Research Document - 2015/073

Ecological impact assessment of the use of European-origin Atlantic Salmon in Newfoundland aquaculture facilities

By D. Cote, I.A. Fleming, J.W. Carr, and J.H. McCarthy

Abstract

Aquaculture companies operating along the south coast of Newfoundland have requested permission to use farmed European-origin Atlantic salmon in their operations to increase their competitiveness. Canada’s National Code on Introductions and Transfers of Aquatic Organisms requires that a risk assessment be conducted in evaluating requests for importation or transfers of fish. This document examines the potential ecological risks that farmed European-origin Atlantic salmon and their hybrids present to native Atlantic salmon populations through competitive and predatory interactions, as well as disease transmission.

Based on many generations of selective breeding and very distinct origins, farmed European-origin Atlantic salmon are expected to have considerable genetic and phenotypic differences compared to native wild fish. These differences may cause negative impacts through interbreeding, disease transfer, or competitive interactions but the likelihood of these to occur is very much context‑dependent and, therefore, difficult to predict. Escape events from aquaculture facilities are common and should be considered inevitable for farmed European-origin Atlantic salmon. Assuming escapes originate predominantly from the marine environment, most negative interactions will be dependent on the ability of farmed European-origin Atlantic salmon to mate with wild or farmed Atlantic salmon. Negative ecological interactions of these progeny can arise through direct competition with wild fish or through outbreeding depression (e.g., reduced disease resistance, etc.).

Known interactions of wild and farmed salmon along the south coast of Newfoundland are not widespread; however, relatively little effort has been put towards monitoring farmed-wild fish interactions relative to other areas where impacts have been documented. The declining abundance of wild stocks along the south coast, however, makes populations in these rivers more vulnerable to negative impacts.

Past decisions regarding the importation of farmed European-origin Atlantic salmon in eastern North America highlighted the lack of certainty regarding the extent and severity of farmed European-origin Atlantic salmon-wild salmon interactions as the primary reason for recommending against importation. Despite many advances in the understanding of wild–farmed interactions, the uncertainties associated with this issue remain large when paired with the potential magnitude of negative effects on imperiled wild stocks.

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