'Snooping' on Dolphins Reveals Hotspots for Food and Friends

For dolphins, the ocean is a world of sound. Their whistles carry social information, helping them communicate and stay connected, while echolocation - rapid-fire clicks - function like underwater sonar, helping them navigate their surroundings and detect potential prey.

But dolphins aren't the only noise makers. Fish make sounds in the underwater soundscape and so do vessel traffic and other human activities. For dolphins and their prey, the sounds they make may be just as important as the sounds they hear.

By eavesdropping on these cetaceans, researchers from Florida Atlantic University 's Harbor Branch Oceanographic Institute have uncovered new clues about how dolphins navigate and use their underwater world - including evidence suggesting that dolphins themselves may be eavesdropping on their prey and that their prey may be eavesdropping on them.

Using an autonomous wave glider equipped with an acoustic recorder, the team spent two months listening across the East Florida Shelf, capturing a rare glimpse into the acoustic lives of dolphins along Florida's Atlantic coast. Published in the journal PeerJ, the findings reveal distinct patterns in dolphin whistles and echolocation, suggesting dolphins may favor different habitats for socializing and hunting.

Over two months, the wave glider captured nearly 62 hours of underwater sound, with dolphins detected in more than 1,600 recordings. Researchers then compared dolphin whistles and echolocation with environmental conditions, including depth, temperature, salinity, currents, productivity and human-generated noise, revealing not just where dolphins were detected, but what may have shaped their behavior.

Findings reveal that whistle activity, which is primarily associated with social behavior, was more frequently detected in nearshore waters and was influenced by factors including location, water temperature, sound levels and chlorophyll-a concentration. Two prominent areas of predicted whistle activity emerged near St. Augustine and Ponce Inlet, with additional areas near Melbourne Beach and north of Ponce Inlet, suggesting that portions of the nearshore environment may be particularly important for dolphin social activity.

Echolocation told a different story - and offered perhaps the most intriguing clue of all. The rapid-fire clicks were concentrated from Melbourne to Ponce Inlet and offshore toward Long John Reef, where sound-producing fish were also abundant. The overlap suggests dolphins may be using acoustic clues from their prey as they hunt, giving researchers a way to pinpoint potential feeding grounds without ever seeing a dolphin or its prey.

"What we're seeing is a fascinating separation between the acoustic behaviors dolphins use for social life and those they use for finding food," said Greg O'Corry-Crowe, Ph.D., co-author, a research professor at FAU Harbor Branch and a National Geographic Explorer. "The fact that echolocation was associated with sound-producing fish, while whistles were linked to a different set of environmental conditions, suggests dolphins may be responding to their surroundings in very different ways depending on what they are doing. In essence, the same ocean can become a different habitat to a dolphin depending on whether it is looking for a meal or communicating with other dolphins."

Researchers also found mismatches between fish and dolphin activity, suggesting that fish may quiet down when they detect dolphins.

"Everybody is snooping on everybody else," said O'Corry-Crowe. "This raises a fascinating question for our future research: Are dolphins listening for fish, and are fish listening for dolphins?"

The timing of dolphin detections also shifted, with more activity in March than April, possibly reflecting seasonal movements of different dolphin populations along Florida's Atlantic coast.

The study also highlights a challenge for dolphins and researchers: vessel noise can mask their calls, making communication harder for dolphins and detection harder for scientists. Some high-whistle areas also experience heavy vessel traffic, suggesting that important dolphin habitat may overlap with noisy waters.

"By listening to the sounds dolphins produce, we can begin to understand what they may be doing in different areas of the ocean and identify places that may be especially important for social activity or feeding," said Jessica Carvalho, first author and a research scientist at FAU Harbor Branch. "That information can ultimately help us better protect critical dolphin habitat, particularly in coastal waters increasingly affected by human activity."

At the heart of the study was a wave glider, an autonomous, wave-powered vehicle that served as a continuously operating underwater listening station. It allowed researchers to monitor a broad area over an extended period without the limitations of boat-based surveys.

"The ocean is filled with sounds that humans rarely hear, and autonomous platforms give us a way to enter that hidden acoustic world," said Laurent Chérubin, Ph.D., senior author and a research professor at FAU Harbor Branch. "A wave glider can travel through the ocean and listen continuously, allowing us to detect patterns that would be almost impossible to capture with occasional boat surveys. It is like giving researchers an ear that can remain in the ocean for weeks at a time, revealing a world of animal behavior that is otherwise largely unknown to us."

The study highlights the power of sound to reveal how dolphins use their environment. By identifying areas of concentrated social and foraging activity, acoustic monitoring could help pinpoint important dolphin habitats and guide efforts to protect them.

"Every sound gives us another piece of the puzzle," O'Corry-Crowe said. "When we combine dolphin vocalizations with the sounds of their prey and the physical characteristics of the ocean, we begin to see the underwater environment from the dolphins' perspective. That can fundamentally change how we think about their habitat."

This work was support by the Harbor Branch Oceanographic Institute Foundation Specialty License Plate "Protect Wild Dolphins" and "Protect Florida Whales."

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Researchers spent two months eavesdropping on dolphins along Florida's Atlantic coast, using an autonomous wave glider to capture their underwater sounds and clues about where they socialize and hunt.

-FAU-