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.