Variability in brood size and female length of Euphausia pacifica among three populations in the North Pacific

Abstract

We compared brood sizes among adult female Euphausia pacifica Hansen, 1911 from 3 populations in the North Pacific: Puget Sound, Washington, USA; Toyama Bay, Japan; and the Ore- gon coast, USA. Additionally, we used multiple linear regression models to compare the interspecific brood size as a function of female length and location. The females from Oregon attained larger brood sizes (maximum 600 eggs brood -1 , mean 152 eggs brood -1 ) and were longer (mean length 20.1 mm) than females from the other 2 regions (means: 96 eggs brood -1 and 15.9 mm; 113 eggs brood -1 and 18.5 mm for Puget Sound and Toyama Bay, respectively). The brood size for females from the 3 populations increased with size, reaching a maximum when females attained lengths ranging from 19 to 22 mm. The brood size decreased substantially for larger individuals. When the relation- ship between brood size and length was corrected for differences in female length, the median brood sizes were statistically indistinguishable among the 3 regions, indicating an inherent reproductive potential probably associated with the carapace volume available for the gonads for a given female length.