An investigation of underwater click sounds of biological origin in UK shallow waters

Abstract

This study investigated a clicking sound which is often heard when deploying a hydrophone in UK shallow waters. This sound has often been described as being produced by snapping shrimp yet very few snapping shrimp have been found in UK waters. This work has identified the sound of snapping shrimp and shown that a similar sound, while present throughout the year, is not the dominant component of the click field during the summer and autumn.

This work has shown that the click sounds are heard in the southern half of the UK only and that click activity has a strong dependence on the annual and diurnal cycles peaking in late summer and during daylight hours. It has also shown that the click activity is dependent on the bottom type with little activity over uniform sand or mud sea beds.

Three principal types of click have been identified although it is believed that a greater number of different species contribute to the click field. Localisation of the click sources using one, two and four hydrophone arrays has shown that the majority of the clicks are produced above but close to the seabed. There is also more click activity in the deeper channel than in the inter-tidal shallows at the main study site in the Fleet, Dorset. It has also demonstrated very little click activity over the nearby sand flats.

The use of cameras to try and capture pictures of an animal producing the clicks both in the wild and in aquaria and in rock pools has not been successful. This may be due to a number of reasons which are discussed in this report.

Although this work has failed to identify the click-producing species it has provided a much better understanding of the characteristics of the clicking sound and recommendations are made for future work that should lead to an identification of the click-producing species.

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ORCID for Paul White: orcid.org/0000-0002-4787-8713

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