Population differentiation and structure are important topics of evolutionary biology, and morphology and genetics are the main methods of researching these topics. migrates annually from the overwintering field to the spawning ground, and for a long time, it has been thought that the breeding period of its inshore populations was as long as two months. In addition, during the grouping period, the specification of arriving in different stages showed a decreasing trend with arrival time. Thus, the objectives of this study were to characterize the population structure and clustering phenomenon in over time, and discover why the parental specification diminished during spawning of the mature animals in Qingdao. The morphological characteristics and genetic differentiation during three different migratory periods (early, middle, and late) of inhabiting the coastal waters of Xuejia Island were analyzed using morphology and DNA markers. The results showed that the cumulative contribution rate of the first three principal components was 60.067% in the principal component analysis (PCA), which was lower than 85%. The discrimination accuracy ranged from 66.7% to 82.1% in the discriminant analysis (DA). The scatter plots of PCA and DA showed a similar result, which is the species was not clearly dispersed among these three migratory periods. Analysis based on microsatellite markers indicated that genetic distances () ranged from 0.12 to 0.16 and the genetic differentiation index ( from the three different migratory periods. The optimal number of theoretical groups was 1 according to the genetic structural analysis. These findings suggested that there was no obvious population differentiation among early, middle, and late migratory periods of in Qingdao, owing to the low values of morphological differences, genetic distances, and genetic differentiation, although the population showed a large difference in mantle length and body weight in specifications. The differences in the swimming ability of small and large individuals may be the main reason behind the long period of 's clustering and the decrease of its specification over time. It is undeniable that the differences in morphology and genetics among populations of marine cephalopods populations of fish are unpredictable yet significant. Macroscopic identification methods, such as morphological studies, are vulnerable to the influence of living environment, and at the same time, marine fish with good dispersal ability usually exhibit very low genetic differentiation within a wide geographic range. Therefore, the strong athletic ability of may also lead to a similar genetic structure of its populations.