Tutorial: Adding multi-stanza groups
The purpose of this exercise is to demonstrate how to add multi-stanza groups to an EwE model. You can do this with an existing version of the Anchovy Bay model, which likely would have these functional groups:
Whales, seals, cod, whiting, mackerel, anchovy, shrimp, benthos, zooplankton, phytoplankton, detritus.
On Ecopath > Input > Basic input select Define groups (also available from the menu on top: Ecopath > Define groups). Place your cursor at the Mackerel, then click Edit > Insert on the right side of the form that pops up. We will make mackerel an age-structured (‘multi-stanza’) group, therefore enter “Mackerel juv” as name for the new group, and enter “Mackerel” under the “Multi-stanza group name”. Then perhaps change the name of the mackerel group to “Mackerel ad” and use the down arrow in the multi-stanza column at the row for Mackerel ad. and select “Mackerel” from the drop-down menu (this is to make sure that the stanza name is spelled the same way). Also set the Stanza age to 0 months for the juveniles, and 3 months for the older stanza. On the right panel, you may also want to click the Colours > Alternate all, to change the group colours from the default to some darker that will work better on Ecosim plots. Click OK.
Next, click the baby pram / Edit multi-stanza Ecopath > input > Basic input form. Set the growth curvature parameter to 0.3 year-1 for mackerel (= the average k value from FishBase); total mortality for Mackerel juv. should be 4 year-1, and “leading” should be checked for Mackerel ad. for both biomass and consumption/biomass. Click Calculate, and the model should parameterize the age structured model.
You will also have to add diets for juvenile mackerel (maybe zooplankton) and consider which of the predators that may be preying on juvenile mackerel. Do what you find reasonable and check if you can get the model to balance.
That’s really all that’s required to change a group from biomass dynamics to using an age-structured population dynamics model.
