Acoustic estimation of krill biomass in R.V. KAIYO MARU SIBEX I survey area (Indian Sector of the Southern Ocean)

• Main Authors: Kunio Shirakihara, Kakusuke Nakayama, Yuzo Komaki
• Format: Report
• Language: English
• Published: Shimonoseki University of Fisheries 1986
• Subjects: Austral; Indian; Southern Ocean; Euphausia superba; Memoirs of National Institute of Polar Research; Polar Research
• Online Access: https://nipr.repo.nii.ac.jp/?action=repository_uri&item_id=1883; http://id.nii.ac.jp/1291/00001883/; https://nipr.repo.nii.ac.jp/?action=repository_action_common_download&item_id=1883&item_no=1&attribute_id=18&file_no=1

During the austral summer of 1983-84,the acoustic survey to estimate the biomass of krill (Euphausia superba) was carried out twice in the area between 65°and 75°E and south of 61°S in the Indian Sector of the Southern Ocean by the R. V. KAIYO MARU participating in SIBEX I. The southern limits of the study areas were 64°S for the first survey and 69°S for the second. The mean volume back-scattering strength was measured by horizontal interval of 1nnautical mile and 7 vertical channels in the depth range between the top depth (10-25m) and 200m, using the 200kHz echo sounder with a digital integrator. The scattering strength was converted into the weight density using the constant mean target strength per kg. The estimated mean weight density per unit surface area in the nighttime was significantly lower than the density in the daytime. The tendency for krill to rise near the surface at night might give a lower bias to the nighttime estimate. The analysis using only the daytime data (3346 intervals throughout the whole survey) resulted in the mean surface density of 15.9g/m^2 in the area (3.45×(10)^5(km)^2). The total biomass estimated from the survey was 5.49 milliont. Discussion was made on possible errors or biases of the estimate, derived from adequacy of the absorption attenuation coefficient adopted in the survey, statistical sampling error, occurrence of krill beyond the depth range of the acoustic detection, and target strength error.