Jess JuradoMolina

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Climate Forcing effects on trophically linked
groundfish populations Implications for
Fisheries Management

• Jesús Jurado-Molina
• School of Fisheries, University of Washington

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Changes in the Bering Sea
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Objectives

• To apply the single and multispecies forecasting
  models to assess the effects produced by climate
  regime shifts and fishing on spawning biomass of
  some species from the Bering Sea.
• Determine relative roles of fishing, climate
  regime, and predation in population dynamics

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Biomass flow in the system defined for the
eastern Bering Sea
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MSVPA and MSFOR equations
BS - suitable prey biomass S - suitability
coefficient of prey p for predator i R - annual
ration of the predator i W - weight at age of
prey p M1- residual mortality M2 - predation
mortality
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Input and output data for the MSFOR model
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Multispecies forecasting assumptions

• M M1 M2
• Predators annual ration constant
• Average constant suitability coefficients (from
  MSVPA)
• Other food of predators remains constant
• Suitability coefficients reflect the preferences
  of the predator, the vulnerability and the
  availability of the prey and other factors such
  as the overlapping of predator and prey
  populations etc.
• Suitabilities define the predation interaction
  dynamics in the forecasting models

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Environmental forcing in the eastern Bering Sea

• El Niño Southern Oscillation (ENSO)
• Duration of 2 to 7 years
• Global influence
• Pacific Decadal Oscillation (PDO)
• Persistency of 20 to 30 years
• Main influence in the North Pacific and North
  American sector

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Environmental forcing in the eastern Bering Sea

• If recruitment success were dependent on a
  sequence of events, then a semi-permanent shift
  in ocean conditions would influence only one of
  several conditions necessary for successful
  recruitment. Stocks that exhibit this type of
  recruitment response would show a change in the
  probability of a strong year class, or a change
  in the amplitude of strong year classes when they
  occurred, expressed as a change in the mean level
  of recruitment (Hollowed and Wooster, 1995) .

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Recruitment assumptions associated with climate
regimes

• There is a mean recruitment and variance
  associated with each climate regime
• Recruitment of age-0 individuals takes place in
  the third quarter
• Recruitment is log-normal distributed
• First scenario 1977 temperature Regime continues
  beyond
• Second scenario There is regime shift in 1989

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Methods

• MSVPA run updated to 1998 data to obtain average
  suitabilities, average recruitment values and
  population initial values (1998) for all species.
• ANOVA analysis and comparison of the CVs for the
  recruitment from MSVPA for the periods 1979-1988
  and 1989-1998
• Multispecies forecasting using the mean and
  standard deviation of recruitment values
  associated with the two regime shifts, average
  suitabilities, initial population values (1998)
  and four levels of fishing mortality, F30, F40,
  F50 and no fishing mortality
• Single species forecasting using the
  corresponding input parameters.
• Spawning biomass ratio selected as indicator of
  performance
• SSB ratio SSB(2015)/SSB(1998)

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Results recruitment scenarios
ANOVA and CVs comparison results for the
1979-1989 and 1989-1998 periods

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Results frequency distribution of spawning
biomass ratio of pollock in 2015 (F40)
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Results Forecasting of pollock SSB ratio under
two climate regimes and F40 level of fishing
mortality

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Results Forecasting of cod SSB ratio under two
climate regimes and F40 level of fishing
mortality

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Results effect of two levels of fishing
mortality and climate regimes in the forecasting
of SSB ratio in 2015

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Results effect of two levels of fishing
mortality and climate regimes in the forecasting
of SSB ratio in 2015

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Resultseffect of two levels of fishing mortality
and climate regimes in the forecasting of SSB
ratio in 2015

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Results temporal trend of the median of SSB
ratio of walleye pollock
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Results temporal trend of the median of SSB
ratio of walleye pollock
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Conclusions

• Climate regime shifts produced an effect
  comparable to the ones produced by fishing and
  predation on the species analyzed from the
  eastern Bering Sea, therefore accurate models for
  fisheries management will require considering all
  three factors and their potential interactions.
• To incorporate regime shifts in fisheries
  management it is necessary to have a better
  understanding of recruitment behavior during a
  particular climate regime and a reliable way to
  identify a potential shift based on biological
  and/or physical indices.
• Species respond differently to both climate
  change assumptions and fishing mortality
  depending on their position on the food web and
  on their generation time. Responses are complex
  and difficult to predict therefore it is
  necessary to take an even more conservative
  approach in managing the species with the largest
  potential variation.

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Future tasks

• Analysis of additional indicators including
  predation mortality, total population and catch.
• Inclusion of stochastic Ricker and Beverton and
  Holt recruitment

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The end