Spatial distribution and population structure of Euphausia pacifica in the Yellow Sea (2006-2007)

We studied spatial distribution patterns, population structure and egg production rates of Euphausia pacifica in the Yellow Sea from April 2006 to August 2007 during eight cruises. We investigated the distribution of the developmental stages in relation to environmental factors (temperature, salinity and chlorophyll a). We used principal components analysis and Pearson's correlation to analyze the covariation and correlation between E. pacifica abundances and environmental factors. The spatial distribution of E. pacifica was controlled primarily by seawater temperature and the adults preferentially inhabited cold water. Euphausia pacifica occurred nearly throughout the entire study area in spring and winter. When surface seawater temperature was over 20 degrees C in summer and autumn, E. pacifica was mainly located in the Yellow Sea Bottom Cold Water (YSBCW) area where the temperature below the thermocline was 8-10 degrees C. On-board incubation experiments showed that the brood size of E. pacifica was highest in spring. We conclude that E. pacifica can undergo its whole life history and maintain high abundance in the Yellow Sea. Recruitment is mainly in spring, after which it is very low. In summer and autumn, the population is mainly distributed in the YSBCW, which offers animals a refuge from warm surface waters.