Grouper source levels and aggregation dynamics inferred from passive acoustic localization at a multispecies spawning site

Abstract

Red hind ( Epinephelus guttatus) and Nassau (E. striatus), black (Mycteroperca bonaci), and yellowfin grouper (M. venenosa) form spawning aggregations in Little Cayman, Cayman Islands and produce sound during these aggregations. Continuous observation of these aggregations is challenging because traditional methods are limited in time and space. Passive acoustic localization can overcome some of these challenges in case of sound-producing species, allowing observations over long durations and fine spatial scales. A hydrophone array was deployed in February 2017 over a nine-day period that included Nassau grouper spawning. Hyperbolic localization was used to find positions of the grouper producing calls during this time, to measure call source levels, and evaluate spatiotemporal aspects of calling. During the days Nassau grouper spawned, calling peaked after sunset from 19:00 to 21:00. Similarly, when red hind calls were most abundant, they peaked from 16:00 to 21:00. The mean peak-to-peak source levels of calls was 143.7 dB for yellowfin grouper and 154.9 dB for Nassau grouper (re: 1 μPa at 1 m for 70 to 170 Hz). The measured source levels can be used to determine communication and detection ranges and develop passive acoustic density estimation methods for these fishes.