~34- obtained before Wahoo contained Np239, Rul03-Rpyl03, and Te!32-1132 but no detectable amounts of the other radioisotopes which were found in the smaller fish and in the plankton. Samples of whole shrimp and squid had high levels of Np239 and relatively higher levels of Te 132-7132 than the plankton. However, they contained no detectable amounts of Mo99-Te 99M, Because these data indicate that som* discrimination occurs in the uptake of radioisotopes by marine organisms, it would be of interest to determine which isotopes are incorporated or metabolized by these organisms. Some of the radioisotopes were concentrated rapidly by samples mixed plankton species; knowledge of of their concentration and fate in single species of plankton would be of interest. SUMMARY 1. A survey of the radioactivity of sea water and marine organisms. was conducted at the Eniwetok Test Site from May 3, 1958 to May 20, 1958, immediately before and after an underwater nuclear detonation. 2. Seventy-two hours after the underwater nuclear detonation, Wahoo, the radioactive water mass thus produced extended more than 50 miles westward from site zero, both above and below the thermocline. ase A> oo