WinchesterLakesMeeting_6_24_26

Warmwater Habitat Considerations for Wisconsin Fisheries Greg G. Sass, Ph.D. Wisconsin DNR, Office of Applied Science Escanaba Lake Research Station “We would like to accept ruffed grouse from Wisconsin for our reintroduction program; however, the habitat is not quite appropriate yet”. Kentucky Wildlife Biologist Where is the HABITAT in Inland Fisheries Management? Literature Search: “Habitat and Wildlife Management” vs. “Freshwater or Inland Habitat and Fisheries Management “ 0 100000 200000 300000 400000 500000 600000 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 2015 Google Scholar Habitat and Wildlife Management Habitat and Fisheries Management Marine Habitat and Fisheries Management Freshwater (solid) or Inland (dashed) Habitat and Fisheries Management 0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 2015 Web of Science Marine Habitat and Fisheries Management Habitat and Wildlife Management Habitat and Fisheries Management Freshwater (solid) or Inland (dashed) Habitat and Fisheries Management Cumulative number of publications -Since 1950, the cumulative number of publications about “freshwater or inland habitat and fisheries management” has been 60-95% less than those considering “habitat and wildlife management”. Sass et al. (2017). Fisheries Cumulative number of publications What is Habitat? Sass et al. (2017) definition • “Adequate abiotic and biotic conditions required to complete all aspects of a species life history during a generation or lifespan, which results in fitness”.” • Acknowledges that habitat conditions can wax and wane over time and that fitness may correspond with those changes in the long-term Previous definitions • Habitat is simply the place where an organism lives. Physical, chemical, and biological variables (the environment) define the place where an organism lives (Hudson et al. 1992; Hayes et al. 1999). • Fundamentally similar definition to a “niche”. Sass et al. (2017). Fisheries Coarse Woody Habitat and Lakes 0 10 20 30 40 50 Building Density (no./km) 0 100 200 300 400 500 600 700 800 900 1000 CWH Density (logs/km) Christensen et al. (1996) Marburg et al. (2006) Jennings et al. (2003), Francis and Schindler (2006) Coarse Woody Habitat and Fish Growth Schindler et al. (2000) Sass et al. (2006) 475 logs/km 344 logs/km 128 logs/km 344 logs/km Little Rock Lake Vilas County Significant decline in LMBS growth rates Coarse Woody Habitat and Fish Population Sustainability Sass et al. (2006) – CWH physical removal Gaeta et al. (2014) – CWH removal by drought and water level decline CWH Loss in Lakes • Natural Variation -Riparian Forest Composition (Roth et al. 2007) -Decomposition (lake aging) • Anthropogenic Effects -Shoreline Development* -Deforestation -Physical Removal from Lakes -Water Level Declines* -Beaver Control -Fire Suppression Marburg et al. (2006), Sass et al. (2006)* Christensen et al. (1996)* Gaeta et al. (2014)* Importance of CWH for Fisheries – Food Web • Degradation of new CWH provides slow release of nutrients over time • Nutrient release stimulates periphyton growth…. Importance of CWH for Fisheries – Food Web • Periphyton on CWH attracts grazing benthic invertebrates, which…. • attracts predatory benthic invertebrates, which…. • attracts fish…. Importance of CWH for Fisheries – Food Web • CWH then attracts piscivorous fish and anglers • CWH as a microecosystem Importance of CWH for Fisheries – Attraction • CWH then attracts piscivorous fish and anglers Newbrey et al. (2005) – 16 fish species observed, branching complexity, and type of tree matters Importance of CWH for Fisheries – Spawning/Refuge “FISH STICKS” ARE BORN Structural Habitat Additions as Micro-ecosystems….. • Structural habitat additions intended to serve as micro- ecosystems within larger ecosystems • GOALS – slow lake aging, increase fish productivity and fisheries quality (abundance, size, catchability) Roth et al. (2007) Lake Aging Reservoirs Natural Lakes Fish Productivity Autochthonous Age Allochthonous Autochthonous = produced within a system Allochthonous = material imported into a system • Lake aging has resulted in declines in fish productivity over time Ploskey (1981) Rypel et al. (2018) Importance of CWH for Fisheries – Fish productivity • Pace et al. (2004) found that about 50% of the carbon in largemouth bass in a north- temperate lake was derived from terrestrial sources • Carbon from leaf litter and CWH incorporated into lake food webs influences fish productivity Constraints on Fish Productivity: Is Habitat Limiting? • Reproduction -Spawning Substrate • Growth -Food quality (terrestrial vs. aquatic) and quantity -Foraging conditions (prey encounter rates) • Survival/Mortality/Recruitment • What limits fish productivity in an ecosystem context? • Are the processes associated with CWH? When CWH is Limiting in Reservoirs and Lakes….. Natural Materials Artificial Materials Structural enhancements often constructed to maximize surface area for bottom-up production and fish refuge (micro-ecosystems) When CWH is Limiting in Reservoirs and Lakes….. Natural Materials Artificial Materials Structural enhancements often constructed to maximize surface area for bottom-up production and fish refuge (micro-ecosystems) Cooke et al. (2023), Sass et al. (2023) -Illegal in Wisconsin waterbodies Case Study: Whole-lake Addition of CWH to a Northern Wisconsin Lake • Sanford Lake – Vilas County, WI – 92 acres, 51 feet – 160 tree drops • Goal: Increase fish community productivity Case Study: Northern Wisconsin Fish Community Productivity Pre-CWH Addition 0 10 20 30 40 50 60 70 Sanford Lake Rangewide Production (kg ha-1 y-1) Fish community 0.0 0.2 0.4 0.6 0.8 1.0 Sanford Lake Rangewide Production (kg ha-1 y-1) Walleye 0 1 2 3 4 Sanford Lake Rangewide Production (kg ha-1 y-1) Smallmouth Bass 0 2 4 6 8 Sanford Lake Rangewide Production (kg ha-1 y-1) Yellow Perch 0 10 20 30 40 50 Sanford Lake Rangewide Production (kg ha-1 y-1) Bluegill • Low productivity fish community common to north- temperate lakes • Production locked up in top predators Case Study: Northern Wisconsin Fish Community Responses Post-CWH Addition Abundance 41” Muskellunge Behavior Smith et al. (2021) Case Study: Northern Wisconsin Fish Community Responses Post-CWH Addition Wilkinson et al. (2026) Case Study: Northern Wisconsin Fish Community Responses Post-CWH Addition Wilkinson et al. (2026) Case Study: Northern Wisconsin Fish Community Responses Post-CWH Addition Wilkinson et al. (2026) Fish Community Productivity Doubled! Water Quality, Zooplankton, and Bugs CHANGE PRE- vs. POST CWH • Water temperature (±) • Dissolved oxygen (+) • Water clarity (±) • Chlorophyll a (+) • Large Grazing Zooplankton (-) • Lake-wide benthic macroinvertebrates (±) • Aquatic macrophytes (+) • Escanaba Lake served as reference lake Preul-Stimetz et al. (2024) Preliminary Conclusions • Fish community productivity doubled for fishes lower in the food web (bluegill, rock bass, yellow perch) -Will lower food web productivity transfer up to upper food web (muskellunge, smallmouth bass, walleye)? • Increased use of offshore habitats by muskellunge, smallmouth bass, and walleye -Will behavioral changes persist or become more focused on CWH? • No negative change in water quality or benthic macroinvertebrates • ADDITIONAL TREE DROPS IN 2023 (237 TREES), CONTINUED MONITORING FOR THE NEXT 15 YEARS, STAY TUNED… PERCEPTION… vs. REALITY Acknowledgments • Dairymen’s Inc. and Dairymen’s Foundation Questions? Greg G. Sass, Ph.D. Gregory.sass@wisconsin.gov