A short review of the effects of environmental factors on distribution, migration and recruitment of Pacific saury

The purpose of this paper is to provide a summary of previous insights into the effects of the environmental factors on the distribution, migration and recruitment of Pacific saury. The distribution and migration route of Pacific saury in autumn fluctuated from west to east depending on the period. In general, a suitable environment for the distribution of Pacific saury is formed along the Oyashio in autumn, thus they migrate through Oyashio. The mechanism of the eastward shift of the distribution and migration route in autumn has recently been explained by two factors: 1) the change of the pathway of Oyashio making it difficult to form a suitable habitat of Pacific saury in the waters around east of Hokkaido, and 2) eastward shift of the distribution of Pacific saury in early summer. Many studies on the relationship between recruitment fluctuations of Pacific saury and the environmental variations have been conducted. All of them found correlations between the environmental factors in the spawning and nursery grounds (or climatic indices that affect them) and the recruitment. In recent years, several studies have shown that the different environmental factors could correlate with recruitment in different periods. This may be related to the complexity of the life history of Pacific saury such as the interannual change of dominant seasonal cohorts. When considering the environment in stock management of Pacific saury, we need to note the possibility that environmental indicators that are correlated with recruitment in one period may become uncorrelated in another.