Euphausia pacifica brood sizes: a North Pacific synthesis

Abstract

Euphausia pacifica occupy a remarkably wide range of ecosystems. We examined the differences in brood sizes from eight regions of the North Pacific to explore how variation in the brood size might contribute to their success over such a range. We show a compilation and analysis of short-term E. pacifica brood size incubations from around the North Pacific rim, ranging from the Yellow Sea (YS) (Korea) to southern California (SC), USA. Brood sizes for E. pacifica are highly variable in all regions and range from 5 to 697 eggs overall. Median brood sizes were largest in the YS and off Newport, Oregon and the maximum brood sizes were greatest in the regions off the coasts of Oregon and Washington, USA followed by the YS. Quantile regression analysis revealed that there was a significant relationship between the female length and the maximum brood size (95 quantile) for broods from SC, Oregon, and Washington, USA as well as Toyama Bay, Japan, indicating that the maximum brood size is limited by the female length in these regions. This suggests that other factors, hydrographic conditions, food quantity/quality or physiological condition of females, may limit maximum brood sizes in the other regions examined here.