Interannual summer variability in euphausiid populations on the eastern Bering Sea shelf during the recent cooling event (2008-2010)

The recent cooling in the eastern Bering Sea resulted in a series of cold years (2008-2010) marked by extensive ice coverage and late ice retreat. In the present study, we examined the spatial and temporal variability of three predominant euphausiid species Thysanoessa raschii, Thysanoessa inermis, and Thysanoessa longipes in the summers of 2008-2010. Simple box-and-whisker plots as well as generalized additive models (GLMs) were applied to examine habitat selection for three euphausiid species. The coefficients of dispersion were calculated for three species to examine potential changes in spatial patterns. Results showed that T. raschii was broadly distributed in the inner and middle domains. The abundance of T. raschii was related to water temperature, salinity and chlorophyll a concentration. T. inermis was primarily distributed in the middle domain and was related to water temperature and salinity. T. longipes was mostly distributed in the outer domain and was only related to salinity. The proportion of T. raschii, a coastal species in the inner and middle domains, showed large interannual variation with the highest in 2008 and the lowest in 2009 (a >50% decline). This same species did not show large interannual variation in the spatial distribution. T. longipes, a shelf species in the outer domain, did not show large interannual variation in abundance, but the center of mass distribution consistently shifted northward and offshore from 2008 to 2010. T. inermis, a coastal species in the middle and coastal domains, did not show large interannual variation in abundance and spatial distribution. In summary, euphausiid populations showed large spatial and temporal variability among cold years. Different species could be affected by different processes in the southeastern Bering Sea.