Search

Redlip mullet (Chelon haematocheilus) is distributed in coastal waters of the North-Western Pacific Ocean and is a cultured fish in Korea. A hydroacoustic technique constitutes a useful method to assess the biomass and spatial distribution of mullet in sea cages or in coastal waters, and acoustic target strength (TS) information of the target fish is an essential parameter in using this method. In this study, ex situTS measurements of 16 live mullets were made in an aquaculture sea cage in Korea. The split-beam scientific echo-sounder used for measurements was comprised of 38, 120, 200, and 420 kHz frequencies. An underwater video camera was simultaneously used to observe the mullets' behavior during the TS measurements. The mullet TS data was analyzed from a wide range of total fish length (FL: 14.3–40.3 cm). As results for all frequencies, the frequency dependence of the mean TS values were relatively low, and the difference in mean TS was within 2.5 dB. When the slope of the least-squares regression line was forced to 20 into the TS equation, the resulting value for the constant term (b20) at each frequency was −67.0 dB, −68.3 dB, −66.3 dB, and −68.5 dB, respectively. The data tended to be frequency dependent. Additionally, the maximum TS appeared between tilt angles of 0° and 10°. These results indicate that TS measurements can be applied to estimate the biomass of the mullet in sea cages or in coastal waters. [ABSTRACT FROM AUTHOR]

We conducted a TS study of yellow croaker (Larimichthys polyactis), a major commercial fish in Asia that has not been studied before. Ours is the first study that examines the relationship between target strength (TS) and fish length using 38, 70, and 120 kHz split-beam echosounders. We measured TS in five size groups of yellow croaker (Larimichthys polyactis) based on length (8.2–26.5 cm total length) in a seawater tank and calculated the Kirchhoff-ray mode (KRM) model. When the slope of the least-squares regression line was forced to 20 in the TS equation, the resulting values for the constant term (b 20) at each frequency (38, 70, and 120 kHz) using the caged method were –67.69, –67.52, and −68.83 dB, respectively. The swimming angle (mean ± S.D.) in the net cage was − 4.2 ± 21.9°. The b 20 values for the KRM model were –65.01, –64.74, and −66.27 dB at 38, 70, and 120 kHz, respectively. In both methods, the KRM model's b 20 values were relatively higher than those of the caged method by 2.68, 2.78, and 2.56 dB at 38, 70, and 120 kHz, respectively. Such TS ex situ measurements can be applied to improve the yellow croaker's acoustic abundance estimates. [ABSTRACT FROM AUTHOR]

Redlip mullet (Chelon haematocheilus) is distributed in coastal waters of the North-Western Pacific Ocean and is a cultured fish in Korea. A hydroacoustic technique constitutes a useful method to assess the biomass and spatial distribution of mullet in sea cages or in coastal waters, and acoustic target strength (TS) information of the target fish is an essential parameter in using this method. In this study, ex situ TS measurements of 16 live mullets were made in an aquaculture sea cage in Korea. The split-beam scientific echo-sounder used for measurements was comprised of 38, 120, 200, and 420 kHz frequencies. An underwater video camera was simultaneously used to observe the mullets’ behavior during the TS measurements. The mullet TS data was analyzed from a wide range of total fish length (FL: 14.3–40.3 cm). As results for all frequencies, the frequency dependence of the mean TS values were relatively low, and the difference in mean TS was within 2.5 dB. When the slope of the least-squares regression line was forced to 20 into the TS equation, the resulting value for the constant term (b20) at each frequency was −67.0 dB, −68.3 dB, −66.3 dB, and −68.5 dB, respectively. The data tended to be frequency dependent. Additionally, the maximum TS appeared between tilt angles of 0° and 10°. These results indicate that TS measurements can be applied to estimate the biomass of the mullet in sea cages or in coastal waters.