Using ecosystem modeling for fisheries management

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Using ecosystem modeling for fisheries management
Villy Christensen
Cape Town, September 2006
IncoFish WP4 Workshop
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Are ecosystem models useful for fisheries
management?
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One of those really smart quotes
We believe the food web modelling approach is
hopeless as an aid to formulating management
advice the number of parameters and assumptions
required are enormous. Hilborn and Walters
(1992, p. 448)
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Willie asked the right question...

• Why dont the fish eat them all, dad?

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(No Transcript)
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A key aspect of EwE modeling

• Prey behavior limits predation (foraging arena
  assumptions)

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Organisms are not chemicals!
Ecological interactions are highly organized
Reaction vat model
Foraging arena model
Prey behavior limits rate
Predator handling limits rate
Big effects from small changes in space/time scale
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Foraging arena
Predator, P
aVP
Available prey, V
v(B-V)
vV
Unavailable prey B-V
v behavioral exchange rate (vulnerability)
predator-prey specificbased on foraging arena
theory (Walters and Juanes, 1993)
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Time predictions from an ecosystem model of the
Georgia Strait, 1950-2000
With mass-action (Lotka-Volterra) interactions
only
With foraging arena interactions
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A critical parameter vulnerability
Top-down/bottom-up control carrying capacity
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Predation mortality effect of vulnerability
Predicted predation mortality
Traditional
Ecosim
Ecopath baseline
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Carrying capacity
Predator abundance
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So how do we get estimates of carrying capacity?

• Surveys
• Assessments
• Stock reduction analysis

Numbers (x 1000)
Blue whales
Fin whales
Year
Year
Christensen, LB, 2006
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Evaluation of simulations

• Can the model
• replicate historic trends?
• make plausible extrapolations to novel situations?

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Fitting to time series learning from ecosystem
history

• A proliferation of ecosystem modeling activities
  has in recent years produced many apparently
  credible models that fit historical data well and
  make reasonable policy predictions

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Ecosystems where EwE models have been tested
using historical trend data

• E Bering Sea
• Aleutian Islands
• WC GoAlaska
• E GoAlaska
• W Vancouver Island
• Hecate Strait
• British Columbia Shelf
• Strait of Georgia
• NE Pacific
• CN ET Pacific
• NWHI, Hawaii
• Gulf of California
• Central Chile

• Bay of Quinte
• Oneida Lake
• Scotian Shelf
• Chesapeake Bay
• Tampa Bay
• S Brazil Bight
• Norwegian Sea
• North Sea
• Baltic
• S Benguela
• Gulf of Thailand
• South China Sea

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Formal estimation
Modeling process fitting drivers
Fishing
Ecosystem model (predation, competition,
mediation, age structured)
(Diet0)
Log Likelihood
Predicted C, B, Z, W, diets
(Z0)
( BCC/B0)
Observed C,B,Z,W, diets
Nutrient loading
Habitat area
Climate
Search
Judgmental evaluation
Choice of parametersto include in final
estimation (e.g., climate anomalies)
Errorpattern recognition
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Confounding of fishery, environment, and trophic
effects monk seals in NWHI
Initial Ecosim runs fishing trophic
interactions together could not explain monk
seal decline. Predicted lobster recovery
1970
2000
Satellite chlorophyll data indicate persistent
40 decline in primary production around 1990.
Explains both continued monk seal decline and
persistent low lobster abundance
Low Chl
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Are seals causing fish declines in the Georgia
Strait? Is it fishing? Is it environ-mental
change?Or, is it all three?
1950
1950
2000
2000
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Strait of Georgia

• EwE PP Index of Fraser River runoff
  (March-April salinity at two measuring stations)

Dave Preikshot, UBC FC
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BC Shelf biomass changes
Dave Preikshot, UBC FC
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BC shelf Upwelling index in May, June, and July.
10 year period
Dave Preikshot, UBC FC
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Northeast Pacific biomass changes
Dave Preikshot, UBC FC
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Northeast Pacific PDO index (Pacific Decadal
Oscillation), April to July. 50 year period
Dave Preikshot, UBC FC
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Why have Steller sea lions declined?
Guenette, Heymans, Christensen Trites (CJFAS
Nov 2006)
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Alaska
Aleutian Islands
Guénette, Heymans, Christensen Trites (MS)
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General finding multiple factors impact
ecosystem resources (in all but the easiest
cases)
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Evaluating trends

• Fishing pressure
• Trophic impact, including competition
• Environmental impact
• Nutrient loading
• As a rule All of the above contribute

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Are we finally able to develop useful predictive
models for ecosystem management?

• Its beginning to look like it
• We can with some credibility describe agents of
  mortality and trophic interdependencies
• Evaluation of relative impact of fisheries and
  environmental factors is progressing
• As a rule we need to invoke fisheries and
  environmental drivers to fit models.

• When we have a modelthat can replicate
  development over time we can (with some
  confidence) use it for ecosystem-based policy
  exploration.

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Report card Using models to address ecosystem
management questions
CONCERN GRADE COMMENT
Bycatch impacts A- We are not bad at predicting direct effect of fishing in general
Top-down effects(of predator culling or protection) C Trophic effects of fishing can be classified as top down or bottom up with respect to where management controls are exerted
- on valued prey B Changes in M for prey species already subject to assessment
- on rare prey F Outbreaks of previously rare species
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Modeling report card (cont.)
CONCERN GRADE COMMENT
Bottom-up effects(effects of prey harvesting on predator stocks) C Uncertainty here is about flexibility of predators to find alternative food sources when prey are fished
Multiple stable states B Cultivation-depensation mechanism appears to be main mechanism that could cause flips
Habitat damage D Lack of understanding about real habitat dependencies, bottlenecks
Selective fishing practices/policies F We have not yet looked closely at options in this area!
Production regime changes B Models look good when fitted to data, but have not stood test of time
Regime shifts C Policy adjustments in response to ecosystem-scale productivity change
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So are ecosystem models actually used for
fisheries management?
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Use of EM for fisheries management

• Multispecies models
• Estimating predation mortality for stock
  assessment
• Limit harvest of prey species to meet consumer
  demands
• Impact of changing mesh size, North Sea
  roundfish
• Minke whale and harp seal culling?
• Environmental Impact Assessment (EIA), Alaska
  groundfish
• Target species response to TACs, Bering Sea.

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Use of EM for fisheries management

• EwE
• Evaluate impact of shrimp trawling, GoCalifornia
• Evaluate impact of bycatch, GoCalifornia
• Evaluate impact of predators on shrimp, GoMexico
• Demonstrate ecological role of species, GoMexico
• Impact of proposed fisheries interventions,
  Namibia?
• EIA of proposed fisheries interventions, Bering
  Sea
• EIA of alternative TACs, Bering Sea and
  GoAlaska
• Target species response to TACs, Bering Sea
• Closed area sizing, Great Barrier Reef, Australia
• Valuation of cormorant impact, Ortobello, Italy
• South Africa pelagic fisheries in progress.

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So why arent ecosystem models used more for
management?

• Lack of experience using ecosystem models for
  predictive purposes
• Ecosystem modeling is for strategic management,
  and supplements the tactical single species
  assessment
• Fisheries management process is trapped in
  tactical management
• Strategic decisions are virtually non-existing.

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Data gap for modeling

• We need longer-term data than typical in
  assessments to avoid shifting baselines, e.g.,
  1950-present
• Data mining is required
• There is much more information out there
  Catches, CPUE, w,
• Assessments should be expanded back in time
• Stock Reduction Analysis
• Biggest information gaps for
• Mid-TL forage fishes
• Novel conditions (vampires in the basement)
• Estimates of mortality rates.

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Our empirical knowledge is limited

• Habitat and environmental changes (including
  those caused by fishing) and intensive fishery
  removals are creating novel situations, which we
  can only handle with difficulty
• We do not to understand the mechanics of
  ecological response well enough to be able to
  predict all important responses to these novel
  situations
• Make models one can play with

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Our capability to provide advice about
large-scale dynamics is limited

• We cannot resolve uncertainty about how
  ecosystems change based on models and time-series
  data only

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Predictive approaches are uncertain, for some
obvious reasons

• Lack of long-term monitoring data on non-target
  species and life stages
• Concentration of interaction effects (trophic,
  habitat) on early life stages (recruitment) that
  are difficult to monitor
• Confounding of fishery, environmental, and
  trophic effects in historical data
• Failure to anticipate new problems (vampires in
  the basement) due to unpredictable changes in
  system structure, (exotic invasions, fisheries
  inventions)
• Unpredictable pre-adaptations to habitat
  alterations.

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Ecosystem modeling for adaptive management
requires a very different approach to assessment

• Modelers must attempt to uncover alternative
  models that equally well explain historical data
  but imply different policy choices
• Environmental vs. fisheries vs. trophic effects
• Policy options would include diagnostic
  management experiments to distinguish between the
  alternative models
• Spatial closures to test recovery predictions
• Ecosystem modification to test trophic
  interaction effects.

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Models are not like religion

• you can have more than one

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The new Ecopath with Ecosim

• Four year project funded through Lenfest Ocean
  Program
• Lenfest Ocean Futures Project
• New generation of EwE to be released Sep 07
• Single-player game version 2008
• Multi-player game version 2009

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