Hawaiian monk seals are among the world’s rarest marine mammals. Now, researchers have uncovered something just as rare — a complex array of underwater sounds never before documented in this species.

Using passive underwater recorders, scientists captured over 23,000 vocalizations from free-ranging monk seals. The data revealed at least 25 distinct call types, many of them never recorded until now, according to the Marine Mammal Research Program at the University of Hawaiʻi.

Hawaiian monk seals produce at least 25 distinct underwater call types.

More Than Just Noise

These weren’t random sounds. The calls included sequences that combined different elements — a structure known as “combinational calling.” No other pinniped species has ever been observed producing vocal sequences this intricate, researchers said.

Many of the calls were low-frequency, ranging from 100 to 1000 Hz. That places them directly in the path of growing underwater noise pollution from shipping and tourism. Oceanographic Magazine notes these sounds are vulnerable to being drowned out by human activity.

Scientists recently discovered 20 seal vocalizations never recorded before.

Listening for a Purpose

The seals weren’t just making sounds — they were using them while swimming, diving, and even feeding. One call type, labeled a “whine,” was linked to foraging behavior. According to SciTechDaily, this could be only the second known case of seals vocalizing while hunting.

These calls might help seals locate prey, communicate with mates, or avoid territorial conflicts. But scientists are still decoding what each sound means.

Some monk seal calls are made in combination, like vocal sequences.

From Sound to Survival

The findings could change how conservationists monitor this endangered species. Seals are difficult to track across vast ocean areas. But now, acoustic tools can detect their presence and behavior non-invasively.

By creating a reference library of calls, researchers hope to develop automated systems that can identify monk seal vocalizations in real time. This technology could monitor populations in remote or inaccessible regions, Kaua‘i Now News reports.

More Than a Whisper

This research reveals a rich vocal world once hidden beneath the waves. It proves these seals are not silent survivors — they're speaking a language we’re only just beginning to hear.