Evaluating the ability of sound, an air curtain, and high-intensity light, both alone and together, to deter bighead and common carps

Abstract

There is an urgent need to develop deterrent systems to impede the spread of invasive silver carp (Hypophthalmichthys molitrix), bighead carp (H. nobilis) and common carp (Cyprinus carpio). Sound, light and air curtains have all been shown to deter carp; however, no study to date had systematically compared the responses of carp to each of these deterrents. The overarching goal of this dissertation was to determine whether and how sound, light and air might be used, either on their own or together, to impede the movement of invasive carps while having minimal effects on other fishes. Four laboratory and one field study were conducted. When tested in a dimly-lit laboratory flume, bighead and common carps were more deterred by a 20-2000 Hz cyclic sound than a broad-spectrum outboard-motor sound (10-10,000 Hz) (p < 0.05). Further, coupling these sounds with an air curtain enhanced their ability to block fish passage in the laboratory (> 97% blocked by the coupled cyclic sound and air curtain). A second laboratory experiment showed that lake sturgeon (Acipenser fulvescens) and brown trout (Salmo trutta) were less deterred by the broad-spectrum outboard-motor sound than either bighead or common carps. However, none of these fishes were deterred by this sound when frequencies lower than 1000 Hz were removed. Another laboratory experiment showed that constantly-lit and strobing lights blocked 80% of bighead carp in a dimly-lit flume, while a constant light worked better than a strobing light in a well-lit background (80% and 33% blocked, respectively) (p < 0.05). Largemouth bass were similarly repelled by light in a dimly-lit flume, but attracted to the light in a well-lit environment. The last laboratory experiment examined the response of bighead carp to different combinations of light, sound and air curtains. Greater than 90% blockage for carp was observed when strobing light (but not constant light) was combined with sound and/or an air curtain. A final field study, conducted in a lock chamber, found that although adult common carp were initially deterred by the outboard-motor sound in the lock, they habituated after single exposure; whereas in the laboratory, habituation occurred only after three exposures. Several factors, including differences between sound fields observed in the laboratory and field, may have been responsible. Together, these experiments suggest broad-spectrum sounds are well suited to block carp, especially if they are coupled with an air curtain and strobing light. Field tests are needed to fully evaluate their potential.