state of the lake huron prey fish community in 1999: progress toward fish community objectives jeff...
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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
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:
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
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
Is the Prey Base Matched to Predatory Demand?
• What prey species are present?
• What species are eaten?
• Can we see effects of predation?
The Prey Community is Diverse: 32 species
rainbowsmelt(44%)
alewife 28 %
sculpins 10 %
coregonids 6 %
other species 12%
Numerical Abundance
Alewife
(29%)
Other spp.
(15%)
Planktivore Biomass Dominated by Three Species
Bloater
(27%)
R. Smelt
(29%)
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
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
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
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
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
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
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)
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
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)
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
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)
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
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
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
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
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