R/calc_numbers_at_length.r
calc_numbers_at_length.RdGiven the landings (expanded by length), and the length-weight relationship, the number of fish at a given length is calculated.
calc_numbers_at_length(expLandings, lengthWeightParams)Tibble. Expanded langings by length (from expand_landings_to_lengths)
List. alpha = intercept, betas = slope(s), var = residual variance used to formulate the mean (?see Notes section below)
A Tibble of expanded landings to represent weight of landings by length
Year of landings
3 digit gear code as defined in cfdbs.gear
Quarter/Half year of landings (The presence of this field depends on whether it was present in the landingsData
Market code assigned to landed fish (The presence of this field depends on whether it was present in the landingsData
Length of sampled fish
number of sampled for fish stated LENGTH
expanded weight (mt) of all fish of given LENGTH in YEAR, NEGEAR etc..
THIS NEEDS TO BE GENERALIZED.
The length weight relationship (see fit_length_weight) is fit assuming log normal errors (normal on the log scale).
Therefore when exponentiating a correction for the estimate is required:
E(W) = \(\alpha L^\beta exp(\sigma^2 / 2)\)