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    Oceanological factors affecting formation of mackerel icefish aggregations in the South Georgia area during different seasons
    of the year

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    Document Number:
    Zh.A. Frolkina (Russia)
    Agenda Item(s)

    In wintering period icefish do not form aggregations, is feeding inactively and disperse at the depths more than 250 m within rather narrow temperature range (1.6-1,7ºC). In this period the water temperature is a limiting factor restricting fish distribution.
    In spring-summer icefish are feeding at the water temperature from 0.0ºC to 1.9ºC in the South Georgia area and to 2.0ºC near Shag Rocks. High level of energy exchange, intensive supply of food allow fish to distribute in the wider depths and temperature range. Taking in account the fact that in other habitats icefish occur at the water temperature below zero and never at the temperature higher than 2ºC, it is possible to assume that low water temperatures restrict fish distribution into the water waters.
    Autumn includes the feeding and pre-spawning periods. Pre-spawning fish do not depend on the forage species distribution and migrate to the spawning grounds. These migrations occurred in the near-bottom layer. The impulse of the spawning migration beginning is the near-bottom water warming in the spawning ground up to 1.6º?. The amount of accumulated fat affects an individual fish readiness to spawning. Icefish spawning in the current year continue feeding, but the feeding activity decreases considerably and fish are gradually shifting to the wintering grounds.
    Therefore, during the feeding period the abiotic conditions mainly affect indirectly icefish aggregations formation through the food items, distribution of which depends on hydrodynamic conditions, temperature, illumination, sea roughness, availability of phytoplankton aggregations, etc. During pre-spawning and spawning periods, icefish distribution and spawning beginning depend directly on the abiotic conditions, primarily with temperature. The same is true for the wintering period.