Effects of vessel sound on oyster toadfish Opsanus tau calling behavior

In coastal waters, anthropogenic activity and its associated sound have been shown to negatively impact aquatic taxa that rely on sound signaling and reception for navigation, prey location, and intraspecific communication. The oyster toadfish Opsanus tau depends on acoustic communication for reproductive success, as males produce ‘boatwhistle’ calls to attract females to their nesting sites. However, it is unknown if in situ vessel sound impacts intraspecific communication in this species. Passive acoustic monitoring using a 4-hydrophone linear array was conducted in Eel Pond, a small harbor in Woods Hole, MA, USA, to monitor the calling behavior of male toadfish. The number of calls pre- and post-exposure to vessel sound was compared. Individual toadfish were localized, and their approximate sound level exposure was predicted using sound mapping. Following exposure to vessel sound, the number of calls significantly decreased compared to the number of calls pre-exposure, with vessel sound overlapping the frequency range of male toadfish boatwhistles. This study provides support that anthropogenic sound can negatively affect intraspecific communication and suggests that in situ vessel sound has the ability to mask boatwhistles and change the calling behavior of male toadfish. Masking could lead to a reduction in intraspecific communication and lower reproductive efficiency within the Eel Pond toadfish population.

Sound characterization and fine-scale spatial mapping of an estuarine soundscape in the southeastern USA

Estuaries are areas known for biological diversity, and their soundscapes reflect the acoustic signals used by organisms to communicate, defend territories, reproduce, and forage in an environment that has limited visibility. These biological sounds may be rhythmic in nature, spatially heterogeneous, and can provide information on habitat quality. The goal of our study was to investigate the temporal and spatial variability of sounds in Chechessee Creek (Stns CC1 and CC2) and an adjacent saltwater impoundment (Great Salt Pond, GSP) in South Carolina, USA, from April to November 2016. Fixed recording platforms revealed that sound pressure levels (SPLs) were significantly higher in CC1 and CC2 compared to GSP. We detected some biological sounds in GSP (snapping shrimp genera Alpheus and Synalpheus, silver perch Bairdiella chrysoura, oyster toadfish Opsanus tau, spotted seatrout Cynoscion nebulosus, Atlantic croaker Micropogonias undulatus, and American alligator Alligator mississippiensis); however, biological sound was much more prevalent in CC1 and CC2. In Chechessee Creek, snapping shrimp, oyster toadfish, and spotted seatrout sounds followed distinct temporal rhythms. Using these data, we conducted spatial passive acoustic surveys in Chechessee Creek. We discovered elevated high frequency SPLs (representing snapping shrimp acoustic activity) near an anti-erosion wall, as well as increased low frequency SPLs (indicating spotted seatrout spawning aggregations) near the anti-erosion wall and at the mouth of Chechessee Creek. This study has demonstrated the utility of combining stationary and mobile recording platforms to detect acoustic hotspots of biological sounds.

Wall structure and material properties cause viscous damping of swimbladder sounds in the oyster toadfish Opsanus tau

Despite rapid damping, fish swimbladders have been modelled as underwater resonant bubbles. Recent data suggest that swimbladders of sound-producing fishes use a forced rather than a resonant response to produce sound. The reason for this discrepancy has not been formally addressed, and we demonstrate, for the first time, that the structure of the swimbladder wall will affect vibratory behaviour. Using the oyster toadfish Opsanus tau , we find regional differences in bladder thickness, directionality of collagen layers (anisotropic bladder wall structure), material properties that differ between circular and longitudinal directions (stress, strain and Young's modulus), high water content (80%) of the bladder wall and a 300-fold increase in the modulus of dried tissue. Therefore, the swimbladder wall is a viscoelastic structure that serves to damp vibrations and impart directionality, preventing the expression of resonance.