Interactions between seals and atlantic salmon (Salmo salar) in rivers and estuaries of Newfoundland and Labrador

Lenky, Crystal C. (2007) Interactions between seals and atlantic salmon (Salmo salar) in rivers and estuaries of Newfoundland and Labrador. Masters thesis, Memorial University of Newfoundland.

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Abstract

The causes for the decline in some Atlantic salmon (Salmo salar) stocks in eastern Canada are uncertain but many resource users consider predation by seals in rivers and estuaries to be a contributing factor. During the 1990s, the Department of Fisheries and Oceans (DFO) received reports from resource users of increased seal-salmon interactions on several rivers in Newfoundland and Labrador. To address these concerns, semi-directed interviews (n=57) were conducted from 2004 to 2006 with resource users on 29 rivers throughout the Province. Respondents were requested to comment on any changes in the relative abundance, timing of migration, habitat use and foraging behavior of seals frequenting the area during the last 5 years (2000-2005), during the 1990s, and 1980-1990. Starting in the mid 1990s, harp seals (Pagophilus groenlandicus) increased their residency time in some rivers and estuaries by 1-3 months. Potential harp seal predation on salmon was considered to be high for half of the 16 rivers frequented by harp seals on the northeast coast of Newfoundland and southern coast of Labrador. In 6 of these rivers, the reported increase in the occurrence and relative abundance of seals was concurrent with the migration or spawning of pelagic forage fish (e.g. capelin) in the area. One river was influenced by variable local ice conditions during late spring, and one river was affected by both of these conditions. The presence and relative abundance of harbor seals (Phoca vitulina) in some rivers and estuaries increased during the 1990s; potential predation was considered to be high on 10/24 of these rivers. In the case of grey seals (Halichoerus grypus), relative abundance has increased in some Labrador rivers since 2000, with 3 rivers considered to have high potential predation. -- A directed harp seal diet study was carried out in 2005 and 2006 on the Campbellton River, one of the rivers considered to have high potential for predation during the smolt salmon run. A total of 122 seal stomachs were analyzed and no evidence was found that seals were feeding on salmon. Capelin, an energy-rich forage fish, was the major prey component in both years. Although information from resource users suggested that the potential for harp seal predation on salmon had increased since the mid-to late 1990s, the diet component of the project indicated that they were not necessarily feeding on salmon when these species co-occurred. Similar investigations on other seal species and rivers with high potential will be necessary before it can be concluded that harp, grey or harbour seal predation of salmon stocks is not occurring.

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