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

Why juveniles?

From: Pearcy W.G. 1992. Ocean Ecology of North Pacific Salmonids.

Early ocean life is the most “critical” time for a

year class

Juvenile Salmon

Upper Trophic Levels

Top-down

Lower Trophic Levels

Bottom-up

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

Total Biomass B(t)

Fish Weight W(t)

Number of Fish N(t)

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

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

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

•Fish abundance

•Fish weight

Coho salmon

•Trophic demands

•Abiotic preferences

1999 – 2002May, June, September

•Temperature

•Salinity

Model simulations

Indiv

idual

wei

ght

Number of fish

Total biomass

0 45 90 135 180Days

Sensitivity analysis

• Vary the values of different parameters

• Record the response of the juvenile salmon

• Determine the most important factors

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

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

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

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%

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

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

Research priority

Study predators

•Abundance

•Food habits

•Feeding rates