Friday, 1 March 2013

Ocean noise (part 1!)

I thought it was about time I wrote my first ‘fascinating science’ blog post, and considering I recently co-authored a report on ocean noise, and just gave a lecture on ‘human noise in the sea’, I thought this would be a good topic.

Listening for sperm whales & beaked whales in the Bahamas
I have spent a lot of time listening to the sounds of the sea, sitting on boats with earphones strapped to my ears connected up to a hydrophone (underwater microphone) being towed behind the boat.  The sound of the sea can be soothing (is there any better sound than sitting on a beach listening to waves crashing?)… I’ve sat listening to a cacophony of snapping shrimp (sounds like popcorn popping or small firecrackers), breaking of waves, the soothing sound of rain on the surface of the sea, the slow echoey clicks of sperm whales, and the joyful sound of dolphins whistling away.  Even snorkelling you hear all sorts of sounds from marine life – marine life is surprisingly noisy.  So it can be a soothing life, the life of a bioacoustician (that’s what they call us – scientists who study the sounds of life) – sitting listening to the sounds of the sea (and admittedly sometimes falling asleep to the sound of the sea!). [For a good collection of sounds of the sea check out the DOSITS (Discovery of Sound in the Sea) website here]

But the sea is full of human noise too, sitting on ships listening to the sea obviously there is the continuous sound of the ship as it moves through the water.  I have worked mostly on quiet scientific ships with ‘quiet’ propellers, but there were times when the quietened propellers didn’t work well and at certain boat speeds there would be a loud high pitched constant squeal, giving you a headache as you tried to pick out any dolphin and whale sounds in the background.  Ships contribute an enormous amount of noise to the marine environment.  Propellers, flow noise of water around the ship, engine noise… all help to make a boat noisy – and there are A LOT of ships in the ocean.  Just think of all those ships transporting goods around the world, not to mention all the other boats that use the seas.  Studies have shown that shipping is responsible for a 3dB/year (that’s a doubling) in low frequency noise in the oceans (< 50 Hz – we can hear from 20 Hz to 20 kHz).  The sea is full of a constant hum of noise. Why does it matter? Low frequency sound can travel over massive distances – it propagates well.  In fact it propagates so well that some whales like blue whales make sounds of similarly low frequency to communicate across ocean basins – thousands of kilometres.  Scientists believe that this allows them to communicate for breeding purposes.  However with the increase in low frequency ocean noise, this now means that whales are only able to communicate over 100s of kilometres instead of 1000s of kilometres [see this article]. Who knows what the consequences of such changes are… if these sounds are used for finding mates then how are the whales coping not being able to communicate over such large distances?  Whales range over such large distances it makes it difficult to know how many of them there are and therefore how they are doing – we don’t know whether this increase in noise is having knock-on consequences on breeding success.  But what is increasingly being shown is that shipping noise is stressful for marine life.  There are a very few but increasing number of studies showing increasing levels of stress in animals exposed to increased shipping noise.  For whales, there is the wonderful study carried out on right whales:

Picture this: right whales have suffered over time… they are called right whales because they were the ‘right’ whales to hunt and were pretty decimated by the whaling industry.  But they hung on in there, but now struggle because they are prone to getting hit by ships.  Scientists did some wonderful studies looking at how they used the sea and found that there were certain areas that were most important for the animals for feeding purposes but these were right in the middle of the shipping lane – they told the government and managed to get the shipping lane adjusted so it avoided the right whale critical habitat [see this article].  What a win for conservation science!  The scientists continue to monitor the whales and started recording ocean noise.  Then along came 9/11, the shock of the plane going into the twin towers in New York (I remember seeing it on the internet working on one of the top floors of the second highest building in Manchester – I still remember the feeling of shock). Traffic to & from the US stopped.  This included a substantial reduction in shipping – in fact there was such a reduction in shipping that noise levels in the right whale habitat reduced by 6dB.  Meanwhile scientists continue to study the whales – now they were following the whales and getting dogs to sniff out their poo after they’d dived.  They collected that poo and analysed it for stress hormones.  They showed that right whales were less stressed during the time of reduced shipping noise, but much more stressed with the substantially higher level of ship noise [see this article].  So if right whales are more stressed from high levels of shipping noise other marine mammals are likely to be stressed out too.  This will have knock-on consequences for animal health, reproduction, and overall fitness.

And it’s not just whales that have been shown to get stressed due to high levels of noise – a study that was published only this week showed that shore crabs exposed to ship noise had a higher metabolism – ‘crabsget crabby exposed to ship noise’.  Similar studies have been done with shrimp showing lower levels of growth and lower reproductive rates with higher noise levels [see this paper].

So as our seas are getting noisier from all the ships travelling around the world delivering goods, there is a growing body of works showing that we are stressing out marine life.  I’m not sure what the solution is… ship builders are making quieter ships – but it takes a long time to change over a shipping fleet – ships are operational for decades.  It’s something to ponder over…

p.s. I see this blog as ‘ocean noise part 1’ because there are many other sources of human noise in the sea which cause problems for marine life… so watch this space for future blogs on ocean noise ;)

pps. Blog posts have been a bit slow because our household was hit by a 4 week flu virus (2 batches with not much recovery between).

1 comment:

  1. I was really interested in this, Clare, thanks. I knew human noise under the sea was an issue but not the details, and hadn't heard at all about the crabs. I'm looking forward to the next part. Hope you and the family are all feeling better now!