CCAMLR

Dynamics of distribution, growth, life span and feeding were studied in the endemic Antarctic euphausiid Euphausia crystallorophias in the central part of the Indian sector of the Southern Ocean during the austral summer, from 1977 to 1990, and in the Lazarev Sea during the summer 1990/91. Both larvae and adult E.crystallorophias were found in abundance in shelf waters of 100-500 m depth. Maximum abundances of larvae (up to 7688 ind.∙m-2) and adults (up to 1267 ind. ∙m-2) were found in the Prydz Bay region. Size frequency analysis indicated that the generation time was ~ 3 years in the Indian sector of the Southern Ocean. Total life span of E.crystallorophias may exceed 5 years in the Prydz Bay region and 4 years in the Cosmonaut Sea. Analysis of size distribution by sex showed that male E.crystallorophias had a shorter life span than females, although their growth rates were similar. Assuming growth for only 180 days per year, mean growth rates ranged from 0.070-0.075 to 0.019-0.022 mm per day during the first and the fourth year, respectively. Von Bertalanffy growth curves calculated for different areas were similar to those obtained by Siege1 (1987) in the Antarctic Peninsula region. In the Prydz Bay and the Cosmonaut Sea, spawning of E.crystallorophias appears to peak from the end of November to early December and may extend to the beginning of January. Most larvae were in the stage of metanauplius/calyptopis I at the beginning of January and calyptopis III/furcilia I during February. The year-l cohort was identified in January-February and exhibited a mean length in the range 10.8-16.8 mm. In situ feeding rates were estimated in the Lazarev Sea using the gut fluorescence method. Ingestion rates during austral summer l990/91 ranged from 52 to 471 ng (pigm)∙ind-1∙h-1 in adults and from 2.5 to 25.2 ng (pigm)∙ind-1∙h-1 in calyptopis III larvae. Total population impact on the phytoplankton stock varied between 160-2860 and 215-652 μg (C)∙m-2∙d-l for adults and larvae, respectively. This is equivalent to 0.06-1.12% and 0.02-0.07% of total daily production. In areas with dense E.crystallorophias swarms, however, daily consumption rates may attain levels as high as 13.6-96.5% of daily primary production. The longterm monitoring of different populations of E.crystallorophias allowed the identification of covariance patterns between its abundance, spawning success and the formation of coastal polynyas, especially in the Prydz Bay region.

The distribution and abundance of Antarctic krill (Euphausia superba) were estimated from four acoustic surveys conducted in the vicinity of Elephant Island, Antarctica, from mid-January to mid-March, 1994. The first and last surveys covered approximately 15,000 n.mile2 around Elephant Island and the eastern end of King George Island; the second and third surveys covered approximately 2100 n.mile2 immediately north of Elephant Island. During the first survey, the highest densities of krill were mapped north of King George Island and over a broad band northwest of Elephant Island. For a portion of the survey area centered on Elephant Island (aproximate1y 12,000 n. mile2), biomass was estimated to be 401 X 106 t. Five weeks later highest densities of krill were mapped north of Elephant Island and biomass in the same survey portion was estimated to be 359 X 106 t. During the second and third surveys high densities of krill were mapped in the shoal waters to the north of Elephant Island; biomasses were estimated to be 87 X l06 t and 97 x 106 t, respectively. Average bill densities were the lowest observed during the last five years of AMLR surveys in the Elephant Island study area and one-fifth of the 1990-1992 average density. In spite of the low krill densities, the reproductive success of land-breeding predators did not appear to be adversely affected.

The CCAMLR Secretariat has been requested to provide annual calculations of the catch of krill within the critical period-distance of land-based predators in Subareas 48.1 and 48.2 (100km from colonies, December - March). This index of the overlap of predators and the fishery is unsuitable for a number of reasons. An alternative method of calculating an index of fishery-predator interaction is developed, which is based on a detailed model of the supposed functional interaction between these two utilisers of the krill resource.

Being prepared by a collective of authors, this paper demonstrates some approaches to mathematical modelling of Antarctic krill population in the Cooperation Sea. The choice of investigation area is not casual since there are data on YugNIRO long-term observations over kri11 biological state here, its stocks, other pelagic system components, inhabitancy conditions, landing by FVs for the period from 1978 to 1984 and 1988.
The objective of the researches was to reveal causes of sharp fluctuations in krill abundance in the Cooperation Sea basing on mathematical modelling. The main task was to assess variations in parameters of the ecosystem and its staunchness against their impact.
A possibility is shown to apply logical-information modelling for future creation of a prognostic model of functioning of Antarctic krill population.

Preliminary analyses of this topic identified some problems with the data originally submitted. To clarify these problems and to provide additional data to enhance the accuracy and relevance of the overall model, this paper provides quantitative information on potential biases associated with estimation of survival rate, observed rates of population increase (both maxima and at study colonies from which the data derived) and diet for black-browed albatross, gentoo penguin and Antarctic fur seal at Bird Island, South Georgia. In addition, year-specific data for a) black-browed albatross breeding population size and success and adult survival (1976-1992); b) gentoo penguin breeding population size and success (1977-1993) and c) Antarctic fur seal adult female survival (1984-1993, including allowance for tag loss), pregnancy rate, pup production, pup growth rates and mortality rates and foraging trip duration (1984-1993) are presented.

The model of the krill fishery presented in 1993 (wg-Krill-93/14) refined and applied to both Japanese and Chilean krill fishing fleets in Subarea 48.1. A stochastic element is introduced to account for variability in catch rates. The most successful management regime is found to be one which restricts fishing within 75 km of breeding penguins during January and February. For this regime the model predicts a 90% reduction in overlap with foraging predators, and a 15 to 20% reduction in catch. Closure of Livingston Island for the breeding period resulted in a 60% reduction in overlap with predators and 0 to 15% reduction in catches.