Anatomy of a sighting

49° 00‘ S, 12° 55‘ O +++ +5°C, 2 m swell, 1 m wind sea +++

27 January 2015
(by Sacha Viquerat; translation: Ina Lefering)

The Antarctic wind that our three brave marine mammal observers have to face is freezing cold. The three have reached half time of their last shift of the day, working on the crow’s nest in their bright red polar suits. The amount of sightings has been pretty slim so far: the only thing that caught their attention was the blow of a group of minke whales at around 6:10 am. They spotted it in dense ice and crystal blue water. But suddenly, at 6.14 am, another blow appears in between the ice floes. The sighting is called out and taken note of in a computer program. The first guess: it’s another minke whale.

Now, the details of the sighting have to be determined, for example size of the group and identification of the species. This can be challenging without further equipment when the animals are 3 km away. The blow is a first indication about the species, but even the slightest breeze affects its shape. So, we can not rely on the blow alone to ensure a high data quality. But thanks to the photo cameras that we have with us all the time, we are able to take a few shots of the sighting with our fingers stiff from the cold. These pictures will later be used for a proper identification of the individual. This time we are surprised: the spotted animal can be identified as a blue whale (Balaenoptera musculus) swimming under the ice! We are very lucky because this behaviour has rarely been observed. The 33m long and 120 tons heavy animals usually prefer open water conditions and are usually not associated with ice covered areas. That is why our first guess of the sighting was a minke whale. Minkes are known to stay in ice covered areas and feed on the krill living directly under the sea ice.

The next picture clearly shows the pattern on the back of the blue whale. This pattern is unique for an individual animal and can be used to track its migration and study its history when it has been logged during previous sightings. We, for example, cooperate with the experts of the Antarctic blue whale division, who will compare our pictures with other blue whale sightings in their data set. We are now very happily expecting the end of our shift knowing that not only the water has been shining blue today.