Sensitivity analyses of the equilibrium state in SKEBUB : a biomass-based fisheries ecosystem simulation model
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Sensitivity analyses of the equilibrium state in SKEBUB : a biomass-based fisheries ecosystem simulation model

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    Sensitivity analyses have been performed on the biomass-based fisheries ecosystem simulation, SKEBUB, developed at the Northwest and Alaska Fisheries Center. This simulation contains an equilibration routine that forces it to an equilibrium state by adjusting the species biomasses. Sensitivity analyses were performed at this equilibrium state. Preliminary analyses indicated a GH'Biplot of Monte Carlo error analysis data to be more useful than a fractional factorial analysis of variance, because the Biplot simultaneously analyzes all output variables. Response surfaces of sensitive output variables were generated to study nonlinearities in response. The biomass at equilibrium and the predation/biomass ratio were the most sensitive output variables, and their sensitivities were species-specific. The consumption/biomass ratio was not a sensitive output variable in this simulation. The simulation was most sensitive to the following input variables: growth, the food requirement for growth and maintenance, the availability to predation, percent contribution to other species diets, and the rate of prey switching by predators. Again the sensitivities of the different species to these parameters was species-specific. In general, variability in input parameters was increased by approximately an order of magnitude in the output variables. This increased variability would be reduced if simulations in the sensitivity analyses were required to reach an equilibrium state at least as stable as that of the baseline run. Response surfaces had limited applicability because of the many variables and interactions excluded; however, they did show the presence of multiple equilibria in the silver hake and flatfish groups. The particular equilibrium state which is chosen as the baseline for the sensitivity studies is anticipated to influence the outcome of the sensitivity analyses. Sensitivity analyses will thus be specific to both the simulation model and the data input to that model.
  • Content Notes:
    by Nicholas J. Bax.

    "Report for NOAA, NMFS contract no. 80-00155."

    "Compass Systems Inc."

    "This report does not constitute a publication and is for information only. All data herein are to be considered provisional"--Cover.

    "July 1983."

    Also available online in PDF format via AFSC and the NOAA Central Library.

    Includes bibliographical references (pages 18-19).

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