THE SIGNIFICANCE OF UPWELLING ON THE SHO RIVER RIVERINE NATURE

Abstract

In 2004 natural spawning of chum salmon (Oncorhynchus keta) was observed in the Sho River, in the western part of Toyama Prefecture, because the salmon trap installed at the lower reaches of the river had been destroyed. Investigation of their spawning-related habitat and emerged salmon fry showed that the spawning sites clearly coincided with the upwelling (or spring) area located at the base of the Sho River alluvial fan. Upwelling water provided various types of riverine environmental components such as side pools, secondary channels, and these water areas derived from upwelling maintained a higher water temperature than other water areas. These properties contributed significantly to both salmon reproduction as well as environmental diversity and biodiversity.