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

In order to clarify population structure of local herring in eastern Hokkaido, and to design an effective release program of seed fish artificially cultivated in aquariums, five samples of Pacific herring, Clupea pallasii, were caught from four spawning grounds. Six meristic characters were counted and statistically analyzed. Furthermore, allele frequencies of two enzymatic loci, GPI and PGM, were examined by using a starch gel electrophoresis. The sample from Yudo Lake had significantly fewer numbers in the upper and the lower gill rakers than in the others. A cluster analysis using the six meristic measurements on five samples showed that there are two local populations in the eastern Hokkaido, i.e, Yudo population and others, the former was a morphologically specific population different from the latter. In addition, Nei's genetic distances using allozyme data of the two loci also suggested that the Yudo sample is the farthest distances from all other samples. It is suggested that the singular characteristics of the Yudo population were connected with a later spawning time in this ground than in others.