Size limit management procedures

A set of size-selectivity MPs that adjust the retention curve of the fishery.

matlenlim(x, Data, reps, plot = FALSE)

matlenlim2(x, Data, reps, plot = FALSE)

minlenLopt1(x, Data, reps, plot = FALSE, buffer = 0.1)

slotlim(x, Data, reps, 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?
buffer

Parameter controlling the fraction of Lopt to set the minimum length of fish caught: minlen=Lopt*(0.7+buffer).

Value

An object of class Rec with the SL slot(s) populated

Details

The the LF5 and LFR slots in the Rec object are modified to change the retention curve (length at 5 per cent and smallest length at full retention respectively). A upper harvest slot limit can be set using the Rec@HS slot. The underlying selectivity pattern of the fishing gear does not change, and therefore the performance of these methods depends on the degree of discard mortality on fish that are selected by the gear but not retained by the fishery (Stock@Fdisc).

The level of discard mortality can be modified using the Rec@Fdisc slot which over-rides the discard mortality set in the operating model.

The selectivity pattern can be adjusted by creating MPs that modify the selection parameters (Rec@L5, Rec@LFS and Rec@Vmaxlen).

Functions

  • matlenlim: Fishing retention-at-length is set equivalent to the maturity curve.

  • matlenlim2: Fishing retention-at-length is set slightly higher (110\ than the length-at-maturity

  • minlenLopt1: The minimum length of retention is set to a fraction of the length that maximises the biomass, Lopt. The aim of this simple MP is restrict the catch of small fish to rebuild the stock biomass towards the optimal length, Lopt, expressed in terms of the growth parameters Lopt=b/(M/k+b) (Hordyk et al. 2015)

  • slotlim: Retention-at-length is set using a upper harvest slot limit; that is, a minimum and maximum legal length. The maximum limit is set here, completely arbitrarily, as the 75th percentile between the new minimum legal length and the estimated asymptotic length Linf. This MP has been included to demonstrate an upper harvest slot limit.

Required Data

See Data for information on the Data object

matlenlim: L50

matlenlim2: L50

minlenLopt1: Mort, vbK, vbLinf, wlb

slotlim: L50, vbLinf

Rendered Equations

See Online Documentation for correctly rendered equations

References

Hordyk, A., Ono, K., Sainsbury, K., Loneragan, N., and J. Prince. 2015. Some explorations of the life history ratios to describe length composition, spawning-per-recruit, and the spawning potential ratio ICES Journal of Marine Science, doi:10.1093/icesjms/fst235.

Examples

matlenlim(1, DLMtool::Atlantic_mackerel, plot=TRUE)
#>   LR5   LFR 
#> 90.25 95.00 
matlenlim2(1, DLMtool::Atlantic_mackerel, plot=TRUE)
#>     LR5     LFR 
#>  99.275 104.500 
minlenLopt1(1, DLMtool::Atlantic_mackerel, plot=TRUE)
#>      LR5      LFR 
#> 89.74689 99.71877 
slotlim(1, DLMtool::Atlantic_mackerel, plot=TRUE)
#>      LR5      LFR       HS 
#>  99.2750 104.5000 142.5475