New research has completely changed our understanding of how Hawaiian monk seals communicate underwater. Scientists discovered that these critically endangered animals are far more vocal than previously thought, using a surprisingly complex system of calls to navigate their world. The findings, published in Royal Society Open Science, were made possible by analyzing thousands of hours of underwater recordings collected across the Hawaiian archipelago.
The study, led by the University of Hawaiʻi’s Marine Mammal Research Program (MMRP), initially focused on confirming six known call types from monk seals kept in captivity. However, they uncovered something much more remarkable: at least 25 distinct vocalizations. This is a staggering increase and reveals a hidden world of acoustic communication within these marine mammals.
The study deployed passive acoustic recorders—devices that record sounds underwater without disturbing animals—at various monk seal habitats. These recordings revealed not only new calls but also an intriguing communication strategy never before observed in pinnipeds (seals, sea lions, and walruses). Researchers identified “combinational calls,” where seals link different vocal types together, adding layers of complexity to their interactions.
“We were surprised by the sheer diversity and complexity of monk seal vocalizations,” said Kirby Parnell, lead author of the study. “The discovery of combinational calls suggests a previously unknown level of sophistication in pinniped acoustic communication.”
Adding to the surprise was the identification of a new call type called the “Whine,” produced specifically during foraging. This is only the second known instance of seals using sounds while hunting, hinting at their potential use of sound for locating prey.
Understanding Impacts and Protecting Acoustic Habitats
This newfound knowledge about monk seal vocalizations has major implications for conservation efforts in Hawaiʻi. The Hawaiian monk seal, native only to these islands, faces numerous threats including habitat loss, entanglement in fishing gear, and disease. The discovery that their calls overlap with the low-frequency sounds produced by human activities like shipping traffic is particularly concerning.
This research underscores the importance of protecting their acoustic habitats from increasing ocean noise pollution. “Knowing how monk seals use sound for critical life events, such as mating and finding food, helps us understand how human-generated noise might disrupt those behaviors,” explained Lars Bejder, Director of MMRP and co-author of the study.
The next steps involve linking these vocalizations to specific behaviors (like hunting, socializing, or reproduction) to gain even deeper insights into their social lives. The development of automated detection systems will allow for more efficient monitoring of monk seal populations, offering a powerful tool for conservation management in the years ahead.
