Research Document - 2001/082
A simple matrix based analysis of multiple area tagging data applied to the northern cod stock of Newfoundland
By J. Pope and J. Brattey
Abstract
A simple model for the analysis of tagging data is developed. This accounts for both harvest within stock components and migration between components, as well as initial tagging mortality, tag loss, tag reporting rates, and assumed natural mortality. An exact matrix solution is provided for the simple case where all components are tagged in a year and extensions of this are constructed to handle the singular matrix situations where not all data are available for all years. This model is applied to inshore components of the Newfoundland northern (NAFO Divs. 2J3KL) cod (Gadus morhua) stock and to inshore and offshore components of the southern Newfoundland NAFO Subdiv. 3Ps cod stock. Post-moratorium fisheries being conducted only in the inshore areas (Lilly et al 2001) complicate assessment of the northern cod stock. These inshore areas are not fully covered by ground-fish surveys which provide the main link to the pre-moratorium population estimates. Hence, assessments of abundance of these inshore sub-populations must rest heavily on the results of tagging experiments. Results indicate that the biomass of inshore components of the northern cod have remained at about 40Kt for the past three years and that harvest rates have typically been of the order of 10% on the major 3L inshore North component and rather higher on the inshore 3K component during this period.
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