Extending the Northern Cod (Gadus morhua) assessment model - part II : quantifying the impact of Capelin and Seals

Abstract

Understanding the dynamics of marine ecosystems is crucial for effective fisheries management. The dynamics of Northern cod (Gadus morhua) are influenced by various ecological factors, including the availability of key prey species like Capelin (Mallotus villosus) and consumption by predators such as seals. Previous research has explored the impact of Capelin availability and Harp Seal (Pagophilus groenlandicus) predation on Northern cod mortality; however, specific age-related effects and the combined influence of these factors on natural mortality rates remain less understood. Here we show that Capelin abundance significantly affects the rates of natural mortality experienced by Northern cod, especially the older age groups. Additionally, our study indicates that Harp Seals have an impact on cod, particularly younger age groups. This study contributes to existing knowledge by uncovering nuanced age-related influences of Capelin and Harp Seals on cod mortality. Integrating these factors into predictive models enhances our ability to forecast changes in cod populations and underscores the importance of considering multi-faceted ecological interactions in fisheries management. Overall, this research represents an effort to move away from a purely descriptive assessment and towards a more mechanistic explanation of changes in Northern cod productivity. The overarching goal is to support an ecosystem approach to managing this important stock.