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State of the Lake Huron Prey Fish Community in 1999: Progress toward Fish Community Objectives
Jeff Schaeffer, Gary Curtis, Ray Argyle
USGS Great Lakes Science Center, Ann Arbor, MI.
Great Lakes Science Center
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Prey Objective
“Maintain a diversity of prey species at population levels
matched to primary production and to predator demands”
DesJardine, R.L., T.K. Gorenflo, R.N. Payne, and J.D. Schrouder. 1995. Fish-Community Objectives for Lake Huron. Great Lakes Fish. Comm. Spec. Pub. 95-1.
Source:
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Is the Prey Base Matched to Primary Production?No apparent changes in primary production
Major changes in food web- zebra mussel proliferation- decline in deepwater benthic invertebrates
Effects of food web changesLake whitefish emaciationImproved growth of Saginaw Bay yellow perch
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Hammond Bay
Thunder Bay
Ausable Point
Harbor
Beach
Detour
Lake Huron
Fall Survey,1973-9112-m trawl
Bloater Survey,1980-199121-m trawl
Combined Survey,1992-9921-m trawl
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Is the Prey Base Matched to Predatory Demand?
• What prey species are present?
• What species are eaten?
• Can we see effects of predation?
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The Prey Community is Diverse: 32 species
rainbowsmelt(44%)
alewife 28 %
sculpins 10 %
coregonids 6 %
other species 12%
Numerical Abundance
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Alewife
(29%)
Other spp.
(15%)
Planktivore Biomass Dominated by Three Species
Bloater
(27%)
R. Smelt
(29%)
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Prey Base dominated by two species!
•Major Chinook Prey items:
• alewife• rainbow smelt• sculpins, sticklebacks, other species
Alewife(50 %)
Smelt(24%)
Other species(26%)
Source: Interagency chinook diet data collated by MSU
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Sculpins, Sticklebacks, Troutperch
Year
1970 1975 1980 1985 1990 1995 2000
Me
tric
to
ns
x 1
00
0
0
20
40
60
80
100
120
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Bloater Biomass is Cyclic
Year1970 1975 1980 1985 1990 1995 2000
Me
tric
to
ns
x 1
00
0
0
25
50
75
100
125
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Rainbow Smelt Biomass
Year1970 1975 1980 1985 1990 1995 2000
Me
tric
to
ns
x 1
00
0
0
25
50
75
100
125Y = -0.803x + 1619
r2 = 0.26
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Alewife Biomass
Year
1970 1975 1980 1985 1990 1995 2000
Me
tric
to
ns
x 1
00
0
0
25
50
75
100
125No significant linear trend
Average
biomass
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Alewife Biomass: 5 Year Intervals
Time Period75-79 80-84 85-89 90-94 95-99
Av
era
ge
Bio
ma
ss
0
10
20
30
40
50Large alewifeSmall alewife
Long-term Average
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Alewife abundance
Time period
80-84 85-89 90-94 95-99
Me
an
ca
tch
pe
r to
w
0
500
1000
1500
2000
Large (>150 mm)Small (<150 mm)
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Age-0 Alewife
Year
1985 1990 1995 2000
Me
an
Le
ng
th
50
75
100
125
150
Y = -1.76 X + 3600.8
r ² = 0.43
8.9 g
4.1 g
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Alewife: 1990-1999
Year1988 1990 1992 1994 1996 1998 2000 2002
Me
an
ca
tch
pe
r to
w
0
250
500
750
1000
1250
1500
1750
2000
Large (>150 mm)Small (<150 mm)
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Rainbow Smelt Biomass: 5 year intervals
Time Period75-79 80-84 85-89 90-94 95-99
Av
era
ge
Bio
ma
ss
0
10
20
30
40
50Large R. SmeltSmall R. Smelt
Long-term Average
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Rainbow Smelt Abundance
Year80-84 85-89 90-94 95-99
Me
an
ca
tch
pe
r to
w
0
500
1000
1500
2000
2500
3000Large (>150 mm)Small (<150 mm)
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Alewife as Prey• Prey availability may
depend on age-0 fish
• Year class strength– Good year: small prey– Poor year: few prey
• Growth may be important– Affects prey biomass– overwinter survival– Size-selective predation
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Rainbow Smelt as Prey
• May no longer be a resource for large predators– Too rare– Very few large fish
• Scarcity may increase pressure on alewife
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Conclusions• Major changes in the food web
• Total planktivore biomass decreasing– Decline in bloater not due to predation– Declines in R. smelt and alewife consistent – with predation, but growth may be important
• Prey size structure declining– Few large alewife or rainbow smelt– Trends are consistent with predation
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Prey Fish Objectives
• May be difficult to attain (numbers)– Food Web changes– Predator demand high– Pelagic planktivores declining
• Other 0bjectives may be enhanced– Greater proportion of native species in biomass– Reduced interactions with exotics– New approaches now possible