Research Document - 2006/082

Exploitation of Atlantic cod (Gadus morhua) in NAFO Subdivision 3Ps: estimates from mark-recapture experiments for the October 2006 assessment

By Brattey, J., and B. Healey

Abstract

This document provides an update of the results from a multi-year tagging study of Atlantic cod (gadus morhua) in NAFO Subdiv. 3Ps, initiated during spring 1997. Since inception, a total of 66,976 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 13,693 (20.4%) have been reported as recaptured to 1 October 2006. During December 2005, a further 1,490 tagged cod were released in an offshore area (3Psh) with the assistance of industry. Estimates of exploitation for cod tagged in each region in each year were computed using methods we reported previously. Estimates of short-term tagging mortality, tag loss, and reporting rate were obtained and are incorporated into the estimation. No tagging has been conducted inshore since 2003, and the cod tagged inshore and captured during 2005 would typically be at least six years old; consequently, the exploitation estimates given here for inshore tagging pertain to year classes produced prior to 1999 (6+ cod) and managers should be aware that these estimates exclude cod newly recruited to the fishery (2000-2001 year classes). Also, this makes differences in exploitation rates across the time-series more difficult to interpret. Among cod tagged in Placentia Bay (3Psc) mean annual estimates of exploitation have declined from 35% in 1999 to 21% in 2005. For cod tagged in Fortune Bay (3Psb) mean annual estimates have been similar (8-12%) during 2000-2005, with tag returns indicating considerable movement of cod between Fortune Bay and Placentia Bay. For cod tagged in 3Psd (Burgeo Bank) the estimate for 2004 was 1.3%, the lowest estimate since 1998, but similar to the 2004 value (range 1.3-9.1%). Mean annual estimates of exploitation for cod tagged in offshore areas (3Psh) are marginally higher for 2005 (5.5%, compared with 1.5-3.2% during 1998-2004) but remain lower than those for inshore areas in spite of offshore landings of >6,000 t. The timing of offshore tagging in 3Psh/g was changed from April to December during 2003-2005 and a total of over 4,200 tagged cod have now been released. However, only 90 of the cod tagged offshore in December have been reported as recaptured. In terms of distribution of recaptures, results were almost identical to those for cod tagged offshore April, with recaptures taken mostly in the local offshore area (3Psh/e) and inshore within Placentia Bay (3Psc).

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