Research Document - 2002/97

Movements of Atlantic cod (Gadus morhua) in NAFO Subdiv. 3Ps and updated estimates of exploitation from tagging experiments in 1997-2002

J. Brattey, D. R. Porter, and C. W. George

Abstract

A tagging study of Atlantic cod (Gadus morhua), initiated in 3Ps in spring 1997 was continued with an additional 8,263 tagged fish released during 2002. In this study, a total of 52,500 live cod tagged with single, double, or high-reward t-bar anchor tags has now been released at various inshore and offshore locations off the south coast of Newfoundland. Approximately 8,400 tagged cod have been reported as recaptured up to September 2002. 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 exploitation annually for each batch of tagged cod. The spatial distribution of recaptures from tagging in each area was summarized each year with numbers recaptured adjusted to account for region-specific reporting rates. The stock appears to comprise several offshore components, as well as resident inshore components in Fortune Bay and Placentia Bay, with limited mixing between them. Portions of the offshore components migrate to the inshore and mix with inshore cod during summer and fall. As in previous years, exploitation estimated from tag returns differed markedly across the stock area. Among cod tagged in Fortune Bay, mean annual estimates of exploitation have been reasonably consistent, ranging from 0.14 to 0.16 during 1998-2001. Among cod tagged in Placentia Bay, exploitation estimates have ranged from 0.11 to 0.23 with highest values during 1999 and a mean of 0.18 for 2001. Estimates of exploitation in 2001 for cod tagged in Placentia Bay are generally lower than those observed in 1999 and 2000, although 5 of 21 estimates still exceed 20%. Among cod tagged in the Burgeo Bank-Hermitage Channel area (3Psd), estimates of exploitation have been low, ranging from 0.04 to 0.08 during 1998-2001. Cod tagged in Halibut Channel (3Psh) have consistently shown lowest mean annual estimates of exploitation (0.02 to 0.03), in spite of substantial offshore landings. More extensive spatial and temporal tagging coverage of the offshore unit areas 3Pse and 3Psh (St. Pierre Bank and Halibut Channel) may be required to improve the reliability of the exploitation estimates for these offshore regions.

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