R/meanTLLandings.R

In marindicators: Marine Ecosystem and Fishing Pressure Indicators

#'@title Calculates the Mean Trophic Level or Marine Trophic Index of fisheries
#'  landings
#'@description This function calculates the Mean Trophic Level or Marine Trophic
#'  Index of fisheries landings for \eqn{j} areas and \eqn{i} years.
#'@details Mean trophic level of fisheries landings (\eqn{TL_{Land}}):
#'  \deqn{TL_{Land} = \Sigma (TL_i*Y_i)/Y} where \eqn{TL_i} is the trophic level
#'  of species \eqn{i}, \eqn{Y_i} is the landings of species \eqn{i}, and
#'  \eqn{Y} is the total landings of all species. Trophic Level of individual
#'  species can be estimated either through an Ecopath model or dietary
#'  analysis, or taken from a global database such as Fishbase.
#'
#'  This indicator captures the average trophic level of the species exploited
#'  in the fishery. In general, it reflects a transition from long-lived, high
#'  trophic level, demersal fish toward short-lived, low trophic level pelagic
#'  fish and invertebrates (Pauly et al., 1998).
#'
#'  The marine trophic index is calculated similarly to \eqn{TL_{Land}}, but
#'  only includes species with trophic level greater than or equal to an
#'  explicitly stated trophic level minTL. For instance, Pauly and Watson 2005
#'  adopted a trophic level minTL of 3.25 to emphasize changes in the relative
#'  abundance of higher trophic level fishes, and Shannon et al. 2014 used a
#'  minTL of 4.0 to examine changes within the apex predator community. If used
#'  in this way, this indicator highlights changes in the relative abundance of
#'  the more threatened high-trophic level fishes (Pauly et al., 1998).
#'@inheritParams landings
#'@param TL.table A dataframe with columns \code{SPECIES} and the corresponding
#'  \code{TL_LAND} (trophic level). Entries in the \code{SPECIES} column should
#'  be the unique values of species codes in \code{land} (or a subset thereof).
#'  Other columns in \code{TL.table} are ignored.
#'@param minTL The minimum trophic level of species to include. Set \code{minTL
#'  = 0} to calculate the mean trophic level of the landings; Set \code{minTL =
#'  3.25} to calculate the marine trophic index. Default is \code{minTL = 0}.
#'@return Returns a dataframe with three columns: \code{ID}, \code{YEAR}, and if
#'  \code{minTL = 0}: \code{MeanTL.Landings}, if \code{minTL = 3.25}:
#'  \code{MTI.Landings}, or if \code{minTL} is a different value:
#'  \code{MeanTL.Landings_minTL}.
#'
#'  If there are no observations in land for spatial scale \eqn{j} in year
#'  \eqn{i}, indicator value is set to \code{NA}.
#'@family fishing pressure indicators
#'@references  Bundy A, Gomez C, Cook AM. 2017. Guidance framework for the
#'  selection and evaluation of ecological indicators. Can. Tech. Rep. Fish.
#'  Aquat. Sci. 3232: xii + 212 p.
#'
#'  Pauly D, Christensen V, Dalsgaard J, Froese R, Torres F. 1998. Fishing Down
#'  Marine Food Webs. Science 279:860-863
#'
#'  Pauly D, Watson R. 2005. Background and interpretation of the Marine Trophic
#'  Index as a measure of biodiversity. Philos Trans R Soc B Biol Sci 360:415
#'  423
#'
#'  Shannon L, Coll M, Bundy A, Gascuel D, Heymans, JJ, Kleisner K, Lynam CP,
#'  Piroddi C, Tam J, Travers-Trolet M and Shin Y. 2014. Trophic level-based
#'  indicators to track fishing impacts across marine ecosystems. Marine Ecology
#'  Progress Series, 512, pp.115-140.
#'@author  Danielle Dempsey \email{Danielle.Dempsey@@dfo-mpo.gc.ca}, Adam Cook,
#'  Catalina Gomez, Alida Bundy
#'@examples
#'# Compile data
#'data(land)
#'data(species.info)
#'
#'# Calculate indicators
#'# Mean trophic level of landings
#'meanTLLandings(land, TL.table = species.info, minTL = 0, years = c(2014:2019))
#'# Marine trophic index
#'meanTLLandings(land, TL.table = species.info, minTL = 3.25, years = c(2014:2019))
#'@export

meanTLLandings <- function (land, TL.table, minTL = 0, years) {
  
  uI <- unique(land$ID)                                     # extract the spatial scale ID's
  DF <- createDataframe(uI = uI, years = years)             # create a dataframe that matches each area ID to each year
  
  TL.table <- na.omit(TL.table[, c("SPECIES", "TL_LAND")])   
  land.TL <- merge(land, TL.table, by = "SPECIES")

  land.TL$id <- land.TL$TL_LAND >= minTL                                                         # returns TRUE when TL is >= minTL
  land.TL$pp <- land.TL$CATCH * land.TL$id                                                                                        # accounts for the proportion of the same species at different TL
                                                                                             # and species with two+ RV codes but one commercial code
  land.TL$LL <- land.TL$pp * land.TL$TL_LAND * land.TL$id                                         # calculates landings_species.i * TL_species.i

  ind <- merge(aggregate(LL ~ ID + YEAR, data = land.TL, FUN = sum),   # sum of landings of species i * TL of species i
               aggregate(pp ~ ID + YEAR, data = land.TL, FUN = sum))   # total landings
	ind$ind <- ind$LL/ind$pp                                             # calculate mean trophic level of landings weighted by species landed                                     
	ind$LL <- NULL                                                       # rm col LL
	ind$pp <- NULL                                                       # rm col pp
	 
	ind <- merge(DF, ind, by = c("ID", "YEAR"), all.x = T)               # merge ind with DF so that years without data are set to NA 
	
	if(minTL == 0) {
	  ind.name = "MeanTL.Landings"
	} else ind.name = paste("MTI.Landings_", minTL, sep = "")
	
	names(ind) <- c("ID", "YEAR", ind.name)
	ind <- ind[order(ind$ID), ]
	ind

}