CCAMLR

During the 1990/91 and 1991/92 fishing seasons, two longliners carried out exploratory fishing over the western shelf break of the Kerguelen shelf (Division 58.5.1). Scientific monitoring of fishing carried out by one of these longliners has allowed a description of fishing methods to be made. Bottom longlines are generally used at depths of 400 to 600 m. The mainline (1 to 2 miles long) carries about 2 400 to 3 600 straight hooks, which are from 61 to 75 mm in length. The bait used is either imported fish (horse mackerel) or squid, or species (e.g.Champsocephalus gunnari) which are caught locally by trawlers. The vessel is equipped with an automatic longline baiter which has an efficiency of about 75%. The catch rate has been assessed as being about 10.9%, but this average is reduced by the fact that fish become unhooked along the side of the ship, which leads to a real catchability value in the order of 10.2%. The catch is almost exclusively made up of Dissostichus eleginiodes, by-catches being extremely small (0,28%).
Length frequency distributions (LFD) observed for Dissostichus eleginoides confirm that fish caught are large, their average length being greater than that in catches made previously by trawlers in the same area. This average length is comparable for the two successive fishing seasons (93.4 cm in 1990/91 and 92.95 cm in 1991/92). The fish caught are for the most part adults, and a clear difference can still be observed between the LFD for males (L = 88.09 cm in 1990/91 and 88.13 cm in 1991/92) and that of females (L = 98.70 cm in 1.990/91 and 98.61 cm in 1991/92). The sex ratio is almost equally balanced.

Following on from the apparent failure to satisfactorily assess the status of the C. gunnari population in Subarea 48.3 at WG-FSA-91 using VPA, attempts were made to re-work the analysis using Laurec-Shepherd and ADAPT tuning techniques, from 1991 back to 1977. The predicted age structure, dominated in recent years by the 1987 year class (1 year olds in 1988), was quite robust, despite the use of various combinations of survey and cpue indices for tuning. According to the VPA the population in 1991/92 was composed of a large proportion of 5 year olds, which was not observed during the survey on Falklands Protector in January 1992. Breakdown in the credibility of the VPA results in most recent years is attributed to the invalid assumption of constant M and contradictions in the input data. A conservative approach to management for 1992/93 is recommended, based on the results of surveys by Falklands Protector in 1990/91 and 1991/92.

The diet composition and feeding intensity of mackerel icefish (Champsocephalus gunnari) around Shag Rocks and the mainland of South Georgia was investigated in January/February 1985, January/February 1991 and January 1992 by analyzing appr. 9,000 stomachs. Main prey items were krill (Euphausia superba), the hyperiid Themisto gaudichaudii, mysids and in 1985 also Thysanoessa species. The proportion of krill and Themisto in the diet items varied considerably between the three seasons, whereas the proportion of mysids in the diet remained fairly constant. krill is obviously the prefered diet. In years of krill shortage, such as in 1991, krill is replaced by Themisto gaudichaudii and sometimes Thysanoessa. Variation in food composition between sampling sites was high. This high variation can be primarily attributed to differences in prey availability, but appears to be much less influenced by differences in length composition of the fish between sampling stations. Feeding intensity varied also considerably between seasons. It was highest in 1992.