rec_const: The constant stock recruitment function
In LeMaRns: Length-Based Multispecies Analysis by Numerical Simulation

Description Usage Arguments Details Value See Also Examples

Calculates the number of recruits as given by the constant stock recruitment function.

1	rec_const(SSB, rec_args)

`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` for each species. `a` is a positive numeric value, often referred to as the density-independent parameter. The default is 1.

The number of recruits is defined as the value of a.

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

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

# 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)

rec_const(SSB[1], recruit_params[[1]])