Research Document - 2003/032

Exploitation rates and movements of Atlantic cod (Gadus morhua) in NAFO Divs. 3KL based on tagging experiments conducted during 1997-2002

By Brattey, J., and Healey, B.

Abstract

A large-scale mark-recapture study of adult (>45 cm) Atlantic cod (Gadus morhua), initiated in spring 1997, was continued. During 1997-2002 a total of 26,401 live cod were tagged with single, double, or high-reward t-bar anchor tags and released at various inshore locations off the east coast of Newfoundland. Approximately 3,870 tagged cod have been reported as recaptured up to 8 February 2003. Tag returns were adjusted to account for region-specific reporting rates, and the number of tagged cod available for capture was adjusted to account for tagging mortality, tag loss and assumed natural mortality. These data were used to estimate annual exploitation rates for each batch of tagged cod. To indicate where exploitation was taking place, the spatial distribution of recaptures from tagging in each area was summarized annually, with numbers recaptured adjusted to account for annual region-specific reporting rates. Estimates of exploitation for cod tagged in 3K in 1999 were high (29-63%) for 1999, but dropped dramatically (3.9-8.8%) during 2000 and 2001. Landings in 3K dropped from about 3,500 t in 1999 to only 600 t in 2002. Among cod tagged in Bonavista Bay (3La), estimates of exploitation were also highest for 1999, ranging from 6.0 to 18.4% with most estimates around 15%. Estimates for subsequent years were lower, except among more recently tagged cod released in 3La during 2001 and 2002 (4.5 - 24.5%). Estimates of exploitation for cod tagged in Trinity Bay (3Lb) during 1999 tended to be lower (3.5-13.2%) than those for Bonavista Bay. For 2000 and 2001 most estimates for cod tagged in 3Lb were between 5 and 15%. There was a marked increase in the estimates for 3Lb during 2002, particularly among cod tagged in Smith Sound where 5 of 12 estimates exceeded 20% giving cause for concern; most of the exploitation of these cod occurs outside Smith Sound as these fish disperse northward along the inshore during summer. The exploitation estimates for Conception Bay (3Lf) and the eastern Avalon (3Lj) tended to be low (<10%) and annual reported landings in these regions were low (300 - 600 t) throughout 1998-2002. In contrast, cod tagged in St. Mary's Bay (3Lq) were more heavily exploited throughout 1998-2002 with 19 of 25 annual estimates exceeding 15%. Most of the exploitation of cod tagged in southern 3L occurs in Placentia Bay (3Psc), suggesting that many of the fish in this area are migrants from the neighbouring stock area. Cod in the inshore of northern 3L and 3K appear to comprise a separate stock component and do not appear to mix to any great extent with cod from southern 3L or 3Ps.

Complete document (PDF, 1147 KB)

Accessibility Notice

This document is available in PDF format. If the document is not accessible to you, please contact the Secretariat to obtain another appropriate format, such as regular print, large print, Braille or audio version.