CCAMLR

A net sampling survey for krill was carried out by RV ‘Meteor’ along the Antarctic Peninsula from 26 December 1989 to 14 January 1990. Results were compared with data of an identical survey with RV ‘Polarstern’ in 1987/88. Seasonal variation between summer and winter abundance/biomass data exceeded a factor of 35 times, while interannual variability between available surveys reached only a factor of 1.6 times. Krill mortality was calculated by linearized catch curve analysis and resulted a rate of Z=0.88 (1989/90) and Z=0.96 (1987/88). Production was estimated and resulted a P/B ratio of 0.88 to 0.94 for different years. The exchange rate of water masses and krill biomass within one summer season was roughly estimated as 2 times from which follows a maximum total effective biomass (including production) of 4.3 and 5.0*106 tonnes passing through the survey area during the respective summer.

To delineate zooplankton distribution and abundance in Bransfield Strait, in relation to hydrographic condition, a total of 29 sampling stations was occupied for the CTD casts and plankton towings in a systematic grid from December 29, 1989 to January 7, 1990. Comparisons of temperature and salinity distributions and T-S diagrams suggest that the cold and saline Weddell Sea water entered from the Antarctic Sound flows southwest along the Antarctic Peninsula coast, turns to the north at the east of Trinity Island, then joins the Bellingshausen Sea water (warm and less saline water) near the south of Deception Island, and meanders northeastward in the surface layer of the northern strait. Bellingshausen Sea water enters near Low Island, then, mainly flows toward Deception Island. A total of 39 taxa of zooplankton were identified from samples. Several species of copepoda were the most abundant (57.7%) in terms of number, and followed by salpa (27.7%), chaetognatha (6.7%), and euphausia (1.3%). However, noticeably, macrozooplankton salpa (Ihlea sp. and Salpa sp.) predominated over the entire Bransfield Strait occupying 20 stations, and showed the highest biomass in zooplankton community. The highest number of salpa was shown in the northeastern entrance of Bransfield Strait, but low numbers were found along the stations near the Antarctic Peninsula coast. Fish larvae and euphausia were rarely found in the entire strait

In-situ measurements of individual krill target strength are presented (modal value = -69db). Net samples obtained immediately before the experiment indicate that the animals were reproductively mature and averaged 47.44mm in length. Results agree well with recent predictions of acoustic target strength based on extrapolations of other field experiments using the bent cylinder model of sound scattering by elongated zooplankters. The modal value of the measurements is 6.7dB lower than that predicted by the BIOMASS equation for 47.44mm krill.

Clarification of main tendencies of spatial changeability of size composition of E.superba was undertaken by means of comparision of various size groups of curstacean distribution in the region of the South Orkney islands and adjacent waters. Materials of 14 separte expeditions were used (Table 1), which cover 20-years period (from 1965 to 1985). Data on size composition of E.superba for each survey are showed on reparate maps (Fig. l-14). Consideration of age of animals is outside of attention, and we operate here only by modal groups, which valuated on the maxima on cures of size distribution.
Distribution of size groups demonstrates superficially rather irregular tendencies. Nevertheless, comparision shows, that these animals, which distribute to the north from south part of the South Antilles Ridge have rather simple size composition (one or two size groups), but at the level or to the south of the South Antilles Ridge size composition of E.superba is more complex. Intermediate group (or groups) present here, and for size distribution curves is characteristic more compressed position of separate maxima, than in the norhtern part of the region. These featurese are concerned mainly to E.superba with lenght from 40 mm and more.
Complication of E.superba size composition increase also due to the addition of more small animals (adolescent). It is very interesting, that adolescent E.superba was found not only in the southern part of the region, but also in eastern and especially to its north-east parts. In this last case adolescents were observed very far to the north from the South Antilles Ridge. As to northern part of the region, adolescent E.superba was captured here not so often.
Comparision of several survevs, which were carried out during the same year shows definite closing to one another of modal groups with size less 48 mm.
Resulting picture reflects well known phenomenon of separate distribution of adolescent and adult E-superba. This phenomenon is mope complicated for the Scotia Sea due to two reasons. Picture complicated due to system of current, namely advection of Weddell Sea waters to the north in eastern part of Scotia Sea. These waters transport adolescent E.superba namely in this direction. Besides of, the waters composition plays also definite role: mutual distribution of Weddell Sea waters and Antarctic circumpolar current waters. Transformed waters of Bellingshausen Sea usually drift namely with the southern peripherie of the second type of the waters. Both of these types of waters (of Weddell Sea and of Bellingshausen Sea), which drift along opposite side of the South Antilles Ridge (near to South Orkney Island at any case), transport, as it may suppose, semarate groups (subpopulations) of E.superba. There is certain reason to expect to find double size gradient zone of E.superba in sum for these tvpes of water. Such gratient zone should be expected primary for area, filled with Weddell Sea waters, but in the case of southern peripherie of Antarctic circumpolar current it may suppose of much more irregularity. Perhaps, adolescent E.superba “are ab1e” keep position inside of inshore gyres of Antarctic peninsula. Adult crustaceans may drift more easier, because its dustribution much far from the shore. It may suppose also seasonal patern of adolescent E.superba drift from Antarctic peninsula side.
At last, the distance between modal maxima on the side distribution curves of bellingshaused’s E.superba more large because more prolonged vegetation season in Antarctic circumpolar current waters. Rate of E.superba growth in these waters should be higher, then in Weddell sea waters.

The problem of acoustic abundance estimation is briefly reviewed. Under proper conditions, fish density can be measured with high accuracy along line transects. Observed variations in fish density consequently reflect biological variations, or inhomogeneity in spatial distribution. The particular problem of estimating fish abundance over an area from line-transect measurements of fish density is defined. Related problems of estimating the variance of the abundance estimate and of mapping the spatial distribution are also defined. A partial list of candidate methods for solving the several problems is given. Among these, the so-called spatial statistical techniques appear to be most promising because of their exploitation of the observed spatial structure.