Modélisation d'une croissance en deux stances chez l'albacore (Thunnus albacares)

Abstract

The composite model that is generally used to describe the two growth stanzas of yellowfin in the Eastern Atlantic is re-examined. The value of the t0 parameter is corrected. The growth function is expressed in terms of a conventional age. Limitations of this model are underlined. Various continuous models are fitted to Capisano's and Fonteneau's data (1991), who estimate age by polymodal decomposition of the length frequencies of purse seine catches between 1983 and 1988. Fitting the 3- or 4-parameter models (Gompertz, Richards, and Von Bertalanffy generalized) appears unsatisfactory. A 5-parameter model is proposed that combines a linear function and a generalized Von Bertalanffy model. Validity and fitting of this model are discussed. The growth is correctly described for fork lengths from 40 to 150 cm and for ages from 0.25 to 4.25 years. In order to model the growth during the whole exploited phase up to 170 cm length and 6.0 years of age with a single equation, the model is fitted again to data simulated by the previous models. The growth for the exploited phase is then expressed as follows: L(t) = 37.8 + 8.93×t + (137.0 - 8.93×t) × [l - exp(-0.808×t)]7.49 The relevance of this equation is discussed in relation particularly with a probable sexual growth dimorphism. Some hypotheses are developed to explain the juveline slow growth stanza, followed by a growth acceleration at about 47 cm and then by an inflexion point at about 90 cm. The succession of two growth stanzas seems, in particular, to be related to the migrations of this species within the Eastern Atlantic and towards the Western Atlantic. © IFREMER-Gauthier-Villars, 1992.