DLMtool (version 5.2)

ICI: Index Confidence Interval

Description

The MP adjusts catch based on the value of the index in the current year relative to the time series mean and standard error.

Usage

ICI(x, Data, reps = 100, plot = FALSE)
ICI2(x, Data, reps = 100, plot = FALSE)

Arguments

x

A position in a data-limited methods data object

Data

A data-limited methods 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

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

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.

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

# NOT RUN {
ICI(1, Data=DLMtool::Atlantic_mackerel, plot=TRUE)

ICI2(1, Data=DLMtool::Atlantic_mackerel, plot=TRUE)
# }