Because of the economic importance of tuna fiahing in the Western Pacific, a project was undertaken to sample commercial fishery catches landed in Japan, since this appeared to be the best means of obtaining the coverage required to sample the area. From a total of 572 fish, 2722 samples were taken, including specimens of dark and light muscle, skin, liver, heart, kidney, spleen, stomach, stomach content, intestine, gonad, gill, and bone. In those samples containing radioactivity, Zn™ contributed 75 to 92 per cent of the total, with Fe'®, Fe®®, co®’, cof, Co, and Mn™ accounting for most of the remainder. In no case were the levels of radioactivity greater than the maximum permissible concentration for drinking water. Following the completion of the testing program, the region including the EPG and the area westward to Guam was surveyed to determine the amount, kinds, and extent of radiological contamination of the western Pacific Ocean. The survey was conducted in two sections: The USS Collett (DD-730) was uséd to survey the restricted area in August 1968, and the USS Silverstein (DE-534) was used for the survey in September extending to Guam. The The latter survey included an area bounded by 10°20' and 17°00'N and '144°50' and 161°51'E. The upper, mixed layer of the ocean was sampled at stations on a grid at about 50-mile intervals. Samples included water, plankton, and fish at depths to 300 meters. During the August trip W'™ was found on plankton (19 x 10° d/m/g dry weight) collected 155 miles northwest of Eniwetok Atoll. This center of radioactivity had shifted 150 miles westward by the time of the second sur- vey, and all the w'® had been lost from the plankton. The major remaining radioisotopes were Co®#, Ba'“-La!@, Zn, Col”, CoM, and Zr*-Nb™. The leading edge of the radioactive body of water was 200 miles east of Guam Island. by September 1958. Samples of crater material and sea water were collected in the target area of the Umbrella detonation and analyzed for radioisotope content. The anions Np, U2" Tels!2 wo%-Tc™™ accounted for 90 to 98 per cent of the total radioactivity in the samples. The isotope content of particles greater than 0.5 micron from the sea water was different from that in the fraction smaller than 0.5 micron. The long range radiation ecology study at Rongelap was continued. Major emphasis was placed on studies of the soil-plant relationship, aquatic bird populations, and mineral transport, as well as evaluations of the uptake of specific isotopes by plants and animals used as food by the natives. 58