lopt: Lopt

In flr/FLife: Methods for Modelling Life History Traits

Lopt

Description

Lopt, the length at which a cohort achives its maximum biomass, can be used as a reference point to identify growth over- or underfishing. Since taking fish below or above this size results in potential loss of yield. The total biomass of a cohort changes through time as a result of gains due to an increase in mean size-at-age and losses due to natural mortality. Lopt can therefore be estimated from the natural mortality and weight-at-age vectors.

Usage

## S4 method for signature 'FLPar'
lopt(
  params,
  m = function(length, params) exp(0.55) * (length^-1.61) %*% (params["linf"]^1.44)
    %*% params["k"],
  growth = FLife::vonB,
  ...
)

Arguments

params	an FLPar object with parameter values for the natural mortality and growth functions, and the exponent b of the length/weight relationship.
m	natural mortality function, by default Gislason
growth	length or weight-at-age function, by default von Bertalanffy
...	any other arguments

Details

Lopt is a function of growth and natural mortality-at-age and there are several approximations such as 2/3 L_{\infty} and L_{\infty}\frac{3}{3+k/m}. If the life history parameters and relationships are known then $L_opt$ can be found by finding the time (t) and hence length at which the maximum biomass is achieved i.e. L(T)^a e^{\int_0^T m(t)} where m(t) can be found from the relationship of mortality at length using the relationship of Gislason, assuming the von Bertalanffy growth curve.

Value

FLPar with $L_opt$ the length at which a cohort achives its maximum biomass

See Also

gislason, vonB, lhRef, lhPar, lhEql,

Examples

## Not run: 
params=lhPar(FLPar(linf=100,k=0.1,t0=-0.1,b=3))
lopt(params)

## End(Not run)

flr/FLife documentation built on March 29, 2024, 5:50 p.m.