The song is that of a humpback whale, a marine giant beloved by whale watchers for its docile nature and spectacular leaps from the water, and was recorded by scientists in March 1949 in Bermuda, said researchers at Woods Hole Oceanographic Institution in Falmouth, Massachusetts.

Just as significant is the sound of the surrounding ocean itself, said Peter Tyack, a marine bioacoustician and emeritus research scholar at Woods Hole. The ocean of the late 1940s was much quieter than the ocean of today, providing a different backdrop than scientists are used to hearing for whale song, he said.

The recovered recordings “not only allow us to follow whale sounds, but they also tell us what the ocean soundscape was like in the late 1940s,” Tyack said. “That’s very difficult to reconstruct otherwise.”

A preserved recording from the 1940s can also help scientists better understand how new human-made sounds, such as increased shipping noise, affect the way whales communicate, Tyack said. Research published by the National Oceanic and Atmospheric Administration states that whales can vary their calling behavior depending on noises in their environment.

The recording predates scientist Roger Payne’s discovery of whale song by nearly 20 years. Woods Hole scientists on a research vessel at the time were testing sonar systems and performing acoustic experiments along with the U.S. Office of Naval Research when they captured the sound, said Ashley Jester, director of research data and library services at Woods Hole.

The scientists didn’t know what they were hearing, but they decided to record and save the sounds anyway, Jester said.

“And they were curious. And so they kept this recorder running, and they even made time to make recordings where they weren’t making any noise from their ships on purpose just to hear as much as they could,” said Jester. “And they kept these recordings.”

Woods Hole scientists discovered the song while digitizing old audio recordings last year. The recording was on a well-preserved disc created by a Gray Audograph, a kind of dictation machine used in the 1940s. Jester located the disc.

While the early underwater recording equipment used to capture the sound would be considered crude by today’s standards, it was cutting-edge at the time, Jester said. And the fact that the sound is recorded on a plastic disc is significant because most recordings of the time were on tape, which has long since deteriorated, she said.

Whales’ sound-making ability is critical to their survival and key to how they socialize and communicate. The sounds come in the form of clicks, whistles and calls, according to NOAA scientists who study them.

The sounds also allow the whales to find food, navigate, locate each other and understand their surroundings in the vast ocean, scientists say. Several species make repetitive sounds that resemble songs. Humpback whales, which can weigh more than 55,000 pounds (24,947 kilograms), are the ocean’s most renowned singers, capable of complex vocalizations that can sound ethereal or even mournful.

The discovery of long-lost whale song from a quieter ocean could be a jumping-off point to better understanding the sounds the animals make today, said Hansen Johnson, a research scientist at the Anderson Cabot Center for Ocean Life at the New England Aquarium.

“And, you know, it’s just beautiful to listen to and has really inspired a lot of people to be curious about the ocean, and care about ocean life in general,” said Johnson, who was not involved in the research. “It’s pretty special.”

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This story was supported by funding from the Walton Family Foundation. The AP is solely responsible for all content.