Demographic studies of Antarctic krill Euphausia superba Dana in the Cooperation and Cosmonaut Seas (Indian sector of the Southern Ocean)

The reproductive state and size composition of Euphausia superba collected in the Indian sector of the Southern Ocean from 1985 to 1990 were analyzed to estimate its growth, life span and mortality rates. The duration of the life cycle of E.superba exceeded 5 years in the Cosmonaut Sea and 6 years in the Cooperation Sea. Assuming growth for only 180 days per year, growth rates ranged from 0.120-0.133 mm.d-1, during the first year of life, to 0.019-0.022 mm.d-1 during the fifth year. Von Bertalanffy growth curves calculated for different areas are similar to those obtained by Australian researchers in the Prydz Bay region for 1981-1985. In mid summer, E.superba of age 2+ to 4+ were predominant in all hauls made south of the Antarctic Divergence, while north of the Divergence the krill stock was clearly dominated by individuals of age 4+. The coefficients of natural mortality (M) of E.superba in the Indian sector of the Southern Ocean, calculated by the methods of Alverson & Carney, Richter & Efanov and Beverton & Holt, varied from 0.72 to 0.87, from 0.52 to 0.57 and from 0.76 to 2.92, respectively. The value of age-dependent natural mortality of E.superba derived using Zikov & Slepokurov’s method ranged from 0.52, during the maturation period, to 1.1-2.41, during the first and last years of life. Based on long-term observations, the relationship between E.superba age composition and its spawning success is examined for the coastal areas of the Cooperation and Cosmonaut Seas.