CCAMLR

A tagging programme for toothfish (Dissostichus eleginoides)w as undertaken around South Georgia during early 2000. Details of the programme are given. A total of 359 toothfish were tagged during a trawl survey on the Shag Rocks shelf and a further 135 were tagged on the continental slope around South Georgia and Shag Rocks. The programme has been advertised widely amongst industrial fishermen operating in the region.

To undertake the 'ecosystem approach' to fisheries management recommended by CCAMLR, an understanding of the trophic relationships of exploited species is vital. Toothfish, (Dissostichus eleginoides), represents an important target species for fisheries not only in the study area around South Georgia (CCAMLR Sub-area 48.3), but also in other CCAMLR areas. To improve the knowledge on the trophic relationships of this species, stomach analyses were performed on individuals caught during the toothfish pot fishery trials undertaken in the area during the period March to May 2000. 3,640 individuals were examined and their stomach contents identified. The proportion of individuals found with empty stomachs was greatly reduced in fish caught using pots rather than longlines, increasing sample sizes. This was hypothesised to result from fish caught in pots suffering reduced levels of trauma. The most common prey item for fish caught using pots was prawns. This prey category was localised in location and depth. However prawns were not common in the stomachs of fish caught from this location using longlines. The next most common prey category was fish, as found in previous studies of this species. This confirms that D. eleginoides s an opportunistic carnivore, whose feeding habits vary dependent on the availability of food items as well as Factors such as depth.

Trials of a method of fishing for toothfish using pots were undertaken by FV Argos Georgia from March to May 2000. A significant bycatch of crabs was encountered. Paralomis spinosissima occurred in shallow water, generally shallower than 800m. P. anamerae, which has not been reported for this area previously, had an intermediate depth distribution from 400 – 800m. P. formosa was present in shallow waters but reached much higher catch levels (and, presumably, densities) between 800 and 1400m. There were some differences in catch rate5 between areas, with lowest catch rates being encountered between Shag Rocks and South Georgia, and highest for P. formosa in deep water north of South Georgia. Few crabs (3% of P. spinosissima and 10.5% of P. .formosa) were males above the legal size limit and could be retained. All other crabs were discarded. Mortality rates estimated from re-immersion experiments indicated that about 10% of apparently lively discarded crabs would die.

During the period March to May 2000, the UK undertook trials of a pot fishing method to catch D. eleginoides around South Georgia (Sub-area 48.3). This method has the potential to minimise, or eliminate, incidental bird mortality when compared to the standard longline method. This paper describes the trial, the results, and discusses the commercial viability of this fishing method for toothfish fisheries in the CCAMLR area. While the method successfully caught D. eleginoides, there was a large bycatch of crab species. The catch rate of toothfish was notably lower than that achieved in the longline fishery. Importantly, the use of pots eliminated bird bycatch. To capitalise on this feature, there is a need to improve the commercial viability of the method and minimise the quantity of bycatch. A number of potential changes are suggested to this end.

Morphological information is given on specimens of Raja georgiana that were caught during a demersal trawl survey in Subarea 48.3, South Georgia. It is concluded that, in spite of allometric growth, proportional measurements are best referenced to total length rather than disc width. Additional biological information is given: total mass=0.00000646x(total length)3.06. Based on data from male fish, they are thought to mature at about 800mm total length.

A survey was conducted by the UK around South Georgia and Shag Rocks, Subarea 48.3, from 11 January to 2 February 2000, using the FV Argos Galicia. The design followed similar surveys by the UK conducted throughout the late 1980s and 1990s. The swept area estimates of the standing stock of Champsocephalus gunnari were about 24,800 t. Estimates for other major species are given.

In the period from 11 December 1999 to 31 January 2000 Russian trawler "Zakhar Sorokin" carried out fishing the icefish Champsocephalus gunnari feeding consent rations in the western shelf of the South Georgia Island. Icefish 26-40 cm in length, with the average size of 30.3 cm made up the bulk of the catches. Length-frequency distribution was characterized by bimodality, with frequency peaks under 27-29 and 33 cm for fish aged 3 and 4 years. The by-catch of small size Champsocephalus gunnari (with the length of 24 cm and less) amounted to, on the average, 0.6% per a haul.
The male/female ratio, on the average, equalled to 1/1.2. The active process of gonad maturation, more rapid in females, was observed. In December gonad maturation stages II and II-III and in January - II-III and III, respectively, prevailed.
Icefish feeding intensity remained to be relatively high during all the period of observations. Mean stomach fullness amounted to 2.5. Antarctic krill Euphausia superba, the occurence of which in the stomachs was estimated at 86%, and Themisto gaudichaudii (27.8%), were the main feeding objects.
Mean prevalence and intensity of Champsocephalus gunnari infestation by leech Trulliobdella capitus was 11.9% and 1.3 and by parasitic copepods Eubrachiella antarctica - 37% and 3.

The dynamics of daily vertical migrations of icefish Champsocephalus gunnari was studied and some quantitative estimates were obtained by results of analysis of more than 150 fragments of echograms obtained with the use of an echograph of the "Priboi-101" echo sounder during the directed fishery for icefish in the subarea 48.3 in December 1999 – January 2000. The commercial concentrations of icefish can be considered by the type of the vertical distribution as bottom/pelagic ones, and the pelagic component of their biomass is great either during the night or day time. Of this, it can be concluded that assessments of Champsocephalus gunnari stock based on the results of bottom trawl surveys can be underestimated.