- 60 0. 8 percent of the total activity. Two fish muscle samples collected in January 1955 were reported in USNRDL-454 (Table 4.5) to have Sr?° levels of 0.2 percent of the total beta activity. The muscle and bone of terns, which feed on fish, contained no Sr?9 In contrast to the strictly marine forms, the coconut crab, which feeds principally on land plants, had sr?° levels of 3 percent in the muacle and 12 percent in the hepato-pancreas or liver, where calcium salts are stored. The radioisotopes in salts leached from the carapace were found to consist entirely of sr90 + y99 The levels relative to total activit y would be expect- ed to remain constant in the salts of the carapace, to increase in muscle, as gr9° makes up a greater proportion of the total activity with the passage of time, and to be variable in the liver depending on the physiological state of each crab with respect to molting. sr? levels in the liver would be ex- pected to be at a peak immediately pre- and post molt. In the lagoon bottom samples collected in October 1955, 0.7 percent of the activity was Sr99. Estimates of total radiostrontium content of Rongelap lagoon are discussed in the soils section. Radiocesium (Table 14). The highest Ca!87 levels were found in the land plants and the coconut crab, 26 percent-100 percent. Ce 137 in marine algae, fish muscle and fish-feeding birds was absent or present in only small amounts (maximum 4. 8 percent). Radiocerium (Table 14). The levels for Cce!44 were highest in marine birds and algae, 26 percent-71 percent. In tuna muscle, however, ce!44 accounted for only 0.6 percent of the total activity. There was none in