BECKYHITCHIN
A not-so-silent world
Having touched on underwater acoustics and beaked whales , Becky Hitchin turns to the wider issue of noise in the sea
Last month I left all the rebreather divers feeling smug at not producing the normal Darth Vader-esque inhalations and exhalations of open circuit divers . And yes , Darth Vader ’ s breathing noises were recorded from regulators . Dacor ones , as it happens . Now I ’ m going to disabuse that smugness . Well , at least slightly . This month I want to discuss the noises that we scuba divers put out into the water column , and also consider one of the man-made noises that we used to get to hear .
So how do we make noise underwater ? Mainly from the creation of bubbles . These can be from obvious sources , such as the bubbles created on exhalation through a regulator , but also a huge number of less obvious sources , such as from fin movements and even inhalation . Also , that well-known high-pitched squeaking at your buddy when you see a lumpsucker or other such desired critter , or when you realise your drysuit zip isn ’ t quite done up properly .
There have been several scientific studies looking at the types and magnitudes of noise emissions from various sets of diving equipment – open circuit , semi-closed and closed circuit , using a variety of makes and models of both open and closed circuit . Results from trials in New Zealand were particularly interesting . Scientists found that they could easily hear divers in the sea over the ambient levels of noise using not only open , but also semi-closed and closed systems , though of course open circuit systems were found to be loudest and more rhythmical .
They also found that noise levels tended to be louder at greater depths . Experiments showed that sounds from divers wearing both open circuit or semi-closed systems were detectable by fish more than 200m away from the diver . Detection did drop dramatically for the closed system , but fish could still detect the noise at 12.5m .
So that ’ s the minimum noise you produce . Anything above that is up to you . Tank bangers , horns , DPVs , singing songs to yourself will all increase your noise load . Of course , your total noise load over a dive will also depend on whether you slip into the sea like a selkie returning to their natural state , or if you ’ re more like me , splashing , almost falling over and laughing a lot - either from the shore or a boat .
Should we also count the boat thrusters and propellers ? The lift
“ Experiments showed that sounds from divers were detectable by fish more than 200m away ” entering the water to pick each diver up ? The swearing as you wade back to shore through entangling strands of seaweed seemingly trying to drag you back down into the sea ?
So , what can a diver hear ? It depends on location . Coral reefs are jam packed with noise , from bubbles making their way through three dimensional mazes of coral to parrotfish very loudly crumbling the aforementioned coral to grind it to sand . There are mantis shrimps breaking the sound barrier exploding from their burrows to ensnare prey . It ’ s known widely now that ecosystems have their own soundscapes and a healthy coral reef has been said to sound like popping corn .
In more temperate climes , parrotfish will unfortunately be absent , and many sounds heard may be man-made . Boat traffic , ferries with their deep thrum as they pass nearby , but also seal scarers and acoustic deterrent devices ( ADDs ). You ’ ll know these ADDs underwater – they let out a constant stream of pings at just a frequency where you ’ re not sure whether you ’ re imagining the sound or not . Over 10 per cent of all noise measurements in Scotland in 2016 captured signatures of ADDs , though this is likely to have dropped over the last few years .
When we dive , we enter a world full of sound , and become part of that ongoing soundscape . Science is showing that marine animals use sound to navigate , settle , reproduce . While it ’ s unlikely that any one diver could significantly impact a habitat with the sounds they are making ( though I can think of some buddies with regs so squeaky that that might not be the case ), it ’ s worth knowing how you are affecting the world you ’ re entering – and to understand the noises you hear in this incredible world under the water . �
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