Calculate deterministic equilibrium reference points

Calculates MSY under a fixed fleet allocation, selectivity, and biology. This is an equilibrium calculation, independent of the projection engine.

Usage

opal_msy(
  x,
  fleet_weights,
  year = x$data$n_year,
  uncertainty = c("fit", "mcmc"),
  draws = NULL,
  u_max = 1,
  grid_size = 201L,
  name = "msy"
)

Arguments

x

A fitted or sampled opal_obj.

fleet_weights

Non-negative fleet allocation weights, normalised to sum to one. Required because the fleet mix is a scientific choice.

year

Model-year index supplying selectivity and weight at age.

uncertainty

Use the fitted point or complete joint MCMC draws.

draws

Optional retained draw indices when uncertainty = "mcmc".

u_max

Maximum scalar seasonal harvest intensity, in (0, 1].

grid_size

Number of harvest intensities used to bracket maxima.

name

Name of the stored result.

Value

An updated object. opal_derived() returns per-draw MSY, spawning output at MSY, recruitment at MSY, seasonal intensity at MSY, depletion at MSY, terminal spawning output relative to MSY, and status probabilities.

Details

Fleet harvest fractions are u * fleet_weights[f] * selectivity[f,a]. Natural mortality follows seasonal fishing, matching historical dynamics. Yield is total catch in the units of weight_fya_mod, including fleets whose input catches use numbers. Beverton-Holt equilibrium recruitment is solved analytically without recruitment deviations or bias corrections. No positive continuation is accepted as a biological equilibrium.

These are deterministic, fixed-biology reference points, not stochastic MSY or management advice. Spawning potential at recruitment age must be zero to match the dynamics' spawning-before-recruitment convention. An upper-bound optimum is flagged and should not be treated as a resolved MSY. Posterior calculations use each draw's own biology and do not discard invalid draws. Equal draw weights are used in status probabilities.