Date Published: June 27, 2017
Publisher: Public Library of Science
Author(s): Daniel P. Zielinski, Peter W. Sorensen, Craig A Radford.
Behavioral responses of silver carp (Hypopthalmichthys molitrix), bighead carp (H. nobilis), and common carp (Cyprinus carpio) to a complex, broadband sound were tested in the absence of visual cues to determine whether these species are negatively phonotaxic and the roles that sound pressure and particle motion might play mediating this response. In a dark featureless square enclosure, groups of 3 fish were tracked and the distance of each fish from speakers and their swimming trajectories relative to sound pressure and particle acceleration were analyzed before, and then while an outboard motor sound was played. All three species exhibited negative phonotaxis during the first two exposures after which they ceased responding. The median percent time fish spent near the active speaker for the first two trials decreased from 7.0% to 1.3% for silver carp, 7.9% to 1.1% for bighead carp, and 9.5% to 3% for common carp. Notably, when close to the active speaker fish swam away from the source and maintained a nearly perfect 0° orientation to the axes of particle acceleration. Fish did not enter sound fields greater than 140 dB (ref. 1 μPa). These results demonstrate that carp avoid complex sounds in darkness and while initial responses may be informed by sound pressure, sustained oriented avoidance behavior is likely mediated by particle motion. This understanding of how invasive carp use particle motion to guide avoidance could be used to design new acoustic deterrents to divert them in dark, turbid river waters.
Acoustic energy propagates through water as a traveling pressure wave with accompanying particle motion and is used by fish to mediate numerous life cycle functions including migration, communication, prey detection, and avoidance. To use sound efficiently, fish need to be able to both distinguish signals above background noise and then use this information to orient, or move in a directed fashion. While sound pressure, a scalar quantity, cannot provide fish with any immediate directional information on its own, particle motion, a vector quantity, is inherently directional and could. However, although the capacity for directional hearing in fish is relatively well described [1–4], only a handful of experimental studies have tested how it is mediated. These studies have shown that both sound pressure and particle motion can play very different, and independent roles in the oriented movement of fish seeking a sound source (positive phonotaxis) [5–9]. In contrast, although sound induced repulsion (negative phonotaxis) has also been described in a few species of fish, the sensory cues responsible for these responses have not yet been explicitly described so are unknown [10–14]. How fish might orient toward and away from sound sources has both basic implications for understanding how fish might use sound to meet their ecological needs as well as strong implications for how sound might be used to either attract or repel fishes of concern in the natural world. The present study characterized the orientation mechanisms used by three species of invasive carp as they avoided a sound source and the two sensory fields it created in the absence of visual cues.
This study found that silver, bighead, and common carp exhibited negative phonotaxis when exposed to the sound of a complex, broadband sound in a dark, featureless environment but that this response habituated. Avoidance behaviors were strongly and consistently characterized by individual fish swimming along a curvilinear trajectory when sound pressure reached about 130–140 dB (ref. 1 μPa) (at a distance of 30 cm) from a hidden speaker and then swimming parallel to the axes of local particle acceleration before leaving the sound field. All carp followed extremely consistent trajectories with a nearly perfect 0° orientation to the axes of local particle acceleration. All three carp species showed very similar behaviors. Given the comparable hearing abilities of these species, it is not surprising that their avoidance responses and orientation strategies were similar. These results suggest that while pressure sensitive fishes such as carp and other ostariophysians may become aware of aversive sound by detecting changes in sound pressure, they likely then use particle motion to orient avoidance responses in the absence of visual landmarks. Presumably this would be the case in turbid river waters.
Behavioral responses of silver, bighead, and common carp to a stationary complex sound were observed to characterize whether and how these species avoid sound in the absence of visual cues. Plotting showed all three species exhibit an oriented avoidance response which habituated after two trials. Swimming trajectories correlated strongly with the axes of local particle motion by trending towards 0°. Fish also turned away from the speaker at a distance of 20–30 cm where the sound pressure level was above 140 dB (ref. 1 μPa). Future studies should examine how carp accomplish this type of orientation, how common it might be, and whether and how other sensory cues might enhance orientation capability. The findings of this study nevertheless suggest that acoustic deterrents could be used to control invasive carp, but that field testing is needed to address issues including range, the roles of other sensory stimuli in different environments, habituation, and non-target effects, especially in low light environments. Different sounds might also be considered.