A.5.9 EcoOcean

A.5.9.1Introduction
EcoOcean is an ecosystem model complex that can evaluate fish supply from the world's oceans. The model is construct­ed based on the Ecopath with Ecosim modeling approach and software, and includes a total of 42 functional group­ings. The spatial resolution in this initial version of the Eco-ocean model is based on FAO marine statistical areas, and it is run with monthly time-steps for the time period from 1950. The model is parameterized using an array of global databases, most of which are developed by or made avail­able through the Sea Around Us project. Information about spatial fishing effort by fleet categories will be used to drive the models over time. The models for the FAO areas will be tuned to time series data of catches for the period 1950 to the present, while forward looking scenarios involving optimization routines will be used to evaluate the impact of GEO4 scenarios on harvesting of marine living resources.

A.5.9.2 Model structure and data
The Ecopath with Ecosim (EwE) modeling approach has three main components:
•     Ecopath—a static, mass-balanced snapshot of the sys­tem;
•     Ecosim—a time dynamic simulation module for policy exploration; and
•     Ecospace—a spatial and temporal dynamic module pri­marily designed for exploring impact and placement of protected areas.

The initial EcoOcean model will be composed of 19 EwE models. The EwE approach, its methods, capabilities and pitfalls are described in detail by Christensen and Walters (2004).
     The foundation of the EwE suite is an Ecopath model (Christensen and Pauly, 1992; Pauly et al., 2000), which cre­ates a static mass-balanced snapshot of the resources in an ecosystem and their interactions, represented by trophically linked biomass "pools." The biomass pools consist of a sin­gle species, or species groups representing ecological guilds. Ecopath data requirements are relatively simple, and gen­erally already available from stock assessment, ecological

studies, or the literature: biomass estimates, total mortality estimates, consumption estimates, diet compositions, and fishery catches. The parameterization of an Ecopath model is based on satisfying two "master" equations. The first equation describes how the production term for each group can be divided:

     Production = catch + predation + net migration + biomass accumulation + other mortality

The second "master" equation is based on the principle of conservation of matter within a group:

     Consumption = production + respiration + unassimilated food

Ecopath sets up a series of linear equations to solve for un­known values establishing mass-balance in the same opera­tion.
     Ecosim provides a dynamic simulation capability at the ecosystem level, with key initial parameters inherited from the base Ecopath model. The key computational aspects are in summary form:
•     Use of mass-balance results (from Ecopath) for param­eter estimation;
•     Variable speed splitting enables efficient modeling of the dynamics of both "fast" (phytoplankton) and "slow" groups (whales);
•     Effects of micro-scale behaviors on macro-scale rates: top-down vs. bottom-up control incorporated explic­itly.
•     Includes biomass and size structure dynamics for key ecosystem groups, using a mix of differential and differ­ence equations. As part of this EwE incorporates:
- Age structure by monthly cohorts, density- and risk-dependent growth;
- Numbers, biomass, mean size accounting via delay-difference equations;
- Stock-recruitment relationship as "emergent" property of competition/predation interactions of juveniles.
Ecosim uses a system of differential equations that express biomass flux rates among pools as a function of time vary­ing biomass and harvest rates, (Walters et al., 1997, 2000).