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Juvenile salmon survival in coastal waters of the Northeast Pacific Ocean: top-down or bottom-up
control?Vladlena Gertseva, Thomas
Wainwright, Vladimir Gertsev
October 19, 2004
PICES XIII Annual Meeting
Research Funded by GLOBEC
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Why juveniles?
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From: Pearcy W.G. 1992. Ocean Ecology of North Pacific Salmonids.
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Early ocean life is the most “critical” time for a
year class
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Juvenile Salmon
Upper Trophic Levels
Top-down
Lower Trophic Levels
Bottom-up
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Research objectives
• Summarize knowledge on juvenile salmon interactions in coastal oceanic waters
• Develop a mathematical model of juvenile salmon dynamics
• Identify processes controlling the survival of juvenile salmon
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Total Biomass B(t)
Fish Weight W(t)
Number of Fish N(t)
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B(t)
Natural mortality
Stochastic elimination
Cannibalism
Temporal migrations
Temperature
Salinity Light Dissolved oxygen
Predation
Trophic demands
Initial number, N0
Competition
Food availability
Initial weight, W0
Maximum weight, Wmax
ResourcesTrophic coefficient,
kT
Y
W(t)N(t)
Anthropogenic effect
N(t) W(t)
Bottom-upTop-down
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0
1000
2000
3000
4000
5000
6000
0 200 400 600 800
Time, days
Wei
ght,
gram
s
Modeling individual growth
tkQ
0
0max
max
T1eW
WW1
W)t(W
W0 – initial weight of fish
Wmax– maximal weight of fish
Q1 – buffer coefficient
kT – trophic coefficient
t – time
Juvenile stage
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Modeling fish abundance
)tYQexp(N)t(N 20
N0– initial number of fish Y – additive loss Q2– buffer coefficient t – time
0.00
200.00
400.00
600.00
800.00
1,000.00
0 200 400 600 800
Time, days
# of
fish
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•Fish abundance
•Fish weight
Coho salmon
•Trophic demands
•Abiotic preferences
1999 – 2002May, June, September
•Temperature
•Salinity
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Model simulations
Indiv
idual
wei
ght
Number of fish
Total biomass
0 45 90 135 180Days
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Sensitivity analysis
• Vary the values of different parameters
• Record the response of the juvenile salmon
• Determine the most important factors
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0 45 90 135 180Days
effect of variations in predation on total biomass
150000
75627
1255
Total Biomass
1:Predation=0.03 2:Predation=0.035 3:Predation=0.04 4:Predation=0.045 5:Predation=0.05
Model predictions
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0 45 90 135 180
Total Biomass
Model predictionseffect of variations in trophic coefficient on total
biomass
150000
75627
1255
Days
1:Trophic coefficient=1 2:Trophic coefficient=0.95 3:Trophic coefficient=0.9 4:Trophic coefficient=0.85 5:Trophic coefficient=0.8
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Growth of juvenile coho salmon
0
100
200
300
400
500
600
May Jun Sep
Month
Fis
h W
eig
ht
(g)
1999
2000
2001
2002
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Abundance of juvenile coho salmon
01020304050607080
May June Sep
Month
# fi
sh c
aug
ht
per
day
1999
2000
2001
2002
2.5%
4%
2%
3.5%
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Conclusions
• Juvenile salmon biomass in the coastal waters is primarily defined by variations in activity at upper trophic levels rather than lower ones
• Juvenile salmon survival is primarily controlled by a top-down, but not a bottom-up mechanism in the nearshore oceanic ecosystem
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Theoretical implications
• Provides a theoretical insight into complicated relationships between juvenile salmon and their environment
• Enables a simultaneous study of both upper and lower trophic level effects
• Sets the range of data necessary for studying the survival of juvenile salmon
• Defines future research priorities
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Research priority
Study predators
•Abundance
•Food habits
•Feeding rates