Research Document - 2009/075

Smallmouth Bass (Micropterus dolomieu) Invasion of Gulf Region Rivers: Evaluating the Impact on Atlantic Salmon (Salmo salar) Populations

By A. Valois, R.A. Curry, and S.M. Coghlan

Abstract

The introduction of species outside their native range can lead to significant declines in native fish species, including Atlantic salmon (Salmo salar). The rapid natural and human-facilitated expansion of smallmouth bass (Micropterus dolomieu) throughout New England and the Maritimes has brought increased attention to possible negative effects of these introductions on efforts to maintain and restore Atlantic salmon. Although the negative effects of invasive smallmouth bass on other native fishes (e.g., cyprininds, Pacific salmonids) are well-documented, we have no direct studies assessing predatory and competitive interactions with Atlantic salmon. The predation risk leading to the most significant potential threat to Atlantic salmon will be consumption of juveniles, i.e., emerging fry to smolts. Smolts probably have lower risk of predation than younger parr owing to the larger body size of smolts. Studies of habitat use and foraging behaviour of juvenile smallmouth bass in streams suggest functional similarities and potential habitat overlap with Atlantic salmon that could result in competitive interactions with age 0+ smallmouth bass. These negative effects resultant from competition with smallmouth bass would be most pronounced during energetically-stressful summer periods of high water temperatures, reduced stream flows, and decreased prey availability. The effects of smallmouth bass on native fish species are most significant when systems are less biologically and physically complex. In most eastern rivers inhabited by Atlantic salmon, both conditions are common: there are few fish species, and, habitats for smallmouth bass would be slow, deeper waters. Consequently, a significant degree of interaction between Atlantic salmon and smallmouth bass is predicted to occur in eastern rivers.

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