Thomas A. Wesche

Status of Instream Flow Legislation and Practices in North America

Abstract This paper presents the results of two nonstatistical surveys (completed in 1981 and 1986) that solicited information from state and federal agencies concerning instream flow issues and practices in North America. Forty-six states and 12 Canadian provinces responded to the survey. Fifteen of the 46 states reported legislative recognition of instream flows for fisheries protection. In Canada, individual provinces generally lacked instream flow legislation, although federal legislation existed that could be used. The most commonly applied method (in use in 38 states or provinces) for assessing instream flow requirements, as reported in the survey, was the Fish and Wildlife Service Instream Flow Incremental Methodology (IFIM). Major research needs cited by survey respondents included (1) more species habitat information and preference curves, (2) techniques for determining instream flows for atypical conditions, and (3) testing of fish habitat:flow: production relationships.

Winter Stream Conditions and Use of Habitat by Brook Trout in High-Elevation Wyoming Streams

Abstract Winter stream conditions at elevations between 2,280 and 3,205 m above mean sea level and the use of winter habitat by adult brook trout Salvelinus fontinalis above 2,990 m were evaluated in 1983–1984 and 1984–1985. Little surface ice was observed at elevations above 2,900 m, which was associated with high snow accumulation; moderate surface ice and anchor ice formation were observed at elevations from 2,550 to 2,900 m; extensive surface ice formation occurred at 2,550 m. Little snow accumulated at 2,550 m and surface ice physically excluded substantial brook trout habitat. In late fall, brook trout at elevations above 2,990 m tended to move into low-gradient areas where they remained active throughout the winter. During winter, brook trout appeared to select for areas with maximum velocities of 15 cm/s or less, measured during summer low flow, and for deeper water, but not for substrate type.

Relations of geomorphology to stream habitat and trout standing stock in small Rocky Mountain streams

Abstract Evidence that drainage basin morphology and trout standing stock are related through a functional link between geomorphic features and stream habitat quality is presented. Numerous significant univariate correlations were found between geomorphic variables, stream habitat variables, and trout standing stock in both high-elevation forest and low-elevation rangeland streams. Canonical correlations between geomorphic variables and stream habitat variables provided insight into the form of the functional link. Multiple-regression equations predicting trout standing stock were dominated by geomorphic variables. When geomorphic variables alone were incorporated into regression models they predicted trout standing stock as accurately as did stream habitat variables.

Modified Habitat Suitability Index Model for Brown Trout in Southeastern Wyoming

Abstract The habitat suitability index (HSI) model for brown trout Salmo trutta in stream systems, developed by the U.S. Fish and Wildlife Service, was tested with data from 30 reaches on nine streams in southeastern Wyoming. The HSI was not significantly correlated (P > 0.05) with brown trout standing stock. We analyzed 14 individual suitability index variables from the HSI model plus 25 other habitat variables for their relation to standing stock. Two HSI model variables and seven of the additional variables had significant correlations with brown trout standing stock. When these nine variables were used in multiple regression analysis, the best model (R2 = 0.52) for predicting standing stock (S, kg/hectare) of brown trout included measures of cover and flow regime: S = 1.71MTCR + 114.3 V14 - 0.60; MTCR is a measure of cover availability and V14 is the average annual base flow expressed as a percent of average annual daily flow. An index of fishing pressure was also developed and found to significantly ...

Snorkeling as an Alternative to Depletion Electrofishing for Estimating Abundance and Length-Class Frequencies of Trout in Small Streams

Abstract Trout counts and length-class frequencies determined by snorkeling were compared with estimates determined by electrofishing in 25 reaches of small (≤11-m wetted width) streams of the Bighorn Mountains, Wyoming. The numbers of trout (brook trout Salvelinus fontinalis, rainbow trout Oncorhynchus mykiss, and cutthroat trout O. clarki) counted by snorkeling were highly correlated (r 2 = 0. 90–0.99) to depletion estimates of abundance determined by electrofishing, averaging 65% of depletion estimates. Inclusion of instream cover and underwater visibility significantly improved predictions of all salmonid species combined in regression models that predicted depletion estimates by electrofishing from snorkeling counts. Length frequencies obtained by snorkeling and electrofishing were similar when frequencies of trout in three length-classes (0–100, 101–300, and >300 mm) were adjusted (observed length by snorkeling divided by 1.25) for underwater visual magnification. Snorkeling was an alternative to el...

Contribution of Riparian Vegetation to Trout Cover in Small Streams

Abstract Cover is an important trout habitat component resulting from the geomorphologic characteristics of a stream channel, the stream-bank interface with the riparian community, and the stream flow. By means of regression analysis, this study quantitatively describes the relative importance of three cover parameters (overhead bank cover, rubble-boulder-aquatic vegetation areas, and deepwater areas) and two cover models as indicators of trout standing stock in eight small streams in southeast Wyoming. Results indicated that overhead bank cover, provided primarily by riparian vegetation, is the cover parameter that explains the greatest amount of variation in trout population size.

Selection of Measures of Substrate Composition to Estimate Survival to Emergence of Salmonids and to Detect Changes in Stream Substrates

Abstract Biologists have attempted to link intragravel survival of juvenile salmonids to changes in stream substrate quality caused by land management, but the failure to standardize measures of substrate composition has hindered this effort. We compared 15 such measures in laboratory tests that evaluated survival to emergence of Colorado River cutthroat trout Oncorhynchus clarki pleuriticus in substrates ofdifferent composition. We also evaluated the sensitivity of three measures of substrate composition to the modification of stream substrates by spawning brook trout Salvelinus fontinalis and to the deposition of sediment in former redds of Colorado River cutthroat trout. Different estimates of the geometric mean particle size accounted for the greatest proportion of the variation in survival to emergence in laboratory tests, but the percentage of substrate less than 0.85 mm in diameter was the most sensitive measure of known changes in substrate composition in the field. We concluded that a single meas...

Description of Brown Trout Redds in a Mountain Stream

Abstract We sampled redds of brown trout Salmo trutta in a mountain stream to describe egg location and substrate composition after spawning and during egg incubation. A single-probe freeze-coring device was used to sample egg depth and substrate composition. We found eggs throughout redds but most often in the front half of the tailspill (the substrate mound that accumulates as the redd is excavated progressively upstream). Eggs were buried between 2 and 23 cm below the substrate surface but were most frequently 9–12 cm deep. Spawning fish cleaned substrate particles less than 6.3 mm in diameter from egg pockets, yet the percentage of particles smaller than 1.7 mm in egg pockets was correlated with that outside redds. Egg pockets contained particles larger than 50 mm more often than did any other location, indicating that particles of this size were used as egg pocket centrums. The percentage of 1.7-mm and smaller particles in egg pockets was higher in winter than in fall. We conclude that (1) spawning b...

Effects of Fall-to-Winter Changes in Habitat and Frazil Ice on the Movements and Habitat Use of Juvenile Rainbow Trout in a Wyoming Tailwater

Abstract Overwinter declines in the abundance of small rainbow trout Oncorhynchus mykiss have been observed in a section of the Big Horn River that lies downstream from Boysen Reservoir, where reservoir releases prevent surface ice formation. To provide insight into the possible causes of these declines in abundance, radiotelemetry was used to determine movement and microhabitat use of juvenile (20–25 cm total length) rainbow trout during the fall and winter of 1995–1996. Throughout the fall and winter, both stocked (hatchery) and naturally spawned (wild) fish were generally found in main-channel pools with cover that reduced current velocities to less than 2 cm/s near the bottom and with nearby (<2 m) water velocities that were greater than 15 cm/s. These locations provided refuges from the current, with adjacent flowing water that could deliver drifting aquatic invertebrates. The fish were generally associated with cover that was formed by aquatic vegetation early in the fall, but they shifted to cobble...

Substrate Alteration by Spawning Brook Trout in a Southeastern Wyoming Stream

Abstract To measure the changes in substrate composition produced by spawning brook trout Salvelinus fontinalis, we collected 187 freeze-core samples, both before and after spawning, from egg pockets, inside redds but excluding egg pockets, and outside redds. In the upper strata of reddassociated samples, we found that the proportions of particles 0.85–1.70, 0.425–0.85, 0.212–0.425, and less than 0.212 mm in diameter were significantly lower in egg pockets than outside redds, and the proportions of particles 0.425–0.85, 0.212–0.425, and less than 0.212 mm in diameter were also lower in egg pockets than in other areas inside redds. Samples collected outside redds were similar to samples collected before spawning. We observed no significant correlations between the proportion of fine sediment in samples from outside redds (and presumably the proportion present before spawning) and the proportion of fine sediment in egg pockets. In vertically stratified samples, the lower strata contained a greater proportio...