1. 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.

2. 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

3. $ $ $ $ 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

4. 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

5. 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

6. 2005 June August October September September 5km diel stationF B C D
5km diel station
(mg/l)
June B H D
August
October
September
Depth (m)
Site B
Depth (m)
Site B B A H
September

7. 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

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

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

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

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

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

13. 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

14. 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

15. 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.

16. 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

17. 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

18. 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

19. 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.

20. 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

21. Ecological Consequences of Hypoxia in Lake Erie:
Piscivorous Fish
Invertivorous Fish
International Field Year in Lake Erie (2005)
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