Matt Nahorniak, SFR
ISEMP coded the Wisconsin Bioenergetics [1,2] model into R, a free open source programming language. The Bioenergetics model calculates fish growth by solving the energy balance equation:
Consumption = Respiration + Egestion + Excretion + Growth
The model inputs initial fish weights and information about the habitat (temperature, prey information), from which it calculates growth over time, based on species-specific equations for consumption, respiration, egestion, and excretion. For a given species, one of three consumption equations will be specified. Similarly, one of two respiration equations and one of three egestion/ excretion) equation sets are used for a given species. This implementation of the model does not include weight losses due to reproduction.
The Bioenergetics model can be run in three different simulation modes. The first mode takes temperature, p-value, and initial fish weights as inputs, and outputs fish growth. For the 2nd mode, total fish growth is instead used as an input, and average p-values are calculated. For the 3rd mode, total consumption is input by the user and average p-values are calculated.
A single species of fish can be modeled with each run of the model. However, multiple sites can be modeled simultaneously, for as many time steps as the user requires. “Site” is defined, for this program, as a set of temperature, p-value, and prey inputs over time of the simulation. All sites simulated simultaneously must be run the same number of time steps (days). For each site modeled, the user may model more than one fish (as defined be start weight, and, if applicable, end weight or consumption).
Findings and Uses
The ISEMP bioenergetics model is used in conjunction with temperature data and models to support growth-survival based inputs to ISEMP life cycle models. The model has been written in the free, open-source R programming language, which is designed specifically for statistical computing and graphics.
The R software and documentation are available free to all users interested in bioenergic growth modeling at: http://www.r-project.org/.