Antarctic minke whales (Balaenoptera bonaerensis) are still a mystery to marine biologists, who don’t know how many of these whales there are, or where exactly they live, mate and give birth to their calves. A few years ago, however, it was discovered that Antarctic minke whales produce certain characteristic sounds. These calls, which often sound a bit like the quacking of a duck, provide incontrovertible proof of the presence of the small whales, which measure up to eleven metres in length.
AWI biologist Diego Filun and his team are now using these sounds in the first-ever comprehensive, long-term observation of Antarctic minke whales in the Weddell Sea. “We’ve been monitoring our underwater microphones for nine years. They were deployed at 21 points throughout the Weddell Sea and along the prime meridian, allowing us to record the whales’ acoustic activities in regions where research vessels rarely venture. Thanks to the recordings, we now finally understand in what parts of the Weddell Sea the minke whales prefer to be at different times of year, and know that at least some of them stay there for the winter and don’t migrate to warmer waters,” Filun explains.
The recordings from 2008 to 2016 show that, in summer and winter alike, Antarctic minke whales tend to stay in those regions of the Weddell Sea that are covered with sea ice. Yet the frequency of their calls appears to change with the season: they can be heard far more often in the autumn and winter months (April to October) than in the summer months (December to March). In addition, the acoustic observations call into question certain previous assumptions: “On aerial survey flights over the Weddell Sea in the summer, minke whales were primarily sighted near the sea-ice edge and less frequently in areas with thick sea ice. But our audio recordings showed just the opposite: the minke whales were rarely found in the marginal ice zone, and much more often under thick ice – most likely in an attempt to avoid their archenemies, killer whales,” Filun reports.