‘Bio-Duck’: The Ocean Sound That Stumped Scientists For Decades Is Finally Solved
After more than 50 years of trying to find the source of a mysterious oceanic sound, scientists captured an acoustic recording that allowed them to identify the animal. The sound, nicknamed "bio-duck," was finally analyzed using data from a multi-sensor acoustic recording of intense sounds, which led researchers to single out the Antartic minke whales as its owner.
Researchers recorded sound in the Southern Ocean, which sounds oddly duck-like, but it has also been located in the Antarctic waters and off the Australian west coast. The findings are published in the Royal Society journal Biology Letters.
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"It was hard to find the source of the signal. Over the years there have been several suggestions... but no one was able to really show this species was producing the sound until now," Denise Risch, lead researcher from the U.S. National Oceanic and Atmospheric Administration (NOAA) Northeast Fisheries Science Center in Massachusetts, told BBC News.
In February 2013, researchers captured acoustic recordings that distinguished two marine mammals that could have possibly made the sound, however it wasn't until this new long-term acoustic recording gave them a definitive answer.
"It was either the animal carrying the tag or a close by animal of the same species producing the sound," Risch said.
The two Antarctic minke whales located off Western Antarctica, were tagged by Risch's colleagues with suction-cup tags with the original intent of studying the whale's feeling behavior and movement. The tags also contained underwater microphones, and once they analyzed the acoustic recordings Risch realized they contained the duck sounds, along with downward-sweeping sounds previously linked to the whales.
After analyzing the sounds they "can now be attributed unequivocally to the Antarctic minke whale," Risch and her team wrote in the study.
The sound that was necessary to make a positive identification had been difficult to capture because the Antarctic minke whales inhabit a sea-ice environment that is difficult to access. This has led to failed efforts to capture the sound, especially since the environment changes rapidly in certain regions.
During the winter and spring, scientists have recorded the bio-duck sound in both Western Australia's coast and the Weddell Sea located southeast of the Antarctic Peninsula in the Southern Ocean. According to their findings, the bio-duck sound has been one of the most prevalent sounds in the Southern Ocean during austral winters and its identification has been a priority to the International Whaling Commission.
This drew the conclusion that the species they were following divided into one group that were seasonal migrators and another population that had a year-round presence in the Antarctic waters.
The Antarctic minke whale had been labeled as a subspecies in 1804, but after studying their genetic data it was given full species status in 1998, according to the Society for Marine Mammalogy. At maturity, the minke whale is 30 to 35 feet long, or about the length of a standard school bus. This specific whale species lives up to 60 years and is divided into a northern and southern group, with the northern species slightly smaller.
Researchers are still trying to understand the reason for the distinct sounds, however they do know that they are generated close to the surface right before the whales dive deep into the water for their food, such as krill.
"Identifying their sounds will allow us to use passive acoustic monitoring to study this species," said Risch, who has been recording in the Southern Ocean for the last few years.
Being able to distinguish and I.D. a whale's sound to a particular species is valuable for researchers to monitor and understand the behavior and patterns of the Antarctic minke whale
"That can give us the timing of their migration — the exact timing of when the animals appear in Antarctic waters and when they leave again — so we can learn about migratory patterns, about their relative abundance in different areas, and their movement patterns between the areas," she added.
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