Research Document - 2011/016
A preliminary evaluation of the impacts of Grey Seal, (Halichoerus grypus), predation on the 4T ecosystem and possible effects of their removal on cod (Gadus morhua) recovery
By L. Morissette and M.O. Hammill
Abstract
In this research document, we use an Ecopath with Ecosim (EwE) model to examine the trophic role of grey seals in the southern Gulf of St. Lawrence ecosystem and assess their direct and indirect impacts on Atlantic cod populations and other species interconnected with them. We assumed different feeding scenarios for grey seals, and simulated to which extent reducing their population is likely to affect the recovery of Atlantic cod. 11 harvest scenarios were tested. Our results suggest that the removal of seals could help the recovery of cod in some circumstances, but additional work is needed to tune the model to better mimic the decline in the southern Gulf of St. Lawrence cod stock, to examine how long recovery might take, to examine a strategy where seals in areas of high overlap with cod could be targeted, examine the impacts of removals on other depleted stocks of hake, and skate and potential effects on other ecosystem components including other fisheries. Additional scenarios need to be examined to explore a more complete range of possible outcomes under different grey seal removal strategies.
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