Growth Von Bertalanffy

Von Bertalanffy growth

When the growth.java.classname.sp# is equal to fr.ird.osmose.process.growth.VonBertalanffyGrowth.java, a von Bertalanffy growth function is used. It is the defaut one.

$$ L(a) = L_{egg}\ if\ a=0 $$

$$ L(a) = L_{egg} + (L_{thres} - L_{egg}) \times \left(\frac{a}{a_{thres}}\right)\ if\ a>0\ \&\ a\lt a_{thres} $$

$$ L(a) = L_{\infty} \times \left(1 - \exp^{-K\left(age - t_0\right)} \right)\ else $$

with

$$ L_{thres} = min\left[L_{egg}, L_{\infty} \times \left(1 - \exp^{-K\left(a_{thres} - t_0\right)}\right) \right] $$

A Von Bertalanffy model is used to calculate mean length increase above a threshold age $a_{thres}$ determined for each HTL group from the literature. Below $a_{thres}$, a simple linear model is used. The rationale behind this is that Von Bertalanffy parameters are usually estimated from data excluding young individuals of the year or only including very few of them. Assuming a linear growth between age 0 and $a_{thres}$ ensures a more realistic calculation of mean length increases for early ages of HTL groups (@Travers2009).

Parameter	Description
species.linf.sp#	$L_{inf}$ (cm)
species.k.sp#	$K$
species.t0.sp#	$t_0$
species.vonbertalanffy.threshold.age.sp#	$a_{thres}$ (years, default=1 year)