Hybrid surveys using hydroacoustic and fish sampling gears such as trammel net, trap were conducted to investigate total biomass, distribution and dominant fish species of the demersal fishes in the marine ranching area (MRA) of Jeju. Four surveys were carried out in June, August, October and November using 38kHz quantitative echo sounder. Catch data using trammel net and trap were used to calculate biomass and to examine dominant fish species. Fish schools were mainly detected in the waters of 20 meters below and around Chagwido waters. By the result of fishing experiments, fish species living in MRA of Jeju were about 40 species, dominant fish species of a detectable fish such as Family Sparidae and Family Monacanthidae etc. were identified 59.4~68.8% of total biomass. Based on the hydroacoustic data, fish length-weight function and target strength information, mean density of the demersal fish estimated were as
A mooring‐type underwater positioning system (UPS) to measurethe bag‐net movements in a set‐net by acoustic telemetry techniqueswith five transponders was reconstructed. The field experimentswere conducted in Jaran Bay, Kosung, Korea on 6 October 2000 (neaptide) and 28 November 2000 (spring tide). The average UPS fixingerrors of x‐axis, y‐axis and z‐axis were less than0.6 m, 0.8 m and 1.2 m, respectively.The longitudinal movement range, the latitudinal range and the verticalrange of the bag‐net at the neap tide were 3.2 m, 3.4 mand 2.1 m, respectively. At the spring tide, these rangeswere 7.8 m, 7.8 m and 5.0 m, respectively.It was confirmed that the UPS system could be used for measuringa part of the bag‐net movement.
Although ex situ target strength (TS) measurements using dual-and split-beam systems have become the primary approach of estimating fish abundance, theoretical model estimation is a powerful tool for verifying the measurements, as well as for providing values when making direct measurements is difficult. TS values for 20 samples of live bambooleaf wrasse (Pseudolabrus japonicus) whose target length (TL) ranged between 13.7 and 21.3 cm were estimated theoretically using the Kirchhoff-ray mode model, and the TS values for 18 live fish samples were additionally measured at ~0º tilt angle to the swimming aspect using a tethered method at a frequency of 120 kHz to verify the theoretical values. The digitizing intervals used to extract the fish body and swim bladder morphology in the X-ray photographs significantly affected the calculated TS patterns, but variations based on the speed of sound and density ratio values for the general range of fish flesh were relatively small (within 1 dB). Close agreement was observed between the measured and theoretical TS values, and the correlation between the average TS and body length of the fish could be calculated accurately as = 20logTL (cm) -71.6 using the theoretical method.
High-and multi-frequency acoustic measurement systems and the multi-frequency inversion (MFI) method have been used to measure spatial distributions and abundances of zooplankton by size. In this study, the calibration method for high-and multi-frequency systems was developed and the validation of MFI method was carried out by scatterer measurement. The standard sphere calibration method that has not been applied to such high-and multi-frequencies was applied to calibrate our high-and multi-frequency system, TAPS-6 (Tracor Acoustic Profiling System, BAE Systems). An optimum size of standard sphere of tungsten carbide of 1 mm radius was derived to have a small target strength variation for the six frequencies of TAPS-6, and the practicability and precision of the standard sphere calibration method was confirmed for those frequencies. A school or cluster of dummy scatterers of zooplankton with small tungsten carbide spheres were designed to validate the MFI method, and volume back-scattering strength values were measured by the multifrequency system. By comparing the result of the inversion with their real composition, the features of the MFI method could be validated and examined.KEY WORDS: dummy scatterers of zooplankton, multi-frequency inversion method, standard sphere calibration.
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