Oyster toadfish (Opsanus tau) boatwhistle call detection and patterns within a large-scale oyster restoration site

Abstract

During May 2015, passive acoustic recorders were deployed at eight subtidal oyster reefs within Harris Creek Oyster Sanctuary in Chesapeake Bay, Maryland USA. These sites were selected to represent both restored and unrestored habitats having a range of oyster densities. Throughout the survey, the soundscape within Harris Creek was dominated by the boatwhistle calls of the oyster toadfish, Opsanus tau. A novel, multi-kernel spectral correlation approach was developed to automatically detect these boatwhistle calls using their two lowest harmonic bands. The results provided quantitative information on how call rate and call frequency varied in space and time. Toadfish boatwhistle fundamental frequency ranged from 140 Hz to 260 Hz and was well correlated (r = 0.94) with changes in water temperature, with the fundamental frequency increasing by ~11 Hz for every 1°C increase in temperature. The boatwhistle call rate increased from just a few calls per minute at the start of monitoring on May 7th to ~100 calls/min on May 10th and remained elevated throughout the survey. As male toadfish are known to generate boatwhistles to attract mates, this rapid increase in call rate was interpreted to mark the onset of spring spawning behavior. Call rate was not modulated by water temperature, but showed a consistent diurnal pattern, with a sharp decrease in rate just before sunrise and a peak just after sunset. There was a significant difference in call rate between restored and unrestored reefs, with restored sites having nearly twice the call rate as unrestored sites. This work highlights the benefits of using automated detection techniques that provide quantitative information on species-specific call characteristics and patterns. This type of non-invasive acoustic monitoring provides long-term, semi-continuous information on animal behavior and abundance, and operates effectively in settings that are otherwise difficult to sample.

Acoustic communication in fishes: Temperature plays a role

“…No such correlations to temperature are described at other locations. Instead, Monczak, Berry, Kehrer, and Montie ()and Ricci, Bohnenstiehl, Eggleston, Kellogg, and Lyon () mention seasonal, lunar and daily calling rhythms as well as differences between recording locations (Montie et al., ) (Table ). Amorim, Vasconcellos, Marques, and Almada () observe seasonal patterns of emission of different sound types (croaks, grunt trains, boatwhistles) in Lusitanian toadfish ( Halobatrachus didactylus , Batrachoididae); these patterns are significantly correlated to the temperature in the Tagus estuary, Portugal.…”

“…While many studies revealed a relationship between calling activity/sound characteristics and temperature, several studies failed to report such a relationship (cod—Brawn, ; oyster toadfish—Monczak et al., ; Ricci et al., ; Lusitanian toadfish—Amorim et al., ). A drop in the calling activity of the Lusitanian toadfish in late July despite high temperatures (Figure b) most likely reflects seasonal androgen changes according to the authors (the effects of sex steroids on fish acoustic communication are reviewed in Maruska & Sisneros, ).…”

“…While many studies revealed a relationship between calling activity/sound characteristics and temperature, several studies failed to report such a relationship (cod-Brawn, 1961; oyster toadfish- Monczak et al, 2017;Ricci et al, 2017;Lusitanian toadfish-Amorim et al, 2006). Maruska & Sisneros, 2015).…”

Localizing individual soniferous fish using passive acoustic monitoring

“…However, at least three hydrophone are needed to pinpoint exact source location because multiple TOAD bearings can be calculated and intersected (Watkins and Schevill, 1972;Spiesberger and Fristrup, 1990;Møhl et al, 2001;Wahlberg et al, 2001). Hydrophone arrays potentially can determine fish distributions that could not be obtained with single hydrophone recordings, but require a higher level of sophistication for setting up, operating and analyzing the data (Ricci et al, 2017).…”

“…In comparison, fixed and towed hydrophones are now a popular tool for localizing the spatial and temporal nature of spawning populations of fishes that actively produce advertisement calls to attract mates (Rice and Bass, 2009;Locascio and Mann, 2011). This type of non-invasive monitoring provides long term, continuous information on animal behavior and abundance, and calling measurements in settings that are otherwise difficult to sample (Ricci et al, 2017).…”