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Estimating population age structure using otolith morphometrics: a test with known-age Atlantic cod (Gadus morhua) individuals

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Abstract:

Traditional age reading is a rather subjective method that lacks true reproducibility, producing ageing error that propagates up to stock assessment. One alternative is represented by the use of otolith morphometrics as a predictor of age. An important issue with such a method is that it requires known-age fish individuals. Here we used known-age Atlantic cod (Gadus morhua) from the Faroe Bank and Faroe Plateau stocks. Cod populations usually show quite large variation in growth rates and otolith shape. We showed that including otolith morphometrics into ageing processes has the potential to make ageing objective, accurate, and fast. Calibration analysis indicated that a known-age sample from the same population and environment is needed to obtain robust calibration; using a sample from a different stock more than doubles the error rate, even in the case of genetically highly related populations. The intercalibration method was successful but generalization from one stock to another remains problematic. The development of an otolith growth model is needed for generalization if an operational method for different populations is required in the future.

La méthode courante de lecture des âges est plutôt subjective et elle manque de véritable reproductibilité; elle produit donc une erreur de lecture des âges qui se répercute jusque dans l’évaluation des stocks. Une méthode de rechange est l’utilisation des données morphométriques des otolithes comme variables de prédiction de l’âge. Un problème important associée à cette méthode est qu’elle requiert des poissons individuels d’âge connu. Nous utilisons ici des morues franches (Gadus morhua) d’âge connu des stocks du banc et du plateau des Féroé. Les populations de morue affichent généralement une variation assez importante des taux de croissance et de la forme des otolithes. Nous démontrons que l’inclusion de l’étude morphométrique des otolithes dans les processus de détermination de l’âge peut potentiellement permettre une estimation de l’âge qui soit objective, précise et rapide. Une analyse d’étalonnage indique qu’un échantillon de poissons d’âge connu provenant de la même population et du même milieu est nécessaire pour obtenir un étalonnage robuste; l’utilisation d’un échantillon d’une autre population plus que double le taux d’erreur, même lorsqu’il s’agit d’une population fortement apparentée du point de vue génétique. La méthode d’interétalonnage est efficace, mais les généralisations d’un stock à un autre restent problématiques. Il sera nécessaire d’élaborer un modèle de croissance des otolithes pour faire des généralisations, si on a besoin dans le futur d’une méthode opérationnelle applicable à différentes populations.

Document Type: Research Article

Publication date: November 1, 2008

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  • Published continuously since 1901 (under various titles), this monthly journal is the primary publishing vehicle for the multidisciplinary field of aquatic sciences. It publishes perspectives (syntheses, critiques, and re-evaluations), discussions (comments and replies), articles, and rapid communications, relating to current research on cells, organisms, populations, ecosystems, or processes that affect aquatic systems. The journal seeks to amplify, modify, question, or redirect accumulated knowledge in the field of fisheries and aquatic science. Occasional supplements are dedicated to single topics or to proceedings of international symposia.
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