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Competition in cultured and wild salmonid juveniles with emphasis on competitive interactions between farmed Atlantic salmon (Salmo salar) and wild coho salmon (Oncorhynchus kisutch) or coastal cutthroat trout (O. clarki clarki) Blann, Camela A.

Abstract

The purpose of my research was to investigate the relative competitive ability of cultured and wild salmon to provide insight into the potential effects of introduction of cultured salmon on Pacific salmon species. Aquarium trials involving equal contests (i.e. size matched, simultaneously introduced individuals) indicate that wild coho salmon (Oncorhynchus kisutch) populations (from Salmon River and Street Creek) were competitively matched in contests with farmed coho salmon (originally from Kitimat River). In equal contests between farmed Atlantic salmon (Salmo salar) (Mowi strain) and these wild coho salmon populations or coastal cutthroat trout (O. clarki clarki), Atlantic salmon were subordinate in all cases. When Atlantic salmon were given a residence advantage, however, they were competitively equal to both wild coho salmon populations, but remained subordinate to coastal cutthroat trout. Contests in which Atlantic salmon were given a 10-30% length advantage indicate that Atlantic salmon juveniles competitively match Street Creek coho salmon, but remained subordinate to Salmon River coho salmon. Behaviour and growth rates of wild or hatchery coho salmon and farmed Atlantic salmon competing for food and space in artificial stream channels were also investigated. Individually marked fry were introduced to stream channel sections consisting of both riffle and pool habitat and behavioural interactions and distribution were recorded daily. Length and weight were measured prior to introduction and at the end of the 12 or 15 day experiments. In equal contests, both coho and Atlantic salmon grew significantly more in the presence of the other species than when alone. It appears that coho salmon obtain additional food ration by out-competing Atlantic salmon, whereas Atlantic salmon are stimulated to feed more in the presence of coho salmon competitors. My results suggest that underyearling wild coho salmon and cutthroat trout outcompete farmed Atlantic salmon of a similar size, however, size and residence advantage improves the competitive ability of farmed Atlantic salmon. The greater competitive ability of Pacific salmon species may be, in part, responsible for the failed attempts to introduce Atlantic salmon to the Pacific coast in the past. However, as farmed salmon are competitively equal in some instances, farmed salmon could cause adverse effects on Pacific salmonid populations, particularly if farmed fish are introduced in large numbers relative to wild populations.

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