Distribution of target strength and fish density in Kapota Atoll, Wakatobi Waters

¹ Department of Marine Science and Technology, IPB University, Bogor 16680, Indonesia
² Oceanography and Ecological Science, Shanghai Ocean University, Shanghai 201306, China

^* Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Abstract

Target strength (TS) is an acoustic backscatter measurement that reflects fish size, whereas fish density is an important indicator of aquatic ecosystem conditions. This study aimed to describe the distribution patterns of TS and fish density in Kapota Atoll, Wakatobi Waters, using hydroacoustic technology with a single-beam chosounder, Simrad EK-15. The results showed that TS values ranged from -51.8 dB to -37.6 dB, with an average of -42.5 dB, and tended to increase with depth, indicating the presence of larger fish. The spatial distribution of fish density varied significantly both horizontally and vertically. The highest density was detected at depths of 21–25 m, with a maximum of 45,602 individuals/1000m³ and minimum of 2 individuals/1000m³. An average density of 514 individuals/1000m³ reflects a good environmental carrying capacity. The lagoon area tended to be the center of fish aggregation because of its more complex habitat, whereas depths beyond 33 m showed a significant decrease in density. The negative relationship between TS and fish density indicates that larger fish are more commonly found in deeper layers but in lower numbers. These findings provide a scientific basis for sustainable fisheries management in the Kapota Atoll.