Concentrations of artificial radionuclide 137Cs and natural radionuclide 40K in Dall’s porpoise, Phocoenoides dalli, from the Pacific coast
of northern Japan in 1996 are presented. Concentrations of 137Cs in muscle tissue from two male Dall’s porpoises were 0.153 ± 0.011 and
0.234 ± 0.016 Bq kg- 1 wet weight, and those of 40K were 104.0 ± 0.3 and 107.8 ± 0.9 Bq kg-1 wet weight, respectively. Concentration
factors (CF, concentration in animal/concentration in sea water) for the two porpoises are 59 and 90 for 137Cs, respectively. These
concentrations and CF values are within published ranges for marine fish in coastal waters. The CFs obtained in this study suggest that the
trophic position of Dall’s porpoises is similar to that of the large piscivorous fish in the marine community in coastal waters of Japan.