W. Carl Saunders

Improved Grazing Management Increases Terrestrial Invertebrate Inputs that Feed Trout in Wyoming Rangeland Streams

Abstract Research in forest and grassland ecosystems worldwide indicates that terrestrial invertebrates can be a significant source of prey for fish, providing about 50% of their annual energy. We examined whether input of terrestrial invertebrates to rangeland streams in western Wyoming provides an important prey resource for brown trout Salmo trutta and brook trout Salvelinus fontinalis and how it is modified by livestock grazing. During summers of 2004 and 2005 we sampled falling invertebrate input and trout diets in five pairs of streams that had riparian zones under two different grazing systems: High-density, short-duration (HDSD) grazing versus season-long (SL) grazing. The biomass of riparian vegetation and the input of terrestrial invertebrates were two to three times greater in reaches with riparian zones under HDSD than under SL grazing management. Likewise, the afternoon diets of individual trout in HDSD reaches had, on average, about twice as much terrestrial invertebrate biomass during summe...

Accurate Estimation of Salmonid Abundance in Small Streams using Nighttime Removal Electrofishing: an Evaluation using Marked Fish

Abstract Estimation of stream fish abundance using removal electrofishing is common and allows sampling of fish populations during a single site visit. However, recent evaluations have demonstrated that removal estimators can substantially underestimate fish abundance, raising concerns about using this method. We evaluated removal estimates of trout (family Salmonidae) abundance using night electrofishing in 200–300-m reaches of 8 Rocky Mountain streams and analyzed the data using new methods in Program MARK to account for potential sources of bias. The removal estimates were validated using populations of previously captured and marked resident fish. Overall, removal estimates were accurate estimates of the number of marked fish in study reaches (mean bias, −2.4% [<1 fish/reach]), and removal and mark–recapture estimates of total fish abundance also differed by less than 1 fish/reach on average. In general, capture probabilities were high (average = 97% over three passes), and removal estimates had narro...

Ecosystem experiment reveals benefits of natural and simulated beaver dams to a threatened population of steelhead (Oncorhynchus mykiss).

Beaver have been referred to as ecosystem engineers because of the large impacts their dam building activities have on the landscape; however, the benefits they may provide to fluvial fish species has been debated. We conducted a watershed-scale experiment to test how increasing beaver dam and colony persistence in a highly degraded incised stream affects the freshwater production of steelhead (Oncorhynchus mykiss). Following the installation of beaver dam analogs (BDAs), we observed significant increases in the density, survival, and production of juvenile steelhead without impacting upstream and downstream migrations. The steelhead response occurred as the quantity and complexity of their habitat increased. This study is the first large-scale experiment to quantify the benefits of beavers and BDAs to a fish population and its habitat. Beaver mediated restoration may be a viable and efficient strategy to recover ecosystem function of previously incised streams and to increase the production of imperiled fish populations.

Comparison of Tributary Survival Estimates of Steelhead using Cormack–Jolly–Seber and Barker Models: Implications for Sampling Efforts and Designs

AbstractWe conducted simulations to compare the precision and bias of survival estimates from Cormack–Jolly–Seber (CJS) and Barker models to known parameter values based on empirical data for steelhead/resident Rainbow Trout Oncorhynchus mykiss from the John Day River, Oregon. We simulated seasonal differences in recapture and survival rates, and we varied the number of fish tagged, recapture and resight rates, sample site size, and fish movement (migratory or resident). Survival estimates from the Barker model had higher precision and lower or equal bias in comparison with estimates from the CJS model under almost all simulation scenarios. The precision of Barker survival estimates increased the most as the number of tagged fish increased from 50 to 200 (CV = 0.4–0.09). The Barker models superior performance was dependent on the availability of resight data; such data are becoming more readily available, especially in places where large numbers of individuals are PIT-tagged and where an interrogation in...

A Lota lota Consumption: Trophic Dynamics of Nonnative Burbot in a Valuable Sport Fishery

AbstractUnintentional and illegal introductions of species disrupt food webs and threaten the success of managed sport fisheries. Although many populations of Burbot Lota lota are declining in the species’ native range, a nonnative population recently expanded into Flaming Gorge Reservoir (FGR), Wyoming–Utah, and threatens to disrupt predator–prey interactions within this popular sport fishery. To determine potential impacts on sport fishes, especially trophy Lake Trout Salvelinus namaycush, we assessed the relative abundance of Burbot and quantified the potential trophic or food web impacts of this population by using diet, stable isotope, and bioenergetic analyses. We did not detect a significant potential for food resource competition between Burbot and Lake Trout (Schoener’s overlap index = 0.13), but overall consumption by Burbot likely affects other sport fishes, as indicated by our analyses of trophic niche space. Diet analyses suggested that crayfish were important diet items across time (89.3% of...