CCAMLR

The materials on Euphausia superba biological state and size composition in the Indian Antarctic seas for the period from 1985 to 1990 are analyzed to form an opinion about its growth, life duration, as well as about the interannual variability in the above parameters.
According to our data, duration of E.superba life cycle somewhat exceeds 5 years in the Sea of Cosmonauts and 6 years in the Sea of Sodruzhestvo. E.superba growth rate ranges from 0.126- 0.133 mm per day in the first year 0f life to 0.028-0.041 mm per day in the fifth year under condition that E.superba grows 180 days per year.
Bertalanffy growth curves calculated for different areas are close to that obtained by Australian researchers (Hosie et al., 1988) for the Prydz Bay by data for 1981-1985.
Basing on long-term observations, relations are noted between E.superba age composition and its spawning efficiency in coastal areas of the Seas of Sodruzhestvo and Cosmonauts. The presence of relatively independent (self-reproducing) groupings of E.superba is assumed in these areas.

Data on the size and age composition of Euphausia superba were collected in the Cooperation and Cosmonaut Seas from 1985 to 1990.
The coefficients of instantaneous natural mortality of E.superba in the Indian sector of the Southern Ocean were calculated according to Alverson-Carney’s (1975), Richter-Efanov’s (1977) and Beverton-Holt’s (1958) methods. Values varyed from 0.72 to 0.87, from 0.41 to 0.59 and from 0.94 to 2.30, respectively.
The estimation of the annual extinction rate of E. superba was obtained using the method of Zikov,Slepokurov (1982) and results were best fitted by a parabolic equation. The coefficients of natural mortality of E. superba derived with this method range from 0.49, during the maturation period, to 1.17 and 3.22 during the first and last years of life, respectively.

An initial attempt is made to develop the model1ing framework suggested by the Joint Meeting of the CCAMLR's WG-Kril1 and WG-CEMP in 1992 to address this issue. First. estimates are made of the parameters of predator survival rates as functions of krill abundance, by considering a krill dynamics model incorporating recruitment fluctuations together with information on adult survival and breeding success patterns for certain krill predator species. A "one-way" interaction model is developed, in which krill abundance fluctuations impact the predator population, but not vice versa. Computations based on this model indicate that variability in the annual recruitment of krill results in predator populations being less resilient to krill harvesting than deterministic evaluations would suggest. However, the analyses also raise a number of questions about the proper interpretation of the available predator population dynamics information in the context of the models developed, and about the model1ing of the predator survival rates as functions of krill abundance. It is suggested that these questions merit discussion at the forthcoming WG-Kril1 and WG-CEMP meetings. A formalism for a "two-way" interaction model (including also the effect of differing predator consumption levels on krill) is developed, but computations based on this approach are deferred pending clarification of the Questions raised above at the WG-Krill and WG-CEMP meetings.

The results of Butterworth et al. (1992) relating potential krill yield to a pre-exploitation survey estimate of kril1 biomass are extended to incorporate most of the amendments specified by the Third and Fourth Meetings of Working Group on Krill. The most important of these extensions is integration over the ranges of uncertainty for a number of the model parameters. Results are provided for the probability of spawning biomass falling below various fractions of its median pre-exploitation level (Ksp), as a function of the fraction of the biomass estimate which is set as the catch for a 20-year period. Three alternative fishing seasons are considered. The model extensions requested by the Third Meeting make little difference to the results of Butterworth et al. (1992). Winter fishing is marginally preferable to a summer harvest. However, the imposition of an upper-bound of 1.5 yr-1 on the effective annual fishing mortality, as specified by the Fourth Meeting, results in marked reductions in the probabilities of krill spawning biomass falling below specified fractions of Ksp.

Data from several summer surveys to the Antarctic Peninsula region were analysed to calculate length and age at maturity for the Antarctic krill Euphausia superba. L50 values of 34.62 to 35.90 mm for female krill are the best estimates for the high spawning season. Males attain sexual maturity later at a length between L50 = 43.33 and 43.79 mm. Length at maturity, and length at first spawning are identical for krill. Comparisons with length at age data show that females mature in the third year of the life cycle (age class 2 +), while males reach maturity in the fourth year as age class 3 +. Both sexes show knife-edge maturity.

Previous studies have established that ocean color information from Nimbus-7/CZCS{Coastal Zone Color Scanner) could be related to distribution of phytoplankton pigment (Chlorophyll-a + pheopigments) concentrations. CZCS data from polar regions have been utilized only a limited number because of many problems as cloud cover, large solar zenith angles, bio-optical algorithm and other logistic constraints. This papar discusses the characterization of phytoplankton pigment concentrations.

The influences of biological and physical factors in the environment upon krill (Euphausia superba) distribution were studies in the area north of South Shetland Islands during 1990/91 austral summer. Krill showed a distinct offshore-inshore heterogeneities in abundance and maturity stage in mid-summer the abundance was low in the oceanic zone (8.5 g/m2), while higher in the slope frontal zone (37.3 g/m2), and the highest along the shelf break (135.1 g/m2) in the inshore zone ; krill were reproductive in the oceanic and frontal zones, whereas non-reproductive in the inshore zone. The following factors were considered to be responsible for this characteristic distribution of krill. Diatoms were the main food of krill, and a spatial correlation between distributions of krill and diatoms were observed. Hence, higher diatom biomass may be one of factors forming krill concentrations in the inshore and frontal zones. The water flow was sluggish in the inshore zone (3.2 km/day), while meandering in the oceanic zone (7.9 km/day) and straightforward in the frontal zone (13.8 km/day). Especially, in the inshore zone, convergent complex eddies were generated along the shelf break, where krill were densely aggregated. Hence, the mechanical accumulation may another factor concentrating non-reproductive krill there. The frontal zone was considered to be favorable spawning ground for krill : not only because of the greater depth (which prevents krill embryos from being predated by benthic animals) and of the presence of warm Circumpolar Deep Water (which helps the development of the embryo) ; but also because of the higher chance of larvae's being transported to their nursery ground. Based on above mentioned factors, we further discussed why the change in spatial distribution of krill occurs from early to late summer.

The possibilities of natural regionisation of antarctic krill's geographic area with emphasis on fisheries regions distribution are considered on the base of consisting data of spatial structure of krill's geographic area. More then 43% of regions, where usually present concentrations of krill (this percent includes all recently acting fishery regions) lay inside of secondary fronts. These fronts are natural boundaries of supposed krill's stocks (subpopulations). Such position of regions of increased abundance of krill creates strong difficulties for determination of the membership crustacean to that or another stock on the basis of recent knowledges.
Problem may be solved, if new multidisciplinar surveys will be undertaken. These expeditions should get information on spatial composition of waters, ways of krill drift as well as on main biological characteristics of crustaceans. These surveys should cover rather large districts, which must include corresponding fishery regions as well as other regions of incresed abundance of krill and also regions of low abundance of krill. Changeability of situations (seasonal and annual) rises the necessarity to repeate these observations during several years, which is very expensive and impossible in reality. Information of observers from commercial trawlers as well as data from searching ships are a serious help in this respect for intermediate years beetween the seasons of wide scientific expeditional activity.