‘For whate‘Our oil supply is secure, not because our government threatens to use force against those who would make it insecure, but because the world’s oil suppliers want to make money.’ver we lose (like a you or a me)
David R. Henderson, as quoted in Handbook of Oil Politics: 2012
it’s always ourselves we find in the sea.’
Sound is an amazing perception, to use the physiological term. As one of the five senses we humans have been blessed with, it’s presence in our lives is taken for granted most of the time. It’s only when we start losing that perception that we realise just how important sound and hearing are to us. One of the more intriguing, and seemingly (on the face of it) contradictory, properties of sound, is the speed at which it moves through various mediums. Sound travels through the air and liquid in longitudinal, or compression, waves, and through solids in both longitudinal and transverse waves. We won’t go into the scientific explanations for these wave forms: if we start talking about shear stress, compressibility and adiabatic indexes, you are likely to go away and make a cup of coffee, which means you’ll miss out the really interesting bits.
The speed of sound, as we normally refer to it, is the speed of sound through the air, which is 1,235 km/h. Once sound hits a denser medium though, unlike light, it speeds up: the denser the medium, the quicker it travels. As sounds relies on a the medium to transmit the waves, the denser the substance, the quicker the wave will move. Temperature also affects the speed of sound: air at 0˚C transmits sound at a reduced speed of 1 192 km/h. To quote the oft-repeated mantra: ‘In space nobody can hear you scream’. Of course not – in a vacuum at absolute zero, there is nothing for the sound to reverberate off or through. If you going on a spacewalk, take a cellphone. Through water (and you’ll soon see where we are going with this) sound travels at 4.3 times the speed of sound in the atmosphere, in iron at around 15 times that speed, and through that beautiful medium, diamond, at 35 times the speed in air.
Not surprisingly it’s the ‘sound through water’ aspect that we want to concentrate on here. Marine mammals, such as whales, dolphins, and porpoises, are much more dependent on sound for communication and sensation than are land mammals, because their other senses are of limited effectiveness in water. Sight is very limited, and smell – well, smelling under water is not recommended for creatures that are airbreathing. Don’t try it. Molecules diffuse more slowly in water, so creatures that can ‘taste’ the surroundings may be getting messages that are way out of date. All marine mammals are therefore highly dependent on sound propagation to communicate and feed; and ‘whale song’ has become a great focal point for cetologists. (Marine mammal scientists.) Sperm whales and dolphins are not as melodious as the whales beloved of New Age musicians, they communicate through a complicated series of clicking sounds. These rapid, rhythmic clicks have been observed to identify individual dolphins in groups, and to guide pods to feeding areas.
When discussing marine mammals, it is unlikely that the conversation would turn to melons, but strangely, it should. Each individual mammal has a mass of adipose tissue in their foreheads called a melon, and this is the organ that focusses and modulates the animal’s vocalisations, and acts as a sound lens. It is key to the underwater communication and echolocation that these creatures are completely reliant upon. It’s a complex structure, despite being made of made of triglycerides and wax, and it creates a sound velocity gradient that refracts sound directionally. Sounds also bounce off the skull and air sacs that surround the melon. The melon can actually be focussed by the animal, changing the size, shape, direction, and frequency composition of the echolocation beam.
Which all brings us to a current pressing issue: could you imagine trying to communicate with a gun being fired off next to your head every few seconds? It would drive you insane in a very short period of time, and yet we humans are prepared to do it underwater in one of the greatest marine reserves on the planet, all in the name of searching for a source of carbon-based fuel that is being outmoded and legislated against. The oil and gas exploration off the Wild Coast is a mind-boggling enterprise, and the effects on the underwater creatures – not only the mammals – have not been properly considered or taken into account. Six months of these airgun explosions – loud enough to register to a depth of ten kilometres into the sub-ocean terrain – will blow the melons of marine mammals to perdition.
Our world ocean is under threat from all sides. Pollution is rampant; overfishing – legal and illegal (China has over one million fishing boats in the world’s ocean) – is endemic; spilt oil is creating havoc (rogue ships at sea illegally dump used oil; it’s estimated that each year twice as much oil is jettisoned by vessels than was lost by the Exxon Valdez in a crippling oil pollution disaster); and breeding sites are being destroyed. We ask that all our guests and visitors educate themselves on the protection and restoration of the waters that surround us. Once a species is gone, it’s gone – there is no turning back.
Join us for a cruise and you’ll understand exactly why this wonderful, beautiful, world of diversity needs to be saved from greed and selfish motives. Not only for us, but for all the succeeding generations to come.
