The number of genetically distinct herring stocks is determined by the number of distinct, geographically stable larval retention areas. Spawning sites in these areas may be highly localized or dispersed. Absolute population size mostly depends on the retention area available to the density-dependent larval-postlarval stage. Although the extreme seasonal range of spawning time shown by Atlantic herring is not fully accounted for by a new hypothesis, current theory is not supported by the hypothesis or by empirical data. The management implications are discussed.