ACOUSTIC PROPERTIES OF INDIAN MACKEREL (RASTRELLIGER KANAGURTA), YELLOWTAIL SCAD (ATULE MATE) AND JAPANESE SCAD (DECAPTERUS MARUADSI) BASED ON FREQUENCY RESPONSE ANALYSIS

Multi-frequency acoustic data collected during ex situ target strength measurements in Catba Island, Vietnam was used to calculate frequency response for Japanese scad, Indian mackerel and Yellowtail scad. Total of 168 echotraces of Yellowtail scad, 291 of Japanese scad and 53 of Indian mackerel were generated for frequency response analysis. Results indicated significantly different in r(f) of three species (Post Hoc Tukey Test, p < 0,001). A discriminant function analysis used frequency response at 38, 120 and 200 kHz and backscattering cross section at 38 kHz as independent variable was able to differentiate between species. Approximatly of 87% echotraces of these species was classified correctly. Frequency responses at 38 kHz, 120 kHz and backscattering cross section at 38 kHz were the most important independent variables. This study revealed that Japanese scad, Yellowtail scad and Indian mackerel could be identified acoustically; a finding may be important for acoustic surveys for small pelagic fish in Vietnam.