Tutorial: MPAs in Anchovy Bay
The cod population in Anchovy Bay has been depleted, and there is concern for its recovery. Here, we will do a retrospective analysis to evaluate the potential impact of using protected areas as a management tool.
We will use a version of the Anchovy Bay model that has been modified slightly and fitted to time series. Download the Anchovy Bay Spatial.ewemdb database. Open the EwE software and load the model. If there’s a time series in the model, then load it. Next, load the Ecospace scenario included in the model, named BayOfAnchovies, and run Ecospace. Extract results (for all groups and fleets) from the Ecospace Results form.
Now it’s time to add MPAs and examine how they function,
- On the Ecospace Maps form, right hand side, click the pencil to the right of MPAs, and on the pop-up Define MPAs form, click Add, and OK. The form will close, and you now have one type of MPA, by default called MPA1 (but you can change it), in your model.
- Open the MPAs form again. If you select the MPA1 layer (click on it), you can now edit the layer, the tools at the bottom of the right-hand side provides drawing tools for the editing. Sketch a nice big MPA covering part of the area where cod occur.
- Reset all fishing effort, Ecosim > Input > Fishing effort, Reset All. Then set the effort for trawlers to 2.
- Go back to Maps, and make a nice big MPA covering part of the area where cod occur.
- On Ecospace > Input > Ecospace fishery > MPA enforcement, you can allow or disallow fleets from operating in the MPA. By default no fleets will be allowed inside, but change this so that only trawlers are not allowed inside (i.e. remove the check mark for the other fleets).
- Run Ecospace and check the impact for cod. Do you see any?
- Try changing the base dispersal rate for all groups from the default 300 km/year to 10 km/year, (Ecospace > Input > Dispersal)
- Run Ecospace again and see if you can see any impact of the MPA for cod and other species (both within the MPA and overall)
- Extract the results and compare to the original run. Which groups change?
- Did catch value change?
So, dispersal rates are important for spatial modelling, and especially for the performance of MPAs. That’s a fact, both in modelling and for actual efficiency of MPAs. Ideally, MPAs will allow populations to build up, and the spill-over effects to neighbouring areas be large enough to sustain the people who rely on the fisheries for their livelihood.
