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    Peculiarities of Euphausia superba size composition in Statistical Subarea 48.2 (South Orkney Islands)

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    Número de documento:
    V.I. Latogursky and R.R. Makarov (USSR)
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    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.