Size structure, age-size dynamics and life history variation
Heino, Mikko; Boukal, David S.; Falkenhaug, Tone; Piatkowski, Uwe; Porteiro, Filipe M.; Sutton, Tracey T.
Original version
This report is not to be quoted without prior consultation with the General Secretary.Abstract
Here we present a new technique to study life history variation when only length distributions
of populations are known. Shape of length distribution in a population is to a significant extent
determined by the degree to which an average individual approaches its asymptotic
maximum size. Statistically, the shape of a length can be characterised by its skewness, measuring
the degree of symmetry in the distribution. Positive skew (long right tail) in a length distribution
suggests that relative few individuals survive long enough to approach asymptotic
size in a population, whereas the opposite is true for negative skew (long left tail). With a
simple model of age-size dynamics in a population showing indeterminate growth, we show
that skewness is strongly correlated with the ratio between mortality rate and the growth parameter
k in the von Bertalanffy growth model; this ratio is a dimensionless number that is
one of Beverton’s ‘life history statics’. We demonstrate the new technique with data from
deep-pelagic fishes collected during the 2004 Mar-Eco expedition along the northern Mid-
Atlantic Ridge.
Keywords: Dimensionless numbers, growth trajectory, life-history invariants, mortality