We will, once again, use the ecosystem model of Anchovy Bay that we constructed in the very first tutorial in this text book, but in a slightly modified form (Anchovy Bay noise.ewemdb). You can download it (along with a couple of CSV files) from this link.

Modelling impact of noise

Ecosim can incorporate non-trophic effects through what we call mediation. The mediation functionality can also be used in Ecospace, which can pick up the mediation functions that are defined in Ecosim, but spatial driver layers will need to be defined for use in Ecospace. In this tutorial, we illustrate how to incorporate effects of external factors, i.e. factors that are not modelled directly in EwE. We illustrate this through modelling impact of vessel noise on marine mammals.

The key question for modelling impact of noise is: what is the impact of noise? You need to consider that question, there is no model that will know it – models are not very smart, but they are good at analysis. So, a reasonable way to handle this uncertainty is to read the literature, and evaluate a reasonable scenario, plus a high and a low impact scenario, as a minimum. Or, make a suite of potential scenarios and evaluate all. That can be automated, EwE can be run from scripts.

In this tutorial, we illustrate the procedure for how to model impact of noise, and note that the procedure can be used for other external factors as well, e.g., light impacts.

Implementation in Ecosim

Open the Anchovy Bay noise model, then open a new scenario in Ecosim, (and name it, e.g., “noise mediation”). Go to Ecosim > Output > Run Ecosim, and run the model to see how it behaves. It should have whales increasing because of the biomass accumulation rates, we provided for this group.

To model impact of vessel noise, we need a mediator, in this case it can be Vessel traffic. Add a fleet to your model: Ecopath > Input > Fishery > Fleets > Define fleets, click Insert and name the new fleet “Vessel traffic” (or any name, as you please). You do not need to enter any landings for the fleet, but you will get a warning when you proceed that there are no landings for this fleet. Just disable the warning.

Next open Ecosim, and load the time series file “vessel noise.csv” (Ecosim > Input > Time series > Import, then browse to find the CSV file). Check if there are errors (warnings in the first column) and load if not (or fix errors if any). You will for instance get an error if you did not add a fleet.

Run Ecosim, and check (Ecosim > Input > Fishing effort) that the vessel noise increases over time. Next to to Ecosim > Input > Mediation, and add or modify a mediation function. Click Change shape, and define a linear function with Start = 1.5 and End = 0.5. Give the function a name, e.g., Noise impact. Click OK.

Figure 1. Screenshot from EwE showing a mediation shape that can be used for modelling the impact of noise. The vertical (blue) dotted line represents the Ecopath baseline situation and it can be moved.

You should now have a shape as in Figure 1. The stippled line represents the Ecopath baseline (time 0 in Ecosim), move the stippled line to the left (as in Figure 1). This shape now indicates that if vessel traffic increases 6-7 times, this will result in something (whatever will end up being at the Y-axis), decreasing from unity to around 0.4. If vessel traffic increases more than 6-7 times (i.e. beyond the scale of the X-axis), the Y-factor will remain at 0.4.

Next, just below to the right of the mediation shape, click Define mediating groups and fleets, and assign Fleet 6, Vessel traffic, to the shape by clicking it in the left column to move it over to the right. Notice that if you for instance have noise impact for each fleet, you could assign more fleets – with corresponding weighting factors – some are noisier than others.

Go back and run Ecosim (Ecosim > Output > Run Ecosim), and click Show multiple runs.

Next define what is mediated; Ecosim > Input > Mediation > Apply Mediation (consumer), click 1 in the top row. This will bring up the Apply Mediation interface, where you can apply the Noise impact function over to the right, let it impact Search rate (the default). Click OK, and the Noise impact should now be impacting the feeding of whales. More noise decreases the efficiency of their search rate. Go back and run Ecosim again. Any difference?

You can put numbers on the difference, by extracting biomass integrated over time from the Ecosim results form (Ecosim > Output > Ecosim results) after each run.

Implementation in Ecospace

Load an Ecospace scenario. Go to Ecospace > Input > Maps, and in the right-hand column, select Fisheries (), Sailing cost, and select Vessel traffic in the drop-down list. Double-click the label Sailing cost – Vessel traffic and a form with a spreadsheet will pop up. Here, select Import > From CSV and browse to find the file called Anchovy Bay-Sailing cost (6-Vessel traffic).csv. This will load a “sailing cost” which will be used to distribute the Vessel noise (from the fleet effort) spatially. This approach is a “hack”, which we can use for now – we will be adding a more explicit and direct way to include such impacts in a coming software update.

Run Ecospace and evaluate the results with and without the noise mediation. Compare. An easy way to model with and without in succession is to go back to Ecosim and remove (or insert) the Apply mediation to whales.

Compare the impact of noise between Ecosim and Ecospace runs. Where is it most pronounced? Why?