Estimation of cod (Gadus morhua) growth in NAFO subdiv. 3Ps and divs. 3KL in 1997-1999 from tagging experiments / Noel Cadigan and John Brattey. : Fs70-1/2000-074E-PDF

This paper develops a model for estimating growth of Atlantic cod in NAFO Subdivision 3Ps and Divisions 3KL during 1997-1999. Tag-returns are used from the commercial, sentinel and food fisheries in these regions during 1997-1999. The returns are from numerous tagging experiments conducted in 3Ps and 3KL during 1997-1999. Many of the tags that are returned supply the length of the fish at capture, and this information is used to estimate growth based on known lengths-at-release and times-at-liberty. The Von Bertalanffy growth model is used, modified to accommodate seasonal variations in growth. A measurement bias component is also incorporated in the estimation because the tag-return data suggest that there is some bias in the lengths-at-capture reported by fishermen. The basic approach used has been studied fairly extensively in the fisheries literature, and review of this literature is presented. Important biases in estimating growth from tagging data have been identified in the literature, and the magnitude of the bias is assessed in the analysis using a simple simulation. The conclusion from the simulation is that the bias may not be substantial for the population. The estimated model is used to predict cod growth for times-at-liberty ranging from 0-3 years, and for fish lengths ranging between 40 and 90 cm. for example, it is estimated that a 40 cm fish will grow 22 cm during 1997-1999, but in the same period a 90 cm fish will grow only 10 cm.

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