CCAMLR

Combined studies on the inner shelf and outer shelf of the Kerguelen islands (1989/90 to 1992/93) provides new informations about Champsocephalus gunnari stock. An inner shelf quaterly programme allows to identify each year, both from the ichthyoplanktonic surveys and bottom trawlings, an annual cohort. Strong differences in abundance of larvae are observed yearly. One cohort seems dominant in the samples along the study. It would explain the previouly observed three years cycle. Spawners have been observed in mass only once during the studied period and are fishes of the 1988 cohort first spawning during the winter 1991/

To determine mackerel icefish Champsocephalus gunnari age, otolith mass was used. The material was collected in July0August 1987 during the joint Soviet-Australian expedition on board R/V PROFESSOR MESYATSEV to heard Island shelf area. The otoliths were weighted with an electric balance to within 0.0001 g. Then the obtained data underwent statistical processing with application of the cluster analysis method. Five age groups were defined. Bertalanffi linear growth equation was calculated:
Lt=41.73 (1-e-0.5149(1+0.05225))
On this basis the size-age key for this season has been estimated.

In the season of 1990/1991, fishing operations in subarea 58.4.4. (Lena Bank) wer4e carried out by only one vessel - RTMA ZVEZDA KRYMA in April-June 1991. The total harvest in that period made 971 t of grey rockcod Notothenia squamifrons and 29 t of Patagonian toothfish Dissostichus eleginoides. The real catch excels the data in the Statistical Bulletin… nearly two-fold. In this connection it is necessary to update the relevant documents.
The size-age composition of catches did not suffer significant changes. The mean fish age made 7.0 years. Interannual fluctuations in size-age composition of populations are rather connected with the quality and period of sampling than reflect objective changes in populational structure of the species.

Basing on materials of research expeditions and fishing cruises to the Kerguelen Islands shelf in the period from 1970 to 1991, dynamics of size- age structure of marbled rockcod (Notothenia rossii rossii) population is shown. Data on age determination for 1970-1989 (Tankevich, 1990) and the data collected in the joint Soviet-French expedition on board RTMA Orlinoye in May-Jine 1991 were used to characterise the age composition. It was determined that in the initial years of exploitation of the stock, the major part of catches (more than 80%) was formed by repeated spawning fish. then as a result of fisheries, the share of the fish spawning for the first time increased considerably in catches and in some years (1981-1985) fisheries were based practically on recruitment. After the closure of the specialised fishery in 1985 and after the marbled rockcod by-catch at other fisheries was limited to 500 tons, a stable trend towards increase in the mean age and fish length was noted in catches. In May-June 1991 the mean length was 59.2 cm, mean age was 7.4 years; some 70% of catch consisted of repeated spawning fish. The author consideers the demographic populational structure in 1991 to be close to that observed in the initial years of exploitation and further closure of marbled rockcod specialised fishery can lead to increase in natural mortality of the population as the whole. Fish removal of older age groups is recommended to start in the nearest years. It will make it possible to control size- age structure changes in the spawning part of the population.