Density Estimation of Antarctic Krill in the South Shetland Island (Subarea 48.1) Using dB-Difference Method

Summary

Researchers measured Antarctic krill populations in the waters around South Shetland Islands using sound-based technology (acoustic dB-difference methodology) in April 2016. They found an average krill density of 33.65 grams per square meter across the 90,700 square kilometer study area, though this varied considerably (45.97% coefficient of variation) from place to place. The heaviest concentrations of krill were found near South Island and Elephant Island at depths around 200 meters. This study shows that acoustic technology can effectively survey large ocean areas quickly to measure krill populations, providing valuable data to support CCAMLR's sustainable fisheries management in Subarea 48.1.

Geographic location and timing of Antarctic krill populations detected through acoustic analysis comparing sound reflections (minimum volume backscattering strength, Sv) between 120 kHz and 38 kHz sonar frequencies. Krill create a distinctive acoustic signature when the backscattering difference ranges from 0.4 to 14.3 decibels (∆MVBS120-38 kHz), which distinguishes them from other marine life.

Key Findings

Average krill population density: 33.65 grams per square meter, with high variation (45.97% coefficient of variation) across different areas

Krill body size: Ranged from 25-60 millimeters in length, with most averaging 45.5 mm (± 6.9 mm standard deviation)

Geographic distribution: Krill populations were most concentrated in waters near South Shetland Islands and Elephant Island

Depth preference: Krill reached their highest densities at approximately 200 meters below the surface

Acoustic detection accuracy: The sound-based method (dB-difference range of 0.4-14.3 dB) successfully identified krill populations

Species confirmation: Nearly all net catches (99.9%) contained Antarctic krill, with only one sampling station showing different species

Abstract

This study is aimed to estimate the density of Antarctic krill that inhabit in the area around South Shetland Island by using a dB-difference method. An acoustic survey was conducted from 13 to 24 April in 2016 in the sea of South Shetland. Acoustic data on frequency 38 and 120 kHz were collected. The Antarctic krill echo was extracted for the SV120-38 kHz range of 0.4–14.3 dB, which was obtained by applying the size of the collected Antarctic krill in this study (25–60 mm). The mean Antarctic krill density across the survey area was 33.65 g m−2(CV = 45.97%).

Published in

Sustainability

2020

Authors

Choi, S.-G., Chae, J., Chung, S., Oh, W., Yoon, E., Sung, G., Lee, K.

Institutions

Distant Water Fisheries Resources Research DivisionMarine Environmental Research & Information LaboratoryDivision of Fisheries ScienceFisheries Resources Research Center

Methods

DataAcousticFieldBiological sampling

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