Morphometric characteristics of Antarctic krill (Euphausia superba) and finfish bycatch in the krill fishery in the waters of South Orkney Islands during the 2022/23 fishing season

Summary

This study examined accidental fish catches (bycatch) in Antarctic krill fishing operations around the South Orkney Islands during the 2022/23 fishing season. Scientific observers documented 676 fish specimens, identifying 17 species from 8 families, including three dominant icefish species and four other important species.Researchers measured fish body dimensions, particularly width, to determine optimal bar spacing for bycatch reduction devices. Since krill have a maximum body width of approximately 10 millimeters, they recommend 10-millimeter bar spacing in reduction grids. This would allow krill to pass through while enabling significant fish escape rates: 94% of one dominant icefish species (Champsocephalus gunnari), 76% of another (Chaenocephalus aceratus), 54% of the third (Pseudochaenichthys georgianus), and 100% of one important species (Gobionotothen gibberifrons).

Map showing fishing locations for continuous fishing - with conveyor hose systems (red triangles) and conventional trawling (black dots) conducted by the fishing vessel SHEN LAN in South Orkney Islands waters. Each position on the map represents the midpoint between the starting and ending coordinates of each fishing operation.

Key Findings

A total of 676 accidental fish catches were collected, with 665 identified to the species level (17 species from 8 fish families).

Three dominant bycatch species were all icefish: Champsocephalus gunnari, Pseudochaenichthys georgianus, and C. aceratus.

Four other important bycatch species came from the lanternfish, rockcod, and jonasfish families.

A 10-millimeter bar spacing would allow 93.94% of C. gunnari, 53.99% of P. georgianus, 76.25% of C. aceratus, and 100% of G. gibberifrons to escape through the nets.

Fish body measurement data is essential for designing bycatch reduction devices and maintaining sustainable krill fishing operations.

Different fishing methods (conventional versus continuous trawling) resulted in varying compositions of accidental fish catches.

Abstract

Determination of bar spacing of bycatch reduction devices (BRDs) should consider species composition and morphometric characteristics (particularly width) of target species krill and bycatch. This study conducted a scientific investigation of the finfish bycatch in the Antarctic krill (Euphausia superba) trawl fishery by the fishing vessel SHEN LAN in the waters surrounding the South Orkney Islands from December 24, 2022, to February 20, 2023. The results show that scientific observers sampled 676 individuals of finfish bycatch. Of these, 665 were identified to species (17 species from 8 families), while the remaining 11 specimen were juveniles of the Nototheniidae family that could not be identified to the species level. IRI (index of relative importance) calculations showed three dominant (IRI value greater than 1,000) finfish bycatch species (Champsocephalus gunnari, Pseudochaenichthys georgianus, and C. aceratus from the Channichthyidae family) and four important (IRI value between 1,000 and 100) finfish bycatch species (Electrona carlsbergi and Gymnoscopelus nicholsi from the Myctophidae family, Gobionotothen gibberifrons from the Nototheniidae family, and Notolepis coatsi from the Paralepididae family). Our study provides morphometric data (particularly body width) that is crucial to model the potential for bycatch reduction by use of bycatch reduction devices (BRDs) and to determine the appropriate candidate bar spacings for BRD sea trials. Predictions suggest that a 10 mm (the maximum body width of krill) bar spacing releases a significant amount of dominant and important bycatch species (93.94% of C. gunnari, 53.99% of P. georgianus, 76.25% of C. aceratus, and 100% of G. gibberifrons). Reduced fishing pressure would reduce the risks to dominant and important bycatch species to make the krill fishery sustainable. We recommend that future BRD sea trials should initially test a 10 mm bar spacing. If marked loss of krill is observed, wider spacings (e.g. 15 mm) must be tested.

Published in

Frontiers in Marine Science

2024

Authors

Wang, Z., Ma, S., Wang, Y., Wang, L.

Institutions

East China Sea Fisheries Research Institute, Chinese Academy of Fishery SciencesQingdao Marine Science and Technology Center

Methods

Biological sampling DataField

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