Research Document - 2005/047

Exploitation and movements of Atlantic cod (Gadus morhua) in NAFO Divs. 3KL: further updates based on tag returns during 1995-2004

By Brattey, J., B.P. Healey

Abstract

During 1997-2002, a mark-recapture study was used to provide information on cod stock structure and migration patterns and estimates of exploitation for cod in the inshore of NAFO Divs. 3KL. However, the directed cod fishery in 2J+3KL was closed during 2003 and 2004 and reported landings of cod were reduced substantially. Most (82%) of the landings in 2003 (1,041 t) came from a fish-kill in Smith Sound in April, and almost all of the landings in 2004 (629 t) came from the winter flounder, Pseudopleuronectes americanus (Blackback flounder) fishery in July and August. These fisheries resulted in a total of 497 tag returns from 3KL in 2003 (with 418 from the fish kill in Smith Sound alone) and only 66 returns in 2004, substantially less than the annual totals for the preceding five years. We used these tag returns to estimate annual exploitation rates for 2003 and 2004, using methods described in our previous documents. Estimates of exploitation for 2003 for cod tagged in 3K or 3La were low (<5%), but were marginally higher (5-8%) for some groups of cod tagged in southern 3L (3Lq) due to recaptures in the neighbouring stock area where the directed cod fishery remains open. A notable result was the high 2003 estimates (10-24%) for 11 of 22 experiments that involved release of tagged cod in 3Lb during 1999-2002; most of the tag returns came from the fish kill in Smith Sound. This result indicates that the fish kill resulted in mortality of a substantial proportion of the cod that had been tagged in the local area in recent years. None of the tagged cod found during the fish kill had been in tagged in 3Ps or in 4RS3Pn. All of the estimates of exploitation for 2004 were low (<6%). Estimates of exploitation for the period 1997 to 2002 were also updated, but showed only minor differences from those reported in our previous analyses. These observations lend further support to our previous conclusion that there is a resident inshore component within the northern cod stock area. Tagging results from the period 1995-2004 indicate that this stock component largely remains within an area bounded by the 3Kd/3Ki border in the north and the 3Lb/3Lf border to the south. Southern 3L (3Lf/j/q) appears to be inhabited mainly by seasonal migrants from neighbouring 3Ps that return to that area during late fall and winter.

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