Catchability of trawls by fish length — LengthDependentLengthDistributionCompensation • RstoxBase

This function compensates for length dependent herding by the trawl doors into the net, or length dependent selectivity by the mesh size.

LengthDependentLengthDistributionCompensation(
  LengthDistributionData,
  CompensationMethod = c("LengthDependentSweepWidth", "LengthDependentSelectivity"),
  LengthDependentSweepWidthParameters = data.table::data.table(),
  LengthDependentSelectivityParameters = data.table::data.table()
)

Arguments

LengthDistributionData: The LengthDistributionData data.
CompensationMethod: The method to use for the length dependent catch compensation, one of "LengthDependentSweepWidth" for adjusting the sweep width according to the fish length dependent herding effect and "LengthDependentSelectivity" for compensating for mash size selectivity (not yet implemented).
LengthDependentSweepWidthParameters: A table of parameters of the LengthDependentSweepWidth method, containing the columns SpeciesCategory, LMin, LMax, Alpha and Beta (see details).
LengthDependentSelectivityParameters: A table of parameters of the LengthDependentSelectivity method, containing the columns SpeciesCategory, LMin, LMax, Alpha and Beta (see details). Currently not supported.

Value

A LengthDistributionData object.

Details

This function estimates the effective sweep width and divides the length frequencies (WeightedNumber in the LengthDistributionData) by this effective sweep width (in nautical miles). The result is a LengthDistributionData object with LengthDistributionType starting with "SweepWidthCompensated". In the case that the input LengthDistributionData is normalized (LengthDistributionType = "Normalized") the output will hare LengthDistributionType = "SweepWidthCompensatedNormalized", which is equivalent to area number density.

The IndividualTotalLength is truncated to the interval $[LMin, LMin]$, i.e., IndividualTotalLength < LMin is set to LMin and IndividualTotalLength < LMax is set to LMax

When CompensationMethod = "LengthDependentSweepWidth" the sweep width is modeled as $$Alpha * IndividualTotalLength^{Beta}$$

When CompensationMethod = "LengthDependentSelectivity" the sweep width is modeled as $$Alpha * exp(Beta * IndividualTotalLength)$$.