Goliath grouper 'guards' could serve as undersea sentinels protecting US waters

The Goliath grouper is the king of its domain. Living along reefs and shipwrecks in South Florida waters, the world's largest grouper species does, well, whatever it wants to do.

Being one of the reef culture's largest citizens, the Goliath grouper eats what it wants when it wants. It swims where it wants. It investigates whatever it is curious about.

Checking in at up to 700 pounds affords the Goliath grouper that choice. After all, this fish is so big, not even sharks mess with it.

Anglers who fish the reefs in these waters regularly may encounter one while attempting to reel in a snapper or a cobia. Divers who frequent these spots to spearfish for a fresh dinner also have occasional encounters. Sometimes a curious Goliath grouper decides to try to swipe a speared hogfish perhaps out of curiosity or to express its dominance as the true apex predator of the reef.

Boomer

But what if these giants of the sea had another skill yet to tapped? Researchers working with Florida Atlantic University's Harbor Branch Oceanographic Institute in Fort Pierce may be close to unlocking mysteries in the fish's ability to communicate.

Armed with that knowledge, could the Goliath grouper one day be drafted into service as sentinels for the Navy, Coast Guard and Homeland Security?

"Goliath grouper, like many other species of fish, use their swim bladders to produce sound," said Harbor Branch associate research professor Laurent Chérubin. "It tends to be low frequency — around 60 hertz. The fish produces the sound when it is spawning and sometimes when they are approached by scuba divers."

The sound produced by Goliath groupers has been described by divers as akin to a "sonic boom" underwater.

Listening in

Chérubin said Goliath grouper, and other grouper species, have been observed and recorded using acoustic communication when fighting or staging to fight, too. Chérubin said it has led to the creation of "Grouper Guard," a four-year project led by him to to record and analyze vocalization cues from Goliath grouper in an effort to use the fish as a lookout for enemy undersea activity off the U.S. coast. The program recently received a $5 million research grant from the Defense Advanced Research Projects Agency as part of the Persistent Aquatic Living Sensors program.

Florida Atlantic University's multidisciplinary research team, which includes co-principal investigator assistant research professor Matthew Ajemian and Department of Computer and Electrical Engineering and Computer Science professors Hanqi Zhuang and Nurgun Erdol, will work to better understand the dynamics between bio-physical oceanography, fish ecology and behavior, passive acoustics, computer science, machine learning, field logistics and underwater communications.

Eventually, the effort could lead to a communication network where the giant fish — and one day perhaps other sea creatures — could alert military outfits about enemy movements in U.S. waters.

It sounds like a plot from a Tom Clancy novel. But FAU Harbor Branch executive director James Sullivan said the link is actually possible.

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“The Grouper Guard PALS system being developed by Chérubin and Ajemian's team leverages a naturally dominant and territorial species," he said. "Our researchers will specifically develop knowledge of Goliath grouper response within controlled and simulated ecosystem experiments to develop robust acoustic training data sets."

That will enable scientists to translate the biological responses of the fish into information that can be used by the military, Sullivan added.

Warning

Chérubin said one day, the sea floor near where a Goliath grouper lives may be outfitted with surveillance devices to monitor its behavior. 

“Our non-invasive undersea surveillance and monitoring technologies will be subtly integrated into goliath grouper habitats,” Chérubin said. “An acoustic response will alert authorities to the presence of a potential threat or intruder, or indeed to any object that is suspicious or ‘out of place’ within this species’ usual visual and acoustic landscape.”

The network could augment the Department of Defense's existing hardware-based maritime monitoring system.

Chérubin said presently the research program is working with Goliath grouper found nearshore. Working with Goliath groupers is somewhat involved. Because of overfishing in the 1980s, the species was protected from harvest in Florida state and federal waters in 1990. Once some research protocols are approved, Chérubin said they will be able to learn more about the fish's behavior while working with Mote Marine Laboratory in Sarasota.

It is then Chérubin said his research team hopes to unlock the difference between a sound produced to warn away an intruder and one produced in order to attract a mate. It would be the first research of its kind.

"We want to learn their language, posture, behavior and how they use the space they are in," Chérubin said. "Once we have some in captivity, we will attach sensors to them and expose them to stimuli."

They can then take those signals and learn what they mean.

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“Passive acoustics has been used for more than 60 years in fish biology and fisheries surveys and is being used routinely today to determine habitat use, delineate and monitor spawning areas, and study the behavior of fishes,” said Ajemian. “In addition to defense-related applications, the project provides a tremendous opportunity to delve deeper into the behaviors of Goliath grouper, a species that was previously decimated by overharvest but has experienced considerable recovery in Florida waters.”

To learn more about research efforts underway at Harbor Branch, go to https://www.fau.edu/hboi.