Ecopath

The Ecopath model provides the basic parameterization for the temporal dynamic Ecosim simulations and for the temporal-spatial dynamic Ecospace simulations. It relies on a food web that typically is constructed to represent the average conditions in a given period of time (often a year). Ecopath provides a "snapshot" of the ecosystem groups and of the energy flow between the groups at this given point in time.

Parameterization calls for the following parameters in the table below. Notice though, that to ensure mass balance, only 3 out of the 4 basic parameters (i.e., B, P/B, Q/B and EE) needs to be entered. If all four are entered, the mass balance routine of Ecopath can estimate either NM or BA instead.

For functional groups or species (using the default biomass pools):

For functional groups or species, using an optional age-structured population dynamic model:

• Define a number of "stanza" age groups that jointly represent the ontogeny of the group/species

• For the overall group/species enter,

  • von Bertalanffy growth parameter (K, year^-1)

  • Weight at maturity / asymptotic weight (proportion; default is 0.09 corresponding to L_mat/L_inf = 0.45)

• For each stanza enter,

  • Start month (e.g., 0, 12, 24, 36 – any interval is fine)

  • P/B (year^-1)

  • Diet composition (proportion)

• For one of the stanza's (the "leading" stanza) enter,

  • B (t km^-2)

  • Q/B (year^-1)

• From this, Ecopath estimates B and Q/B for the remaining stanzas

For fishing fleets:

• Define any number of fishing fleets

• For each enter,

  • Catch (t km-2 year-1) by functional group/species (or stanza for age-structured groups)

  • Price (optional input, any currency)

• EwE includes an optional value chain module that can be used to describe the full pathway from sea to end consumer

Based on these parameters a quantified food web can be constructed and used for the further dynamic analysis. Properties of the food web can also be explored, e.g., through network analysis – for which there are a number of routines included in EwE.