knife_edge_length: Length based knife-edge selectivity function

In mizer: Dynamic Multi-Species Size Spectrum Modelling

Length based knife-edge selectivity function

Description

A knife-edge selectivity function where individuals with a length greater or equal to knife_edge_length are fully selected and no fish shorter than this length are selected.

Usage

knife_edge_length(w, knife_edge_length, species_params, ...)

Arguments

w	Vector of sizes (weights).
knife_edge_length	The length at which the knife-edge operates.
species_params	A list with the species params for the current species. Used to get at the length-weight parameters a and b.
...	Unused

Details

You would not usually call this function directly. Instead, set the sel_func column in gear_params() to "knife_edge_length" and provide knife_edge_length as an additional column. setFishing() will then call this function automatically when calculating the selectivity array.

As the mizer model is weight based, and this selectivity function is length based, it uses the length-weight parameters a and b to convert the cut-off length to a weight:

w_{\text{cut}} = a \cdot l_{\text{cut}}^b

Value

Vector of selectivities at the given sizes.

See Also

gear_params() for setting the knife_edge_length parameter.

Other selectivity functions: double_sigmoid_length(), knife_edge(), sigmoid_length(), sigmoid_weight()

Examples

# Knife-edge at 20 cm using length-weight parameters a = 0.01, b = 3
sp <- list(a = 0.01, b = 3)
knife_edge_length(w = c(1, 10, 100, 1000), knife_edge_length = 20,
                  species_params = sp)

mizer documentation built on Aug. 31, 2026, 5:08 p.m.