For decades, scientists have studied the biology, movements, and population trends of the endangered Hawaiian monk seal (estimated wild population: 1,600). However, until recently, their underwater communication remained largely a mystery. New research, published in 2021, has changed that, uncovering 20 previously undocumented calls among 25 distinct vocalizations. This discovery isn’t just about cataloging sounds; it’s about understanding how these seals interact, hunt, and survive in a rapidly changing ocean.
The Silent World Revealed
Researchers from the University of Hawaiʻi at Mānoa deployed underwater recorders (SoundTraps) across the Hawaiian archipelago to collect over 4,500 hours of acoustic data, resulting in more than 23,000 recorded vocalizations. The analysis revealed that Hawaiian monk seals aren’t silent creatures. They use sound extensively, particularly underwater, where vision is limited. This reliance on acoustics makes their communication vital for finding mates, locating food, and maintaining social cohesion.
A Complex Vocal Repertoire
The study identified six “elemental” calls (basic sounds) and 19 “combinational” calls—unique sequences of these basic units strung together without pauses. This level of complexity is unusual among pinnipeds (seals, sea lions, walruses). One researcher, Kirby Parnell, described the ability to combine calls as something she hadn’t observed in other seal species. For instance, seals combine the “croak,” “hum,” “growl,” and “whoop” into distinct vocalizations that may carry specific meanings.
Why This Matters: Conservation Implications
Understanding these vocalizations is crucial for conservation efforts. The Hawaiian monk seal is an endangered species facing threats from human activity, including noise pollution. Loud underwater sounds from shipping, sonar, and construction can disrupt their communication, making it harder for them to find mates or evade predators.
The researchers found that monk seals vocalize at low frequencies (below 1 kHz), which are particularly susceptible to interference from human-generated noise. Knowing this allows scientists to assess the impact of human activity on their behavior and hearing. The study is a foundational step towards protecting these animals, as understanding their communication is essential for mitigating threats and ensuring their survival.
Field Observations Confirm Vocal Behavior
Experts like Dana Jones, director of Hawaiian Monk Seal Preservation Ohana, have long observed the seals’ vocal nature firsthand. She recalls a seal nicknamed “KP2” who vocalized incessantly when orphaned as a pup, and another that vocalized loudly while hunting in a local canal, disturbing residents. These anecdotes support the scientific findings: seals aren’t just quiet beach-sleepers; they actively communicate underwater.
The Future of Seal Communication Research
The next phase of research involves deploying recorders for extended periods (up to a year) to identify seasonal patterns in vocalizations. Researchers are also using seal-mounted tracking devices with video and audio recording capabilities to link specific calls to observed behaviors, such as foraging or mating rituals. One theory suggests the “whine” call may be associated with food searching.
“These are foundational studies and just tiny pieces of the overall puzzle…Working with an endangered species, we need to understand everything that we can, and this is one piece of the puzzle,” says Kirby Parnell.
By unraveling the secrets of Hawaiian monk seal communication, scientists hope to better understand their behavior, protect them from human interference, and ensure the survival of this endangered species.
