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The University of Southampton

Research project: The sources of underwater click sounds of biological origin in UK shallow waters - Dormant

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Deploying a hydrophone in many areas along the south coast of the UK during the summer will result in a loud clicking sound being heard. These can be very loud and can occur at up to 20 clicks per second. A literature search and talking to other researchers has failed to suggest the source of the clicks. The sounds were first heard by the author in Durlston Bay in 1994, and subsequently at sites from Falmouth Harbour to the Isle of Wight. The clicks are typically very short wide bandwidth clicks with significant energy in the band 0.5-150 kHz.

Work on this project has established two monitoring stations in Durlston Bay and in the Fleet, both in Dorset. In addition, recordings have been made at 20 other sites around the southern part of the UK. This acoustic data has been analysed in some detail and four distinct types of click identified. It is believed the type A click comes from a snapping shrimp, probably Alpheus macrocheles. The type B click is the most common and may come from a species of fish. The type C click is only heard in the spring and may originate from a species of Goby. The type D click appears to originate from breaking wavelets rather than a biological source and is only heard under very specific weather conditions.

The equipment at the monitoring sites has been programmed to look for the clicks using a simple form of spectrogram correlation and the pattern of click activity through the diurnal and tidal cycles investigated. This has produced conflicting data for the two sites with most click activity at night at Durlston and during the day in the Fleet. In addition, there is clear evidence of a dawn and dusk chorus at Durlston, and none in the Fleet.

In order to investigate the distribution of the clicks a multi-hydrophone array is being constructed which will localise the source of the clicks. This will be combined with a video camera and it is hoped that the combined evidence will catch the species concerned ‘in the act’ of clicking.

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