growth: Biological Growth Functions

In TobieSurette/gulf.data: Southern Gulf of St Lawrence Data Access

Biological Growth Functions

Description

Animal growth can be expressed in various ways. Fish species growth is generally modeled as length-at-age, while crustacean growth is normally modeled as growth-at-moult size increment, i.e. the expected size increase. An common example of a fish growth model is the von Bertalanffy curve. For crustaceans, the discrete nature of growth and maturation frequently induce a stepwise behaviour. Thus, crustacean growth-at-moult increments are well modeled by a two-component piecewise linear model, with the first component describing immature growth, which is relatively fast, and the second component describing adolescent and mature growth, which has a lower relative growth rate.

Usage

growth(x, ...)

## Default S3 method:
growth(x, species, sex, theta, error = FALSE, density = FALSE, ...)

Arguments

x	Specimen size, length-frequency or other object.
species	Species.
sex	Biological sex.
theta	Named parameter for growth model.
error	Logical value specifying whether to return the estimated standard error associated with growth. Note that this does not correspond to estimation error, but rather the prediction error.
n	Length-frequencies

Value

If x is left unspecified, then a function is returned which can be used for evaluating growth for given size inputs.

Methods (by class)

• growth(default): Default growth function.

Note

Note that growth increments are returned rather than the new size.

Examples

# Snow crab growth parameters:
theta <- c(intercept = 0.276, transition = 38.2, slope = c(0.32, 0.126), window = 1.6, log_sigma = -2)
x <- seq(10, 120)
y <- growth(x, theta = theta, error = TRUE) # Include error estimate in the output.  
plot(x, y$mu, type = "l")
lines(x, y$mu - y$sigma, lty = "dashed")
lines(x, y$mu + y$sigma, lty = "dashed")

TobieSurette/gulf.data documentation built on Jan. 19, 2025, 7:50 p.m.