INFLUENCE OF HYPOXIA ON THE ECOLOGY OF ZOOPLANKTIVOROUS AND BENTHIVOROUS FISHES IN LAKE ERIE’S CENTRAL BASIN. T.O. Höök1,2,*, S.A. Ludsin2, S.A. Pothoven3, J.J. Roberts1,2 , T.F. Nalepa2, H.A. Vanderploeg2, S.A. Ruberg2, and S.B. Brandt2. 1Cooperative Institute for Limnology and Ecosystems Research, University of Michigan, Ann Arbor, MI. 2National Oceanic and Atmospheric Administration, Great Lakes Environmental Research Laboratory, Ann Arbor, MI. 3National Oceanic and Atmospheric Administration, Great Lakes Environmental Research Laboratory, Muskegon, MI. *(thook@umich.edu)

Hypoxia in Lake Erie: Natural phenomenon -Modified by various factors Warm epilimnion West Central East Cool Low oxygen Source: Murray Charlton, NWRI Cool hypolimnion (becomes hypoxic) Natural phenomenon -Modified by various factors (e.g., nutrients, climate, water levels) As I am sure we are all aware, hypoxia is prevalent in numerous systems worldwide, both freshwater and marine. However, hypoxia is especially prevalent in coastal systems, as this map clearly illustrates Today, I am going to talk about 3 coastal systems in particular, Gulf of Mexico, Chesapeake Bay and Lake Erie Although the exact mechanisms driving the magnitude and extent of hypoxia vary among these three systems, each has shown a propensity for severe hypoxia during summer in recent decades

$ $ $ $ Recreational Fisheries Commercial Fisheries Effects of Hypoxia on Yellow Perch and Rainbow Smelt $ Recreational Fisheries $ Walleye $ Commercial Fisheries $ Yellow perch Rainbow smelt Most abundant species in L. Erie’s central basin. Benthic invertebrates Zooplankton

Diel vertical migrations Effects of Hypoxia on Yellow Perch and Rainbow Smelt Day Night Diel vertical migrations thermocline thermocline Yellow perch Rainbow smelt Hypoxia may alter: -Distributions -Diets -Growth/Condition Omnivory Benthic invertebrates Zooplankton

24-hr paired-vessel sampling Zooplankton Temperature Dissolved oxygen Light levels Chlorophyll a Fish Biomass -Zooplankton net and pump sampling -Ponar grabs (benthos) -Midwater and bottom trawling

2005 June August October September September 5km diel station F B C D 5km diel station 0 4 8 12 (mg/l) June B H D August October September Depth (m) Site B Depth (m) Site B B A H September

Effects of Hypoxia in Lake Erie. Strength of evidence Distributions of perch and smelt. Diets of perch and smelt. Condition/Growth of perch and smelt. high low All data from Station B

Vertical Distributions of Yellow Perch and Rainbow Smelt Night Day High Depth (m) High

Vertical Distributions of Yellow Perch and Rainbow Smelt Night Day Depth (m) Low Hypoxic High High

Vertical Distributions of Yellow Perch and Rainbow Smelt Night Day High High Low Hypoxic High High

Vertical Distributions of Yellow Perch and Rainbow Smelt ln(cpue+1) June Aug Sep (hypoxia) Oct Rainbow smelt

Diets of Yellow Perch and Rainbow Smelt Zooplankton Benthic Invertebrates Chironomid Pupae June Aug Sep (hypoxia) Oct Diet (% of diet items) Rainbow smelt

a a a a a b c c Diets of Yellow Perch and Rainbow Smelt Yellow perch Dry weight of stomach contents (g g-1) June Aug Sep (hypoxia) Oct a b Rainbow smelt c c

a b b b a b c d Cumulative effects on condition and growth Yellow perch a b b b % Dry/Wet weight June Aug Sep (hypoxia) Oct a b c d Rainbow smelt

Quantifying Growth and Condition Traditional measures of growth and condition. -Integrate feeding history and energetic utilization over the whole life-time of an organism. RNA:DNA Ratios -DNA concentrations within cells remain fairly constant. -RNA concentrations increase as protein synthesis increases. -A recently well-fed, growing individual should have a high RNA:DNA ratio compared to a starving individual.

a ab no b data a a a no data Instantaneous effects on growth Yellow perch ab no data b RNA:DNA (liver) June Aug Sep (hypoxia) Oct a a a no data Rainbow smelt

a a a no data a a b no data Instantaneous effects on growth Yellow perch no data RNA:DNA (muscle) June Aug Sep (hypoxia) Oct a a b no data Rainbow smelt

Effects of Hypoxia in Lake Erie. Distributions of perch and smelt. Lower overall catches during hypoxia. Avoid bottom waters during hypoxia. Diets of perch and smelt. ↑Zooplankton; ↓Benthic invertebrates Ration may be affected Seasonal patterns may mask hypoxia effects Condition/Growth of perch and smelt. Potential cumulative and instantaneous growth effects high Strength of evidence low

Daytime Zoopl. vulnerability and individual growth may increase. Daphnia mendotae (preliminary data) Daytime August June August September RNA:DNA September Length (mm) Preliminary RNA:DNA patterns for Daphnia mendotae collected (via whole water column tows) in central Lake Erie during 2005.

Does hypoxia affect production of L. Erie fishes?? Next Steps 2007 Field sampling. Focus on spatial patterns. Experimental evaluations of yellow perch and walleye growth. Modeling analyses (EcoFore Project). Statistical analyses, GRP, IBM, CASM, EcoPath/EcoSim

Ecological Consequences of Hypoxia in Lake Erie: Piscivorous Fish Invertivorous Fish International Field Year in Lake Erie (2005) www.glerl.noaa.gov/ifyle NOAA-GLERL led effort to understand the causes and ecological consequences of seasonal hypoxia in Lake Erie. Benthic invertebrates Zooplankton Phytoplankton Microbes Nutrients Physical Processes