CCAMLR

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.

On the grounds of materials collected by biologists-02servers from October 1989 to June 1990 near South Orkney Islands the growth of males and females are characterized according to size groups, distinguished using the probability paper. Six size groups both for males and females were distinguished. Period of the intensive growth of the males continued from December to April, and for the females from November to February. The males increased their size for different size groups by 7-10, females by 8-10 mm. The rate of growth for the males was higher among the small specimens and vice versa for the females. Growth rates are similar to those observed in 1984-1985 in the South Orkneys and in the Admiralty Bay (King George Island).

Temporal and spatial variability of krill distribution characteristics was investigated in an 8 x 6 mile micropolygon, where eight consecutive hydroacoustic surveys were carried out. Krill aggregations occurred a s fields of small swarms whose spatial distribution characteristics (size and density of swarms, swarm field density, number of swarms per mile) varied considerably from tach to tack within each survey. The maximum horizontal extension of swarms was 120 m, although about 70% of swarms were of 30 m in length, with density up to 200 g/m3. About 75% of all swarms revealed biomass to be less than 1 tonne. Average statistical parameters of swarms in the polygon varied insignificantly from survey to survey, while the swarm number varied within the board range from 1 918 to 7 000 and further to 1 554 units. Krill biomass in the polygon varied spasmodically within the range from 1 091 to 6 085 tonnes. Krill distribution variability revealed in the polygon suggests an irregular import and export of krill from the polygon due to transport by the current. Additionally, in the upper layer of 0 to 50 m swarm number was almost constant, and krill redistribution due to transport and diurnal migrations occurred in the layer of 50 to 150 m. Estimated velocity of krill swarm displacement corresponded to the estimated water transport velocity in the polygon, suggesting that passive krill transport occurred.

The mathematical model of a fishery object contact against a mesh, while escaping through a trawl chafer, is presented. Based on it t the equations are provided to calculate the object elimination probability caused by cath and mortality in fishery operations. The coefficient of trawl ecological safety is offered, which is the ratio of the amount of the objects caught and objects caught and died during fishery. The equations are presented to estimate the gross removal of an object by the fleet group. Mathematical model is illustrated by a numeric example from the krill fishery. Thus, the calculated gross removal estimate exceeded the catch rate, based on commercial data in December 1984 in the South-Shetland area, only in 1,5 - 26 %, depending on the fishing intensity, i.e. it was within the range of stock estimate bias.