AUTHORS: Josey L. Ridgway, U.S. Geological Survey; Jesse R. Fischer, U.S. Geological Survey; Jessica M. Howell, U.S. Fish and Wildlife Service; John Schulte, Missouri Department of Conservation; Adam C. Jones, U.S. Geological Survey; Jason M. Goeckler, U.S. Fish and Wildlife Service; Robin D. Calfee, U.S. Geological Survey.
ABSTRACT: Invasive Silver Carp (Hypophthalmichthys molitrix) populations can reach extremely high densities and severely affect biodiversity and ecosystem function. There are currently few sampling or monitoring techniques available to natural resource managers that reliably quantify population responses to management actions. Consumer-grade sonar offers a cost-effective approach for mapping distributions and evaluating density before and after intensive control efforts. Recent advancements in consumer-grade technologies have vastly improved resolution and dependability sufficient for fisheries research and management. We developed cost efficient semiautonomous watercraft for surveying fish and aquatic habitats by combining low-cost, consumer-grade technology (i.e., sit-on-top kayaks, electric trolling motors, side-scan sonar). Semiautonomous watercraft are advantageous for surveys of invasive Silver Carp populations because of GPS-guidance capabilities with consistent tracking and speed, quiet propulsion system to minimize fish disturbance, and the potential to deploy multiple survey vessels for increased survey efficiency, while minimizing the effect of fish movements. We used two semiautonomous watercrafts to conduct repeated surveys on a population of Silver Carp in Creve Coeur Lake, St. Louis, Missouri, USA (130-ha oxbow lake of the Missouri River). Surveys were conducted at night (≥1h after sunset) and were 2-h in duration. We used an image-analysis software to automate fish target detection and size estimation to estimate density and biomass. Fish targets in side-scan sonar imagery were apportioned by size using fish community capture data collected using electrified trawl that was conducted approximately one week after seasonal surveys. Bathymetry data were used to convert counts to fish density (number)/volume (m3) and biomass (kg)/volume (m3). Preliminary estimates suggest Silver Carp biomass was over 228,600kg. Repeated surveys will be used to assess variability among estimates and to determine which season is optimal (e.g., limiting fish-boat avoidance) for standardizing future Silver Carp surveys. Final population estimates will assist in establishing harvest objectives for Creve Coeur Lake.
