Saturday, 3 May 2014

Bio-duck mystery solved after 50 years

Bio-duck is the nickname given to a strange, quack-like sound which has baffled researchers since the 1960s, when. the first bio-duck sounds were reported by sonar operators on Oberon class submarines.

Since then, these strange quacking sounds have been frequently recorded in the waters around the Antarctic and western Australia. They are audible within frequencies from 50 to 300 Hz, with the duration of each call being 1.6 to 3.1 seconds. The sounds are recorded from October till December, not to be heard again until the next winter.

The Bio-duck sound

Till now, the source of the bio-duck remained a mystery. Speculations included fish, passing ships even ultra-high-tech military devices!

As time passed,  certain clues pinpointed more and more to a deep-sea animal. As aforementioned, the noise appears only from October to December, and can only been recorded in a limited area near Antarctica. This strongly suggests a migrating animal. 

Now, thanks to new research, there is "conclusive evidence" that the culprit behind these mysterious sounds is the Antarctic minke whale (Balaenoptera bonaerensis).

 Minke whale (Balaenoptera bonaerensis) in Ross Sea
 Minke whale in Ross Sea, Antarctica 

"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." said Denise Risch, lead researcher from the US National Oceanic and Atmospheric Administration (Noaa) Northeast Fisheries Science Centre in Massachusetts

In 2013, Risch's team attached acoustic recorders to two individuals and later recorded the whales making the strange bio-duck noise. 

"It was either the animal carrying the tag or a close-by animal of the same species producing the sound.", added Dr Risch.

The researchers still don't know why the whales make these sounds but they say they are often produced just before the whales dive for food. They still don't know the purpose of these calls and how they are used for communication. Nor do they have an idea why they are only heard at the height of the southern summer.

However, they believe their discovery will help scientists to shed more light into the behavioral patterns of the species.

"Identifying their sounds will allow us to use passive acoustic monitoring to study this species. 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." said Dr Risch.

References & Further Reading
- Risch D, Gales NJ, Gedamke J, Kindermann L, Nowacek DP, Read AJ, Siebert U, Van Opzeeland IC, Van Parijs SM, & Friedlaender AS (2014). Mysterious bio-duck sound attributed to the Antarctic minke whale (Balaenoptera bonaerensis). Biology letters, 10 (4) PMID: 24759372

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