Methods for Evaluating the Impacts of Fisheries on North Atlantic Ecosystems
Ecopath with Ecosim: Methods, Capabilities and Limitations
Villy Christensen and Carl Walters
University of British Columbia, Fisheries CentreAbstract
The Sea Around Us Project uses ecosystem modeling based on the Ecopath with Ecosim (EwE) approach as an important component to characterize the status of North Atlantic ecosystems. For this, ecosystem models will be constructed covering the North Atlantic region, with a minimum of one model for each large marine ecosystem of the North Atlantic. For many of the areas the modeling will include construction of additional models representing the time period before industrialized fisheries had a major impact.
The EwE modeling approach combines software for ecosystem trophic mass balance (biomass and flow) analysis (Ecopath), with a dynamic modeling capability (Ecosim) for exploring past and future impacts of fishing and environmental disturbances. Ecosim models can be replicated over a spatial map grid (Ecospace) to allow exploration of policies such as marine protected areas, while accounting for spatial dispersal/advection effects.
The Ecopath approach and software has been under continuous development since 1990, with Ecosim emerging in 1995, and Ecospace in 1998, leading to an integrated package now called ‘Ecopath with Ecosim’. We present an overview of the computational aspects of the Ecopath, Ecosim and Ecospace modules as they are implemented in the most recent software version. The paper summarizes the capabilities of the modelling system with respect to evaluating how fisheries and the environment impact ecosystems. We conclude by a warning about pitfalls in the use of the software for policy exploration.