Some peculiarities of sounds generated by snapping shrimps in the Black Sea.

During autumn period of 2015-2016 intensive bionoises were recorded in shallow waters of the eastern coast of the Black Sea (Suhum bay) using broadband hydrophone (upper frequency limit - a few hundred kilohertz). When placing a hydrophone in 30-40cm above the bottom surface at a depth of 5 to 10 m the recorded signal contained high frequency noise generated by snapping shrimps. Along with these background signal we observed relatively rare (usually several times per minute), but very intense (up to a few hundred Pa) clicks. They apparently were radiated by single shrimp localized in the vicinity of the hydrophone. Such conditions are allowed to carry out a time-frequency analysis of the signals in natural conditions of the habitat. It has been shown that they consist of the following sections: a short precursor generated by the water jet emitted during the closing of the claws, a powerful ultrasound pulse arising due to the collapse of a cavitations bubble, and multiple reflections from the surrounding elements of the bottom surface (gravel, empty shells of mussels). The rise time of the main pulse may be 7-10 microseconds with total duration of the signal from 0.1 to 0.4ms, varying specificity due to reflections. In many cases along with the main pulse the delayed echo from local artificial underwater objects and from the surface also can be observed. The possible practical applications of the data are discussed.