SUITABILITY OF EMPIRICAL METHODS FOR THE MANAGEMENT OF THE CRITICALLY ENDANGERED EUROPEAN EEL: SKIN COLOUR CHANGES AS DESCRIPTOR OF MIGRATING SILVER EEL STAGE

Author's Name: Fabrizio Capoccioni, Corrado Costa & Eleonora Ciccotti
Subject Area: Life Sciences
Subject Ichthyology
Section Research Paper

Keyword:

European eel, Anguilla anguilla, silvering, conservation, PLSDA, morphometrics, skin colour


Abstract

The European eel is a critically endangered species since stocks are in decline in most of their geographical distribution and their status is considered below safe biological limits. A number of management and conservation measures are being implemented in European countries, in particular applied to silver eels starting their unique spawning migration. A supervised multivariate classification approach (PLSDA) was applied to investigate the relationship between developmental stages of European eel on the basis of skin colour change, and several external and internal parameters. A first model was build using data of European eels collected in the Tiber River in Italy, to explain the co-variation between external morphological measures, and three developmental stages selected a priori, and a second one adding three parameters (otoliths radius, liver and gut weight). Satisfactory percentages of correct classification were obtained for both models. A validation test, based only on external measurements, was performed with the addition of new samples from two Italian coastal lagoons. Results confirm that changes in skin colour reflect the parameters considered, but the efficiency of the PLSDA model is highly site-dependent. The most evident application of this work is the confirmation of the validity of the empirical staging “by eye” between yellow and silver eel that is widely used by different actors of European eel conservation actions.

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