Index Confidence Interval
ICI.RdThe MP adjusts catch based on the value of the index in the current year relative to the time series mean and standard error.
ICI(x, Data, reps = 100, plot = FALSE) ICI2(x, Data, reps = 100, plot = FALSE)
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? |
Value
An object of class Rec with the TAC slot populated with a numeric vector of length reps
Details
The TAC is calculated as:
$$\textrm{TAC}_y=C_{y-1} \alpha$$
where \(C_{y-1}\) is the catch from the previous year, and \(\alpha\) is
defined as:
$$\alpha =
\left\{\begin{array}{ll}
d & \textrm{if } I < \textrm{CI}_L \\
u & \textrm{if } I > \textrm{CI}_H \\
1 & \textrm{if } \textrm{CI}_L \leq I \leq \textrm{CI}_H \\
\end{array}\right.
$$
where \(I\) is the index in the most recent year, \(d\) is 0.75 for ICI and ICI2,
\(u\) is 1.05 and 1.25 forICI and ICI2 respectively, and \(\textrm{CI}_L\)
and \(\textrm{CI}_L\) are the lower and upper bound of the confidence
interval of mean historical index. The confidence interval is
calculated using Z-scores described in the Functions section below.
Functions
ICI: The catch is reduced by 0.75 if the Z-score of the current year's index is less than -0.44. The catch is increased by 1.05 if the Z-score of the current year's index is greater than 1.96. Otherwise, the catch is held constant.ICI2: This method is less precautionary of the two ICI MPs by allowing for a larger increase in TAC and a lower threshold of the index to decrease the TAC. The catch is reduced by 0.75 if the Z-score of the current year's index is less than -1.96. The catch is increased by 1.25 if the Z-score of the current year's index is greater than 1.96. Otherwise, the catch is held constant.
Required Data
See Data for information on the Data object
ICI: Cat, Ind
ICI2: Cat, Ind
Rendered Equations
See Online Documentation for correctly rendered equations
References
Ernesto Jardim, Manuela Azevedo, Nuno M. Brites, Harvest control rules for data limited stocks using length-based reference points and survey biomass indices, Fisheries Research, Volume 171, November 2015, Pages 12-19, ISSN 0165-7836, https://doi.org/10.1016/j.fishres.2014.11.013
See also
Other Index methods:
GB_slope(),
GB_target(),
Gcontrol(),
Iratio(),
Islope1(),
Itarget1_MPA(),
Itarget1(),
ItargetE1()
Examples
#> TAC (median) #> 13.92123#> TAC (median) #> 14.4697
