Our aim was to describe the migratory process of pink salmon Oncorhynchus gorbuscha and to examine the relationship between the migration and physical environments (sea surface temperature and day-length). From tag data for 4,876 individuals for the past thirty years, we examined distribution change, migratory speed and day-length during open sea migration. The open sea distribution was consistent with 4-11 °C sea surface waters as found by past studies. Mean migratory speed was 31.5±27.8km/day. Migratory speed was significantly correlated with day-length, and pink salmon tended to migrate fast around the summer solstice. This result suggests that the photoperiod is an important factor related to the spawning migration of pink salmon.