A Simple Matrix Based Analysis Of Multiple Area Tagging Data Applied To The Newfoundland Northern Cod Stock

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A simple model for the analysis of tagging data is developed. This accounts for both harvest within stock components and migration between components. 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 subdivisions 2J3KL) cod stock and to inshore and offshore components of the 3Ps cod stock. Assessment of this stock is complicated by post moritorium fisheries being conducted only on inshore sub populations, (Lilly et al 2001). These are not fully covered in the groundfish survey which provide the main link to the pre-moritorium population estimates. Hence, assessments of abundance of these sub-populations must rest heavily on the results of tagging experiments. Results indicate that the biomass of components of the Northern cod have remained at about 40Kt for the past three years and that harvests rates have typically been of the order of 10% on the major 3L North component and rather higher on the 3K component during this period.