抄録
This paper introduces a case study of an underwater acoustic and optical surrey method for quantitatively monitoring the biodiversity and marine ecosystem, especially the prey (zooplankton) - predator (fish) relationship in an artificial mound reef. The acoustic and optical survey was conducted from 2009 to 2011 in the eastern Tsushima off, Nagasaki prefecture. In that area, an artificial mound reef had been built with width of about 70 m and a height of about 14 m, which were measured by a multibeam echosounder (70-100 kHz). Acoustic transects were run to investigate the zooplankton and fish school spatial temporal distributions around the artificial mound reef, by the multi-frequency scientific echosounder (18, 38, 70, 120, 200 kHz) calibrated using the standard reference spheres. In addition, an ADCP (75 kHz) simultaneously measured the speed and direction of the ocean currents at multiple depths around the artificial mound reef. Therefore, we used the Sonar Synchronizing Unit (SSU) to eliminate any acoustic interference between the acoustic equipment. Also, we examined whether the multi-frequency technique, the difference between the mean volume-backscattering strength at two frequencies, the so-called Sv difference method, could be used to classify between the zooplankton and fish in the artificial mound reef area. An optical observation and sampling survey by a ROV and a Mocness plankton net were then conducted to verify the validity of the acoustic classification result.
