September 10, 2013
Some Humpback Whales Spend Winter In The Antarctic
Brett Smith for redOrbit.com - Your Universe Online
With an underwater listening device and a little bit of luck, a team of German and American researchers has found that some Southern Hemisphere humpback whales remain in Antarctic waters throughout the entire winter, according to a newly published report in the open-access journal PLOS ONE.
Based on acoustic recordings of whale songs, the new study somewhat contradicts prevailing theories claiming that the entire Southern Hemisphere whale population migrates towards the equator at the end of the Antarctic summer.
Study co-author Ilse Van Opzeeland, a marine biologist at the Alfred Wegener Institute, said the discovery began through a bit of pure luck. One April morning, she unlocked the door to her office and, as she always does, switched on the live audio monitor for the Perennial Acoustic Observatory in the Antarctic Ocean (PALAOA).
What Van Opzeeland heard pouring out of the loudspeakers surprised her – the signature calls of humpback whales. With a listening radius of about 62 miles, Van Opzeeland knew the humpbacks she was hearing were swimming very close to the underwater listening station in the Weddell Sea, just off the coast of Antarctica.
"I was totally surprised, because the textbook-opinion until that day was that humpback whales migrate to Antarctic waters only in the austral summer months,” the German-based researcher explained.
To determine whether the winter-excursion of the humpback whales was just a freak occurrence, Van Opzeeland created a computerized method for the automatic recognition of humpback whale calls and scoured all PALAOA recordings from 2008 and 2009 for audible signs of life from these animals.
"Along with variable, high-frequency calls from the whales, our recordings also contain stereotyped calls that sound a bit like a moan. We concentrated on the latter in our analysis," the whale expert said. "Today, we know that, in 2008, the humpback whales were present near the observatory with the exception of the months May, September and October. In the following year, they were absent only in September.”
“Therefore, it is highly likely that humpback whales spent the entire winter in the eastern Weddell Sea during both years," Van Opzeeland concluded.
The marine biologist said shifting Antarctic ice could explain the absence of humpback calls during some of the winter recordings.
"Near the observatory, open water areas in the sea-ice, also known as polynias, regularly form during winter,” she said. “Such polynias form due to offshore winds which press the sea-ice off the continent out to sea. We suspect that humpback whales use these ice-free areas.”
“When polynias close or change position, the whales may move with them and leave the recording radius of (62 miles), which our underwater microphones are monitoring,” Van Opzeeland continued. “However, we do not yet have proof for this behavior.”
Van Opzeeland said the year-round recording of humpback whales in the eastern Weddell Sea substantiates the region as a habitat for the animals.
"In the light of ongoing discussions regarding designation of marine protected areas, our results show that not only the known feeding grounds in the region of 60 degrees south are important for the humpback whales, but also waters further south, off the Antarctic continent,” she said. “The animals can be found in these regions almost throughout the entire year.”