 mg/L) and Aqui‐SE (50% eugenol; 50, 60, and 75 mg/L) compared with tricaine methanesulfonate (MS‐222; 55, 80, and 100 mg/L), to anesthetize Rainbow Trout Oncorhynchus mykiss for PIT tag implantation surgery. In general, higher doses resulted in faster induction time to stage 4 anesthesia (defined by the cessation of reflex activity). At 204 s, the time to stage 4 anesthesia was slowest using MS‐222 at 55 mg/L, followed by 50 mg/L of either Benzoak and Aqui‐SE, which in turn were significantly slower to induce this level of anesthesia than were Benzoak or Aqui‐SE at 60 or 75 mg/L or MS‐222 at 80 mg/L. At 100 mg/L, MS‐222 had the quickest time, 57 s, to stage 4 anesthesia. Time to recovery was longest for Rainbow Trout exposed to any concentration of Aqui‐SE and shortest for MS‐222, and recovery times from Benzoak were intermediate. Although Rainbow Trout length and weight varied significantly among the treatments, time to anesthesia and recovery were more dependent on the anesthetic and concentration used. In our opinion, doses of either Benzoak or Aqui‐SE of greater than 60 mg/L will induce rapid anesthesia and provide relatively quick recovery times for adult Rainbow Trout.Received July 27, 2012; accepted January 10, 2013
We assessed variation in longitudinal distributions of native and introduced fishes and their occurrences in different habitat types downstream from Boysen Dam in the Bighorn River, Wyoming. The closure of Boysen Dam in 1952 and construction of three downstream water diversion dams have led to channel changes in the Bighorn River causing reductions in the numbers and areas of side channels, backwaters, and riffles. Eleven native and five introduced fish species were collected by seining during 2005. Fish samples were dominated by sand shiner (Notropis stramineus), flathead chub (Platygobio gracilis), and longnose sucker (Catostomus catostomus). Introduced fish species included common carp (Cyprinus carpio), emerald shiner (Notropis atherinoides), plains killifish (Fundulus flavis), yellow perch (Perca flavescens), and sand shiner. Differences in relative abundances of fishes among habitat types were observed. Fathead minnow (Pimephales promelas), longnose sucker, white sucker (Catostomus commersoni), plains killifish, and sauger (Sander canadensis) were found almost exclusively in backwaters, and channel catfish (Ictalurus punctatus) was collected almost exclusively in side channels. Changes from the pre-European fish community are occurring in association with invasions of introduced fish species and losses of side channels, backwaters, and riffles.
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