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Reporting and shedding rate estimates from tag-recovery experiments on Atlantic cod (Gadus morhua) in coastal Newfoundland

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It is important to have good estimates of tag reporting rates when inferring exploitation rates and other mortality rates from tagging experiments. We estimate the reporting rates of single- and double-tagged Atlantic cod (Gadus morhua) caught in commercial fisheries around coastal Newfoundland, Canada, based on an extensive series of multi-reward tagging experiments conducted during 1997–2004. Reporting rates for single-tagged cod varied from 58% to almost 100%, with significant temporal and spatial variability. The odds of reporting a double-tagged cod was almost double that of a single-tagged cod. Returns from double-tagged cod allow us to estimate tag shedding rates. Tag shedding rates suggested that 22% of fish lost their tag during their first year at liberty; subsequently, tag shedding rates were much lower (<10%). We also found that twice as many fish lost tags when the tags were attached anteriorly at the base of the first dorsal fin compared with a position more towards the posterior end.

Lorsque l'on déduit les taux d'exploitation ou d'autres taux de mortalité à l'aide d'expériences de marquage, il est important d'obtenir de bonnes estimations des taux de signalisation des étiquettes. Nous estimons les taux de signalisation de morues franches (Gadus morhua) marquées d'une ou de deux étiquettes dans les pêches commerciales autour de la côte de Terre-Neuve, Canada, à partir d'une grande série d'expériences de marquage assorties de diverses primes menées en 1997–2004. Les taux de signalisation des morues porteuses d'une seule étiquette varient de 58 % à presque 100 %, avec une variabilité temporelle et spatiale significative. La probabilité qu'une morue marquée de deux étiquettes soit signalée est presque le double de celle d'une morue avec une seule étiquette. Les retours obtenus à partir des morues porteuses de deux étiquettes nous ont permis d'estimer les taux de perte d'étiquettes. Les taux de perte indiquent que 22 % des poissons perdent leur étiquette au cours de leur première année en liberté; par la suite, les taux de perte des étiquettes sont beaucoup plus bas (<10 %). De plus, deux fois plus de poissons perdent leur étiquette lorsque celle-ci est fixée en avant à la base de la première nageoire dorsale que lorsqu'elle est placée plus vers la région postérieure du corps.

Document Type: Research Article

Publication date: 2006-09-01

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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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