50 years ago, a mysterious recording of a strange duck-like sound was produced in the waters of Antarctica. Scientists have been trying to get to the bottom of the mystery for decades now and the answer has finally come to light.

The mysterious "bio-duck" recording was taken back in the 60s after crew members onboard submarines patrolling the Southern Ocean heard strange quacking noises originating from the ocean. The low-pitched duck-like sounds were repetitive in nature but aside from the original recording, scientists had little data to study. Due to the predictable and repetitive nature of the noises, experts initially thought the sound was produced by human activities. Moreover, some experts theorized that the sounds were emanating from other submarines in the vicinity of Antarctica. After decades of unfounded speculations, scientists from the National Oceanic and Atmospheric Administration's (NOAA) Northeast Fisheries Science Center have finally found the source of the sounds.

Back in February of last year, a team of NOAA scientists tagged a pair of Antarctic minke whales (Balaenoptera bonaerensis) using acoustic instrumentation. The whales where captured, tagged and released in the waters of Wilhelmina Bay in the western section of Antarctica. The event was also marked as the first time that scientists were able to attach acoustic tags on Antarctic minke whales.

Months later, the team was able to analyze the recordings taken by the acoustic tags and what they found was surprising. The scientists heard sounds that were very similar to the "bio-duck" recordings taken in the 1960s. However, the analysis also brought about a bit of confusing since it was previously thought that all Antarctic minke whales migrated to warmer waters during the changing of seasons.

"These results have important implications for our understanding of this species," said NOAA research Denise Risch. "We don't know very much about this species, but now, using passive acoustic monitoring, we have an opportunity to change that, especially in remote areas of the Antarctic and Southern Ocean."

Aside from identifying the source of the strange duck-like sounds in the waters of the Antarctic, the scientists were also able to gain a deeper understanding of the Antarctic minke whales. Marine biologists now know that while most members of the species take part in the seasonal migrations, some of these elusive creatures remain in the waters of Antarctica throughout the entire year. The researchers published their findings in the online journal Biology Letters.