wsVal: Finds standard weight equation coefficients for a particular...

In fishR-Core-Team/FSA: Simple Fisheries Stock Assessment Methods

Finds standard weight equation coefficients for a particular species.

Description

Returns a vector that contains information about the standard weight equation for a given species, including type of measurement units, reference percentile, method used to derive the equation, and literature source.

Usage

wsVal(
  species = "List",
  group = NULL,
  units = c("metric", "English"),
  ref = NULL,
  method = NULL,
  simplify = FALSE
)

Arguments

species	A string that contains the species name for which to find Ws coefficients. See details.
group	A string that contains the sub-group of species for which to find the Ws coefficients; e.g., things like “lotic”, “lentic”, “female”, “male”.
units	A string that indicates whether the coefficients for the standard weight equation to be returned are in "metric" (DEFAULT; mm and g) or "English" (in and lbs) units.
ref	A numeric that indicates which percentile the equation should be returned for. Note that the vast majority of equations only exist for the 75th percentile (DEFAULT).
method	A string that indicates which equation-derivation method should be used (one of "RLP", "EmP", or "Other"). Defaults to NULL which will result in the only method available being returned or an error asking the user to choose a method for equations for which more than one method is available (which is the case for very few species).
simplify	A logical that indicates whether the ‘units’, ‘ref’, ‘measure’, ‘method’, ‘comments’, and ‘source’ fields should be included (=FALSE) or not (=TRUE; DEFAULT). See details.

Details

This function extracts all known information from WSlit about the following standard weight equation,

log_{10}(Ws) = log_{10}(a) + blog_{10}(L) + blog_{10}(L)^{2}

See WSlit for more information about the meaning of each value returned.

Note from above that the coefficients are returned for the TRANSFORMED model. Thus, to obtain the standard weight (Ws), the returned coefficients are used to compute the common log of Ws which must then be raised to the power of 10 to compute the Ws.

See examples and this article for a demonstration.

Value

A one row data frame from WSlit that contains all known information about the standard weight equation for a given species, type of measurement units, and reference percentile if simplify=FALSE. If simplify=TRUE then only the species; minimum and maximum length for which the standard equation should be applied; and intercept, slope, and quadratic coefficients for the standard weight equation. Note that the maximum length and the quadratic coefficient will not be returned if they do not exist in WSlit for the species.

If no arguments are given to this function then a list of available species names in WSlit will be printed. If the species name is mis-spelled (or mis-capitalized), multiple standard weight equations exist for the species (such that group, ref, or method should be used), or if a standard weight equation does not exist for the species in WSlit, then an error will be issued.

IFAR Chapter

8-Condition.

Author(s)

Derek H. Ogle, [e-mail]

References

Ogle, D.H. 2016. Introductory Fisheries Analyses with R. Chapman & Hall/CRC, Boca Raton, FL.

See Also

See wrAdd and WSlit for related functionality.

Examples

#===== List all available Ws equations
wsVal()

#===== Find equations for Bluegill, in different formats
wsVal("Bluegill")
wsVal("Bluegill",units="metric")
wsVal("Bluegill",units="English")
wsVal("Bluegill",units="English",simplify=TRUE)

#===== Find equation for Cutthroat Trout, demonstrating use of group
wsVal("Cutthroat Trout",group="lotic")
wsVal("Cutthroat Trout",group="lentic")

#===== Find equation for Ruffe, demonstrating quadratic formula
wsVal("Ruffe",units="metric",ref=75,simplify=TRUE)
wsVal("Ruffe",units="metric",ref=50,simplify=TRUE)

#===== Add Ws & Wr values to a data frame (for one species) ... also see wrAdd()
#----- Get Ws equation info
wsBG <- wsVal("Bluegill",units="metric")
wsBG

#----- Get example data
data(BluegillLM,package="FSAdata")
str(BluegillLM)

#----- Add Ws (eqn is on log10-log10 scale ... so log10 len, 10^ result)
BluegillLM$ws <- 10^(wsBG[["int"]]+wsBG[["slope"]]*log10(BluegillLM$tl))

#----- Change Ws for fish less than min.TL to NA
BluegillLM$ws[BluegillLM$tl<wsBG[["min.TL"]]] <- NA

#----- Add Wr
BluegillLM$wr <- BluegillLM$wght/BluegillLM$ws*100

#----- Examine results
peek(BluegillLM,n=6)

#----- Same as above but using dplyr
data(BluegillLM,package="FSAdata")   # reset to original for this example
if (require(dplyr)) {
  BluegillLM <- BluegillLM %>%
    mutate(ws=10^(wsBG[["int"]]+wsBG[["slope"]]*log10(tl)),
           ws=ifelse(tl<wsBG[["min.TL"]],NA,ws),
           wr=wght/ws*100)
  peek(BluegillLM,n=6)
}

fishR-Core-Team/FSA documentation built on June 14, 2025, 10:01 p.m.