Condition stock status on target depletions

Rescales each stock's catchability (its column of sys$Q, across all metiers) so that the open-access equilibrium reaches a target B/Bmsy per stock, while ms_tune() keeps the segment shares of days at sys$segments with total days held fixed (the overall effort level and the catchability scale are not separately identifiable).

Usage

ms_condition(
  sys,
  target,
  range = c(0.05, 1.5),
  cap = 1000,
  gamma = 1.5,
  outer = 4,
  inner = 12,
  tol = 0.02,
  damp = 0.8,
  years = 300,
  verbose = TRUE,
  recost = TRUE,
  ...
)

Arguments

sys: an ms_system (costs already roughly tuned, e.g. by ms_tune()).
target: named vector of target B/Bmsy (names = stock names or codes); NA or missing stocks are free.
range: lower and upper limits of the targets.
cap: fleet capacity (days) by segment.
gamma: profit preference.
outer, inner: number of outer (cost tuning) and inner (catchability) iterations.
tol: tolerance on |B/Bmsy - target| for the inner loop.
damp: damping exponent of the catchability update.
years: years to equilibrium.
verbose: print progress.
recost: if TRUE (default), each metier's daily cost keeps its ratio to the metier's unfished revenue rate as catchability changes, so a metier whose main stock gets a lower catchability does not keep a cost sized for the old one (which would leave it unfished).
...: passed to ms_simulate().

Value

The conditioned ms_system, with attribute conditioning: a data frame of targets and achieved B/Bmsy and F/Fmsy, and the catchability multipliers.

Details

In the discrete Schaefer model B/Bmsy = 2 - F/Fmsy (with F/Fmsy as h/hmsy, see ffmsy()), so each inner step multiplies a stock's catchability by ((2 - target) / current F/Fmsy)^damp. Stocks with an NA target are left free. Targets are clamped to range.