Ecosystems Research Division

BASS is a model that simulates the population and bioaccumulation dynamics of age-structured fish communities. Although bass was specifically developed to investigate the bioaccumulation of chemical pollutants within a community or ecosystem context, it can also be used to explore population and community dynamics of fish assemblages that are exposed to a variety of nonchemical stressors such as altered thermal regimes associated with hydrological alterations or industrial activities, commercial or sports fisheries, and introductions of non native or exotic fish species.

BASS's model structure is very generalized and flexible. Users can simulate both small, short-lived species (e.g., daces, minnows, etc.) and large, long-lived species (e.g., bass, perch, sunfishes, trout, etc.) by specifying either monthly or yearly age classes for any given species. The community's food web is defined by identifying one or more foraging classes for each fish species based on either body weight, body length, or age. The dietary composition of each of these foraging classes is then specified as a combination of benthos, incidental terrestrial insects, periphyton/attached algae, phytoplankton, zooplankton, and/or other fish species, including its own. There are no restrictions on the number of chemicals or the number of fish species that can be simulated, the number of cohorts / age classes that fish species may have, or the number of foraging classes that fish species may have.

Model output includes:

• Summaries of all model input parameters and simulation controls.
• Tabulated annual summaries for the bioenergetics of individual fish by species and cohort. Quantities include: mean annual wet and dry weight, mean growth rate, net weight gain/loss, total annual ingestion, total annual assimilation, and total annual metabolism/respiration.
• Tabulated annual summaries for the chemical bioaccumulation within individual fish by species and cohort. Quantities include: mean whole body chemical concentrations, mean "observed" bioaccumulation factor (BAF), mean "observed" biomagnification factor (BMF), total chemical uptake across the gill, total chemical uptake from food, total chemical excreted and egested, and total chemical biotransformed or biogenerated.
• Tabulated annual summaries for community structure and function by species and cohort. Quantities include: mean cohort population density, mean cohort biomass, total cohort consumption, total cohort predatory and non-predatory mortalities , and total cohort production.
• Plotted annual dynamics of selected model variables as a function of time and age or size class.

The ability to predict accurately the bioaccumulation of chemicals in fish has become an essential component in assessing the ecological and human health risks of chemical pollutants. Accurate bioaccumulation estimates are needed not only to predict realistic dietary exposures to humans and piscivorous wildlife but also to assess more accurately potential ecological risks to fish assemblages themselves. Although the bioaccumulation of many chemicals in fish can often be predicted accurately using simple bioaccumulation factors (BAF) and measured or predicted chemical water concentrations, such calculations frequently fail to predict accurately concentrations of extremely hydrophobic chemicals and metals such as mercury that are often the chemicals of greatest concern. Process-based models like bass that simulate the toxicokinetic, physiological, and ecological processes of fish provide scientifically defensible tools that can overcome many of the limitations and uncertainties associated with the use BAF approaches. In addition, because bass also simulates the growth and predatory-prey dynamics for individual fish and the productivity, recruitment/reproduction, and mortalities of their associated populations, bass provides a tool that can be used to evaluate various dimensions of fish health associated with nonchemical stressors.

BASS is currently being used to investigate methylmercury bioaccumulation in the Florida Everglades and to predict population and community dimensions of "fish health" for a regional analysis of the ecological sustainability of the Albemarle_Pamlico drainage basin in North Carolina and Virginia.

Bioaccumulation and Aquatic System Simulator (BASS) Fact Sheet containing BASS screen shots (PDF, 2 pp., 57 KB, about PDF).

For additional modeling information, please go to the EPA's Council on Regulatory Environmental Modeling (CREM) site. CREM promotes consistency and consensus within the Agency on mathematical modeling issues including model guidance, development, and application, and enhances both internal and external communications on modeling activities. The CREM is the Agency's central point to address modeling issues.

For information on models distributed by EPA's Center for Exposure Assessment Modeling (CEAM), please go to http://www.epa.gov/ceampubl/.

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