While everyone knows that marine mammals are well known sound producers, did you know that many fish species also produce and use sound to sense their environment? Marine environments are teeming with underwater sounds from animals, human activities (shipping, costal development, oil and gas exploration etc.), and geological processes such as rain, wind, and water flow. The combination of the sounds, called a soundscape, can be used to study the ecology of animals that produce, hear, or respond to sound. Grouper Moon Project collaborators recently published two scientific papers highlighting research on the soundscape of the spawning aggregation at the west end of Little Cayman.

During the winter months, the Little Cayman research site is full of sounds produced by aggregating Nassau Grouper, along with other species that use the area for spawning, including Red Hind, Black Grouper, and Yellowfin Grouper, as well as other sound producers like squirrelfish and snapping shrimp. From 2015 to 2107, the Grouper Moon Project collaborated with researchers Katherine Wilson and Ana Širović (previously at Scripps Institution of Oceanography) to deploy an array of hydrophones (underwater microphones) at the Nassau Grouper spawning aggregation site in order to 1) localize the sounds produced by aggregating Nassau Grouper to examine the dynamics of the aggregation overnight and during the periods that are not monitored by our Grouper Moon research team, and 2) analyze the soundscape and the characteristics of all the known sounds produced by grouper at this multi-species spawning aggregation to study the sound communication of these fishes. The latter objective included localizing these sounds to measure sound levels and determine the distance over which fishes can hear each other. 

Results of the three-year study included a detailed analysis of the characteristics of the sounds produced by four grouper species (Nassau, Black, Yellowfin, and Red Hind), as well as daily patterns of sound production. The pitch of Red Hind sounds was uniquely different than that of the other three species, possibly to distinguish the species in the multi-species grouper chorus at the aggregation site. The team also identified distinctive sound patterns for Yellowfin Grouper, which aggregate and spawn by the hundreds just north of the Nassau Grouper aggregation. They also developed a method to accurately localize grouper sounds using triangulation within the array of hydrophones; similar to those used by GPS recievers based on satellite signals. Using a hexagon array of hydrophones, the researchers documented three areas of high sound production by Red Hind within the array, likely the product of male spawning territories. Nassau Grouper sounds were typically produced in the sandy areas between coral formations, with calling ceasing in the area when spawning occurred off the shelf around dusk.

The results were published in two recent scientific publications:

Wilson, KC, BX Semmens, CV Pattengill-Semmens, C McCoy, A Širović. 2020. Potential for grouper acoustic competition and partitioning at a multispecies spawning site in Little Cayman, Cayman Islands. Marine Ecology Progress Series, 634: 127-146. More Details

Wilson, KC, BX Semmens, SR Gittings, CV Pattengill-Semmens and A Širović. 2019. Development and evaluation of a passive acoustic localization method to monitor fish spawning aggregations and measure source levels. OCEANS 2019 MTS/IEEE SEATTLE, Seattle, WA, USA, 2019, pp. 1-7. More Details

A full list of scientific papers that have resulted from the Grouper Moon Project since its inception in 2001 can be found here: https://www.REEF.org/grouper-moon-project-publications.