High-intensity light blocks bighead carp in a laboratory flume

There is a critical need to identify and develop behavioral deterrents that impede the spread of invasive Bigheaded Carp (Hypophthalmichthys spp.) through waterways in North America. High-intensity light has significant advantages over other behavior deterrents because it can be relatively inexpensive, easy to deploy and can be used in shallow waterways. Although previous studies have shown that light has the potential to guide and block the passage of fishes, the efficacy of light has also been found to be species-and situation-specific, and no study has yet examined how well light works for Bigheaded Carp. The present laboratory study sought to determine whether high-intensity white light might be effective at blocking Bighead Carp (H. nobilis) while having minimal effects on another model fish species. We measured the response of juvenile Bighead Carp and Largemouth Bass (Micropterus salmoides) to three types of high-intensity white light (constant light [0 Hz] and strobing light [5 Hz or 12 Hz]) in both a dark [1 lux] and a dimly-lit [100 lux] laboratory flume. High-intensity light consistently blocked at least 74% of Bighead Carp in a dark flume, with strobing and constant light having equivalent effects (p > 0.05). In contrast, a constant light (80%) was more effective than a 5 Hz strobing light (33%) in a dimly-lit flume (p < 0.05). While Largemouth Bass were also blocked by constant light (63%) in a dark flume, both a 5 Hz (82%) and 12 Hz (88%) strobing light were more effective (p < 0.05). When tested in a dimly-lit flume, Largemouth Bass were not blocked by either the constant light or a 5 Hz strobing light (p > 0.05). Taken together, our experiments demonstrate that responses to light can be species-and situation-specific, and that high-intensity constant light has particular promise to block Bighead Carp in both dark and dimly-lit environments without strongly blocking bass. Light might be especially useful in shallow, clear waters that cannot be blocked by other means.