Egg Survival in a Fluvial Population of Masu Salmon in Relation to Intragravel Conditions in Spawning Redds

Abstract
Yamame are a fluvial population of masu salmon Oncorhynchus masou (also known as cherry salmon) that typically live in the mountain streams of Kyushu Island, Japan. We estimated the seepage of water through spawning redds by injecting carbon ink into the redds and periodically sampling the intragravel water. We found that the survival of yamame from egg deposition to the eyed stage was strongly dependent on the permeability of the gravel. We estimated permeability during two periods, just after spawning was completed and after eggs had reached the eyed stage. We found reduced permeability from the time of spawning to the time when the eggs reached the eyed stage. These results imply that the permeability of redds is one of the most important factors in the survival of embryos from fertilization to the eyed stage of development.