The Abundance, Distribution, and Stage-Specific Compositions of Euphausia superba in the Water Around the Antarctic Peninsula

Abstract:

To characterize the structure of Antarctic krill population and to evaluate the fishery resources, we analyzed the stage-specific abundance and distribution of Euphausia superba based on the data collected in the main krill fishing grounds nearby the South Shetland Islands (CCAMLAR subarea 48.1) and the South Orkney Islands (CCAMLAR subarea 48.2) from January 23 to February 13 in 2010. There were two sampling methods used in the survey. One was the vertical haul from 200 m depth to the surface layer using plankton net of which the mesh size was 330 μm. The other was the horizontal haul on surface layer and the mesh size was 500 μm. E. superba was found in 39% of the sampling stations in the surveyed area. The mean density in the water around the South Orkney Islands was 1.92 ind/m3, which was higher than the value of 0.35 ind/m3 in the water around the South Shetland Islands. The developmental stages of the sampled E. superba covered the calyptopsis stages (CI to CIII), the furcilia stages (FI to FIV and FVI), juvenile and adult. Nauplius and furcilia FV were not observed in our samples. Individuals at stages CI to CIII were the most abundant. The length ranges at stages of calyptopsis, furcilia, juvenile and adult were 1.764.96 mm (mean 5.15 mm), 3.9514.80 mm (5.96 mm), 16.8739.85 mm (36.10 mm) and 40.0058.96 mm (43.94 mm) respectively. High growth rates of larval E. superba appeared at stages CIII and FI. According to the portions of individuals from different developmental stages, we deduced that the spawning season of E. superba in the water around the South Orkney Islands started in late September and peaked in early December, which was later than that of krill individuals in the water around the South Shetland Islands. The abundance of E. superba was higher in samples collected with the surface net method than with the vertical haul method, and there was also a remarkable difference in the stage-specific compositions between the two sampling methods. Therefore our study suggested that the surface sampling method could be an effective supplement to the traditional methods in the study of the spatial distribution and the growth of the krill.