fished populations have greater variability (e.g., hsieh, et al 2006)
DESCRIPTION
Dynamic behavior of upper trophic level populations: age -structured models with density-dependent recruitment Louis W. Botsford Wildlife, Fish, and Conservation Biology. Fished populations have greater variability (e.g., Hsieh, et al 2006). Fished. Unfished. - PowerPoint PPT PresentationTRANSCRIPT
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Dynamic behavior of upper trophic level populations: age-structured models
with density-dependent recruitment
Louis W. BotsfordWildlife, Fish, and Conservation Biology
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Fished populations have greater variability (e.g., Hsieh, et al 2006)
After removing the effects of age of maturation on the CV of abundance, fished species have greater CV than unfished species.
Fished
Unfished
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New view
No longer:
Environment Catch
Rather:
VariableEnvironment
DevelopmentFecunditySurvival
Recruitment
Catch
Biomass
Population
t t
PDO Salmon catch
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Population ModelAge-structured model with density-dependent recruitment
n1,t= Rt, recruitment, where
na,t=abundance at age a, time t
na+1,t+1= sa na,t 1<a<A
Where
With fi= fecundity at age i
= annual reproduction
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Mathematical Analysis
(1) Equilibrium level + (2) Variability about equilibrium
Slow change (decadal) Rapid change (inter-annual)
Changes in sa, fa, development rate
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Fecundity, fa
age
Survival, sa
Egg Production
Rec
ruitm
ent
Slope=1/(Lifetime Egg Production)
(1) Equilibrium with fishing
Lifetime
Egg
Production
(Sissenwine and Shepherd 1987)
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Examples of Spawning Age Distributions, Age Truncation
with fishingPacific Ocean Perch, POP
Pacific Whiting, Hake
Coho salmon
Fishing mortality, F
Differences in effect of fishing
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Example of effect of fishing (reduced adult survival, s) on equilibrium recruitment of coho salmon
Egg production
Recr
uitm
ent
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(2) Variability (sensitivity) increases with slope of egg-recruit equilibrium
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Differences in response to fishing
Relative CV of Egg Production
0 collapse Fishing
Relative CV of Recruitment
Relative CV of Catch
POP, Hake, Coho
POP=.8 at 0Hake=.8 at 0Coho=.8 at 0
POP=.13 at 0Hake=.23 at 0Coho=.71 at 0
POP=.12 at 0Hake=.26 at 0Coho=.54 at 0
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1. Populations sensitive to generational frequencies, and low frequencies (more sensitive with narrow spawning ages)2. Age truncation increases this sensitivity
Sensitivity =sout/sin
Frequency Dependence of Sensitivity
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Truncation increases resonance because egg production is a weighted version of past recruitment
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Review: Another example with generic cod and generic salmon
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Fishing changes age structure, changing dynamics, i.e., equilibrium and cohort resonance.
Unfished
Unfished
fished
fished
heavily fished
heavily fished
Salmon
Cod
Egg
Prod
uctio
n (a
) =
surv
ival
(a) x
mat
urity
(a) x
fecu
ndity
(a)
Salm
onCo
d
FLEP=normalized LEP
Collapse value
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Recruitment time series for salmon and cod examples, with white noise forcing early survival
Unfished
Fished
Heavily fished
Grey = codBlack= salmon
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Variance spectra
Generic codGeneric salmon
Unfished
Unfished
FishedFished
Heavily fishedHeavily fished
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What do these results mean for climate change?
• If the frequencies of environmental forcing change (e.g., more frequent ENSOs), that could change variability.
• Slow change with climate will be confounded with greater sensitivity to low frequencies.
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Population dynamic view of the changing climate: time scales or frequencies of ocean conditions
Torrence and Compo (1998)
Example: changing spectrum of ENSO, 1870-1997
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How can EcoFor make use of these results?
• In most UTL populations, environmental variability will be affecting recruitment survival
• This tells us what frequencies recruitment will be sensitive to, but also the effects on other observations: egg production (e.g., CalCOFI surveys, Hsieh, et al. 2007), catch.
• It can be used as the “integration” due to UTL population dynamics (as in Di Lorenzo and Ohman)
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Marine
Ecology
At
The Ag School,
UC Davis
THANKS!