Bull. Jpn. Soc. Fish. Oceanogr.  68(1), Page 36-43 , 2004   Bathymetric Distribution and Migration of Hair Crab, Erimacrus isenbeckii, off the Pacific Coast of Western Hokkaido Eiji Mihara Muroran Branch, Hokkaido Hakodate Fisheries Experimental Station, Funami-cho, Muroran, Hokkaido 051Ð0013, Japan) e-mail: miharae@fishexp.pref.hokkaido.jp The bathymetric distribution and migration of hair crabs were investigated by using sampling surveys off Muroran between March 1999 and March 2001 and tagging experiments conducted in March 1981 and September to October 1991 along the Pacific coast of western Hokkaido. In the sampling surveys, hair crabs were caught mainly at depths from 20 to 60 m between January and May and at depths from 100 to 120 m between September and October. Larger males tended to occur in deeper water than in shallower water. Seasonal changes in bathymetric distribution and bottom temperatures were related with each other. Bottom temperatures were low (2.9-6.4°C) between January and May, rose in shallower waters in June, and peaked (>11°C in waters shallower than 80 m) in September. In male hair crabs, catch per unit of effort (CPUE) tended to be low under high bottom temperature. Hair crabs released in March were recaptured between August and December at sites deeper than the released sites. Hair crabs released in September and October were recaptured between March and July at sites shallower than the released sites. Therefore, hair crabs are mainly distributed inshore in winter and spring, and migrate offshore in summer and autumn to avoid the warmer inshore waters. Key words:hair crab, Erimacrus isenbeckii, bathymetric distribution, migration, bottom temperature, Pacific coast of western Hokkaido