Abstract:During 2009/2010 and 2010/2011 fishing seasons, Antarctic krill Euphausia superba Dana from the south Atlantic Ocean was harvested by Chinese commercial fishery vessels in the CCAMLR subarea 48.1 near the South Shetland Islands and CCAMLR subarea 48.2 near the South Orkney Islands, respectively. The length-frequency and sex ratio of krill collected in both fishing seasons were analyzed to estimate its growth, age structure, and evaluate potential temporal spatial variations of its spawning season. Based on the results of length frequency fitting mixture distribution, five age groups (1+~5+) were observed in the krill population. The age structure and sex ratio of krill varied in the two fishing seasons and subareas. In the waters near the South Shetland Islands of subarea 48.1, E. superba population was dominanted by individuals at age 5+ in January, 2010 and December, 2011. In the two months, gravid female were abundant and consisted over 40 percent of all krill numbers. Gravid females were between age 3+~5+ and dominated by those of age 5+. In contrast, in the waters near the South Orkney Islands of the subarea 48.2, E. superba population was still dominated by individuals of age 5+ in February, 2010, yet subsequently by those of age 3+ in February, March and April, 2011. Although gravid females of age 5+ were observed, their proportions decreased only about 15% in February, 2010 and less than 1% from February to April, 2011. Monthly observation during February, March and April, 2011 showed that it tended to be fewer gravid individuals, more unimodal age structure and increased sex ratio.In addition, the krill growth rate decreased with month and was negative value in March and April. Based on the above results, it could be inferred that in subarea 48.2，E. superba spawning peak in 2010/2011 fishing season should be earlier than February, 2011, while spawning remained in that month of 2009/2010 fishing season.
