rec_BH {LeMaRns}

The Beverton-Holt stock recruitment function

Description

Calculates the number of recruits as given by the Beverton-Holt stock recruitment function.

Usage

rec_BH(SSB, rec_args)

Arguments

SSB

A numeric value representing the Spawning Stock Biomass (SSB) of a given species (g).

rec_args

A list object of length nfish, with each element in the list including a value of a and b for each species. a is a positive numeric value, often referred to as the density-independent parameter. The default is 1. b is a positive numeric value, often referred to as the density-dependent parameter. The default is 0.001.

Details

The Beverton-Holt stock recruitment function is defined as a*(SSB/1e9))/(1+b*(SSB/1e9)).

Value

A numeric value representing the number of recruits of a given species.

References

Beverton, R.J.H., Holt, S.J. (1957). On the Dynamics of Exploited Fish Populations, volume 19 of Fisheries Investigations (Series 2). United Kingdom Ministry of Agriculture and Fisheries.

See Also

calc_recruits, make_rec_fun, get_rec_fun, rec_Ricker, rec_hockey, rec_const, rec_linear and calc_SSB

Examples

# Set up the inputs to the function - species-independent parameters
nfish <- nrow(NS_par)
nsc <- 32
maxsize <- max(NS_par$Linf)*1.01 # the biggest size is 1% bigger than the largest Linf
l_bound <- seq(0, maxsize, maxsize/nsc); l_bound <- l_bound[-length(l_bound)]
u_bound <- seq(maxsize/nsc, maxsize, maxsize/nsc)
mid <- l_bound+(u_bound-l_bound)/2

# Set up the inputs to the function - species-specific parameters
Linf <- NS_par$Linf # the von-Bertalanffy asymptotic length of each species (cm).
W_a <- NS_par$W_a # length-weight conversion parameter.
W_b <- NS_par$W_b # length-weight conversion parameter.
k <- NS_par$k # the von-Bertalnaffy growth parameter.
Lmat <- NS_par$Lmat # the length at which 50\% of individuals are mature (cm).

# Get phi_min
tmp <- calc_phi(k, Linf, nsc, nfish, u_bound, l_bound, calc_phi_min=FALSE,
                  phi_min=0.1) # fixed phi_min
phi_min <- tmp$phi_min

# Run calc_ration_growthfac()
tmp <- calc_ration_growthfac(k, Linf, nsc, nfish, l_bound, u_bound, mid, W_a, W_b, phi_min)
sc_Linf <- tmp$sc_Linf
wgt <- tmp$wgt

# Calculate maturity
mature <- calc_mature(Lmat, nfish, mid, kappa=rep(10, nfish), sc_Linf)

# Create recruitment functions
stored_rec_funs <- get_rec_fun(rep("hockey-stick", nfish))
recruit_params <- do.call("Map", c(c, list(a=NS_par$a, b=NS_par$b)))

# Get an initial population
N0 <- get_N0(nsc, nfish, mid, wgt, sc_Linf, intercept=1e10, slope=-5)

# Calculate the SSB
SSB <- calc_SSB(mature, N0, wgt)

# Run the function
rec_BH(SSB[1], recruit_params[[1]])