By Clare Embling
Image credit Mike Hood
It’s great to be back on the Extended Ellet Line – the last time I came on this survey was 10 years ago on the RRS Charles Darwin. Then and now I was towing a hydrophone behind the ship (an underwater microphone) to listen for whales, dolphins and porpoises (cetaceans). Then it was for my PhD investigating the distribution and habitat use of cetaceans off the west coast of Scotland. This time I bring my PhD student (Leah Trigg) who is looking at the impact of shipping noise on marine mammals.
I use sound as a tool to find out where cetaceans are in the oceans. Out here in the deep blue sea far from land, the sea is often rough, and cetaceans hard to spot, so using hydrophones becomes a much better way of finding them. Our hydrophone is towed 350m behind the ship to distance it from the ship noise, we can hear most cetaceans that vocalise except for the very low sounds of baleen whales (they ‘moan’ below our range of hearing, and below the range of our hydrophone < 100Hz). It’s a shame because we saw a fin whale on our first day out of port, in glassy calm seas (never seen one out here before because the sea conditions aren’t usually good enough!) – it would have been great to be able to hear it too!
Here’s an example of what we’ve heard this trip – it’s a fantastic recording of some pilot whales. If you listen carefully you should be able to hear their whistles (used for communicating between each other – their version of language), echolocation clicks (used for finding their fish or squid food), but also you’ll be able to hear the pings of the ship’s echosounder used to find the bottom in this very deep patch of ocean, the rotating of the propeller, and maybe even some water noise from the waves going over the hydrophone.