Efficacy of oblique bubble screen deterrents on redirecting live eggs and larvae of grass carp (Ctenopharyngodon idella) at different developmental stages
Invasive carp have severely damaged aquatic ecosystems in the USA, particularly in the Mississippi River Basin. Behavioral deterrents have been developed in the last few decades to control population expansion into new ecosystems. However, none of these deterrents are capable of controlling early-life stage carp, which have limited or no mobility during their drifting stage in rivers. Capturing eggs and larvae in large numbers warrants new methods due to their distinct physical and biological properties as well as their lack of behavioral response. We tested a novel method to redirect downstream drifting eggs and larvae for their efficient removal in streams using an oblique bubble screen (OBS) deterrent. We investigated the effects of mean water velocity and airflow rate on redirection of eggs, pre-gas bladder inflation (GBI) larvae, near-GBI larvae, and dead larvae. Although similar OBS configurations had shown high efficacy redirecting plastic spheres (egg surrogates) in previous studies, they underperform redirecting live eggs and larvae. However, distinct patterns were identified for eggs, pre-GBI, near-GBI, and dead larvae. A detailed hydrodynamic analysis showed that eggs closely follow the larger scales of motions created by the OBS, and that larvae can actively respond to turbulence cues. This study yielded new insights into the movement of early-life stage grass carp in a turbulent flow with strong recirculation, and provided important data to improve the design of bubble screen dispersal barriers for invasive carp management and population control.