Eleven cruises were conducted on the Oregon continental slope from April 1973 to March 1975 to assess the biology and ecology of the Tanner crab, Chionoecetes tanneri Rathbun. Bathymetric and seasonal analysis of the distribution of adult Tanner crabs west of Coos Bay, Oregon, revealed no segregation of sexes or seasonal migration. Relative abundance of adult crabs was greatest in the 500-700m depth range. Juveniles were found throughout the adult depth range. Density estimates using a three meter beam trawl were 0-500 crabs/km² (mean = 56) for adult male C. tanneri and 0-1100 crabs/km² (mean = 164) for adult females. Stock estimates for the Oregon coast (500- 700m) and for the Oregon and Washington coasts (457-869m) supported Pereyra's (1972) conclusion that a Tanner crab fishery would not be feasible at this time. Longline pot fishing was suggested as a better method of assessing the commercial potential of the Tanner crab stock. Hydrological and sediment data indicated that the Tanner crab environment is a relatively stable one temporally and spatially in the study area. There was no apparent relationship between the presence or absence of adult C. tanneri and temperature, salinity, dissolved oxygen, sediment organic carbon content, or sediment particle size. / Graduation date: 1976