Research Document - 2003/091

Updated estimates of exploitation from tagging of Atlantic cod (Gadus morhua) in NAFO Subdiv. 3Ps during 1997-2003

By Brattey, J., and Healey, B.

Abstract

This document updates the results of a multi-year tagging study of Atlantic cod (Gadus morhua), initiated in NAFO Subdiv. 3Ps in spring 1997, with about 8,000 additional cod tagged and released during April-June 2003. Since inception, a total of over 60,000 cod have been tagged with single, double, or high-reward t-bar anchor tags and released at various inshore and offshore sites off southern Newfoundland (3Ps) and 9,993 (16.5%) have been reported as recaptured to 30 September 2003. Estimates of exploitation for cod tagged in each region were computed using methods similar to those reported in our previous documents, but with minor modifications. Estimates of short-term tagging mortality, tag loss, and reporting rate were also obtained and are incorporated. Among cod tagged in Placentia Bay mean annual estimates of exploitation have declined from 33% in 1999 to 20% in 2002; however, some individual estimates remain quite high with six of 14 estimates exceeding 20% in 2002. Mean annual estimates for cod tagged in Fortune Bay have been fairly stable at 10% to 11%; however, cod tagged at Poole's Cove are being more heavily exploited than those off Pass Island in the outer reaches of Fortune Bay. Mean annual estimates for cod tagged in offshore areas remain consistently low (4% to 9% among cod tagged in 3Psd; 1-3% among those tagged in 3Psh). Some of the cod tagged in 3Psd (Burgeo Bank) are exploited in the neighbouring 3Pn4RS stock area, suggesting that stock mixing may extend to April in some years. As reported in previous analyses the exploitation estimates for 3Psh are extremely low given annual reported offshore landings ranging from 4,000 - 12,000 t during 1998-2002. Possible reasons include limited offshore tagging coverage, restricted distribution of offshore fishing effort, and low survival of cod offshore for tagging in deep (> 200m) water. In particular, there are substantial landings from areas on St. Pierre Bank (3Pse, 3Psf) that have generated few tag returns, suggesting that there are offshore stock components that have not been tagged. More extensive tagging coverage of the St. Pierre Bank area, particularly during fall, could improve the reliability of the exploitation estimates for the offshore regions.

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