Use of electric and bubble barriers to limit the movement of Eurasian ruffe (Gymnocephalus cernuus)

Abstract

Eurasian ruffe (Gymnocephalus cernuus) is an aquatic invasive species accidentally introduced via ballast water to the Great Lakes in the mid-1980s. Fish barrier technology is being studied to stop the spread of invasive fish species such as ruffe. Electrical barriers have been constructed, most notably in the Chicago Sanitary and Ship Canal, to prevent non-indigenous species such as ruffe from spreading into areas where they are currently absent. Information on the response of an invasive fish to barriers can help managers determine strategies to prevent the spread of these species via artificial waterways. In this laboratory study electrical barriers were set up to determine effectiveness of four electrical settings for repelling Eurasian ruffe measuring 10 cm or more in length. In separate tests, airbubble curtains with two bubble sizes and densities were created to test this type of barrier in blocking movement of ruffe less than 10 cm in length. The most effective electrical settings found (5 ms, 6 Hz) repelled only about half of the attempted passes. When ruffe were offered food or shelter on the opposite side of the electrical barrier, neither food-starved nor shelter-deprived ruffe made significantly more attempts to cross the barrier. Ruffe were significantly repelled by all air-bubble curtains, but a large proportion of passes (4.5 passes per fish on average in the treatments) were still observed. Electrical barrier settings and air-bubble curtains used in this study were found ineffective at completely blocking the movement, but somewhat effective at inhibiting the passage of ruffe.