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

The reproductive state and size composition of Euphausla superba Dana 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 life span of E. superba exceeded 5 yr in the Cosmonaut Sea and 6 yr in the Cooperation Sea.Assuming growth for only 180 d per year, growth rates ranged from 0 120-0.133mm d -' during the first year of life to 0.019-0.022mm d-l 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 to 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 were clearly dormnated 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 denved using Zikov & Slepokurov's method ranged from 0.52 during the maturation period to 1.1-2.41during the first and last years of hfe.Based on long-term observations, the relationship between E. superba age composition and its spawning success 1s examined for the coastal areas of the Cooperation and Cosmonaut Seas.