CCAMLR

The Antarctic silver fish (Pleuragramma antarcticum) is one of the most numerous species in the outer waters of Antarctica. In the Indian sector of the Southern Ocean there are at least three relatively isolated groups. Fish aged from 0+ to 3+ years live in the epi- mesopelagic zone where there are macro aggregations of plankton, while fish aged from 3+ to 12+ years form near-bottom, pelagic schools. Fish belonging to various spatial groups have different growth characteristics, Females mature when they reach 13-16 cm in length and 4-6 years of age. Males reach maturity at 12-18 cm in length and 4-7 years of age. The potential absolute and relative fertility of this species is one of the highest for high-latitude Antarctic fish. Spawning occurs in the winter-spring period. P. antarcticum is a plankton-eater and is itself an important part of the diet of species higher up the food-chain. P. antarcticum has a fairly high level of instantaneous natural mortality, mainly due to its position on the food chain. It would probably be unwise to commence exploratory commercial fishing of this species in areas of international monitoring.

Studies of by-catch of juvenile fish in krill catches by research vessels were conducted during 1985-1988 in the Kosmonavtov and Sodruzhestva seas (Antarctic Indian Ocean sector). Isaacs-Kidd trawl with an opening area of 6.0 m2 was used. Trawls were taken in the 0-200 m surface layer over the bottom depth range from 100 to 5000 m. In 1988, studies included catches taken by a commercial krill trawl with an opening area in a small meshed section of the trawl beg of 100 m2. Catches were mainly taken over depth ranges from 300 to 500 m and from 2 500 to 4 200 m. Most frequently observed species of fish in krill catches were Pleuragramma antarcticum, Electrona antarctica and Trematomus eulepidotus. Other species were observed in catches only occasionally and in small numbers. By-catch of juvenile fish was highest in Prydz Bay and Fram Bank areas. By-catch of juvenile fish in Isaacs-Kidd trawl was usually less than 50 fish per 30 min trawling. By-catch in commercial trawls was from 114 to 1 x 106 fish per tonne of krill caught. Small by-catch of fish was usually observed when krill catches were higher than 2 tonnes (2-12 tonnes) and over the bottom depth less than 1 000 m. Maximum by-catch (up to 1 x 106 fish per tonne of krill) was observed when krill catches were less than 2 tonnes and over the bottom depth from 1 500 to 4 500 m. It was found that areas of maximum concentrations of juvenile fish and krill did not overlap. Therefore, high fish by-catch corresponds to low krill catch and vice versa. It was concluded that krill fishery should be best conducted over the bottom depth more than 1 200 m and on high-density krill concentrations. It was also suggested that in order do avoid large by-catch of juvenile fish, krill fishing should not be conducted in shallow waters over the continental slope

Biological data and fishery statistics collected in 1984-1992 were used for stock size and TAC estimation of the Patagonian toothfish, Dissostichus eleginoides, from the Kerguelen shelf area. Method of R. Jones (1964) was used for estimating population size and TAC. Calculations were done for the 1984/85 and 1991/92 seasons where directed fishery for the species took place. Population size of D. eleginoides for these seasons was estimated at 43-50 x 103 tonnes. TAC was estimated at 7.3-7.5 x 103 tonnes.

Results of length-age composition studies of the Patagonian toothfish, Dissostichus eleginoides, from various fishing grounds of the shelf and continental slope areas of the Kerguelen Islands are presented and discussed in the paper. Detailed results of these studies are compiled in tables such as age-length keys, mean fish length by age, length and age frequency distributions in catches. Soviet vessels had first carded out fishery for the species in the 1984/85 season. Fishing grounds during this period were located in the west shelf area (48°30’ - 49°30’S and 66°50’ - 67°20’E). Total catch was about 6.7 x 103 tonnes. Length composition of catches taken within 300 - 500 m depth range did not fluctuate considerably, mean fish length was 76.0 - 86.6 cm. Fish of two to 14 years old age groups were most abundant in catches, mean age was 8.2 - 9.8 years. In the 1991/92 season fishing for the species was concentrated in the north shelf area (47°10’ - 47°30’S and 66°50’ - 67°20’E). Total catch was about 5.2 x 103 tonnes. In other seasons between 1984 and 1992 catches of the species was taken only occasionally and annual catches were from 0.5 to 3.1 x 103 tonnes. Mean length of fish taken at 300 - 500 m depth was 58.1 cm, mean age was 5.8 years. Mean length of fish taken at 540 - 600 m depth was 85.8, mean age was 9.7 years. Results presented in the paper are in agreement with results of other studies conducted in the past by French and Russian scientists.

There is a lack of information regarding the abundance of exploitable finfish in Subarea 48.1. A comprehensive, bottom trawl survey offish stocks in Subarea 48.1 would make it easier for the Working Group on Fish Stock Assessment to assess the stocks in this region and assist the Scientific Committee in giving management advice to the Commission. A stratified random survey is proposed; the strata correspond to depth ranges (stratum 1: 50-150 m; stratum 2: 151-250 m; stratum 3: 251-500 m). A rule is derived from catch rate data obtained during previous stock assessment surveys around Elephant Island to allocate sampling effort among the three depth strata. One hundred and seventy six trawl stations are randomly selected by gridding the survey area. The survey is designed to cover all of Subarea 48.1.

AtlantNIRO had conducted in 1982-1990 a series of juvenile fish trawl surveys of abundant species around South Georgia Is. Results of these survey were summarised and compared with published data. Juveniles of Champsocephalus gunnari were found to be distributed from the surface to 500 m depth with a maximum density observed at depth between 100 and 200 m. High catches of C. gunnari juveniles were regularly taken in the south, south-west and south-east parts of the shelf. Juveniles of C. gunnari were usually found along the periphery of krill concentrations but not inside these concentrations. Estimated mortality of C. gunnari juveniles is relatively small and was estimated that 0.3 to 0.5% of fish survived up to an age of one year.

Catch and length/age composition data for Notothenia squamifrons from Ob and Lena Banks, Division 58.4.4, are presented for the period from 1978 to 1990 split years. These data were used in VPA analyses made for each bank separately. The CCAMLR VPA program, version 4.1 was used. The resulted biomass estimates for 1990 are 10.2 x 103 tonnes for Ob Bank and 20.7 x 103 tonnes for Lena Bank. These estimates may be used in calculation of TAC which in accordance with our calculations should be 2.0 x 103 tonnes for Ob Bank and 4.0 x 103 tonnes for Lena Bank.

A total of 8 inventory trawling surveys of the bottom fish were made on South Georgia shelf. Ch.gunnari distribution pattern markedly varied by year which can be attributed to differing survey dates.
Most dense Ch.gunnari aggregations observed were mainly in the northern, north-western and north-eastern parts of the island shelf. Near Shag Rocks they could be seen in separate years. Year-to-year fluctuations of catch per unit effort, predominance of certain groups of specimens and mean weight of the fish were obviously governed by the intensity of fishing.