n2f: Evaluate F from Numbers at Age

In hafroAssmt: Hafro Assessment Toolbox

Description

Evaluate fishing mortality rates F_{t,a} from numbers at age N_{t,a} with an assumed natural mortality rate M.

Usage

n2f(Nmat, M=0.2)

Arguments

Nmat	Numbers-at-age matrix, possibly with dimnames of years and ages.
M	Natural mortality rate, constant.

Details

Calculated from N_{t+1,a+1}=N_{t,a}\exp(-Z), where Z=F+M.

Value

A matrix of F_{t,a} one row and one column shorter than Nmat.

Author(s)

Sigurður Þór Jónsson

References

Stefánsson, G. 1994. Undirstöðuatriði stærðfræðilegrar fiskifræði. Útg. 4.4.11/4/94, 60p.

See Also

pope is a simple assessment model to estimate stock size.

hafroAssmt-package gives an overview of the package.

Examples

# Prepare a matrix of catch-at-age from the data.frame 'catage'
catageMat <- tapply(catage$ObsCno, list(catage$year,catage$age), sum)

# Supply a vector of survivors
surv <- c(33845, 31405, 12389, 4199, 5001, 5306, 1141, 2179, 1244, 629,
          213, 111)

# Estimate numbers
Nmat <- pope(catageMat, surv)

# Time series of numbers-at-youngest-age
Nmat[,1]

# Estimate fishing mortalities
Fmat <- n2f(Nmat)

# Arithmetic mean F for a reference age range
# Note matrices have named dimensions
apply(Fmat[,colnames(Fmat) %in% 4:9], 1, mean)

hafroAssmt documentation built on May 2, 2019, 5:47 p.m.