Relationship between distribution of Antarctic krill (Euphausia superba) and environmental index MTEM-200 in the Antarctic Ocean throughout the year

Antarctic krill (Euphausia superba) is the key species of the Antarctic marine ecosystem and human fishing resources. Essentially, relationships between krill distribution and oceanographic conditions have been an age-old recurrent problem and many papers have been published on the subject since the British Discovery Reports. However, there was no remarkable achievement in particular the entire Antarctic Ocean. To clarify the relationship between krill distribution of krill and oceanographic environment, we have analysed two datasets combined. One is krill fishing records from 1973 to 2008 from the CCAMLR database. Another is accumulated water temperature data of the World Ocean Database. We here focus mean-field (climatologic analysis) in all season. First, we have examined fishing depth. The peak of fishing catches clearly appeared around 50 m and 94% of all krill fishing catches occurred in water shallower than 200 m. Furthermore, horizontal distribution of krill fishing points concentrated in three waters in the east Antarctic Ocean, the Scotia Sea, and north of South Georgia Island. From the above results, we calculated mean temperature from the surface to 200 m (MTEM-200) and compared it with horizontal distribution of fishing. The result indicated the strong correlation between krill fishing locations and MTEM-200 in the entire Antarctic Ocean. Waters that were efficient and stable for fishing were distributed in a narrow range with steep meridional gradients between -1.0 and 1.0 °C. Large fishing catches indicated the remarkable two peaks; -0.5~0.1 oC and 0.5~0.8 oC which located in the Scotia Sea, and north of South Georgia Island, respectively. Similarly, the historical krill distribution based on the Discovery Report’s net sampling coincided with this study results and each of the isopleths of MTEM-200 substantially corresponded with each oceanic front in the Southern Ocean. MTEM-200 can be applied for the further analysis of seasonal and/or annual variability.