Set fishing parameters

setFishing(
  params,
  selectivity = NULL,
  catchability = NULL,
  initial_effort = NULL,
  ...
)

getCatchability(params)

getSelectivity(params)

getInitialEffort(params)

Arguments

params

A MizerParams object

selectivity

An array (gear x species x size) that holds the selectivity of each gear for species and size, \(S_{g,i,w}\).

catchability

An array (gear x species) that holds the catchability of each species by each gear, \(Q_{g,i}\).

initial_effort

Optional. A number or a named numeric vector specifying the fishing effort. If a number, the same effort is used for all gears. If a vector, must be named by gear.

...

Unused

Value

MizerParams object with updated catchability and selectivity. Because of the way the R language works, setFishing() does not make the changes to the params object that you pass to it but instead returns a new params object. So to affect the change you call the function in the form params <- setFishing(params, ...).

Setting fishing

Gears

In mizer, fishing mortality is imposed on species by fishing gears. The total per-capita fishing mortality (1/year) is obtained by summing over the mortality from all gears, $$\mu_{f.i}(w) = \sum_g F_{g,i}(w),$$ where the fishing mortality \(F_{g,i}(w)\) imposed by gear \(g\) on species \(i\) at size \(w\) is calculated as: $$F_{g,i}(w) = S_{g,i}(w) Q_{g,i} E_{g},$$ where \(S\) is the selectivity by species, gear and size, \(Q\) is the catchability by species and gear and \(E\) is the fishing effort by gear.

Selectivity

The selectivity at size of each gear for each species is saved as a three dimensional array (gear x species x size). Each entry has a range between 0 (that gear is not selecting that species at that size) to 1 (that gear is selecting all individuals of that species of that size). This three dimensional array can be specified explicitly via the selectivity argument, but usually mizer calculates it from the gear_params slot of the MizerParams object.

To allow the calculation of the selectivity array, the gear_params slot must be a data frame with one row for each gear-species combination. So if for example a gear can select three species, then that gear contributes three rows to the gear_params data frame, one for each species it can select. The data frame must have columns gear, holding the name of the gear, species, holding the name of the species, and sel_func, holding the name of the function that calculates the selectivity curve. Some selectivity functions are included in the package: knife_edge(), sigmoid_length(), double_sigmoid_length(), and sigmoid_weight(). Users are able to write their own size-based selectivity function. The first argument to the function must be w and the function must return a vector of the selectivity (between 0 and 1) at size.

Each selectivity function may have parameters. Values for these parameters must be included as columns in the gear parameters data.frame. The names of the columns must exactly match the names of the corresponding arguments of the selectivity function. For example, the default selectivity function is knife_edge() that a has sudden change of selectivity from 0 to 1 at a certain size. In its help page you can see that the knife_edge() function has arguments w and knife_edge_size. The first argument, w, is size (the function calculates selectivity at size). All selectivity functions must have w as the first argument. The values for the other arguments must be found in the gear parameters data.frame. So for the knife_edge() function there should be a knife_edge_size column. Because knife_edge() is the default selectivity function, the knife_edge_size argument has a default value = w_mat.

In case each species is only selected by one gear, the columns of the gear_params data frame can alternatively be provided as columns of the species_params data frame, if this is more convenient for the user to set up. Mizer will then copy these columns over to create the gear_params data frame when it creates the MizerParams object. However changing these columns in the species parameter data frame later will not update the gear_params data frame.

Catchability

Catchability is used as an additional factor to make the link between gear selectivity, fishing effort and fishing mortality. For example, it can be set so that an effort of 1 gives a desired fishing mortality. In this way effort can then be specified relative to a 'base effort', e.g. the effort in a particular year.

Catchability is stored as a two dimensional array (gear x species). This can either be provided explicitly via the catchability argument, or the information can be provided via a catchability column in the gear_params data frame.

In the case where each species is selected by only a single gear, the catchability column can also be provided in the species_params data frame. Mizer will then copy this over to the gear_params data frame when the MizerParams object is created.

Effort

The initial fishing effort is stored in the MizerParams object. If it is not supplied, it is set to zero. The initial effort can be overruled when the simulation is run with project(), where it is also possible to specify an effort that varies through time.

See also