Fecundity, ovary weight, and egg weights, adjusted for fish length, of anadromous alewivesAlosa pseudoharengusand blueback herringA. aestivalisdiffered among some of four Maritime province rivers. Fecundity was poorly predicted by age. Spawning history (number of previous spawnings) did not affect fecundity and “fecundal senility” was not observed. Fecundity was usually higher for blueback herring than for similarly sized alewives. Reproductive condition (gonadosomatic index) of mature fish differed among rivers for both species. The time of sample collection influenced gonadosomatic index values for blueback herring but not for alewives. Gonadosomatic index values of alewives and blueback herring were uncorrelated with an index of distance upstream × elevation of the sampling site. Two major egg size-groups occurred in mature ovaries of both species. The largest egg size-group consisted of eggs ripening for spawning; the smallest size-group was retained after spawning. Fertility, as a percent of total fecundity, ranged from 38% to 67% for alewives and 39% to 52% for blueback herring, depending upon the estimation method used. Egg weight decreased with increasing fecundity for both alewives and blueback herring. For fish of equal length, fecundity of both species decreased with increasing latitude, whereas egg weight increased for alewives and did not vary significantly for blueback herring. Ovary weights did not vary with latitude for either species. The occurrence of fertility rates substantially lower than total fecundity, of geographic clines in fecundity, and of differences between species in fecundity and egg weight are important for understanding the reproductive strategies of, and for managing, alewives and blueback herring.