TBA: TBA

Description

Calculate the targeted biomass adjustment (TBA), which dampens the influence of proportional rate of change \(rb\) on catch advice when the proportion of abundance targeted by harvest slot limits is small. Optionally, produce a graph showing how TBA varies across a grid of (P_targeted, rb) values.

The TBA is calculated as \(1 + (P_{\mathrm{targeted}} \times rb)\).

Usage

TBA(P_targeted = NULL, rb = NULL, digits = 2, plot = FALSE)

Value

A list with:

P_targeted: Input targeted proportion (numeric scalar).
rb: Input proportional rate of change (numeric scalar).
damped_change: \(P_{\mathrm{targeted}} \times rb\) (numeric scalar).
TBA: Targeted biomass adjustment multiplier \(1 + P_{\mathrm{targeted}} \times rb\) (numeric scalar). TBA > 1 increases advised catch; TBA < 1 decreases it.
plot: (only when plot=TRUE) a ggplot2 object visualizing TBA over a grid.

Arguments

P_targeted: Numeric (length 1) in [0, 1]. Proportion of abundance targeted by harvest slot limits (e.g., from prop_target()).
rb: Numeric (length 1). Proportional rate of change in a biomass index (e.g., from rb()). Typical values lie in [-1, 1], but larger magnitudes are allowed.
digits: Integer. Number of decimal places used to round outputs (default = 2). Set digits = NA to prevent rounding.
plot: Logical. If TRUE, include a ggplot2 plot of the calculated value on a grid of (P_targeted, rb) combinations (default FALSE).

Details

The adjustment dampens large changes in biomass indices when the targeted proportion is small by multiplying rb by P_targeted. The plot shades the surface of \(1 + P \times rb\). A dashed horizontal line marks rb = 0.

Examples

Run this code

TBA(P_targeted = 0.5, rb = -0.5)               # compute only
# \donttest{
# compute + plot (requires ggplot2)
out <- TBA(P_targeted = 0.5, rb = -0.5, digits = 2, plot = TRUE)
out$plot
# }