Estimating Snapping Shrimps Biovolume: An Improved Simulation-Based Approach

Snapping shrimps (SS) can generate snapping sound pressure level (SPL) exceeding 200 decibels, referenced to 1 micro-pascal (200 dB re 1 μPa) which makes them one of the loudest biological sound producers in the water. Due to its high intensity, the snapping sound interferes with underwater communications, naval sonar calibration and bioacoustics monitoring. This makes SS biovolume estimation indispensable. Recently, researchers' interest in this topic have been elevated to unprecedented level and many methods have appeared in the literature. Although these methods' results were satisfactory, but they failed to report on some crucial parameters including the absolute density of SS which exemplifies the real reading of shrimps' numbers. This paper presents an improved simulation-based method that uses a single underwater HydroMoth recorder that can efficiently detect ultrasonic signals in aquatic environments. A sensitivity analysis was conducted to determine the optimal height at which the HydroMoth is to be placed over the predetermined shrimps' bed to minimizes undesired shellfish sounds. In addition, we calculated the absolute density of the SS in each location and measured the temperature, salinity, and turbidity at different times. This research is novel in that: (i) it is the first time to estimate SS biovolumes in three different seas surrounding Türkiye in one research; and (ii) this research reports on the absolute density of SS in 17 locations; and (iii) it tests for agreement between the environmental variables and acoustics parameters. Our results established that spatial environmental variability such as salinity, temperature, and turbidity exert a strong influence on the acoustic behavior and detectability of snapping shrimps and it confirmed that warmer, saline, and clearer waters such as those of the Aegean and Mediterranean Seas enhance sound speed efficiently allowing shrimp snaps to propagate over longer ranges with minimal attenuation. Finally, we compared our results with results from 4 published papers and found that the proposed method results are highly accurate, consistent, and more qualified than those in the other published papers.