Controlling invasive carp ichthyoplankton dispersion using a streamwise-oriented bubble screen: A proof-of-concept validation in a laboratory flume

Recent evidence of invasive grass carp ( Ctenopharyngodon idella ) reproducing in tributaries to the Laurentian Great Lakes has highlighted the need for control efforts targeting multiple life stages. Initial attempts to control dispersal of downstream-drifting invasive carp ichthyoplankton (i.e., eggs and larvae) using an oblique bubble screen (OBS) revealed that nearly neutrally buoyant grass carp eggs and larvae enter helical-like motions driven by the OBS, preventing aggregation within a single capture location. To improve dispersal control methods for such early-life stage carp, we used a laboratory flume to investigate the efficacy of a streamwise-oriented bubble screen to facilitate their near-bank capture. Five early-life stages of grass carp were tested: live water-hardened eggs, pre- and post-gas bladder inflation larvae, dead larvae, and dead eggs (preserved in formalin solution and later rehydrated). A range of mean channel velocities (0.23, 0.45, and 0.75 m/s) was tested for all drifters. Capture percentages increased with increasing airflow. Preserved eggs, for instance, showed capture percentages up to 95 %, 87 %, and 69 % at low, medium, and high water velocities for the highest airflow rate, respectively, in contrast with the lower than 5 % capture measured for zero airflow cases. Symmetric secondary flow structures on either side of the bubble screen induced helical trajectories of drifters and facilitated their capture in net-arrays along each wall. Velocity data were used to estimate helical recirculation timescales, enabling calculation of optimal bubble diffuser and net-array lengths for desired capture rates. This study provides useful guidance for the design of effective systems to control dispersal of downstream-drifting ichthyoplankton of invasive carp in streams.