Results on by-catch of fish during Ukrainian, Polish and Japanese krill fishery in the South Orkney Islands, South Georgia and Shetland Islands areas

Observations on abundance of by-catch fishes were made during fishing operations for krill Euphausia superba Dana conducted by the Ukrainian trawler Grigory Kovtun in the vicinity of South Georgia (May to July, 1992), the Polish trawler Lepus on the fishing grounds of South Orkney Islands and South Georgia (March to May, 1993), and by the Japanese fishing vessels No.3 and No.5 Chiyo Maru in the South Georgia area (July to August, 1992) and Niitaka Maru to the north of the South Shetland Islands (January to February, 1994) to determine the proportion of juvenile fish forms in krill concentrations. In the South Orkney Islands area, eight hauls were subjected to analysis and there was no by-catch of juvenile notothenioids at all in the samples collected. In the area around South Georgia, six notothenioid species including one unidentified bathydraconid fish were found as by-catch juveniles during three surveys by different countries. Among the six species, Lepidonotothen larseni was the most abundant in the Polish and Japanese by-catch samples, and its estimated value of an arithmetic mean was 11541 ind./t krill and 34588 ind./t krill respectively. In the Ukrainian sample, most of by-catch juveniles were referred to Champsocephalus gunnari and L. larseni, and its arithmetic mean was 78523076 ind./t krill and 60352790 ind./t krill respectively. Thirteen species including four mesopelagic fish species were found in krill catches of 25 of 99 examined net hauls made in the South Shetland Islands area. Also among by-catch fish from this area, juvenile L. larseni was the most abundant and its arithmetic mean was 10247 ind./t krill. In all the three areas, a relatively low by-catch of the family Myctophidae was observed. Abundance of by-catch fish could have depended on the density of krill concentration. The large incidental catch of juvenile fish occurred in hauls with the relatively low krill CPUE, and fish by-catch was not found or rare in hauls for krill swarms of higher density.