Increase in Harp Seal Ecosystem Role After the Cod Collapse in Newfoundland & Labrador

Pinniped populations have been increasing worldwide, posing challenges for fisheries management, including damage to fishing gear and competition for resources. In the Northwest Atlantic, harp seal numbers have increased from 1.8 million in 1970 to 6.5 million in 1990, stabilising at 4.4 million in 2024—one of the largest pinniped populations in the world. The large number of harp seals is associated with a high rate of prey consumption, raising questions about their impact on exploited and non‐exploited species. In Newfoundland and Labrador, ecosystems were disrupted with collapses of cod and capelin in the 1990s, and these populations have not yet recovered. This study examines the harp seal ecological role and influence on ecosystem structure and function. Using Ecopath with Ecosim ecosystem models, we simulated various harp seal biomass scenarios for three key periods: pre‐collapse (1985–1987), invertebrate dominance (2013–2015), and partial groundfish recovery (2018–2020). These scenarios explored harp seal depletion and recovery, impacts on cod stocks, and ecosystem effects. Simulations revealed that the ecosystem is driven by both top‐down forces from harp seals and bottom‐up forces from capelin, a key forage species. While moderate reductions in harp seal abundance had limited effects on cod, increasing capelin biomass had positive effects on both harp seals and cod. This study highlights the importance of integrating predator effects into ecosystem‐based fisheries management to anticipate change and increase resilience in dynamic marine systems.