27.02.2019 – So close yet SOFAR

Today our crew and guests had the pleasure of being in the presence of giants. As we left the marina, our crew at sea was informed of a large baleen whale around 2 nautical miles off the coast of Tabua by our spotter. „But first we have dolphins“ our captain, Filipe added. We were in for a little surprise as we approached a group of Bottlenose dolphins (Tursiops truncatus) leisurely socializing amongst a group of logging juvenile Sperm whales (Physeter macrocephalus). One Sperm whale calf even leapt out of the water as the dolphins sped past in an almost playful behaviour. The breach may have also been a form of communication, summoning the older animals from their foraging dives in the deep, dark ocean back to the surface and, surely enough, we soon stumbled upon a larger female closeby.

Of course the complexity of cetacean communication reaches far beyond creating all this commotion at the surface. Toothed whales (Odontoceti) posess an a fatty organ that modifies and propogates sound waves created in the nasal passages in their blowhole. The generated biosonar is then used for hunting, echolocation and communication. Dolphins, for instance, generally produce high frequency whistles and squeaks during close range communication while Sperm whales emit sounds known as „clicks“ during socializing events. Baleen whales, on the other hand, posess actual vocal chords with which they can engage in long-range conversations.

Particularly the larger specimens, the Blue Whale (Balaenoptera musculus) and the Fin Whale (Balaenoptera physalus), the two giants of the animal kingdom, are notorious for producing soundwaves at the lowest frequencies in the entire animal kingdom. The highly migratory and cosmopolitan Fin whales produce popular „20 Hz pulses“, soundwaves for communication which lie at the very minimum of the human hearing range (which ranges from 20Hz-20,000Hz). Whales are also thought to dive to a certain depth in the water column where ideal pressure, temperature and to a lesser part salinity conditions help effectively channel their voices over longer distances, often thousands of miles. This water layer, also referred to as the SOFAR (Sound fixing and ranging) channel, averages at a depth of 750m worldwide and was also used extensively during submarine warfare. We encountered two of these incredible giants in close vicinity to the Sperm whales today. Here, of course, the pair were at close range to one another so no need for any use of the sound channel.

As with the Sperm whale sightings, the Bottlenose dolphins were swiftly swimming around the two baleen whales almost as if they were teasing the gentle giants with their incredible agility. I couldn’t help being grateful to be a spectator of such a scene and share my very first Fin whale sighting here in Madeira with such interested and friendly guests.

By Paula Thake

Sightings of the day

Stenella

15:00 Bottlenose dolphins, Fin whales, Sperm whales