calc_SRR: Calculate abundance from density-dependent mortality

In salmonMSE: Management Strategy Evaluation for Salmon Species

Calculate abundance from density-dependent mortality

Description

Calculates the abundance of survivors after applying either a Beverton-Holt or Ricker stock-recruit relationship.

Usage

calc_SRR(N1, N2 = N1, p, capacity, type = c("BH", "Ricker", "HS"))

Arguments

N1	Numeric, the initial abundance that scales the density-independent survival term
N2	Numeric, the initial abundance that scales the density-dependent survival term
p	Numeric, the productivity parameter that sets the maximum survival as the initial abundance approaches zero
capacity	Numeric, the capacity parameter that set the maximum survivors
type	Character, the functional form of the stock-recruit relationship

Details

The Beverton-Holt stock recruit relationship is of the following form:

\textrm{Smolt} = \dfrac{\alpha N_1}{1 + \beta N_2}

where \alpha = P, \beta = P/C.

The Ricker stock recruit relationship is of the following form:

\textrm{Smolt} = \alpha N_1 \exp(-\beta N_2)

where \alpha = P, \beta = P/(Ce), e is Euler's number.

Productivity P is in terms of abundance per unit of N_1 and N_2.

The hockey stick is of the following form:

\textrm{Smolt} = \begin{cases} p N_1 &, N_1 \le \frac{N_1}{N_2} \times C\\ \frac{N_1}{N_2} \times C &, \textrm{otherwise} \end{cases}

Value

Numeric, the abundance of survivors

See Also

calc_SRRpars()

Examples

N1 <- 100
N2 <- 200
p <- 10
capacity <- 250

calc_SRR(N1, N2, p, capacity, type = "BH")

# Validation
SRRpars <- calc_SRRpars(p, capacity, type = "BH")
a <- SRRpars[1]
b <- SRRpars[2]
a * N1/(1 + b * N2)

salmonMSE documentation built on Aug. 20, 2026, 5:09 p.m.