Extending the Northern Cod (Gadus morhua) assessment model - part I : bridging gaps with additional data and model variations

Abstract

Since 2016, the Northwest Atlantic Fisheries Organization (NAFO) Division (Divs.) 2J3KL (or Northern) cod stock has been assessed with a complex integrated state-space population model called NCAM (Northern Cod Assessment Model). While the time series in base-case NCAM begins in 1983 – when the Research Vessel (RV) survey started covering NAFO Divs. 2J, 3K, and 3L. Older data used in previous assessment models for Northern cod, such as reported landings and catch-at-age, have gone unused. Though limited to selected years, there is also considerable historical data from the tagging program that has yet to be utilized in a formal assessment model. Finally, data from two juvenile cod monitoring programs have yet to be utilized in an assessment model for Northern cod. Here we document the process and assumptions behind the inclusion of additional reported landings, catch-at-age, tagging data, and juvenile survey data into NCAM. Much of these data extend back to 1954. Additionally stock-recruitment (S-R) relationships are explored as are alternate approaches to estimating baseline rates of natural mortality (M; e.g., allometric M). The application of additional data and model variations not only extends the temporal perspective on Northern cod stock trends, but also enhances our understanding of critical aspects such as recruitment, the S-R relationship, and the estimation of M. These extensions bridge gaps in our knowledge, enable the reassessment of reference points, and offer a more robust foundation for informed fisheries management decisions.