# rec_linear: The density-independent stock recruitment function In LeMaRns: Length-Based Multispecies Analysis by Numerical Simulation

## Description

Calculates the number of recruits as given by the density-independent stock recruitment function.

## Usage

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

## Details

The number of recruits is defined as `a*(SSB/1e9)`.

## Value

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

## References

Ogle, D.H. (2016). Introductory Fisheries Analyses with R. CRC Press.

`calc_recruits`, `make_rec_fun`, `get_rec_fun`, `rec_BH`, `rec_Ricker`, `rec_hockey`, `rec_const` and `calc_SSB`
 ``` 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39``` ```# 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_linear(SSB, recruit_params[]) ```