A brief introduction to ecosystem modeling using Ecopath with Ecosim

1. A brief introduction to ecosystem modeling using Ecopath with Ecosim Daniel Pauly and Villy Christensen Fisheries Centre, University of British Columbia, Vancouver, Canada United Nations University Fisheries Training Programme Institute of Marine Science, December 17, 2002 Reykjavik, Iceland

2. The software: Ecopath with Ecosim • The Ecopath with Ecosim software package includes mass-balance (Ecopath), time-dynamic (Ecosim) and spatial simulation (Ecospace) models, and can be used to: • Evaluate biomasses and fluxes; • Address ecological questions; • Evaluate ecosystem effects of fishing; • Evaluate effects of environmental changes. • Explore management policy options; • Evaluate impact and placement of marine protected areas; • Quantify bioaccumulation, and more.

3. Ecopath Master Equation (I) Production = predation + fishery + biomass accumulation + net migration + other mortality

4. Ecopath Master Equation (II) Consumption = production + unassimilated food + respiration

5. Mass balance: cutting the pie Other mortality Harvest Unassi- milated food Predation Harvest Respi- ration Respi- ration Predation Predation Unassi- milated food Other mortality Consumption Other mortality Unassi- milated food Predation Predation Respi- ration

6. Ecopath Master Equation (I): How it is actually implemented • Bi * P/Bi * EEi= Catchi • + j Bj Q/Bj DCji • + Net migrationi • + Biomass accumulationi • Most common input: B, P/B, Q/B, Catch, Net migration (NM), biomass accumulation rate (BA), and diet compositions (DC). • B, P/B, Q/B, EE, NM or BA is estimated by Ecopath. • DC’s are usually modified as required to ensure that EE’s are  1.

7. Key data requirements for Ecopath • Biomass (t·km-2) • Production / Biomass (t·km-2 ·year-1) • Consumption / Biomass (t·km-2 ·year-1) • Ecotrophic efficiency (proportion) • Diets (proportion) • Catches (by fleet) (t·km-2 ·year-1) • Growth parameters for PSD & Ecosim It is possible to use ranges for all parameters (see Ecoranger).

8. Addressing uncertainty: • Pedigree for input data and overall index of model quality; • Sensitivity analysis for documenting the effect of inputs on estimated parameters; • Ecoranger routine for explicit consideration, in a Bayesian context, of the uncertainty inherent in all input; • Closed-loop policy simulations for evaluating the effect of uncertain inputs on the management process.

9. Ecoranger • Semi-Bayesian parameter estimation for Ecopath Input ranges ‘Priors’ 10,000 x Acceptable inputs Mass balance & physiological constraints Selection of possible models Resampling (Sampling Importance Resampling) ‘Posteriors’ Selection of ‘best’ model Accepted inputs Outputs

10. EwE can incorporate all functional groups (100+) and all fisheries (20+)

11. Key Ecopath routines • Ecopath routines for entry of key data on the biology and exploitation of ecosystem groups, and for establishing mass-balance in semi-automatic fashion; • FishBase bridge (www.fishbase.org) established for input data; • Econet: network analysis for study of ecosystem form and functioning, incl. particle size distribution (PSD); • Ecowrite routine for documentation of data and assumptions used when constructing and validating models. Incorporates reference database; • Ecoempire module with empirical relationships, etc.

12. To get started with Ecosim • Ecosim builds on Ecopath • First step is to construct an Ecopath model using the constraints offered by mass-balance and thermodynamics to ensure that parameters are compatible and realistic

13. Representing limited prey vulnerability in Ecosim Predator P aVP v(B-V) Unavailable prey B-V Available prey V vV Fast equilibration between B-V and V implies V=vB/(2v+aP) B = Total prey biomass; V = Vulnerable prey biomass; v = Behavioral exchange rate; P = Total predator biomass; a = Predator rate of search.

14. Data requirements for Ecosim • Flow-control: (top-down to bottom-up); • Incorporates five methods for evaluating this sensitive parameter (sensitivity analysis, time series fitting, two-model comparison, Bunfished/B0 , Fmax/M); • Feeding time adjustment rate; • Predator effect on feeding time; • Ecological interpretation of all parameters; • Monte-Carlo routine linking to Ecoranger.

15. Ecosim incorporates: • Ontogenetic changes (juvenile/adult life history, variable stage, growth/reproduction allocation strategy, seasonal egg production); • Food related behavior changes (diets, feeding time, handling time) • Trophic effects (predator/prey dynamics); • Mediation effects, (e.g., tuna/small pelagics/birds); • Forcing functions (seasonal/long-term; environmental, productivity, …) ; • Fisheries effects (bioeconomic model); • Density-dependent catchability; …

16. Ecosim predicts ecosystem effects of changes in fishing effort Biomass/original biomass Fishing effort over time

17. Building on the past: time series • Ecosim can incorporate (analyses indeed benefit from) time series data on: • Relative or absolute biomasses; • Mortality rates, F, Z, catches; • Effort data; • Forcing factors (notably primary productivity) • Incorporates goodness of fit measure (weighted SS) • Incorporates anomaly fitting (productivity, recruitment); • Sensitivity of the crucial Ecosim parameters can be evaluated, and the model fitted to data; • Ecosim thus incorporates much of the information commonly obtained through single species assessment.

18. North Sea time series from MSVPA (•) compared to Ecosim (line)

19. Ecosim inter-face for evalua-tingtrends over time

20. Ecospace Ecospace is a spatial simulation tool for prediction of spatial patternsand impact of protected areas

21. To get started with Ecospace • Ecospace builds on Ecopath and Ecosim • Use Ecosim to check model behavior • Build an Ecospace scenario (map, habitats, …)

22. Ecospace: a spatial, meso-scale version of Ecosim • Replicates Ecosim dynamics over spatial grid of ‘homogeneous’ cells; • Links cells through dispersal of organisms, and fishing effort movement/allocation; • Incorporates an advection model. • Accounts for spatial variation in productivity and cost of fishing; • Represents habitat ‘preferences’ by differential dispersal, feeding and predation rates;

23. Ecospace dispersal linkage mi,j+1Bij Bij Equal m’s (symmetrical mixing, except at shores, toward preferred habitats)

24. Ecospace: basemap

25. Ecospace can consider advection

26. Ecospace predicts spatial distributions and impact of protected areas & habitat changes

27. Ecoseed • A routine of Ecospace for optimal location and sizing of MPAs; • Ecoseed evaluates one seed cell for each run; • The ‘best’ seed cell is selected as an MPA cell; • Adjacent cells become seed cells; • Process continues until all cells are MPAs.

28. Ecoseed: results from test model Relative rent Non-market value % MPA Rent of fishery Existence value

29. Documentation of methods • Ecopath: Ecol. Modelling (1992) 61: 169-185; • Ecosim: Fish Biol. Fisheries (1997) 7:139-172; • Ecosim: Ecosystems (2000) 3: 70-83; • Ecospace: Ecosystems (1999) 2: 539-554 • EwE overview: ICES J. of Marine Science (2000) • ‘EwE Methods, capabilities and limitations:’ Fisheries Centre Research Report (2001) and Ecol. Modeling (in press) • ‘EwE: A User’s Guide’ (2000); • Ecopath –Autobalance routine: Ecol. Modelling (in press); • Also EwE incorporates complete context-sensitive help.

30. Dissemination • Distributed free-of-charge • 2000+ users in some 150 countries (half in the tropics); • Present rate: 2 new users a day; • 20+ international workshops/training courses; • 150+ published models; • 50+ models known to be in preparation; • 90 peer reviewed papers, incl. some high profile; • 40 other publications; • 12+ universities offering courses; • 13 PhD’s completed; • 10 MSc’s completed; • On average 100 visitors per day to www.ecopath.org.

31. Models are not like religion you can have more than one… and you don’t have to believe them. Thank you.