Research Document - 2016/017
A cohort time-series Von Bertalanffy growth model for Northern cod (Gadus morhua), and estimation of the age of tagged cod
By N. Cadigan and C. Konrad
Abstract
A Von Bertalanffy growth model is presented to estimate length-at-age for Northern cod (Gadus morhua) during 1978‑2012 and ages 1‑12. Our objective is to use these estimates of size-at-age to estimate the age of tagged fish when they were released, using their length-at-release, quarter of year, and location (i.e. Northwest Atlantic Fisheries Organization [NAFO] Division). Model parameters are estimated using the Department of Fisheries and Oceans (DFO) autumn RV bottom trawl survey mean lengths-at-age in NAFO Divisions 2J, 3K, and 3L during 1978‑2012. The model is applied by cohort and NAFO Division but the model is formulated in a mixed-effects framework with fixed parameters for all cohorts and random auto-correlated cohort interactions. The growth model estimates of the age of tagged fish are validated with a small subsample of tagged fish whose ages were estimated at capture using otoliths.
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