The Chesapeake Bay Fisheries Ecosystem Model (CBFEM) is an exploratory tool that helps scientists and others understand the Chesapeake Bay ecosystem. Explorations using CBFEM have focused on interactions between menhaden and striped bass (and other predators), potential effects of hypoxia on fisheries species, and the habitat-mediation effects of submerged aquatic vegetation on blue crab stocks.

More specifically, CBFEM is a trophic model of the Chesapeake Bay developed using Ecopath with Ecosim (EwE) software. The Ecopath module of the CBFEM uses estimates of the biomass of 45 trophic groups representing the fisheries species of the Bay and their predators to create a mass-balanced snapshot of the organisms and trophic linkages in the Bay as they existed in 1950. The 45 biomass pools represent either a single species or a group of species that constitutes an ecological guild. Some biomass pools were divided into ontogenetic age categories (e.g., young-of-the-year and adult).

Ecopath model parameterization is based on satisfying two ‘master’ equations for each model group: one for production and the other for consumption. The Ecosim module of the CBFEM provides a 53-year (1950-2002) simulation that attempts to estimate the current status and dynamics of the Bay’s fish species. This module can be used to simulate various management options for the Chesapeake Bay by varying parameters over time to estimate potential ecosystem changes.

Two kinds of data were compiled for use in EwE for each group: basic input data for 1950 and time-series data for 1950 through 2002. At a minimum, Ecopath requires data about diet composition, catch, and three of the following four parameters for each species or biomass pool in the model: biomass, production-to-biomass ratio, consumption-to-biomass ratio, and the ecotrophic efficiency (if data are only available to estimate three of these parameters, mass balance principles are used to estimate the fourth parameter).

Diet composition data for many species included in the model were based upon advice from local experts at the Chesapeake Bay Ecopath Workshop (Sellner et al., 2001) as well as journal articles with published local data. Other basic input parameter estimates are taken from peer-reviewed literature sources, tagging studies conducted in the Chesapeake Bay by authors of the CBFEM Technical Memorandum (Christensen et al., in press), FishBase, other models, and estimations made by Ecopath itself.

Time-series data is essential for calibrating and validating an Ecosim model; therefore, time-series data depicting trends in relative and absolute biomass, fishing effort by gear type, fishing and total mortality rates, and catches for as long a period as possible are additional data requirements.

The CBFEM currently includes 92 time series. Catch data for many species included in the model were extracted from NOAA Fisheries Statistics and Economics Division’s online database for the Chesapeake Bay region (1950-2002). Other time-series data are from the Atlantic States Marine Fisheries Commission, Northeast Fisheries Science Center, Marine Recreational Fisheries Statistics Survey, Virginia Institute of Marine Science Trawl Survey, Maryland Department of Natural Resources Seine Survey, and various other Bay-specific research programs. The authors of the CBFEM Technical Memorandum (Christensen, et al., in press) conducted additional stock assessments for key species for which no time-series data were available.

Model software can be downloaded from the Ecopath with Ecosim (EwE) web site. The CBFEM database, time series data file, and Technical Memo can be downloaded from the Fisheries Ecosystem Modeling ftp server.

The initial version of the model is complete and is subject of a paper being published by the NOAA/NMFS Scientific Publications Office. Version 2 is being developed with updated data. This e-mail address is being protected from spambots. You need JavaScript enabled to view it.  for more information about CBFEM.

References

Christensen, V., A. Beattie, C. Buchanan, S. Martell, R. J. Latour, D. Preikshot, J. H. Uphoff, C. J. Walters, R. J. Wood, and H. M. Townsend. 2009 (in press). Fisheries ecosystem model of the Chesapeake Bay: Methodology, parameterization and model exploration. NOAA Tech. Memo.

Sellner, K. G., N. Fisher, C. H. Hager, J. F. Walter and R. J. Latour, 2001. Ecopath with Ecosim Workshop, Patuxent Wildlife Center, October 22-24, 2001, Chesapeake Research Consortium, Edgewater, MD.