The MSEtool uses a two-box spatial model. Users can specify the percent of total habitat and fraction of the population in each area. Life-history characteristics do not vary across the two spatial areas.

The fleet allocates fishing effort across areas in response to catch rates unless `Spat_targ`

is used to allow for additional targeting or avoidance behavior, or an area is closed to fishing (see `Fleet@MPA`

or MPs that create closed areas). Movement is parameterized as the probability of an individual staying in a given area for an entire time step.

### Size_area_1

The size of area 1 relative to area 2. The fraction of the unfished biomass in area 1. Please specify numbers between 0 and 1. For each simulation a single value is drawn from a uniform distribution specified by the upper and lower bounds provided. For example, if Size_area_1 is 0.2, then 20% of the total area is allocated to area 1. Fishing can occur in both areas, or can be turned off in one area to simulate the effects of a no take marine reserve. Uniform distribution lower and upper bounds. Positive real numbers.

### Frac_area_1

The fraction of the unfished biomass in area 1. Please specify numbers between 0 and 1. For each simulation a single value is drawn from a uniform distribution specified by the upper and lower bounds provided. For example, if Frac_area_1 is 0.5, then 50% of the unfished biomass is allocated to area 1, regardless of the size of area 1 (i.e, size and fraction in each area determine the density of fish, which may impact fishing spatial targeting). In each time step recruits are allocated to each area based on the proportion specified in Frac_area_1. Uniform distribution lower and upper bounds. Positive real numbers.

### Prob_staying

The probability of individuals in area 1 remaining in area 1 over the course of one year. Please specify numbers between 0 and 1. For each simulation a single value is drawn from a uniform distribution specified by the upper and lower bounds provided. For example, in an area with a Prob_staying value of 0.95 each fish has a 95% probability of staying in that area in each time step, and a 5% probability of moving to the other area. Uniform distribution lower and upper bounds. Positive fraction.

### Custom Parameters

See Custom Stock Parameters for information on specifying a custom movement matrix for more than 2 areas.

### Interactive App

Choose upper and lower bounds for Size_area_1, Frac_area_1 and Prob_staying. Based on these ranges, the MSEtool will display parameter values for 5 simulations in the table. Click on any line of the table to visualize the movement rate for that simulation in the figures below.

- Figure 1 shows the size and a distribution of the population between area 1 (blue dots) and area 2 (green dots) at a given movement rate over the course of 4 years. The initial population distribution is determined by the values selected for Size_area_1 and Frac_area_1. Users can select years 1, 2, 3 or 4 to visualize how individual fish are likely to move under the selected Prob_staying over multiple time steps.