R/Z_BevertonHolt.R

Defines functions Z_BevertonHolt

Documented in Z_BevertonHolt

#' @title 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).
#'
#' @param param a list consisting of following parameters:
#' \itemize{
#'   \item  \code{midLengths} or \code{age}: midpoints of length groups
#'   (length-frequency data) or ages (age composition data),
#'   \item \code{Linf}: infinite length for investigated species in cm [cm],
#'   \item \code{K}: growth coefficent for investigated species per year [1/year],
#'   \item \code{t0}: theoretical time zero, at which individuals of this species hatch,
#'   \item \code{catch}: catch as vector, or a matrix with catches of subsequent years;
#' }
#' @param 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: \code{NA}).
#' @param Lprime_tprime length or age prime, above which all fish are under full exploitation as
#'    mid length or age class.
#'
#' @keywords function mortality Z
#'
#' @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)
#'
#' @details  The first length group or age class within the list object \code{midLengths} or
#'    \code{age} will be used as the Lprim or tprime (length of recruitment to fishery).
#'
#' @return A list with the input parameters and following objects:
#' \itemize{
#'   \item \strong{tmean} or \strong{Lmean}: mean age or length of fish,
#'   \item \strong{tprime} or \strong{Lprime}: some age or length for which all fish of
#'      that length and longer are under full exploitation,
#'   \item \strong{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. \emph{Rapp.P.-v.Reun.CIEM}, 140:67-83
#'
#' Sparre, P., Venema, S.C., 1998. Introduction to tropical fish stock assessment.
#' Part 1. Manual. \emph{FAO Fisheries Technical Paper}, (306.1, Rev. 2). 407 p.
#'
#' @export

Z_BevertonHolt <- function(param, catch_columns = NA, Lprime_tprime){
  res <- param
  catch <- res$catch

  if(class(catch) == "data.frame" | class(catch) == "matrix"){
    if(is.na(catch_columns[1])) stop("Please provide numbers indicating which column of the catch matrix should be analysed!")
    catchmat <- res$catch[,(catch_columns)]
    if(length(catch_columns) > 1){
      catch <- rowSums(catchmat, na.rm = TRUE)
    }else catch <- catchmat
  }

  #   Length based equation
  if("midLengths" %in% names(res)){

    classes <- as.character(res$midLengths)
    # create column without plus group (sign) if present
    classes.num <- do.call(rbind,strsplit(classes, split="\\+"))
    classes.num <- as.numeric(classes.num[,1])
    Lprime_tprime_ind <- which.min(abs(classes.num - Lprime_tprime))

    Linf <- res$Linf
    K <- res$K

    # Error message if catch and age do not have same length
    if(class(catch) == 'numeric'){
      if(length(classes) != length(catch)) stop("Ages and catch do not have the same length!")
    }

    # calculate L prime
    #Lprime <- classes.num[1] -
    #  ((classes.num[2] - classes.num[1]) / 2)
    interval <- (classes.num[2] - classes.num[1]) / 2
    Lprime_tprime <- Lprime_tprime - interval


    # calculate  C * (L1 + L2) / 2
    c_midlength <- catch * classes.num

    # calculate L mean
    c_midlength_for_Lmean <- c_midlength[Lprime_tprime_ind:length(c_midlength)]
    catch_for_Lmean <- catch[Lprime_tprime_ind:length(catch)]
    Lmean <- sum(c_midlength_for_Lmean, na.rm = TRUE) / sum(catch_for_Lmean, na.rm = TRUE)

    Z <- K * (Linf - Lmean) / (Lmean - Lprime_tprime)

    #save all in list
    ret <- c(res,list(
      Lmean = Lmean,
      Lprime = Lprime_tprime,
      Z = Z
    ))
    return(ret)
  }

  #     Aged based equation
  if("midAge" %in% names(res) | "age" %in% names(res)){

    if("midAge" %in% names(res)) classes <- as.character(res$midAge)
    if("age" %in% names(res)) classes <- as.character(res$age)
    # create column without plus group (sign) if present
    classes.num <- do.call(rbind,strsplit(classes, split="\\+"))
    classes.num <- as.numeric(classes.num[,1])
    Lprime_tprime_ind <- which.min(abs(classes.num - Lprime_tprime))

    # Error message if catch and age do not have same length
    if(class(catch) == 'numeric'){
      if(length(classes) != length(catch)) stop("Ages and catch do not have the same length!")
    }

    interval <- (classes.num[2] - classes.num[1]) / 2
    Lprime_tprime <- Lprime_tprime - interval
    #tprime <- classes.num[1] - interval
    catch_for_tprime <- catch[Lprime_tprime_ind:length(catch)]
    classes.num_for_tprime <- classes.num[Lprime_tprime_ind:length(classes.num)]
    sample.size <- sum(catch_for_tprime,na.rm=TRUE)
    sum.age.number <- sum((catch_for_tprime * classes.num_for_tprime), na.rm=TRUE)
    tmean <- sum.age.number/sample.size

    Z.BH <- 1 / (tmean - Lprime_tprime)

    #save all in list
    ret <- c(res,list(
      tmean = tmean,
      tprime = Lprime_tprime,
      Z = Z.BH
    ))
    return(ret)
  }

}

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TropFishR documentation built on June 29, 2018, 5 p.m.