Population structure of Pacific herring Clupea pallasii in the eastern Hokkaido waters

In order to clarify population structure of local herring in eastern Hokkai do, and to design an effective release program of seed fish artificially cu ltivated in aquariums, five samples of Pacific herring, Clupea pallasii, we re caught from four spawning grounds. Six meristic characters were counted and statistically analyzed. Furthermore, allele frequencies of two enzymati c loci, GPI and PGM, were examined by using a starch gel electrophoresis. T he sample from Yudo Lake had significantly fewer numbers in the upper and t he lower gill rakers than in the others. A cluster analysis using the six m eristic measurements on five samples showed that there are two local popula tions in the eastern Hokkaido, i.e, Yudo population and others, the former was a morphologically specific population different from the latter. In add ition, Nei's genetic distances using allozyme data of the two loci also sug gested that the Yudo sample is the farthest distances from all other sample s. It is suggested that the singular characteristics of the Yudo population were connected with a later spawning time in this ground than in others.