Description Usage Arguments Details Value References Examples
View source: R/powell_wetherall.R
A method to estimate the instantaneous total mortality rate (Z) and the infinite length of the von Bertalanffy growth equation (Powell, 1979; Wetherall et al., 1987).
1 2  powell_wetherall(param, catch_columns = NA, savePlots = FALSE,
reg_int = NULL, main = "PowellWetherall plot")

param 
a list consisting of following parameters:

catch_columns 
optional; in case catch is a matrix or data.frame, a number
indicating which column of the matrix should be analysed (Default: 
savePlots 
logical; if TRUE the plot is recorded. Default is FALSE. 
reg_int 
instead of using the identity method a range can be determined, which is to be used for the regression analysis. If equal to NULL identity method is applied (default). 
main 
title of plot (Default is "PowellWetherall plot") 
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).
This function includes the
identify
function, which asks you to choose two points from a graph manually. The
two points which you choose by clicking on the plot in the graphical device represent
the start and end of the data points, which should be used for the analysis. Based
on these points the regression line is calculated. The Powell and Wetherall method
only works with lengthfrequency data.
A list with the input parameters and follwing objects:
tmean or Lmean: mean age or length of fish,
Z: total mortality;
and/or following objects when applying the Powell and Wetherall method:
Lmean_Lprime: dependent variable for regression analysis,
Lprime: some length for which all fish of that length and longer are under full exploitation,
Linf_est: infinite length in [cm] (Linf),
se_Linf: standard error of Linf,
confidenceInt_Linf: confidence interval for Linf,
ZK: total mortality divided by K (Z/K),
se_ZK: standard error of Z/K,
confidenceInt_ZK: confidence interval of Z/K;
Powell, D.G., 1979. Estimation of mortality and growth parameters from the length frequency of a catch. Rapp.P.v.Reun.CIEM, 175:167169
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.
Wetherall, J.A., J.J. Polovina and S. Ralston, 1987. Estimating growth and mortality in steadystate fish stocks from lengthfrequency data. ICLARM Conf.Proc., (13):5374
1 2 3 4 5  data(synLFQ3)
powell_wetherall(synLFQ3)
data(synLFQ5)
powell_wetherall(synLFQ5, catch_columns = 1:12)

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