bridge hydrophone4
As the river flowed out to sea during low-tide, a pair of hydrophones designed by
Jez riley French was lowered from an old wooden bridge (photographed). The hydrophones have caught these mysterious pops and crackles from beneath the surface, whilst from above the faint sounds of cars and pedestrians can be heard.
Kevin Seward identified the sound as Snapping Shrimp. The sound that can be heard is the implosion of bubbles created by the shrimps as they snap their claws at targeted prey. A high-velocity stream of water jets from the claw at approximately 110 km per hour. The sound has been measured at 218 decibels. The energy involved in the release of these bubbles is so strong that it can weaken metal surfaces, such as ship propellors and pumps. Submarines have been known to be strategically positioned in areas of snapping shrimp as it is virtually impossible for sonar to detect them through the cacophony.
Pretty impressive for a crustacean the size of a finger.
SOUNDS LIKE NOISE 
Maybe these fellows:
http://en.wikipedia.org/wiki/Snapping_shrimp
They seem to show up in a lot of hydrophone recordings:
http://www.freesound.org/tagsViewSingle.php?id=12814
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Hi Kevin – wow, it sounds just the same doesn’t it? You’ve solved the mystery within only a couple of hours. I had been wondering if it was some kind of electrical discharge, but the real thing is even better. Thanks for taking the time to write.
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Interesting and very loud pops or cracks. Do you know what it is? …Fish eating candy 🙂
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Ok shrimp
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Kevin has identified the sound as Snapping Shrimp. The wikipedia link he provided describes them as “a major source of noise in the ocean”, and being able to interfere with sonar and underwater communication”. The shrimp snaps its claw to release a high pressure bubble which stuns its prey, and which can reach 218 decibels. The especially inhabit oyster reefs – I know this to be true as for a few horrible minutes the hydrophone lead got entangled amongst them.
I like the idea of fish eating candy though.
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Fascinating! It’s a whole new world under there.
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Yes, the planet is so much more than our daytime terrestrial experience isn’t it? Field recording has really helped emphasise for me the dramatic split between the nocturnal and diurnal worlds. Now with French’s hydrophones the hidden life of the aquatic world is being brought into focus.
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Sounds like me making popcorn before sitting down to watch a movie. Interesting sound, nice capture!
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Looking down through the surface of the river it’s so good to know that there is an unknown world waiting to be explored.
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