Current Research on the Impact of Pinnipeds on Commercial Fish Stocks in the Northwest Atlantic

The impact of marine mammals, particularly seals, on the recovery of depleted fish stocks is a controversial issue and the focus of significant research efforts. Three species of seals are considered important predators in the northwest Atlantic, harp, hooded and grey seals. Harp and hooded seals are seasonal migrants that have shown little or no increase in abundance over the past decade. Grey seals are residents of temperate waters that, after a number of decades of exponential growth, are beginning to show signs of density dependent reductions in growth rates. Consumption of important prey species by seals Atlantic Canada has been estimated using bioenergetics models. Harp seals are important predators in Divisions 2J3KL and 4RS while grey seals are the most important pinniped predator in 4T and 4VsW. Hooded seals feed primarily in 2J3KL and 3M. Recent advances in methods of estimating diet have provided new insights into the importance of individual prey species that will require new estimates of consumption. A number of studies have attempted to determine the impact of seals on fish stocks in the northwest Atlantic, particularly the impact of harp and/or grey seals on Atlantic cod. In general, these studies have indicated that although seals consume substantial amounts of commercial fish species and important forage species, the impact of these removals on the current fish stocks is difficult to determine. Seals are important predators of both large and small cod and could be playing a role in the non-recovery of cod stocks, but seal predation can not account for a large component of mortality in most areas and therefore, the total impact of seal predation cannot be determined. Often, estimates of age specific cod consumption by seals are inconsistent with the high mortality observed among older age groups. Little is known about the functional response of seals to changes in abundance of prey, other sources of mortality, or possible ecosystem effects such as competition for forage fish and positive feedback through seal predation on piscivorous fish. Among other initiatives, the Canadian Department of Fisheries and Oceans and NAFO are organizing scientific meetings in the coming year to improve our understanding of the role seals are having on the population dynamics of their prey.

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