An Ecosystemic Approach to Understand the Relationship Between Species in Risk and Species in Overabundance in the Gulf of St. Lawrence

The St. Lawrence Gulf ecosystem has experienced several perturbations over the last few decades. Cod and some other groundfish stocks crashed largely due to overfishing as well as environmental changes. In spite of very limited fishing over the last two decades, cod have shown only limited signs of recovery and in the southern Gulf, they continue to decline. At the same time, grey seals abundance has increased markedly in the last years. It has been proposed that predation by grey seals is limiting cod recovery in the Gulf and therefore, the population should be reduced. However, the southern Gulf is a complex ecosystem and a grey seal cull may impact other ecosystem components. An ecosystem model (Ecopath with Ecosim) was developed to examine possible ecosystem impacts of a seal reduction within a simulation environment. The simulations show that without grey seal removal, cod and other demersal fish will continue to decline. They also indicate that although a grey seal cull would favour some recovery of these species, additional management measures may be required for full recovery. This study has shown, how a global approach can provide useful insights into possible outcomes from management actions to achieve management objectives.