CCAMLR

Krill stock composition and distributional patterns in the vicinity of Elephant Island during austral summer 1988-1992 are described. Changes in both size and maturity composition over the five year period indicates strong recruitment from the 1987/88 and 1990/91 year classes and poor recruitment from the 1989/90 and 1990/91 year classes. Year class success may be related to the abundance of large mature stages and/or the development state of mature females during early summer. The overall distributional patterns during each year indicate that the older age classes were associated with oceanic/Drake Passage waters while younger classes were associated with water masses to the south. Between-year differences in distribution patterns reflected changes in year class success and maturity stage composition.

Empirical estimates for the target strength of krill are extracted from the literature. These are confined to measurements on aggregations of live euphausiids, which should avoid a frequent cause of bias in single-animal measurements, namely thresholding. Theoretical estimates for the target strength are derived from the deformed-cylinder scattering model assuming specific sets of physical and orientational parameters, for which there is an empirical basis. The theoretical estimates show a non-monotonic dependence of target strength on both animal size and transmit frequency, notwithstanding admitted shortcomings. Some recent single-animal measurements of target strength for live euphausiids and euphausiid-re1ated specimens, made under high signal-to-noise-ratio conditions, are consistent with the general pattern. Several specific recommendations are made for future, improved determinations of krill target strength. Based on the comparisons, general prediction curves for the target strength are presented that are applicable to a wide range of lengths, acoustic frequencies, and orientation parameters.

Main outlines of E. superba material collection (sampling from commercial catches) and positions of samples examination are reviewed and described. These positions include mass-measuring of body length, examination of maturity stages composition (biological analysis), feeding activity observation and body weight determination. Periodicity of sampling and volume of samples for every position of observation are included. Several proposals regarding to Formats filling and Report of biologist-observer construction are included also. These proposals are suggest to consider during WG-KRILL-92.

Investigations of diurnal changeability of size composition of E. superba was carried out during the working period of commercial trawler ‘Grigory Kovtun’ in the fishing area near the South Orkney Islands during March-June 1990. observations at 6 time stations were fulfilled. Every station consisted of series of catches by mean the usual commercial trawl (9-12 tows per every station). Increasing of average size of animals during light time was observed at several stations. These changes are related and were determined by increasing of males proportion as well as by difference between average length of males and females. It were namely males, which first deign diurnal vertical migrations inside of swarms. When diurnal migration are absent (particularly at most later season) the diurnal changes in E. superba size composition became feebler expresses or stop. Significance of these observations in relation to data on E. superba’s size composition accepted during usual surveys (collecting E. superba from every point of survey only once) is considered.
Gradual decreasing of average size of E. superba from end March to June was observed in operation region. As may suppose, these changes are related with drift of swarm, but not with progress of life cycle at winter postspawning non-feeding season. They hardly can be related also with selective stress of fishery activity upon larger specimens of E. superba.

Parameters of the Bertalanfy growth equation for 1928 and 1970–1976 were calculated on the base of summaryed data on Krill age groups singled out using method of Harding.Parameters obtained were used to calculate total Krill mortality using different methods applyed earlier only to the fish recources.
As a result of uncertainty in age groups determination were obtained wide ranging values. The most real values varied from 0.75 to 1,17.
No fishery impact on various parameters of the krill population size structure was found.

An observation program was carried out by a biologist-observer on board the krill fishing vessel More Sodruzhestva in April to August 1991 in Subareas 48.2 and 48.3. The program included observation of krill fishing operations, collection and processing of catch samples for analysing physiological status and size composition of krill and also for determining the level of by-catch of juvenile channichthyids. In general, krill density in Subarea 48.2 was twice as high as that in Subarea 48.3. Catch-per-haul was 9.51 and 4.74 tonnes respectively. Krill of two modal sizes, 45 to 48 mm and 49 to 52 mm, were dominant in catches taken in April/May in the north-west of Subarea 48.2. Krill of modal sizes 31 to 32 mm and 35 to 36 mm made up the bulk of catches in the south-east of the subarea. No by-catch of juvenile fish was observed in Subarea 48.2. Krill of the following three modal groups was dominant in Subarea 48.3: 35 to 38, 39 to 42 and 45 to 46 mm. By-catch of juvenile Champsocephalus gunnari was observed in these subareas during the period 17 to 23 May 1991. Sightings of marine mammals and birds in the vicinity of the vessel were also recorded.

Interannual variations in krill quantative characteristics in the Sodruzhestva Sea area for the period from 1988 to 1990 are discussed in this paper. It has been established, that a considerable increase in the crustacea stock in 1990 was caused by good replenishment owing to the generations of 1986 and 1987 in the conditions of their weak expatriation in 1989–1990.