PROCEEDINGS of the23rd International Congress on Acoustics
9 to 13 September 2019 in Aachen, Germany

Snapping shrimps sounds in the Black sea
Nikolay BIBIKOV1; Oleg OVCHINNIKOV1; Michail IVANOV2; Andrey SEREBRYANY11

JSC N.N.Andreyev Acoustical Institute, Moscow, Russia.
2

St Petersbourg State University.

We have recorded an ambient noise at several sites at the Black Sea shelf zone. In all these sites,in the absence of a strong swell or storm, the recorded signal was almost entirely due to theactivity of snapping shrimps, apparently belonging to the species Alpheus dentipes. We useddifferent recording equipment, but in all cases we tried to provide a wide band of frequency
analysis. In contrast to the data obtained in tropical waters, the rate of the most intense clicks
was comparatively low, which allowed us to analyze their shape in detail and estimate thedistance from the animal to the audiorecorder by analyzing the echo delay from the water
surface. Qualitatively, the signals in different habitats were identical. However, the type ofrecorded signal depended on the nature of the bottom surface and the presence of reflections.
We revealed the existence of a pair of pulses emanating from the same object from the sameposition. The use of high-frequency equipment suggests that the high-frequency edge of thesnapping shrimps click spectrum can reach 300 kHz.
Keywords: snapping shrimps, Black sea, shelf sounds
1. INTRODUCTION
Global warming has significantly changed the geographic range of many species. Thisis especially true of marine invertebrates, who must adapt to changing ambient
temperature to survive. Decapod crayfish belonging to the family Alpheidae, calledsnapping shrimps, in particular have spread rapidly from the tropics and subtropics totemperate zones. Their activity has already been recorded in several points of theMediterranean (1), as well as in Ireland at latitude 51.50 (2). In the 1990s, we recorded andinvestigated the clicks emitted by snapping shrimps in the Peter the Great Bay (Sea ofJapan) at latitude of 42.5o (3). In the past few years, we have observed and studied
snapping shrimps clicks at several points on the shelf zone of the eastern and northernshores of the Black Sea. We gathered the most data of this activity at Sukhum Bay. Theresults obtained in the course of this work were partially published (4). Also preliminary
studies of this activity were carried out in the area of Blue Bay near the Gelenzhik city andat the T.I. Vyazemsky Karadag scientific station (Nature Reserve of the RAS). The resultsfrom each studied location are worth examining.
2. RESULTS
2.1 Sukhum capeAt Sukhum bay (42.979N,40.973E) snapping shrimp signals were first recorded in 2013.
We used a laboratory room located at piles on the distance of 10–17 m from the coast. Atthe place where clicks were recorded, the seafloor had a slope of about 30 o south from the1
2nbibikov1@yandex.ru

20mivanov@mail.ru

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coast - so the depth of the seafloor increased from 5m to 10m. The surface of seafloorwas
covered with pebbles and topped with a layer of dead mussel shells. We performed
acoustical monitoring of this site over several years. We recorded acoustic activity with aBrüle and Kjar hydrophone (uniform frequency response up to about 200 kHz), placed
30-40cm above the bottom. For long routine monitoring we recorded ambient noise in the
10-40 kHz frequency range, but we conducted short-term recordings at a quantization
frequency of 196 kHz.
Since the sizes of pebbles and mussel shells are comparable with the wavelength of themost high-frequency components of a click, the calculation of thedirection and the form of
actual recorded signal turns out to be rather complex.
In contrast to the acoustical activity of these animals that was recorded in tropicalwaters (1) at Sukhum bay the rate of high-intensity clicks was low, which allowed us toanalyze the amplitude and shape of individual impulses in detail. In some cases theamplitudes of individual clicks exceeded the noise level by more than two orders ofmagnitude (Fig. 1)
In many cases, we very clearly observed an echo from distinct click. The response
phases were inverted, indicating that the signal had been reflected from the sea surface. As
a result we were able to estimate the distance from the point of radiation to the point on theseafloor where the hydrophone was located. For the example illustrated in fig 1,
considering the slope of the bottom and assuming that the emitter is situated closer to theshore than the receiver, we obtained an estimate of the distance along the bottom surface ofaround 1.5 meters. Since the amplitude of the signal was high, it is reasonable to conclude
that we obtained a valid recording and that the emitter and receiver were in close
proximity.

Figure 1 – This is a snapping shrimp click recorded with evident echo signal reflected from thewater surface. Abscissa - the time in ms, ordinate –sound pressure in relative units.

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Figure 2 – Two snapping shrimp clicks which were recorded at 8:02 pm with an interclick
interval of 0.84s. Abscissa - the time in ms, ordinate –sound pressure in relative units.
Several times we observed very interesting events – a double click of the same animal
emitted from the same place with an interval of about 1s. An example of such an event ispresented in the fig 2. The shapes of the two clicks with all their peculiarities are virtuallyidentical.
2.2 Blue bay
At the point with coordinates ( 44.575N, 37.982E ) we recorded snapping shrimp
signals using the hydrophone with an upper frequency limit around 200 kHz and with asampling rate of 500 kHz.
3020Amplitude,Pa

100-10-20-30-40-50

00.5

11.5

22.5

3

3.5

4Time,msFigure 3 – This is snapping shrimp click recorded with evident echo signal reflected from thewater surface. Abscissa - the time in ms, ordinate –sound pressure in Pa. 29.06.2018, 6 h 30 m.

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The hydrophone, descended from the pier, was located approximately 2.5 m below thewater surface. The seafloor at this site was sandy and silty. Its surface at a depth of 4 m wasrelatively flat. The delay between the emitted signal and the echo indicated that the soundwas emitted approximately 3m from a point of the bottom just below the suspendedhydrophone.
2.3

Karadag scientific station
In the T.I.Vyazemsky Karadag scientific station (Nature Reserve of the RAS)
(44.911N; 35.202E) we recorded bioacoustic signals using the TC4014-5 hydrophone(RESON, 480 kHz resonance region), equipped with a miniature preamplifier located on
the ceramic sensor. The frequency band of the amplification path was 1 MHz, and thequantization frequency was 5 MHz (14 bits). The analog to digital converter E20-10 has alow pass filter of 1.25 MHz and allow us to record of any digital information to a computer
via the USB channel.
0.2

Amplitude, r. u.

0-0.2
-0.4
-0.6
-0.8
-1

0

0.05

0.1

0.15

0.2

0.25

Time,ms

Figure 4 – This is a snapping shrimp click waveform recorded by a high frequency hydrophone.
Abscissa - the time in ms, ordinate – sound pressure in relative units.
-20-30Level, dB-40-50-60-70
-80

0100

200

300

400

500

600

7008009001000

Frequency,kHz

Figure 5 – Spectrum of the snapping shrimp click recorded by high frequency hydrophone.
Abscissa - the frequency in kHz, ordinate – spectral level in dB in relative units.

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At the site where snapping shrimp clicks were recorded, the seafloor was relatively flatand covered with sand, stones, and algae. The hydrophone was placed less than one meterfrom the surface and three meters above the seafloor. At this location only a few individual
clicks were recorded.
The recorded clicks were very short with very high amplitude. Unfortunately we wereunable to measure its value in Pa, due to the lack of accurate gain calibration. The durationof the click was less than 10 mks (fig. 4). We estimated the spectrum of this signal. We
found that the upper limit of a fairly high spectral power of the click reached 300 kHz (seefig. 5).
3. DISCUSSION AND CONCLUSIONS
The activity of snapping shrimps in temperate waters of the northern hemisphere differs
significantly from their activity in tropical waters. In more habitual and long ago masteredplaces (tropical waters of Australia, Asia and America) individual pulses of animals
belonging to different species often overlap. They also mix with other bioacousticalsignals (5, 6). Snapping shrimps have began to inhabit the Black Sea relatively recently. At
all points where we performed our recordings, high-amplitude single pulses were emittedwith a comparatively low rate (less than once per second). According to (7) and ourpreliminary observations, only one species of snapping shrimp (Alpheus dentipes) lives in
the Mediterranean basin and in particular in the Black Sea at present. This is confirmed by
the fundamental similarity of the shape of clicks recorded at different points.
Other bioacoustical sounds were recorded very rarely. Almost the only sound events
that could be confused with shrimp clicks were echolocation pulses of dolphins. However,upon careful offline examination of the recordings, these signals were excluded based on
the lack of a lower-frequency precursor. In addition, dolphin’s echolocation pulses werealmost always emitted in series with small interpulse intervals.
Regarding the spectral parameters of the emitted clicks, they are determined primarily
by the characteristics of the recording system and, to a lesser extent, by the distance fromthe emitting source to the registration site. Interestingly, higher frequency hydrophones
yelding recorded higher-frequency clicks, we found, suggesting that data obtained withusing low frequency hydrophones significantly underestimate the complexity of click’sspectrums. Under favorable conditions (see Figure 5), the high-frequency edge of the click
spectrum reached 300 kHz.
The presence in many cases of a pronounced inverted echo signal from the surface of
the water allowed us to determine the distance from the transmitter to the recordinghydrophone. Using the records from several hydrophones located in different sites on theseafloor it is possible to achieve a strict localization of the emitter. Such techniques allow
both an investigation of the behavior of individual animals, and monitoring of small
shrimp populations in situ. Obviously, such monitoring could be productive both forassessing population dynamics and for identifying environmental factors, including
anthropogenic influences that may affect the shelf ecology.
ACKNOWLEDGEMENTS
The study was supported by RFBR Grant № 19-52-40007.

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