Fish Community and Aquatic Ecosystem Responses to the Cessation of - - PowerPoint PPT Presentation

Fish Community and Aquatic Ecosystem Responses to the Cessation of Eurasian Watermilfoil Chemical Treatment on Lake Ellwood, Wisconsin

Greg G. Sass Wisconsin Department of Natural Resources Fisheries and Aquatic Research Bureau of Science Services

*Cooperators: Escanaba Lake Research Station, Greg Matzke, Aaron Nelson, Aaron Johnson, Kevin Gauthier, Jen Hauxwell, Laura Sass, Lake Ellwood Association

Lake Ellwood, Florence County

• 135 acres
• smallmouth bass, largemouth bass,

bluegill, rock bass yellow perch, northern pike, black crappie, pumpkinseed, walleye, white sucker, bluntnose minnow

• Invasive EWM and rusty crayfish

present

• Reduced lake levels due to drought
• Substantial lakeshore residential

development

• Abundance of fish cribs
• Fish community historically

dominated by LMBS and BLGL

Lake Ellwood EWM Chemical Treatments

• Treated annually during 2003-2012
• 2003 – 2010 (Navigate – ester)
• 2011-2012 (SculpinG – amine)
• No chemical treatment in 2013 and 2014
• Estimated treatment concentrations in the

seasonal EWM control: some damage to native plants range at maximum

• Some increases in native plant assemblages,

some decreases

Fisheries Management Issue – Largemouth Bass

• At least four consecutive year class failures observed in 2012 for largemouth bass;

suggests persistent recruitment issues

Fisheries Management Issue - Bluegill

• Inconsistent year classes observed in 2012 for bluegill; suggests potential

recruitment issues

• In healthy bluegill

populations, trend would be opposite

Northern Wisconsin Trends in Largemouth Bass and Bluegill

• Relative abundance of largemouth bass has increased significantly over

time; bluegill relative abundance has remained stable over time Indicative of strong largemouth bass recruitment over time

Alternative Hypotheses to Explain Largemouth Bass and Bluegill Recruitment Declines

• Insufficient spawning stock (Not Plausible, NP)
• Lack of spawning (NP; spawning activity visually observed)
• Eggs not viable (~P; smallmouth bass are able to spawn?,

species-specific chemical effects (DeQuattro?))

• Lack of refuge prior to offshore movement of juveniles (P;

refuge and predation effects)

• Fish cribs serving as predator feeding stations (P; predation

effects)

• Lack of sufficient offshore zooplanktonic prey (P; forage base

effects)

• Decline in macrophyte refuge due to EWM chemical

treatments (P; refuge and predation effects)

• Reduced lake levels due to drought (~P; LMBS and BLGL

recruitment not declining in other drought influenced lakes)

Proposed Experimental Lakes

EWM PRESENT CESSATION OF EWM CHEMICAL TREATMENT (2013-2017) TREATMENT - LAKE ELLWOOD EWM ABSENT NO CHEMICAL TREATMENTS EWM PRESENT NO CHEMICAL TREATMENTS REFERENCE – COSGROVE LAKE REFERENCE – SEIDEL LAKE

Proposed Methods

• Identical sampling on all three lakes (2014-

2017)

• AQUATIC MACROPHYTES – sonar surveys,

point transect surveys (late summer)

• FISH – recruitment, relative abundance,

diets, growth, habitat use (monthly)

• LIMNOLOGY – Temp/DO profiles, water

clarity (monthly)

• ZOOPLANKTON – 80 μm tows

Proposed Objectives

1) Test for fish community responses (recruitment, relative abundance, diet, growth, habitat use) to the cessation of EWM chemical treatments. 2) Test for aquatic ecosystem responses (invasive and native aquatic macrophyte relative abundances and species composition, limnology, zooplankton) to the cessation of EWM chemical treatments.

Proposed Benefits

1) Identify anthropogenic, abiotic, and biotic factors that may limit largemouth bass and bluegill recruitment 2) Provide scientists, managers, and lake associations with a better understanding of the response of aquatic ecosystems to the cessation

• f long-term chemical treatments of EWM in

lakes 3) Provide scientists, managers, and lake associations with recolonization rates of EWM to better inform and balance control efforts with fish community and aquatic ecosystem considerations

Questions?