Sea-run migratory behaviour in the Japan Sea form of three-spined stickleback Gasterosteus aculeatus in the tidal pool of eastern Hokkaido Island, Japan.

Juveniles in the Japan Sea form of three-spined stickleback Gasterosteus aculeatus collected from a tidal pool in eastern Hokkaido Island, Japan, had a unimodal standard length (L(S)) frequency distribution in each period, ranging from 11.9 to 31.6 mm, and those of sea-run migrating individuals collected from the outlet of this tidal pool ranged from 17.0 to 36.0 mm, suggesting juveniles of this form would migrate towards the sea when they reached >17.0 mm. In general linear models (GLM) for testing the best model, there was a relationship between the number of sea-run migratory individual and precipitation, which suggests that precipitation may trigger migration.