During the periods 2004-2006, 30 adult chum salmon tagged with an electromyogram (EMG) transmitter and depth/temperature (DT) logger were tracked along both the canalized and reconstructed segments of the Shibetsu River, Hokkaido Japan. To estimate effects of the reconstruction on upstream migration of chum salmon, swimming speed calculated from EMG signals, ground speed, swimming efficiency index (SEI), and time of holding behaviour were compared between males and females. Critical swimming speed (Ucrit) of 13 chum salmon was also measured. Although ground speed and SEI were not significantly different between sexes, swimming speed of males was significantly lower than that of females. Holding time of females in the reconstructed segment was longer than that of males. These results indicate that male chum salmon migrated with reduced muscle activity compared to females because of the larger body size of males. Swimming speeds calculated from EMG signals decreased during holding behaviour that were observed after exceeding Ucrit during moving.