Friday, September 19, 2025

Decoding a decade of grouper grunts unlocks spawning secrets, shifts

Florida Atlantic University

Red Hind Groupers — image:
A group of red hind groupers, which produce sounds associated with courtship, territoriality or mating.
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Credit: FAU Harbor Branch

More than a decade of acoustic recordings of grouper grunts are providing new insight into how sound can be used to monitor and manage vulnerable fish populations. The research by Florida Atlantic University’s Harbor Branch Oceanographic Institute focused on the red hind (Epinephelus guttatus), a commercially important Caribbean grouper species.

Red hind are protogynous hermaphrodites, starting life as females and later becoming males. Each winter, they travel more than 30 kilometers to offshore sites to spawn under the full moon in large gatherings. Males use rhythmic, low-frequency sounds to attract mates and to defend territory. This predictable behavior makes them especially vulnerable to overfishing during spawning season.

Rather than traditional survey methods, FAU Harbor Branch and FAU College of Engineering and Computer Science researchers, in collaboration with HJR Reefscaping, the University of the Virgin Islands, and the University of Puerto Rico, turned to passive acoustic monitoring. This technique enables continuous, long-term monitoring of reproductive behavior, even in remote or hard-to-access areas, without disrupting the animals or their habitat.

To examine how red hind reproductive behavior has changed over time, researchers analyzed more than 2,000 hours of underwater recordings from a single spawning site off Puerto Rico’s west coast, continuously monitored since 2007.

Unlike most acoustic studies that track general sound levels, this research focused on specific mating calls tied to distinct behaviors. Red hind produce two primary sound types – one for courtship and another for territorial defense. Tracking these sounds over time allowed researchers to detect subtle shifts in spawning behavior and population dynamics.

The result, published in the ICES Journal of Marine Science, is one of the most extensive and uninterrupted acoustic datasets ever assembled for a reef fish species.

The analysis confirmed a consistent seasonal pattern in red hind spawning activity, closely aligned with lunar cycles. However, one of the most striking findings was a notable shift in the balance of call types over the 12-year period. Between 2011 and 2017, calls linked to courtship were more common. But starting in 2018, calls linked to competition and territorial behavior became dominant – nearly tripling over the study period.

“This shift could indicate changes in the population, such as an increase in the number of older or more dominant males, changes in sex ratios, or even a shift in the core spawning area,” said Laurent Chérubin, Ph.D., lead author and a research professor at FAU Harbor Branch.

Researchers also observed more frequent and multiple peaks in sound production in recent years, suggesting that spawning may now be spread over more days in each lunar cycle than in the past. These changes could be responses to environmental or population shifts.

Importantly, the study shows that passive acoustic monitoring can be a powerful tool for tracking reproductive behavior over time and detecting early signs of population or behavioral change – information that is critical for managing and conserving red hind and similar reef fish species.

“What’s remarkable is that even a single underwater microphone can reveal so much about fish populations,” said Chérubin. “With consistent long-term monitoring, we can pick up early warning signs – like shifts in spawning behavior or population stress – and give resource managers the information they need to adapt conservation strategies before it’s too late.”

At the center of the analysis was an advanced machine-learning tool called FADAR (fish acoustic detection algorithm research). This custom-built acoustic classifier allowed the team to detect and distinguish between different types of mating calls with extraordinary speed and accuracy.

“This study shows how much we can learn simply by listening,” said Chérubin. “Thanks to FADAR, we processed 12 years of acoustic data in weeks – uncovering patterns that would have taken years to find. It’s a game changer for monitoring and managing reef fish like red hind.”

By using advanced acoustic technology at a single site, researchers can detect shifts in reproductive behavior and population dynamics remotely, providing crucial early warning signs of stress. This kind of data is essential for resource managers developing strategies to protect spawning grounds and sustain fisheries.

“As passive acoustics advances, it’s transforming our understanding of the ocean,” said Chérubin. “By tuning in to underwater soundscapes, we’re discovering not just when and where fish spawn, but how those patterns change over time – offering vital insights into the health of marine ecosystems.”

Study co-authors are Caroline Woodward, United States Geological Survey; Michelle Schärer-Umpierre, Ph.D., associate researcher, HJR Reefscaping and the University of Puerto Rico-Mayaguez; Richard S. Nemeth, Ph.D., research professor, Center for Marine and Environmental Studies, University of the Virgin Islands; Richard Appeldoorn, Ph.D., a faculty member; and Evan Tuhoy, a Ph.D. candidate, both within the Department of Marine Sciences, University of Puerto Rico; and Ali K. Ibrahim, Ph.D., a research engineer in FAU’s Department of Electrical Engineering and Computer Science.

- FAU -

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 www.fau.edu/hboi.

About Florida Atlantic University:

Florida Atlantic University serves more than 32,000 undergraduate and graduate students across six campuses located along the Southeast Florida coast. It is one of only 21 institutions in the country designated by the Carnegie Classification of Institutions of Higher Education as an “R1: Very High Research Spending and Doctorate Production” university and an “Opportunity College and University” for providing greater access to higher education as well as higher earnings for students after graduation. In 2025, Florida Atlantic was nationally recognized as a Top 25 Best-In-Class College and as “one of the country’s most effective engines of upward mobility” by Washington Monthly magazine. Increasingly a first-choice university for students in both Florida and across the nation, Florida Atlantic welcomed its most academically competitive incoming class in the university’s history in Fall 2025. For more information, visit www.fau.edu.

A red hind grouper.
Credit
FAU Harbor Branch

Recording Red Hind Grouper Grunts [VIDEO]

Each winter, red hind groupers gather under the full moon, grunting low-frequency calls to attract mates and defend territory. Researchers used acoustic passive technology to detect their grunts by deploying specialized underwater microphones via the autonomous wave glider, a device they developed themselves.

Audio of Grouper Grunts [AUDIO]

Red hind groupers make low-frequency grunts to attract mates and defend territory.

DOI

10.1093/icesjms/fsaf138

Method of Research

Observational study

Subject of Research

Animals

Article Title

Assessing red hind (Epinephelus guttatus) spawning aggregation changes from long-term relative variations in call types associated with reproductive behaviors

With no prior training, dogs can infer how similar types of toys work, even when they don’t look alike

Cell Press

image:
Gaia with a pile of toys
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Credit: Claudia Fugazza

As infants, humans naturally learn new words and their associations—like the fact that forks are related to bowls because both are used to consume food. In a study publishing in the Cell Press journal Current Biology on September 18, a team of animal behavior experts demonstrate that dogs can categorize objects by function, too. In a series of playful interactions with their owners, a group of Gifted Word Learner (GWL) dogs were able to distinguish between toys used for tugging versus fetching, even when the toys in question didn’t share any obvious physical similarities—and then could remember those categorizations for long periods of time, all with no prior training.

“We discovered that these Gifted Word Learner dogs can extend labels to items that have the same function or that are used in the same way,” says author Claudia Fugazza (@geniusdogchallenge) of Eötvös Loránd University, Budapest, Hungary. It’s like a person calling both a traditional hammer and a rock by the same name, says Fugazza.

“The rock and the hammer look physically different, but they can be used for the same function,” she says. “So now it turns out that these dogs can do the same.”

The studies took place in the dogs’ natural home environments with their human owners. At the beginning, the dogs spent time getting familiar with verbal labels for two functional groups of objects: pull and fetch. Their owners used these words with specific toys and played with them accordingly even though the toys didn’t share any similar physical features.

Next, the dogs were tested to see if they had learned to connect the functional labels to the correct group of toys before playing with more novel toys in the two distinct categories. However, this time, their owners didn’t use the “pull” and “fetch” labels for the dogs.

The team found that the dogs were able to extend the functional labels they’d learned previously to the new toys based on their experience playing with them. In the final test, the dogs showed that they could successfully apply the verbal labels to the toys by either pulling or fetching accordingly, even when their owners hadn’t named them.

“For these new toys, they’ve never heard the name, but they have played either pull or fetch, and so the dog has to choose which toy was used to play which game,” Fugazza says. “This was done in a natural setup, with no extensive training. It's just owners playing for a week with the toys. So, it’s a natural type of interaction.”

The authors note that the dogs’ ability to connect verbal labels to objects based on their functional classifications and apart from the toys’ physical attributes suggests that they form a mental representation of the objects based on their experience with their functions, which they can later recall. These findings provide insight into the evolution of basic skills related to language and their relationship to other cognitive abilities, including memory, the researchers say.

More research is needed to understand the scope and flexibility of dogs’ language categorization abilities. The researchers suggest future studies to explore whether dogs that don’t learn object labels may nevertheless have an ability to classify objects based on their functions.

“We have shown that dogs learn object labels really fast, and they remember them for a long period, even without rehearsing,” Fugazza says. “And I think the way they extend labels also beyond perceptual similarities gives an idea of the breadth of what these labels could be for dogs.”

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Bindi with a pull toy

Caption

Bindi with a pull toy

Credit

Claudia Fugazza

Whisky fetching [VIDEO]

Arya learning assessment test [VIDEO]

This work was supported by National Brain Research Program NAP 3.0 of the Hungarian Academy of Sciences, MTA-ELTE Comparative Ethology Research Group, and TRIXIE.

Current Biology, Fugazza et al. “Dogs extend verbal labels for functional classification of objects” https://www.cell.com/current-biology/fulltext/S0960-9822(25)01079-6

Current Biology (@CurrentBiology), published by Cell Press, is a bimonthly journal that features papers across all areas of biology. Current Biology strives to foster communication across fields of biology, both by publishing important findings of general interest and through highly accessible front matter for non-specialists. Visit: http://www.cell.com/current-biology. To receive Cell Press media alerts, contact press@cell.com.

Journal

Current Biology

DOI

10.1016/j.cub.2025.08.013