![]() Higher concentrations of krill were detected close to the surface during night-time, and lower concentrations during the day. Instead, the vocal frequency matched the diel vertical migration of krill, a main diet of the Antarctic Minke Whales. However, the period with highest vocal activity was also detected during time of minimal irradiance, suggesting that the pattern is not caused by the animals reacting to the sun. The study noticed that during April to August, the vocal activity of Antarctic Minke Whale followed a pattern of high activity at midnight and less at midday. Ī paper published in 2017 suggests that calling behavior could be connected to feeding. It was previously hypothesized that the function of the calls was for navigating areas with dense sea-ice coverage, but multiple acoustic research sources deny this, as bio-duck sounds were also detected at lower latitude areas with no sea ice, such as the coast off Namibia and the Perth Canyon. The function of the calling behavior of the Antarctic Minke Whale is still unknown. Furthermore, since there was a relative increase in calling behavior once sea ice coverage reached 50%, researchers suggest that perhaps a certain threshold must be met in order to significantly affect calling behavior. Another research came to a similar conclusion, determining that there is positive correlation between Antarctic Minke Whales time spent calling and sea ice presence. The researchers concluded that month of the year was the most prominent variable, followed by distance from sea ice and lastly, time of the day. The variables were "distance of sea ice edge" (from recording position), "month of the year" and "time of the day". To investigate what context bio-duck sounds occur, research was conducted off West Coast of South Africa to see if there is any connection between frequency of bio-duck sounds and three variables. Since no other marine mammal species were observed within 1 km of the tagged whales and given that the whales travelled in single species groups, Reich's research team concluded that the source of the sound was either the tagged whale itself, or other Antarctic Minke Whales travelling in the same group. Additionally, low frequency down sweeps, a sound previously associated with the Antarctic Minke Whales were also sampled from the tags. 32 calls were made during this time, of which 6 had similar properties to pre-existing recordings of a bio-duck sound. Each tag recorded for 18 hours and 8 hours respectively, and during that time both whales fed continuously. Both tagged Antarctic Minke Whales travelled in a group with the same species, ranging from 5 to 40 whales per group. The devices were attached directly from a boat using a pole and it collected sound, temperature, pressure, acceleration and magnetic fields. ĭuring austral summer of 2013, a research team led by Denise Risch attached suction cupped recording devices to two Antarctic Minke Whales. Moreover, acoustic research is invaluable since Antarctic Minke Whales inhabit areas of high sea-ice, making conventional ship research challenging. Researchers say that this discovery is significant in estimating seasonal occurrence, migration patterns and abundance of the Antarctic Minke Whales as acoustic research is more cost effective than visual sightings and can be carried out regardless of weather and daylight conditions. Although the role of the sound remains a mystery, it is suggested that it could play a role in mating. The sound is made near the surface, predominantly before feeding dives. The sound is mainly present during austral winter in the southern ocean, detected off Western Australia and the Antarctic waters. The recorded sound has a frequency range between 60 Hz to 100 Hz, harmonics up to 1khz, and an interval of 1.6 to 3.1 seconds between each sound. Once dubbed as the “largest still unresolved mysteries of the Southern Ocean”, the origin of the sound remained a mystery for decades until 2014, when it was concluded that the sound originated from Antarctic Minke Whales. It was first reported in 1960 by submarine personnel, who gave the sound its name, associating it with that of a duck. Bio-duck is a sound recorded in the Southern Ocean, specifically in Antarctic Waters and the West Coast of Australia. ![]()
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