Sonar technology and underwater imagery analysis can enhance invasive Dreissena distribution assessment in large rivers

Dreissena spp. are aggressive invaders of many waterbodies worldwide. However, the accurate assessment of their spatial distribution in large rivers is difficult using traditional sampling techniques such as Ponar grabs or SCUBA diving. The aim of this study was to use sonar technologies and underwater imagery (videos, still images) in tandem with traditional Ponar sampling to predict Dreissena presence, and produce a habitat suitability map to enhance our understanding of its spatial distribution in the lower Niagara River, New York, USA. Geo-referenced maps of environmental variables were generated using three sonar technologies: side scan sonar, multibeam sonar, and an Acoustic Doppler Current Profiler. Dreissena presence/absence was determined at 102 sites along a 10 km stretch using Ponar grabs supplemented by an underwater imagery. Substrate and near-bottom flow were the most important variables affecting Dreissena distribution. Habitats with coarse substrate and near-bottom flow of 0.6–0.80 m/s were predicted to be most often occupied. The habitat suitability model indicates that almost 90% of the stream bed in the river can be considered highly- or moderately suitable habitat. Our results demonstrate that supplementing traditional sampling with sonar technologies and underwater imagery can greatly improve Dreissena distribution assessment at the ecosystem scale.