Newswise — Just as the sun begins to set, for just a couple of months, hundreds to thousands of groupers gather at their favorite hangouts along the shelf breaks in the southeast United States, Gulf of Mexico and the Caribbean Basin to spawn – and luckily they’re pretty vocal about it, providing vital data on their reproductive behaviors as well as their favorite mating spots.

A team of scientists from Florida Atlantic University’s Harbor Branch Oceanographic Institute and the University of the Virgin Islands’ Center for Marine and Environmental Studies have developed a novel sensing approach using a water drone or robot to listen in on groupers mating. The sensor package and grouper acoustic recognition computer algorithms, developed by FAU’s Harbor Branch, have been installed on a Liquid Robotics Wave Glider, which is the first readily available ocean drone of its kind. Spawning season for many commercially important groupers including the Nassau, Warsaw, black, yellowfin and red hind groupers are concentrated within a couple of months each year. The concentrated nature and short duration of their spawning season makes them especially vulnerable to heavy fishing and as a result, many of the spawning aggregations have disappeared or shrunk in the abundance of spawners. Overfishing at these sites can reduce grouper populations significantly, and findings from this study are helping to inform fisheries managers where protective measures are necessary.

“Each grouper species is identified through the unique sounds that are produced by muscles contracting against their swim bladder,” said Laurent Cherubin, Ph.D., associate research professor at FAU’s Harbor Branch. “These sounds can best be described like that of a boom on a beating drum. Often, the fish make these sounds in territorial defense or during courtship of females ready to spawn eggs.”

The new robotic sensing technology is assisting researchers with important conservation measures and making data collection easier and less costly than ever before. The purchase of the Harbor Branch wave glider and their engineering efforts to develop and test the sensor package was funded by a generous grant from the Harbor Branch Oceanographic Institute Foundation (HBOIF).

The surface float of the wave glider, which is approximately 10 feet long, has a solar panel, cell phone and satellite communications antenna, GPS receiver and a weather station that monitors atmospheric conditions like wind speed, humidity and temperature. The glider can record sounds within a 1,000-meter distance under optimal conditions, and transmits real-time data to shore. Because the glider is solar powered and uses wave energy and not a motor to move around, it doesn’t make much noise, making it minimally invasive to fish. It also can survey huge areas of the seafloor and potentially discover new grouper spawning sites. The most recent wave glider mission occurred in April in the U.S. Virgin Islands where sounds were recorded around three known grouper spawning sites. The wave glider also surveyed more than 100 kilometers of deep shelf-edge reef south of St. Thomas and St. John islands as well as Vieques island off Puerto Rico’s eastern coast.

The researchers set out to better understand the relationship between vocalization frequency and fish abundances. Using an underwater listening device, or hydrophone, and a special software program to detect the very distinct sounds that groupers make, Cherubin and his colleagues keenly listened for reproductive activities at these sites in the Virgin Islands. They followed the wave glider in a boat during the day when weather conditions permitted, while it roved alone during the night. Underwater visual surveys with video cameras and laser calipers were used to estimate the density and length of the fish at the study sites, and will help to calibrate the acoustic data and eventually estimate the number of fish.

Since the wave glider transmits acoustic data in real-time, divers can be deployed to verify potential spawning sites as soon as the signals are detected at the various locations. Field testing the application of this technology in the Virgin Islands was funded by a Saltonstall-Kennedy grant from the National Oceanic and Atmospheric Administration (NOAA).

“We only know about 25 percent of the sounds that are made by organisms in the ocean,” said Cherubin. “Once we have created a library of these different calls, we can use this type of technology to monitor the ocean’s health and biodiversity. And, our grouper-listening glider is a very good start.”

In addition to Cherubin, members of the FAU Harbor Branch research team are Fraser Dalgleish, Ph.D., associate research professor; Anni Vuorenkoski-Dalgleish, Ph.D., assistant research professor; and Bing Ouyang, Ph.D., assistant research professor; in collaboration with Richard Nemeth, Ph.D., research professor of zoology and marine biology at the University of the Virgin Islands, and Michelle Schärer-Umpierre, Ph.D., research scientist from the University of Puerto-Rico Mayaguez.

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About Harbor Branch Oceanographic Institute: Founded in 1971, Harbor Branch Oceanographic Institute at Florida Atlantic University is a research community of marine scientists, engineers, educators and other professionals focused on Ocean Science for a Better World. The institute drives innovation in ocean engineering, at-sea operations, drug discovery and biotechnology from the oceans, coastal ecology and conservation, marine mammal research and conservation, aquaculture, ocean observing systems and marine education. For more information, visit

About Florida Atlantic University: Florida Atlantic University, established in 1961, officially opened its doors in 1964 as the fifth public university in Florida. Today, the University, with an annual economic impact of $6.3 billion, serves more than 30,000 undergraduate and graduate students at sites throughout its six-county service region in southeast Florida. FAU’s world-class teaching and research faculty serves students through 10 colleges: the Dorothy F. Schmidt College of Arts and Letters, the College of Business, the College for Design and Social Inquiry, the College of Education, the College of Engineering and Computer Science, the Graduate College, the Harriet L. Wilkes Honors College, the Charles E. Schmidt College of Medicine, the Christine E. Lynn College of Nursing and the Charles E. Schmidt College of Science. FAU is ranked as a High Research Activity institution by the Carnegie Foundation for the Advancement of Teaching. The University is placing special focus on the rapid development of critical areas that form the basis of its strategic plan: Healthy aging, biotech, coastal and marine issues, neuroscience, regenerative medicine, informatics, lifespan and the environment. These areas provide opportunities for faculty and students to build upon FAU’s existing strengths in research and scholarship. For more information, visit

About Harbor Branch Oceanographic Institute Foundation:The mission of Harbor Branch Oceanographic Institute Foundation is to support Harbor Branch Oceanographic Institute, a research institute of Florida Atlantic University. Harbor Branch Oceanographic Institute Foundation (HBOIF) supports marine science and engineering research and education by funding HBOI-FAU efforts to advance understanding of oceans and coastal areas through exploration and scientific inquiry. HBOIF is a 501(c) 3 organization and a Direct-Support Organization (DSO) of Florida Atlantic University benefiting Harbor Branch Oceanographic Institute. For more information, visit