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.
Highlights
Evaluating ecosystem services provided by restored oyster reefs is crucial in determining restoration success
The results provided quantitative information on how call rate and call frequency varied in space and time
The eight sites utilized for this study are part of a broader effort to assess the ecosystem services provided by oyster reef restoration in Harris Creek (Fig 1)
Summary
Evaluating ecosystem services provided by restored oyster reefs is crucial in determining restoration success. Passive acoustics is becoming more widely used in marine environments as a way to monitor these subtidal habitats This approach assumes that the sounds produced by one or more species can be used to track their relative abundance and/or changes in behavior in space and time. A novel multi-kernel spectral correlation approach is used to identify toadfish boatwhistles This pattern matching technique has some potential advantages over other automated techniques, such as traditional acoustic, band-limited energy detectors [5], in that 1) the presence of multiple harmonics and swept character of the signal may be considered in evaluating the detection, and 2) the fundamental frequency of each individual call can be readily returned along with its time and score
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