Mean length and its spread at a set of real ages

Von Bertalanffy growth in Schnute's form, with L1 the mean length at age A1, L2 the mean length at age A2 and K the growth rate. Below A1 growth is linear from L0 at age zero, and a Richards coefficient other than one applies the same form to the lengths raised to that power. The coefficient of variation is CV1 below A1 and CV2 at and above A2, interpolating between them. Equations are in the model equations vignette.

Usage

get_laa_curve(
  x,
  L0,
  L1,
  L2,
  K,
  CV1,
  CV2,
  A1,
  A2,
  cv_type = 0,
  sd_type = 0,
  A2_cv = NULL,
  rho = 1,
  cv_ref = NULL,
  L2_asymptote = 0
)

Arguments

x

Numeric vector of real ages, data rather than parameters.

L0

Length at age zero, the anchor of the linear phase.

L1, L2, K, CV1, CV2

Growth parameters on the natural scale, possibly AD.

A1, A2

Reference ages for L1 and L2. A2 is ignored for the asymptote under L2_asymptote, but still bounds the CV interpolation.

cv_type

Integer, 0 interpolates the CV on length, 1 on age.

sd_type

Integer, 0 has the CV parameters scale the mean, 1 reads them as standard deviations.

A2_cv

Age at and above which CV2 applies, defaulting to A2. Under L2_asymptote there is no second reference age, so Setup_Mod_Biologicals sets A2 to the accumulator age and the interpolation runs to there.

rho

Richards coefficient on the natural scale, possibly AD. One (the default) is the von Bertalanffy curve.

cv_ref

Optional vector of the coefficient of variation at each element of x, used in place of the one this curve implies. It holds the spread at age at a reference year's while the mean moves, which is the convention for a time-varying growth curve.

L2_asymptote

Integer, 0 (default) solves \(L_\infty\) from L1 and L2 at their reference ages, 1 reads L2 as \(L_\infty\) itself. Set from growth_A2 = "Linf" in Setup_Mod_Biologicals.

Value

List with L (mean length), sd (spread), Linf and cv.