Distribution and biomass estimation of Antarctic krill (Euphausia superba) off the South Orkney Islands during 2011-2020

Summary

This study reports findings from a decade-long acoustic survey (2011-2020) that tracked Antarctic krill populations around the South Orkney Islands through collaboration between Norwegian scientists and the krill fishing industry.The South Orkney region consistently supported large krill populations, with biomass averaging between 1.4 and 7.8 million tonnes annually across the 60,000 km² survey area. No significant trends were observed over the ten-year period.Krill concentrated primarily along the shelf edge and submarine canyons on the northern side of the South Orkney Islands. Current harvesting levels remain well below the CCAMLR precautionary exploitation rate of 9.3%.The research demonstrates that commercial fishing vessels can effectively serve as platforms for scientific monitoring, providing a cost-efficient approach to long-term krill population assessment while maintaining sustainable fishing practices.

This map shows the survey design used by the Norwegian Institute of Marine Research around the South Orkney Islands from 2011 to 2020. The area is divided into strata (sections) with systematic transects (survey lines) running through them. The dots indicate fixed locations where trawl sampling was conducted to collect krill specimens. The southwestern portion of the survey area falls within a protected zone where trawling is prohibited, so no sampling dots appear in that region.

Key Findings

Average krill biomass ranged from 1.4 to 7.8 million tonnes during 2011-2020, with high interannual variability

No significant monotonic trends in krill biomass were detected over the 10-year period

Highest krill densities were consistently found associated with the shelf break and submarine canyons on the north side of the South Orkney Islands

Comparison with CCAMLR's 9.3% reference exploitation rate indicates current fishery management is precautionary

Industry-based vessel surveys prove to be a cost-effective approach for long-term krill monitoring

Abstract

Antarctic krill is a key species in the Southern Ocean and subject to the most extensive fishery in the Antarctic. The Norwegian Institute of Marine Research has conducted acoustic-trawl monitoring of krill off the South Orkneys annually since 2011 in collaboration with the krill fishing industry. Average krill biomass within the 60000 km2 survey area ranged from 1.4 to 7.8 million tonnes in the period 2011–2020, strongly supporting that this is among the regions in the Scotia Sea with consistently highest krill densities. There were no significant (p ≈ 0.18, non-parametric Mann–Kendall test) monotonic trends in estimated krill biomass over the 10 years. The highest krill densities were associated with the shelf edge and submarine canyons on the north side of the South Orkneys. Our comparison with the CCAMLR 9.3% reference exploitation rate suggests that management of the krill fishery in the South Orkneys region is precautionary. The monitoring is run on fishing vessels, so e.g. acoustic frequencies applied could not always be in compliance with the standard CCAMLR methodology. Estimated deviance in krill backscatter when comparing 38 kHz to the standard 120 kHz ranged from −1.1% to 12.8%. Our results show that industry-based surveys are cost-efficient approaches to high-quality monitoring of krill.

Published in

ICES Journal of Marine Science

2023

Authors

G. Skaret, G. J. Macaulay, R. Pedersen, X. Wang, T. A. Klevjer, L. A. Krag, and B. A. Krafft

Institutions

Institute of Marine Research, BergenYellow Sea Fisheries Research Institute, Chinese Academy of Fishery SciencesDTU Aqua, National Institute of Aquatic Resource, North Sea Science parks

Methods

AcousticBiological sampling DataField

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