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

• Published in: Canadian Journal of Fisheries and Aquatic Sciences
• Main Authors: Cadigan, Noel G, Brattey, John
• Format: Article in Journal/Newspaper
• Language: English
• Published: Canadian Science Publishing 2006
• Subjects: Aquatic Science; Ecology, Evolution, Behavior and Systematics; atlantic cod; Gadus morhua; Newfoundland
• Online Access: http://dx.doi.org/10.1139/f06-096; http://www.nrcresearchpress.com/doi/pdf/10.1139/f06-096

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.