Predicting the growth potential of a warm water sport fishery:

1. Predicting the growth potential of a warm water sport fishery: a spatially explicit bioenergetics approach Walleye thermal growth limit Figure 4. Thermal profile of Cutler Reservoir (arrows indicate TIR image dates). Figure 3. Walleye thermal growth response. Walleye captured at site 2 Figure 5. Landsat 7 TIR image for April 26th (60 meter resolution). Figure 6. Landsat 7 TIR image for June 29th (60 meter resolution). Figure 1. Site map of Cutler Reservoir. Figure 2. Walleye length at age (error bars represent + - 1 Standard Error). Figure 9. Walleye seasonal condition (Fulton's K). Error bars represent + - 1 standard error. Figure 7. Aerial TIR image for July 30th (3 meter resolution). Figure 8. Landsat 7 TIR image for October 3rd (60 meter resolution). Kirk Dahle, Phaedra Budy, Gary Thiede Introduction: The development of quantitative methods for measuring habitat suitability is a central but challenging task for aquatic biologists (Rosenfeld 2003, Boisclair 2001, Downing et al. 1990). We define fish growth potential as the expected growth rate of a fish placed in a particular volume of water with known biological and physical characteristics. This metric integrates natural fluctuations with anthropogenic disturbances and as such provides an effective metric for measuring habitat suitability (Mason et al. 1995). Temperature, a key abiotic variable, and food availability, a key biotic variable, act in concert with species specific physiological processes to directly influence the individual growth rate of a fish (Kitchell 1977).Ultimately the highest quality habitats should provide the highest growth rates. Results: The quality and quantity of walleye habitat within Cutler Reservoir varies spatially by season (figures 5-8). Growth is possible during all portions of the growing season, but optimal habitat is reduced to less than 1% and suitable habitat comprises only 5% (near site 5) of the reservoir during the hottest portion of the year (figure 7). Average walleye condition for sites 1-4 drops from 1.0 to 0.95 from spring to summer, while walleye condition at site 5 increases from 0.98 to 1.04 during the same period (figure 9). Habitat conditions are sub-optimal but still support relatively high growth rates, > five grams/day for adults, during the early (April) and late (October) growing season. Optimal growth occurs from mid June to the end of September (excluding hot season) for nearly 100% of the reservoir. These results predict, and are corroborated by, the high growth rates of walleye observed in the system with age 2 walleye reaching 500mm TL (figure 2). Study site: Cutler Reservoir, located in northern Utah, demonstrates a wide range of physical conditions and potential water quality problems including high summertime water temperature, low dissolved oxygen, and high nutrient loading. No previous studies have investigated the role of water quality in structuring the fish community of this system. We undertook this project to determine the habitat suitability and potential limiting factors for the predominant sport fish of this system. Objectives: 1. Determine the effect that spatial variability in water quality has on growth potential for the primary sport fish species. 2. Use this information to quantify the amount of suitable habitat available for these species throughout the growing season (April-October). Methods: We conducted three (spring, summer & fall) intensive fish sampling efforts across five representative sites in 2006 (figure 1). We quantified fish distribution, condition, age, and growth (figure 2). We then processed these data using the Wisconsin bioenergetic model to generate a thermal growth response for the systems game-fish species (figure 3). We collected thermal data using temperature loggers and two forms of remote data capture, Landsat 7 Thermal infrared (TIR) imaging and helicopter mounted aerial TIR imaging (figures 4 & 5-8). We used Arc GIS to combine our bioenergetic model outputs with spatially continuous TIR data in order to produce quantitative, thematic maps of growth potential for walleye within Cutler Reservoir (figures 5-8). Discussion: Based on our bioenergetic model, we predict high growth potential for walleye within Cutler Reservoir. Suitable habitat is spatially restricted during the hottest portion of the year; however, annual growth rates are not significantly impacted. Although site 5 provides a habitat refugia during mid summer, fish distribution and condition suggest that walleye do not migrate to this area during this period. Prey fish availability, while generally high, increases during mid to late summer as young-of-year fish attain ingestible sizes. High forage availability coupled with optimal temperatures result in maximal growth conditions for walleye from early August until late September. However, this system experiences localized low dissolved oxygen levels that may affect habitat suitability. This condition may be exacerbated during years of low runoff, as adequate flushing flows delay the onset of low dissolved oxygen. Nevertheless, based on our analysis of temperature and food availability, habitat conditions generally appear to be near optimal for walleye in Cutler Reservoir. Future work: In future versions of this model, we will integrate spatial and temporal information on dissolved oxygen as well as improved spatial resolution of forage availability, in order improve our growth potential estimates for the system. Additionally, we will expand our analysis to include black crappie and channel catfish. References: Downing, J. A., Plante, C., and Lalonde, S. 1990. Fish Production Correlated with Primary Productivity not the Morphoedaphic Index. Canadian Journal of Fish and Aquatic Science 47: 1929-1936 Boisclair, D. 2001. Fish habitat modeling: from conceptual framework to functional tools. Canadian Journal of Fish and Aquatic Science 58: 1-9. Kitchell, J. F., D. J. Stewart, and D. Weininger. 1977. Application of a bioenergetics model to yellow perch (Perca flavescens) and walleye (Stizostedion vitreum). Journal of the Fisheries Research Board of Canada 34:1922-1935. Mason, D. M., Goyke, A. and S. B. Brandt. 1995. A spatially explicit bioenergetics measure of habitat quality for adult salmonines: Comparison between Lakes Michigan and Ontario. Canadian Journal of Fish and Aquatic Science 52: 1572-1583. Rosenfeld, J. 2003. Assessing the Habitat Requirements of Stream Fishes: An Overview and Evaluation of Different Approaches. Transactions of the American Fisheries Society 132: 953-968. Acknowledgments: We would like to thank the Utah Division of Water Quality, and The Nature Conservancy for funding this work. We would also like to thank the technicians, graduate students, and associates of the FEL: Mike Ebinger, Peter MacKinnon, Wes Pierce, Marc Weston, Sam Hill, Andy Tanzosh, Ron Rogers, Amanda Townsend, Bec Dahle, Eriek Hansen, Jeremiah Wood, Kris Homel, Robert Al-Chokhachy and Ben Nadolski for making the project possible.

3. Fig. 6 7/30 Fig. 5 6/29 Fig. 7 10/3 Fig. 4 4/26 Thermal growth limit for walleye