Fleet Size Dynamics Implementation

You can choose to treat dynamics of fleet sizes and resulting fishing effort as unregulated and subject to fisher investment and operating decisions. The models are described in detail in the introductory material.

If you wish to use the fleet/effort dynamics model, you should check the ‘fleet/effort response’ box on the Ecosim parameters form. When this box is checked, Ecosim erases all previously entered time patterns for fishing efforts and fishing rates, (e.g., from the sketch pad or from the time series data file), and replaces these with simulated values generated as each simulation proceeds.

In this model, there are two time scales of fisher response:

1. a short time response of fishing effort to potential income from fishing, and
2. a longer time investment/depreciation model for capital capacity.

You need to set two parameters for the short time response model (‘Effort response power’ and ‘Initial effort/capital capacity’) and two for the longer time model (‘Capital depreciation rate’ and ‘Initial capital growth rate’).

Effort Response Power

Use ‘Effort response power’ to set the parameter p, which represents a “heterogeneity” parameter for fishers: high p values imply all fishers “see” income (I) opportunity similarly, while low p values imply fishers “turn on” their effort over a wide range of mean incomes (see figure 1).

Initial Effort / Capital Capacity

This parameter is the ratio of initial fishing effort to fleet capacity (i.e., the proportion of maximum effort deployed in the first time step). It is used to set the initial fleet capacity K_g,1 as well as the income level needed for half the maximum effort to be deployed (I_hg).

Calculating K_g,1: For each fleet, initial fleet capacity K₁ is calculated as the inverse of ‘Initial effort/capital capacity’ (initial effort is scaled to be 1 at Ecopath base condition), i.e., if ‘Initial effort/capital capacity’ is set at 0.5, then the fleet capacity will be set to 2 because half of the maximum effort is deployed. K_g,t is updated at each time step using the slow time response model.

Calculating I_hg: ‘Initial effort/capital capacity’  is also used to calculate I_hg. When the ratio is set at the 0.5 default value, I_hg is set to the initial income (summed over pools of Ecopath base catches x prices for each fleet).

Capital Depreciation Rate

Set the rate of capital depreciation here. Capital depreciation rates for fishing fleets are typically in the range 0.04 to 0.10 (equipment lasts 10-25 years), although will vary on a fleet by fleet basis.

Initial Capital Growth Rate

Set the initial rate of annual capital growth here. A value of zero would represent a fleet with no growth (e.g., at bionomic equilibrium). For rapidly growing fleets, set the value at 0.5  or higher. If you have data on the maximum effort deployed for a number of years before and after the Ecopath base year, you can estimate this parameter empirically.