Z_BevertonHolt {TropFishR}

Beverton & Holt's Z-Equations

Description

A method to estimate the instantaneous total mortality rate (Z) based on a method derived by Beverton and Holt (1956).

Usage

Z_BevertonHolt(param, catch_columns = NA, Lprime_tprime)

Arguments

param

a list consisting of following parameters:

• midLengths or age: midpoints of length groups (length-frequency data) or ages (age composition data),

• Linf: infinite length for investigated species in cm [cm],

• K: growth coefficent for investigated species per year [1/year],

• t0: theoretical time zero, at which individuals of this species hatch,

• catch: catch as vector, or a matrix with catches of subsequent years;

catch_columns

optional; in case catch is a matrix or data.frame, a number or vector indicating which column(s) of the matrix should be analysed (Default: NA).

Lprime_tprime

length or age prime, above which all fish are under full exploitation as mid length or age class.

Details

The first length group or age class within the list object midLengths or age will be used as the Lprim or tprime (length of recruitment to fishery).

Value

A list with the input parameters and following objects:

• tmean or Lmean: mean age or length of fish,

• tprime or Lprime: some age or length for which all fish of that length and longer are under full exploitation,

• Z: total mortality.

References

Beverton R.J.H and S.J. Holt, 1956. A review of methods of estimating mortality rates in exploited fish populations, with special reference to sources of bias in catch sampling. Rapp.P.-v.Reun.CIEM, 140:67-83

Sparre, P., Venema, S.C., 1998. Introduction to tropical fish stock assessment. Part 1. Manual. FAO Fisheries Technical Paper, (306.1, Rev. 2). 407 p.

Examples

# based on length-frequency data
data(synLFQ2)
Z_BevertonHolt(synLFQ2, catch_columns = 2, Lprime_tprime = 47.5)

# based on age composition data
data(synCAA1)
Z_BevertonHolt(synCAA1, catch_columns = 3, Lprime_tprime = 2.5)