7. September 2013: Surprising underwater-sounds: Humpback whales also spend their winter in Antarctica
Bremerhaven, 7. September 2013. Biologists and physicists from the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, found out that not all of the Southern Hemisphere humpback whales (Megaptera novaeangliae) migrate towards the equator at the end of the Antarctic summer. Part of the population remains in Antarctic waters throughout the entire winter. The scientists report this in a current issue of scientific journal PLOS ONE. This surprising discovery based on underwater recordings from the Antarctic acoustic observatory PALAOA. It is located near the research base Neumayer Station III on the ice shelf and regularly records underwater sounds of humpback whales even in the austral winter months.
Sometimes even scientists need the crucial little quantum of luck to obtain new research ideas. For instance Ilse Van Opzeeland, a marine biologist and expert on large whales at the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI). As she unlocked the door to her office one April morning and, as usual, switched on the live stream of PALAOA, the underwater acoustic observatory, the loudspeakers suddenly resounded with the calls of humpback whales - and this at a time during which the marine mammals should long have been swimming 7,000 kilometres further away in the warmer waters off Africa. "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. And even then, standing believes were that they would only be feeding on krill in the ice-free regions around 60 degrees south latitude. However, our PALAOA observatory monitors an area 70 degrees south – so, much further south than hitherto known feeding grounds. "With this in mind, hearing the animals on a winter morning near our observatory was a double surprise," explains the scientist.
Driven by the question whether the winter-excursion of the humpback whales in the eastern Weddell Sea was a unique event, Ilse Van Opzeeland developed a procedure for the automatic detection of humpback whale calls and analysed all PALAOA recordings from 2008 and 2009 for acoustic 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 marine biologist tells us. "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," says the scientist.
A possible explanation for the absence of humpback whale calls during some months could be the Antarctic sea ice. "Near the observatory, open water areas in the sea-ice, also known as polynias, regularly form during winter. 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 100 kilometres, which our underwater microphones are monitoring. However, we do not yet have proof for this behaviour," Ilse Van Opzeeland explains.
Based on the underwater sounds, the AWI scientists cannot say what the whales are actually communicating and which animals are calling in the winter months: "Possibly, the calls are produced by young whale cows that are not yet pregnant and skip the more than 7,000 kilometres long, energetically-costly migration to Africa's coastal waters. A humpback whale-female loses up to 65 per cent of her body weight when giving birth to and suckling a calf. With this in mind, it appears energetically advantageous, from viewpoint of the young whale cows, to remain in Antarctic waters during winter. Furthermore, the coastal region of the eastern Weddell Sea likely provides krill concentrations substantial enough for the animals to find sufficient food, even in the colder season, to acquire sufficient fat-reserves for reproduction and the long trip in the following year," explains Ilse Van Opzeeland.
These new findings substantiate the significance of the Southern Ocean as a habitat for humpback whales. "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. The animals can be found in these regions almost throughout the entire year," the biologist says.
Van Opzeeland and her team from the AWI "Oceanic Acoustics Lab" now want to find out to which population the humpback whales from the eastern Weddell Sea belong. The scientists are planning to compare calls from the PALAOA recordings with humpback whale song from the coastal waters off Gabon and Mozambique. "Each humpback whale population has its own song. Songs therefore provide an acoustic fingerprint, on the basis of which we will hopefully be able to say where the animals that spend their winters off the Antarctic continent breed," reports the marine biologist.
Breeding presumably takes place in the coastal region off southern Africa. "We know from other humpback whale-populations in the Southern Hemisphere that their spring southbound migration is relatively straight and direct in course. If this also is the case for humpback whales in the Weddell Sea, it is likely that they belong to populations on the east or west coast of southern Africa," Ilse Van Opzeeland states.
Furthermore, the AWI team is analysing data from a chain of underwater acoustic recorders which the Ocean Acoustics Lab scientists have moored along the Greenwich Meridian, 0 degrees longitude, between South Africa and the Antarctic continent some years ago: "We know that humpback whales sing on the breeding grounds, as well as during their migration and that these songs alter from year to year. When and how this change happens, is however still unclear. With the help of the recordings from our chain of acoustic sensors, we may be able to shed more light on how humpback whale song changes between years," says Ilse Van Opzeeland. She will therefore have many more humpback whale sounds to listen to during the coming period.
Further information about the PALAOA observatory:
PALAOA stands for PerenniAL Acoustic Observatory in the Antarctic Ocean. However, Palaoa is also the Hawaiian word for whale and the research station also records the sounds of these ocean giants with its underwater microphones.
The small PALAOA research container is unmanned and located approximately 18 kilometres from Neumayer Station III on the Antarctic ice shelf near Atka Bay. The observatory is maintained during the Antarctic winter by members of the overwinterer teams at Neumayer Station III.
To deploy the four hydrophones of the observatory, approximately 800 metres from the ice shelf edge, holes were drilled through the 100 meter-thick ice shelf to lower the hydrophones with a cable into the ocean underneath the ice.
All sounds that PALAOA picks up are transmitted to Neumayer Station III via wireless LAN and sent to the Alfred Wegener Institute in Bremerhaven via satellite link from there. The following link leads to the live broadcast of what PALAOA records in the Antarctic sea: http://www.awi.de/fileadmin/user_upload/PALAOA/spectrum.html
Notes for Editors:
The study appeared under the following original title:
Ilse Van Opzeeland, Sofie Van Parijs, Lars Kindermann, Elke Burkhardt, Olaf Boebel: Calling in the cold: Pervasive acoustic presence of humpback whales (Megaptera Novaeangliae) in Antarctic coastal waters, PLOS ONE, http://dx.plos.org/10.1371/journal.pone.0073007
Audio files of humpback calls:
If you want to download three audio files of humpback calls recorded by the PALAOA system, please click following links:
- audio 1 (high calls of humpback whales, recorded by PALAOA, length: 1 minute)
- audio 2 ((high calls of humpback whales, recorded by PALAOA, length: 1 minute)
- audio 3 (a short audio snippet of a moan, recorded by PALAOA, amplified and played with double speed - otherwise these calls are not audible, lenght: 4 seconds)
Please credit this audio material with "Audio: PALAOA, Alfred-Wegener-Institut".
Your scientific contact persons at the Alfred Wegener Institute (AWI) are:
· Dr. Ilse Van Opzeeland (Tel: +49 (0)471- 48 31-11 69, E-Mail Ilse.Van.Opzeeland(at)awi.de),
· Dr. Olaf Boebel (Tel: +49 (0)471- 48 31-18 79, E-Mail: Olaf.Boebel(at)awi.de)
Your contact person in the Department of Communications and Media Relations is Sina Löschke (phone +49 471 4831-2008, e-mail: medien(at)awi.de).
The Alfred Wegener Institute conducts research in the Arctic and Antarctic and in the high and mid-latitude oceans. The Institute coordinates German polar research and provides important infrastructure such as the research icebreaker Polarstern and stations in the Arctic and Antarctic to the international scientific world. The Alfred Wegener Institute is one of the 18 research centres of the Helmholtz Association, the largest scientific organisation in Germany.
Aerial photo of a humpback whale next to pieces of ice
This photo is one of the very few images showing one or more humpback whales next to Antarctic sea ice or parts of former icebergs. The photo was made in January 2013 during an Weddell Sea expedition of the German research vessel Polarstern. Photo: ITAW/Carsten Rocholl
Aerial photo of two humpback whales
Two humpback whales are coming up for air in the Southern ocean. Females are usually slightly larger than males and an exceptional individual may be up to 18.9 m in length and weigh 48 metric tons. Photo: ITAW/Carsten Rocholl
Humpback whale distribution
No finishing line for humpbacks at 60°South: For a long time scientists thought that in spring humpback whales would migrate from subtropical and tropical waters to the northern part of the Southern ocean to feed on krill; later on, in autumn they would return. Today we know that some humpback head even further south and stay there for longer than just a summer. This map is based on the latest findings of AWI scientists and shows the potential Antarctic winter range and winter breeding grounds of humpback whales. Map: Ilse Van Opzeeland, Alfred-Wegener-Institut
Searching for krill
Aerial picture of two humpback whales in the Southern ocean. The baleen whales are searching for krill in the Antarctic waters. According to new research of AWI scientist Ilse Van Opzeeland, we have got a good reason to believe that these animals find enough food close to the Antarctic continent even during dark and cold winter months. Photo: ITAW/Helena Feindt-Herr
Humpback whale in the Southern ocean
A humpback whale is descending into the deep after a few deep breaths at the ocean's surface. The photo was made during Polarstern's winter experiment 2013, when the ship crossed the known humpback feeding grounds in the region of 60° South. Photo: Stefan Hendricks, Alfred-Wegener-Institut
PALAOA - the Perennial Acoustic Observatory in the Antarctic Ocean
The Perennial Acoustic Observatory in the Antarctic Ocean (PALAOA) records the underwater soundscape in the vicinity of the ice shelf edge continuously. The recorded data are transmitted via wireless LAN from PALAOA to the German base Neumayer-Station III at a distance of 13 kilometers. From there, a permanent satellite link transmits a highly compressed acoustic livestream to the AWI in Bremerhaven. Photo: Thomas Steuer, Alfred-Wegener-Institut
Humpback whale in Antarctic waters
This photo shows a humpback whale swimming closely to the Antarctic coast. The picture was made in February, a summer month in Antarctica and a time when the humpback whales were thought to feed in an area close to 60° South. Now AWI scientists found out, that some of the whales migrate even further south to the Weddell Sea and spend the winter there. Photo: ITAW/Helena Feindt-Herr