Status of Lake Erie s Western Basin Fish Populations: Trends and Environmental Conditions Jeff Tyson Ohio Department of Natural Resources Ohio Division of Wildlife
Status of the Lake Erie s Western Basin Fish Populations Sampling Programs Ohio harvest assessment programs Ohio gillnet sampling Ohio trawling programs Acoustic sampling program Other programs Lower trophic level Diet assessment
Outline Status of Predators Status of Forage Status of Lower Trophic Levels Environmental Conditions
Predators Walleye abundance has declined Highly variable recruitment Large 2003 year-class Extremely poor year-classes in more recent years Changes in distribution Growth stable Abundance Index Millions of fish 80 60 40 20 0 60 40 20 0 Adult Walleye 1978 1983 1988 1993 1998 2003 2008 Walleye Hatch Strength 1987 1989 1991 1993 1995 1997 1999 2001 2003 2005 2007
Predators Yellow perch abundance has increased Year-class strength highly variable Large 1996 and 2003 yearclasses, average 2007 yearclass Increased growth (due to increased benthos) M illio n s o f F is h 200 150 100 50 0 Abundance Index Adult Perch Western Central 75 78 81 84 87 90 93 96 99 02 05 08 600 500 400 300 200 100 Perch Hatch Strength 0 1987 1990 1993 1996 1999 2002 2005
Predators Declining smallmouth bass abundance in west 1.2 Smallmouth Abundance Round goby effect on spawning success Fish per hour 0.8 0.4 0.0 94 95 96 97 98 99 00 01 02 03 04 05 06 07 Potential cormorant depredation Increasing in abundance in other systems (due to warming)
Predators Increases in number of phytophilic species Associated with more extensive submerged aquatic beds CPHT 32 24 16 8 Black Crappie White Crappie Largemouth Smallmouth Bluegill Pumpkinseed Pike 0 1978 1983 1988 1993 1998 2003 Year Increased number of lake sturgeon, particularly in survey gear
Forage Gradient in prey fish community west to east Higher diversity west Lower diversity east Clupeids, shiners dominate in west West Basin East Basin Rainbow smelt dominate in east
Forage Functional forage groups Large decreases in age-0 white perch Forage abundance (fish/hectare) 15000 10000 5000 West Basin Forage Spiny-rayed Soft-finned Clupeid Decreases in clupeids Increases in shiners 0 1987 1989 1991 1993 1995 1997 1999 2001 2003 2005 2007 Year Emerald Shiners 15 Catch/Ha 10 5 0 1975 1981 1987 1993 1999 2005
Lower Trophic Levels Trends in Dreissenids Zooplankton Biomass Total Phosphorus Zooplankton biomass (ug/l) 0.35 0.3 0.25 0.2 0.15 0.1 0.05 0 1970 1980 1990 2000 Year
Dreissena Biomass Wet weight (g m -2 ) 1200 1000 800 600 400 200 D. polymorpha D. bugensis 1200 1993 1998 1000 800 600 400 200 West Central East West Central East R.Dermott, DFO
Zooplanktivory Zooplankton Mean Length (mm) 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 low high east, offshore west-central, off west, offshore east, nearshore west-central, near west,nearshore 1992 1994 1996 1998 2000 2002 2004 Year
Total Phosphorus St Clair west central east Total phosphorous (µg / L) 150 100 50 40 20 56.7 ± 64.7 Maumee R 8.3 ± 2.7 20.4 ± 10.6 13.5 ± 6.9 8.2 ± 3.5 99 01 03 99 01 03 99 01 03 99 01 03 Year expected decrease west to east (F 2,580 = 135.50, p = 0.00) increasing trend with time (2001 low) (F 4,580 = 7.76, p = 0.00)
Total Phosphorus Tributary Loads and Open Water Values
Environmental Conditions Water Clarity Walleye Aquatic Vegetation http://www.glerl.noaa.gov/ Water quality Blue-green algal blooms Dissolved oxygen Dreissenids Water Level Changes Climate variability/change Surface Temperature Exotic introductions Habitat degradation
Fish Population Health Fish Population Health Fish Population Health
Fish Population Health Management Levers Fish Population Health Fish Population Health
Management Levers - Environment
Conclusions Instability pervasive predators, forage, lower trophics, habitat Fisheries Managers manage at the end of the pipe Assessment Exploitation (harvest) management Production management?