13 do not give the distribution of radioactivity at any one time for the entire survey area. As mentioned above, the values given are those at time of collection and can not be corrected readily to a common date because of the repeated addition to the waters being sampled of radioactive materials from the testing program. Gamma Ray Spectra: Gamma ray spectra were run at the EMBL on a Gamma Spectrometer type TM-10-A developed by the Instruments Branch, HASL, NYOO. hy RESULTS AND CONCLUSIONS Plankton and Water Temperatures: The average value of radioactivity in plankton was 71,000 d/m/g(wet), with the range from 1,300 to 1,100,000 (Table 1). w LO The average value for plank- ton was about 7,100 times the average value for surface water (10,000 d/m/l; Table 3). The minimum level of plankton activity, 1,300 d/m/g, was almost as high as the maximum level of 1,700 d/m/g found Quring the Proll survey, and indicates that the en- tire area covered by the WALTON survey was contaminated to some degree, The contour curves of plankton activity, based on station values as of the day of collection (June 11 to June 21), are Shown in Figure 10. Radioactivity was at a maximum in the re- gion immediately north of Bikini Atoll and diminished rapidly southward and gradually northwestward, suggesting fallout to the rs north and northwest. There was a general decrease in activity westward from Bikini with the exception of a tongue of higher matte at 4