Zebra mussels (Dreissena polymorpha) on the move: Recent detections in Quebec and New Brunswick and implications for spread in eastern Canada

Although zebra mussels (Dreissena polymorpha) have been established in the Great Lakes-St. Lawrence River system for over 30 years, recent detections in Quebec’s inland lakes signal a concerning acceleration in secondary spread. In 2022, the species was detected in Lake Témiscouata, then the easternmost confirmed occurrence in North America. Within three years, mean lake-wide densities increased from < 30 mussels m⁻² to > 5,500 mussels m⁻², exceeding 30,000 mussels m⁻² at one site. A coordinated response was initiated to monitor expansion across eastern Canada. By 2024 they had spread into New Brunswick, with an established population in Edmundston and presence in Mactaquac. In Quebec, surveys detected mussels in four additional lakes, with suspected presence in six others. Detection proved difficult despite multiple sampling methods (i.e., eDNA, veligers, visual surveys). Boater surveys indicated that overland transport of recreational watercraft may facilitate secondary spread, an important concern given the high suitability of many eastern Canadian waterbodies for colonization. Newly infested sites may act as stepping stones for further expansion, highlighting the need for effective prevention strategies.