Community Research and Development Information Service - CORDIS

Deliverable: morphometric classification of harvest location of cod

A database consisting of n = 36.904 morphometric mesurements for n = 1.318 individuals is utilized to characterize the external morphology of the Atlantic cod, and its differentiation during ontogenetic growth and within the geographical range of the species in European waters. The size-related allometry is investigated for every one out of 22 variables from a truss network. A linear model confirms that both life age and geographical origin influence the body shape of cod significantly, the former being more important than the latter. Principal component extraction in factor analysis groups the geographical test groups according to the spatial location of the collection sites, but only when considering one principal component out of five that explains 2.5% of the morphometric variance. Body size variance alone, chiefly due to growth, accounts for 95.5% of the morphological variation. Although the geographical component of shape poylmorphism is rather low, as many as 96.4% of the female cod, and 94.98% of the males, could be assigned as individuals to originate from one out of eight sea basins. Cod of five years of age, or older, are assigned with 100% precision to their origins, whereas two or three years old cod produce somewhat lower assignment rates. Cod from certain geographical populations are assigned with greater precision than are others.

Morphometric data that had been standardized by means of allometric growth functions for every size variable alone-yielded less satisfactory assignment rates than did size-adjusted data that were in addition analysed separately for every single year class. The dual control of ontogenetic shape transformation by (i) estimating the fishes' life age from otolith diagnosis and (ii) size-adjustment of raw data is proposed in order to assign individuals to geographical populations. If life ages are known, year classes permit geographical assignment even without size-standards. Within the truss system of measurements taken in every cod specimen, most body size variables are intercorrelated, but orbital diameter and occiput length retain a certain independence of the remaining measurements.

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