We use management strategy evaluation to test how alternative management procedures are affected by uncertainty. We here use the Anchovy Bay true MSE model, which you can download from this link. It’s a zip file with the database, once unzipped, open it in EwE and use the anch bay Ecosim scenario, and the anchovybay true (annual) time series.

The CEFAS MSE plug-in is found under Tools at the top row menu. Open it, and go through these steps on the Basic setup,

• Data path: you need to browse to a path that you want to use for the (many!) files that the MSE plug-in will need
• Model area: is used to convert the landings per unit area (t km^-2 year^-1) to total landings (t year^-1) and total economic value. Do not change the model area here! If you need to for a later application, go to Ecopath > Input > Model parameters and change it there, but don’t do that now.
• Basic inputs: click to create the MSE file structure. On the pop-op form you can set CV for parameters. For this tutorial, we can leave it as is. Just click Save.
• Survivabilities: For this, leave as is. Save
• Diets: For this, leave as is. Save
• MSE models: create 20 models. Click the little arrow to the right, and the routine will create 20 Ecopath models based on the underlying Ecopath models and the assumed uncertainties

Next, we define fishing strategies. We start by defining some general parameters,

• Max effort increase: default is 10% change from year to year. OK to leave at default
• Stock assessment: defines recruitment parameters for stock assessment model. OK to use default for this tutorial.
• Assessment error: here you can define (1) biomass estimation error by group and (2) fleet implementation error by fleet. Leave at default. In the built-in MSE, these errors can vary over time, here they are assumed constant.
• Quota share: not of concern here as each species is caught by only one group
• Biomass limits: by default, no limit. Leave as is.

Now define a fishing strategy, click Review, and Add strategy. Let’s call the new strategy, “cod rebuilding”. Under Harvest Control Rules (HCR), click Add HCR. Make it biomass group: Cod. Fishing mortality group: Cod. Target or Conservation: Conservation. OK.

Add another HCR. Biomass group: Whiting. Fishing mortality group: Whiting. Target or Conservation: Target. OK

If you select one of the HCRs in the HCR spreadsheet, you can see and edit each HCR. For now, set the max F for both cod and whiting to 0.3 (this is close to FMSY, you can check it in Ecosim > Tools > F_MSY), for other parameters, just leave with default values.

Under Regulations > Trawlers, select Highest value. OK. This option will allow the trawlers to operate until they’ve fished the quota for the highest value stock, i.e. cod.

Set up an additional fishing strategy, very similar to the one above, call it “Cod rebuilding no discarding”, and the only difference from above is that we use Weakest stock as regulation.

On Run MSE, set the number of models to run to 20, and the number of years to project to 10. The MSE plug-in will run the underlying Ecosim model as setup and then project for an additional 10 years for each run. Check Yearly results only. Click the little arrow run button.

The plug-in will come back after making the 20 runs, and let you know if the runs have been successful and that the results are saved (in the results folder). There’ll be more than 700 CSV files in the results, so have fun exploring them all. One by one: isn’t feasible, this calls for a structured approach, e.g., using R. We will not be going there now, but look at some details only.

The results.csv file in the Results folder gives a summary of the 20 runs by strategy. Parameters are biomass min, biomass end, catch, landings, discard mortality, discard survival. Check it for differences in the two strategies.

Details are in the various folders, check for instance biomasses and catches for cod and whiting for the two strategies.

Do the strategies have implications for other species than the two target species?

What are the average catches, average value and variability for the two target species in the strategies?

Are the runs identical for years 1-46? If not, why?

Check out the ChokeGroup folder, file ChokeGroup_Trawlers_FleetNo2.csv file to see if one of the target groups caused fishery closure.

Explore!

Ask questions such as,

• What are the average catches, biomasses, and revenues?
• How variable are these values?
• How often will the fisheries be closed?
• How often will biomasses be below acceptable level?
• What are the implications of a no discard policy?