# Geromont and Butterworth target CPUE and catch MP

`GB_target.Rd`

An MP similar to SBT2 that modifies a time-series of catch recommendations and aims for target catch rate and catch level based on BMSY/B0 and MSY, respectively.

## Arguments

- x
A position in the data object

- Data
A data object

- reps
The number of stochastic samples of the MP recommendation(s)

- plot
Logical. Show the plot?

- w
A gain parameter

## Value

An object of class `Rec-class`

with the `TAC`

slot populated with a numeric vector of length `reps`

## Details

The TAC is calculated as: If \(I_\textrm{recent} \geq I_0\): $$\textrm{TAC}= C_\textrm{ref} \left(w + (1-w)\frac{I_\textrm{rec}-I_0}{I_\textrm{target}-I_0} \right) $$

else: $$\textrm{TAC}= wC_\textrm{ref} \frac{I_\textrm{rec}}{I_0}^2$$

where \(C_\textrm{ref}\) is a reference catch assumed to be a proxy for MSY (`Data@Cref`

),
*w* is a gain parameter,
\(I_\textrm{rec}\) is the average index over the last 4 years,
\(I_\textrm{target}\) is the target Index (`Data@Iref`

), and
\(I_0\) is 0.2 x the average index over the past 5 years.

In the MSE \(C_\textrm{ref}\) is the calculated MSY subject to observation error
defined in `Obs@CV_Cref`

, and \(I_\textrm{target}\) is assumed to be the index at MSY subject
to observation error (`Obs@CV_Iref`

). Consequently, the performance of this method in the MSE
is strongly determined by the specified uncertainty for these parameters.

The TAC is subject to the following conditions:

if next TAC > 1.2 last catch, then TAC = 1.2 last catch

if next TAC < 0.8 last catch, then TAC = 0.8 last catch

## Rendered Equations

See Online Documentation for correctly rendered equations

## References

Geromont, H.F. and Butterworth, D.S. 2014. Complex assessment or simple management procedures for efficient fisheries management: a comparative study. ICES J. Mar. Sci. doi:10.1093/icesjms/fsu017

## Examples

```
GB_target(1, MSEtool::SimulatedData, plot=TRUE)
#> TAC (median)
#> 1698.236
```