عنوان

GCP/RER/010/ITA/MSM-09 (MedSudMed Technical Documents n°9)
Report of the Workshop on Standardization of Fish Age Determination Based on Otolith Samples in the MedSudMed Project Area

1,8 MB

The Workshop was attended by experts from Tunisia, Italy, Libya and Malta and an international expert on fish age determination, Ms Hélène de Pontual, from the Institut Français de Recherche pour l’Exploitation de la Mer (IFREMER). The main objective of the workshop was to study the possibility of elaborating, a standard protocol on ageing in the MedSudMed Project area, based initially on two target species: Merluccius merluccius and Mullus barbatus. The current activities in the Project Area and an overview of the methods now used were presented, including existing national and international protocols and their principal technical characteristics regarding materials, methods, sampling design and data processing. Then the problems of standardizing age-reading methodology for the target species were discussed: choice of the hard structure, sampling, otolith extraction, otolith conservation, preparation techniques, accuracy and precision, validation etc. A laboratory exercise of age-reading techniques for Mullus barbatus was conducted to check the agereading agreement and precision among six readers. The average percentage agreement in respect of the modal age across all ages and readers in the comparison was 55.2% and the average coefficient of variation (CV) was 45.5%. The relative bias showed that all the readers tended to underestimate older age-classes. Finally, the participants agreed on a common protocol for age determination of the target species and proposed a future intercalibration exercise to assess the percentage agreement in age determination among readers.