Humpbacks, Marine…

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Celine van Weelden , WCA Intern

01/10/2016: Humpbacks, Marine Musicians


Humpbacks can be seen off the coast of Mozambique between August and November, on their migration south to their summer feeding grounds in Antarctica.


One of the most common ways to spot them is from their blow. This is the cloud of steam that shoots straight up a couple of metres into the air when they exhale. The height which allows blows to be seen from kilometres away is due to the high pressure that builds up in their lungs from spending long periods underwater. With lungs the size of a small car they can exchange up to 90% of their full capacity in one breath, seen from kilometres away.


Their dorsal fin is proportionally very small which I originally found misleading as it creates an expectation for a much smaller animal. As soon as you get closer however, you are all too aware of their size. Often all you are able to see is their blowholes and the very top of their backs slipping below the surface. This really is only the tip of the iceberg. Leaving you to imagine the rest of their immense body just out of sight beneath the waves.


After one such humbling encounter on a choppy but fresh morning, Mitch had another surprise. He cut the engine and left us bobbing in the swell while he produced a contraption consisting of a small mechanism ingeniously sealed into the bottom of an old plastic bottle to keep it dry. This was dropped over the side into the water; attached to a long reel of cable which he plugged into a small portable speaker. The hydrophone (under water microphone) crackled into life and, after some minor tuning, we could clearly hear the melodic song of a humpback whale.


Humpbacks can communicate over vast distances using a range of pitches many of which are below our range of hearing. These sound waves carry much further through water than air (up to 20 miles!). It is believed that before the extreme disturbance caused by underwater noise pollution, two individuals could communicate with each other anywhere on the globe!


What we were listening to was not the whale we had just seen (which would be deafening at this range) but another individual several kilometres away.


Humpbacks have over one hundred different calls for communication alone consisting of groans, moans, roars, sighs and squeals. The singing, which is done by the males, is believed to be part of the process of attracting a mate. Songs last around 10-20 minutes but can be continuously repeated for hours at a time. Mitch explained how all males in a certain region sing their own version of the same song and the song changes each year. It remains unclear how they know when to change the tune, it is another of the beautiful natural mysteries we have yet to understand.


The low frequency of their calls gives the sound an incredibly soothing quality and we just sat in silence each lost in our own whale-narrated day dream. On another occasion I was lucky enough to experience this phenomenon from underwater. We were snorkelling further out than usual; where the aquamarine sunlight drops quickly away into shadowy depths. Appearing devoid of the life that
teams in the shallows. As I floated there feeling tiny and insignificant in the endless empty blue surrounding me; the song of a distant humpback reminded me of the undiscovered wonders that remain hidden far below the surface.


The day I saw my first breach, the wind was howling and the swell was big with seemingly vertical walls of water rocking the boat. The whales seem to love it when it is rough. It is really quite incredible the way they throw themselves almost completely out of the water before crashing back down. I could not begin to imagine what it would be like to experience it close up.


The opportunity did not take long to present itself. A week or so later, we were at the end of a wonderful swim with a calm and sociable pod of dollies when we heard a shout from the boat that there were some humpbacks 60 metres of so further out. Scrambling back aboard we bounced over the choppy water in the direction of the blows. It appeared to be a mother, calf and escort who were cruising calmly south, surfacing regularly for air. While an adult can hold their breath for up to 40 minutes when necessary, young ones only develop this lung capacity with time and therefore often need to surface more.


Suddenly something launched itself out of the water. Using its tail to propel itself upwards into the air where it hung for a few moments while water droplets ran down the pale underside of its belly and its already impressively long pectoral fins (the longest arm span in the animal kingdom). Then it came crashing down on its back with a foaming splash. The little one wanted to show us his new trick! Only a few months old, the calf was from this season on his first southerly migration.


In the past, close encounters with humpbacks have been common on this section of coast line. This year however, they have been noticeably more cautious; diving as soon as a boat reaches a certain vicinity. This may be due to an increase in human disturbance locally through both the fishing industry, leisure maritime activities and the resulting noise and pollution produced.


The fact that such displays are rarer, makes them even more special. We all sat in delighted shock at what we had just experienced. Watching as the mother led her energetic charge away towards the cooler waters of the Antarctic.


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