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Norine E. Dobiesz
James R. Bence
Prey consumption by key predators in Lake Huron
Predator-prey interactions:
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Overview
• Balancing predator forage demand with prey availability
• Stocking– Widespread since the mid-1960’s
– Major component of predator populations
– Potential for predators to exceed forage capacity
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Main Basin
Georgian Bay
North Channel
Overview
• Review methods
• Consumption in the main basin
• Compare to primary prey abundance
• Consumption in Georgian Bay and the North Channel
• Projected consumption
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Key predators in the open waters
Burbot (Lota lota)
Lake Trout (Salvelinus namaycush)
Chinook Salmon (Oncorhynchus tshawytscha)
Walleye (Stizostedion vitreum)
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Main constituents in the diet of the key predators
Rainbow Smelt
(Osmerus mordax)
Alewife (Alosa pseudoharengus)
Others:
Bloater
Sculpin
Stickleback
Invertebrates
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Estimating consumption in the main basin
Consumption = Production / GCE
•Production-conversion efficiency method
•Year- and age-specific consumption
•Data from stock assessment & bioenergetics
models
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Estimating consumption
Gross production is estimated from• Stock assessment model
–age-specific population abundance–mortality rates
• Weight-at-age
Accounts for consumption by fish that die during the model time step
Consumption = Production / GCE
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Estimating consumption
Gross conversion efficiency (GCE)•Estimated from bioenergetics models
GCE =predator weight gain
prey consumed
– Wisconsin Model (version 3.0b)– Lake Huron specific values– Predicts prey consumption from observed growth
Consumption = Production / GCE
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Chinook salmon and burbot model area
Main basin
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Lake trout areas modeled
North
Central
South
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Walleye areas modeled
SouthSaginaw Bay
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Recruitment MortalityPredator Areas Stocking Natural M SL F MAT
Lake trout 3 X --- X X X ---
Chinook salmon
1 X X X --- X X
Walleye 2 X X X --- X ---
Burbot 1 --- X X X X ---
Summary of age-structured stock assessment models
Models operate on an annual basis
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Chinook salmon
Lake trout
Walleye
Burbot
0
2,000
4,000
6,000
8,000
10,000
12,000
1984 1986 1988 1990 1992 1994 1996 1998
Year
Bio
ma
ss (
metr
ic t
ons)
Estimated predator biomass for main basin, 1984-1998
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Chinook salmon
Lake trout
Walleye
Burbot
0
5,000
10,000
15,000
20,000
25,000
30,000
35,000
40,000
45,000
1984 1986 1988 1990 1992 1994 1996 1998
Year
Co
nsu
mp
tion (
me
tric
ton
s)
. Lake trout & chinook salmon: 77%
Estimated consumption by key predators in the main basin, 1984-1998
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0
5,000
10,000
15,000
20,000
25,000
30,000
35,000
1968 1972 1976 1980 1984 1988 1992 1996
Year
Consum
ption (
metr
ic t
ons)
0
500
1,000
1,500
2,000
2,500
3,000
3,500
4,000
4,500
Bio
mass (
metr
ic t
ons)
ConsumptionBiomass
Estimated chinook salmon consumption and biomass in the main
basin
Timeframe covered by previous graphs
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0
20,000
40,000
60,000
80,000
100,000
120,000
140,000
160,000
180,000
1984 1986 1988 1990 1992 1994 1996 1998Year
Bio
ma
ss (
me
tric
to
ns)
Consumption by predators
Alewife & smelt biomass
(USGS fall assessment)
Comparison to combined alewife and smelt biomass in the main basin, 1984-1998
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Burbot Chinook salmon
Lake trout Walleye
Alewife 1.5 13.6 3.9 1.6
Rainbow smelt 1.1 5.7 3.4 0.5
Other 2.7 2.8 0.3 1.4
Mean consumption in the main basin, 1996-1998 (metric tons x 1000)
Mean consumption: 38.5
Alewife+smelt 2.6 19.3 7.3 2.1
Total alewife+smelt: 31.3
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Consumption(metric tons x 1000)
Predator GB NC MB
Chinook salmon 1.8 3.9 22.1
Lake trout 2.2 5.9 7.6
Double-crestedcormorants*
1.4 2.1 0.7
“Back of envelope” consumptionin Georgian Bay (GB) and
North Channel (NC) vs. main basin (MB)
* McLeish, D.A. 1996
(1996-1998)
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0
5,000
10,000
15,000
20,000
25,000
30,000
35,000
40,000
45,000
50,000
55,000
1984 1988 1992 1996 2000 2004 2008 2012 2016 2020
Year
Consum
ption (
metr
ic t
ons)
.
Baseline
Projected effects of current stocking practices on consumption in the main basin
Mean consumption, 2010-2020: 47,000 metric tons
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0
5,000
10,000
15,000
20,000
25,000
30,000
35,000
40,000
45,000
50,000
55,000
1984 1988 1992 1996 2000 2004 2008 2012 2016 2020
Year
Co
nsum
ption
(m
etr
ic t
ons)
BaselineSea lamprey reduction
Effects of projected reduction in sea lamprey abundance on consumption in the main basin
9%
Mean consumption, 2010-2020: 51,500 metric tons
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0
5,000
10,000
15,000
20,000
25,000
30,000
35,000
40,000
45,000
50,000
55,000
1984 1988 1992 1996 2000 2004 2008 2012 2016 2020
Year
Consum
ption (
metr
ic t
ons)
BaselineChinook stocking reductionSea lamprey reduction
Effects of projected reduction in sea lamprey abundance and 50% reduction in chinook salmon
stocking on consumption in the main basin
31% 25%
Mean consumption, 2010-2020: 35,000 metric tons
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Summary
Major consumers: lake trout & chinook salmon
Consumption by key predators may be approaching prey capacity
Changes in stocking and sea lamprey abundance effect consumption
Importance of continued monitoring of predators and prey