Troy G. Zorn

Distributions of stream fishes and their relationship to stream size and hydrology in Michigan's lower peninsula

Abstract We examined the distribution and abundance patterns of 69 fish species that commonly occur in the rivers of Michigans lower peninsula to develop a simple, empirically based model for describing fish assemblages. We used cluster analysis to group fishes that shared similar abundance patterns at 226 stream sites. The 17 clusters we identified explained about 39% of the variation in species abundances among the stream sites, providing a reasonable, albeit simplified, picture of general associations of fishes in lower Michigan streams. Known ecological differences among species and further analyses suggested that a measure of cluster abundance should not be used to predict the abundances of its constituent species. We selected catchment area (CA) and low-flow yield (LFY; 90% exceedence flow divided by catchment area) as axes for plotting fish distributions and rivers because these variables link catchment-scale features of the landscape to multiple, site-scale characteristics of stream habitat (e.g....

Defining and Characterizing Coolwater Streams and Their Fish Assemblages in Michigan and Wisconsin, USA

Abstract Coolwater streams, which are intermediate in character between coldwater “trout” streams and more diverse warmwater streams, occur widely in temperate regions but are poorly understood. We used modeled water temperature data and fish assemblage samples from 371 stream sites in Michigan and Wisconsin to define, describe, and map coolwater streams and their fish assemblages. We defined coolwater streams as ones having summer water temperatures suitable for both coldwater and warmwater species and used the observed distributions of the 99 fish species at our sites to identify coolwater thermal boundaries. Coolwater streams had June-through-August mean water temperatures of 17.0–20.5°C, July mean temperatures of 17.5–21.0°C, and maximum daily mean temperatures of 20.7–24.6°C. We delineated two subclasses of coolwater streams: “cold transition” (having July mean water temperatures of 17.5–19.5°C) and “warm transition” (having July mean temperatures of 19.5–21.0°C). Fish assemblages in coolwater stream...

Classification Tree Models for Predicting Distributions of Michigan Stream Fish from Landscape Variables

Traditionally, fish habitat requirements have been described from local-scale environmental variables. However, recent studies have shown that studying landscape-scale processes improves our understanding of what drives species assemblages and distribution patterns across the landscape. Our goal was to learn more about constraints on the distribution of Michigan stream fish by examining landscape-scale habitat variables. We used classification trees and landscape-scale habitat variables to create and validate presence-absence models and relative abundance models for Michigan stream fishes. We developed 93 presence-absence models that on average were 72% correct in making predictions for an independent data set, and we developed 46 relative abundance models that were 76% correct in making predictions for independent data. The models were used to create statewide predictive distribution and abundance maps that have the potential to be used for a variety of conservation and scientific purposes.

Use of GIS-Derived Landscape-Scale Habitat Features to Explain Spatial Patterns of Fish Density in Michigan Rivers

Abstract Both site- and landscape-scale processes play important roles in the biological communities of rivers. Understanding the influences of these processes on fish abundance can help direct management and research efforts toward appropriate habitat variables and scales. We used multiple linear regression analysis of a regional fish and habitat database to determine the feasibility of using geographical information systems (GIS)–derived landscape-scale habitat variables to explain the spatial variation in the density of five sport fish species (Chinook salmon Oncorhynchus tshawytscha, steelhead O. mykiss, brown trout Salmo trutta, brook trout Salvelinus fontinalis, and white sucker Catostomus commersonii) in the rivers of Michigans Lower Peninsula. We compared these models with those developed using site-scale variables traditionally measured in the field. Landscape-scale riverine habitat variables obtained through GIS analysis and modeling of catchment characteristics accounted for 18–69% of the vari...

Influences on Brown Trout and Brook Trout Population Dynamics in a Michigan River

Abstract Understanding the influences of local and regional processes on the dynamics of self-sustaining trout populations would help fishery biologists better manage trout populations and protect rivers supporting trout. We explored hypotheses behind long-term temporal variation in density, growth, and survival of brown trout Salmo trutta and brook trout Salvelinus fontinalis using data collected over several decades on Michigans Au Sable River. Regression models developed for these species emphasized the influence of year-class strength on older age-classes, year-class strength being positively related to spawner abundance for both species and negatively related to high spring streamflow conditions for brown trout. Age-class density was also positively associated with high levels of large woody debris (LWD) in streams. Annual growth increments of brown trout and brook trout were often negatively related to increased age-class density and LWD and positively affected by elevated total phosphorus levels, ...

Regional Synchrony of Brown Trout and Brook Trout Population Dynamics among Michigan Rivers

Abstract The ability to describe regional patterns in trout density would be useful for biologists concerned with population status across large regions as well as managers of rivers at the local scale. Noting the importance of flow conditions at the time of emergence to trout year-class strength in Michigan streams and the influence of age-0 trout abundance on subsequent abundance of older age-classes, we assessed the potential for regional synchrony in the population dynamics of brown trout Salmo trutta and brook trout Salvelinus fontinalis among Michigan rivers. We used correlation analyses to look for regional synchrony in May stream discharge (approximating the time of brown trout fry emergence) and fall trout density among many Michigan trout streams. We found a high degree of synchrony in average May discharge among streams, particularly those in the northern portion of Michigans Lower Peninsula. There were significant correlations in the long-term densities of brown trout and brook trout year-cla...

The Relation between Habitat Availability and the Short-Term Carrying Capacity of a Stream Reach for Smallmouth Bass

Abstract We used the behavioral carrying capacity (BCC) technique to test the assumption of the instream flow incremental methodology (IFIM) that a positive linear relation exists between available fish habitat (weighted usable area, WUA) and fish biomass for populations of smallmouth bass Micropterus dolomieu at carrying capacity. The BCC experiments were performed at various streamflows, and WUA was measured at each flow. In each BCC experiment, a section of a stream was overstocked with juvenile smallmouth bass, excess fish were trapped as they emigrated, and the remaining resident fish were collected after a 10-d period. We did not find a positive relation between WUA and BCC, and we found a negative relation between stream discharge and BCC. High BCC values recorded during low-flow experiments resulted from less upstream and downstream movement by juvenile smallmouth bass. Such behavioral changes may prevent smallmouth bass populations from being limited by habitat availability during low flows. The ...

Developing User‐Friendly Habitat Suitability Tools from Regional Stream Fish Survey Data

Abstract We developed user-friendly fish habitat suitability tools (plots) for fishery managers in Michigan; these tools are based on driving habitat variables and fish population estimates for several hundred stream sites throughout the state. We generated contour plots to show patterns in fish biomass for over 60 common species (and for 120 species grouped at the family level) in relation to axes of catchment area and low-flow yield (90% exceedance flow divided by catchment area) and also in relation to axes of mean and weekly range of July temperatures. The plots showed distinct patterns in fish habitat suitability at each level of biological organization studied and were useful for quantitatively comparing river sites. We demonstrate how these plots can be used to support stream management, and we provide examples pertaining to resource assessment, trout stocking, angling regulations, chemical reclamation of marginal trout streams, indicator species, instream flow protection, and habitat restoration. ...

Contribution of Hatchery-Reared Walleyes to Populations in Northern Green Bay, Lake Michigan

AbstractThe effectiveness of stocking hatchery-reared Walleyes Sander vitreus to supplement native populations in large, open systems like the Great Lakes has not been thoroughly evaluated. I quantified recent contributions of stocked Walleye fingerlings to populations in Little Bay de Noc (LBDN) and Big Bay de Noc (BBDN) in northern Green Bay, Lake Michigan. Oxytetracycline-marked Walleye fingerlings were stocked in June, and late summer gill-net and night-time boat electrofishing surveys were used to index Walleye year-class abundance and collect juvenile Walleyes for hatchery mark evaluation. For the 2004–2009 year-classes, 76% of the age-0 to age-3 Walleyes examined from LBDN were of wild origin and 62% in BBDN were naturally reproduced fish. Survey catch rates of juvenile Walleyes were similar for stocked and nonstocked year-classes. Assessment catch rates of age-1 and age-2 Walleyes differed significantly by location, with average catch rates in LBDN often being ten times higher than those in BBDN. ...

A Reconnaissance Survey of the Effects of Sediment Traps on Michigan Streams

Abstract Excess sand bedload can significantly degrade salmonid habitat and populations. Successful use of sediment traps to restore habitat and salmonid populations on two Michigan streams in the early 1980s led to application of traps at well over 100 coldwater streams in Michigan and rivers throughout the USA within a decade. Unfortunately, little quantitative evaluation has occurred other than anecdotal observations for some traps. We conducted a broad-scale survey of 65 Michigan stream reaches with sediment traps by collecting data along transects upstream and downstream of the traps to assess downstream changes in substrate composition, channel depth, and channel stability in response to sediment traps. We found that recent applications of sediment traps (usually as stand-alone instream habitat treatments) had no significant effect on substrate, thalweg depth, or bank stability conditions in the reaches studied. Using reach-based estimates of specific stream power at the 10% annual exceedence flow, ...