Helen -   Well it’s a wonderful thing to see for yourself.  I remember the first time I saw a dolphin swimming in a bow wave and jumping into the air, and it was fantastic.  It’s the sort of thing that’s been observed way, way back in time.  I think the ancient Greeks were telling us about dolphins on bow waves.  They've been doing it for ages and it’s the kind of thing that we don't actually know for sure why they do it.

They certainly do get a power boost.  They’re surfing, essentially, the wave that the boat produces, and if any of you surf, you know how much power you can get from just sitting on a board and racing down a wave towards the beach - that’s essentially what dolphins are doing.

There have been observations of dolphins doing this and maybe associating it with fishing vessels, so they can come along and get some fish for themselves.  That’s one possibility.  But then there’s also been observations of dolphins riding a boat for miles and miles and then just coming all the way straight back again after they've hitched this ride, returning to where they came from.  That’s clearly not going to be any energetic benefit for them. 

They might just be having fun - they are deeply intelligent creatures, we know that.  So why not just have some fun and hang out, and you can hear them talking and whistling to each other as they're going.

I remember something particularly wonderful:  Later on in my research career when I was doing my PhD, I had the lucky time of going to work every day, along on a boat ride across a beautiful emerald lagoon.  Every morning, the same pod of spinner dolphins would join us and I could recognise the patterns on them, and they’d come along and ride our bow wave, on our way to our research site.  Then they would leave us, and later come back with us on the way back.

So, I do think there’s a lot of fun involved.  Occasionally, maybe they are coming to feed, but we don't necessarily know.  They're definitely up to something, and it’s rather fun to be able to watch it.

Ben -   They are very intelligent animals.  We know they communicate with sound, but is there some truth that some of these jumps out of the water are actually communicative as well?

Helen -   It could be.  They do have very complex communications and very complex social groups.  It could well be that they're trying to say things to each other, and it's not all friendly as well!  I hate to break the news that dolphins can be quite aggressive, but that’s also a possibility.  There’s all sorts of things for us still to discover about these wonderful creatures.

Ben -  It might be a bit more complicated than just tracing the pipe back to the pump itself, but you could borrow a technique that they use in medicine that relies on the Doppler Effect.

Now you're probably familiar with the Doppler Effect.  It’s what makes the sound of an ambulance or a police siren change as it’s coming towards you or away from you. 

When the source of the sound is coming towards you, the soundwaves get squashed together and as a result has a higher frequency, it sounds higher. When it goes away, they're stretched - so lower frequency, lower pitch.

Now, you can also use this method in medicine with ultrasound.  In fact, they use the ultrasound Doppler to observe blood flow in a foetus.  This is what we could steal to follow the water in your pipe.

So if you put an ultrasound signal in the pipe and then measure the sound, then if the recorded sound is of a higher pitch, then you can infer that it’s been compressed by the water, and so that should mean the water is moving towards you, I think.  So, you could use it, but I think probably, tracing it through to the pipes is considerably easier.