This document summarizes exploratory analysis of the northern Gulf of St. Lawrence cod (Gadus morhua) tagging database which contains information from about 44,500 releases and 2,371 (5.2%) reported recaptures of cod tagged and released in 3Pn4RS during 1995-2003. Recent catch data from 3Pn4RS cod are summarized to aid in the interpretation of tag returns; reported landings ranged from 3,100 to 6,930 t during 1997-2002. We provide some summaries of the tagging data along with suggestions on how the northern Gulf of St. Lawrence cod tagging study could be improved. The overall return rate of tagged cod is low and there is a strong seasonal pattern in the recovery rate depending on the time of release. Return rates (median percentage returned) was substantially lower (1-2%) for cod tagged in summer (July-September) when surface temperatures could be extremely warm, compared to those tagged during the cooler spring months (6-7%, April-May). There were many experiments with no recaptures and these included several with >100 releases, suggesting that initial tagging mortality was extremely high in some of the experiments; this contrasts with the results of a small number of experiments where tagged cod were held in submersible cages which showed high survival (≥ 82%). Over 2,000 double-tagged cod were released, but the low overall return rate resulted in too few recoveries (215 over 8 yrs) to estimate the parameters of the Kirkwood tag loss model which has been shown to adequately describe the rate of loss of t-bar anchor tags in cod. However, annual grouping of the recapture data from double tagged cod suggested that the rate of loss was not inconsistent with that reported for cod tagged in the adjacent 3Ps stock area. Data from one experiment involving simultaneous release of single-tagged and high-reward tagged cod provided a reporting rate estimate for single tagged cod of 0.38 for 2001. Annual exploitation rates calculated using the methods described by Brattey and Healey (2003) suggest high exploitation rates for cod tagged in some areas, notably 3Pn (typically 12-23% harvested per year), 4Rc (12-18%), 4Rb (5.4-18.7%), but low (4Sw) or variable rates elsewhere (4Ra, 4Rd). These estimates have considerable uncertainty because of the sparseness of the data available to estimate initial tagging mortality, tag loss, and tag reporting rate. The study could be improved by more rigorous training of fishers involved in tagging, combined with simultaneous release of batches of cod with single, double, and high reward tags at several sites throughout the stock area. Much higher proportions of double tags should be used (40%). Cage experiments to monitor initial tagging mortality should be repeated over a wider range of conditions and by the same individuals conducting the field tagging.
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