210 



JACKSON. VESSEY, AND BASTIAN 



TABLE 5 



Summary of Stomach Nematode Distributions 

 Relative to Host Species, Islet, and Atoll 



Species and 

 parasite 



Islet 



No. 

 rats 



No. 

 infected 



% 

 infected 



R exulans 

 (Protospiura 

 muricola) 



(Gongiilonema 

 r\eoplasticum) 



Totals 262 84 32.1 



Northern Marshall Atolls 



602 141 23.4 



602 208 46.5 



•Temme, 1979. 



Responses to Testing Program 



During the Atomic Energy Commission's testing pro- 

 gram, detailed or systematic studies on rodents were not 

 conducted, although several individuals made brief observa- 

 tions and even transplanted rats from islet to islet. In some 

 cases, it was possible to reconstruct the experiments and 

 even correctly identify the rodent species involved. How- 

 ever, it was not until the 1964 Resurvey Program, 

 directed by the University of Washington, that continuing 

 studies of the rodent populations were initiated. 



At that time, roof rats inhabited the larger, highly dis- 

 turbed islets; Polynesian rats inhabited the less disturbed 

 islets. Our radionuclide investigations focused on the roof 

 rat populations on Enjebi and Runit, although we studied 

 populations, including Polynesian rats, on other islets. 



On Runit we examined roof rats at varying distances 

 from Cactus crater at the north end of the islet (Bastian 

 and Jackson, 1975). The rats concentrated the radionu- 

 clides they obtained from plants in their diet. At the 

 crater, levels of ^^^Cs ranged up to about 2000 pCi g^^ 

 (dry weight) in plant tissues; in rat tissues, to 5000 pCi 

 g~' (Table 6). At the south end of the islet (where no test- 

 ing was done) radioisotope levels were close to back- 



TABLE 6 



Average "'Cs Levels (pCi g~' Dry Weight) of 



Soil Samples and Plant and Animal Tissues 



Collected on Runit Islet (1967)* 



Distance from Cactus Crater, m 



'Numbers of samples vary. Data from Bastian and Jackson, 

 1975. 



ground. We felt, on the basis of these data, that rats 

 would make excellent radiation monitors. 



Further efforts to demonstrate the potential monitoring 

 role of rats led to the use of thermoluminescent dosimeters 

 (TLD), which were implanted under the nap>c skin of rats 

 that were released and then recaptured 5 months later 

 (1977 to 1978). Of the 185 implants made, 39 were 

 recovered, even though cleanup operations were under 

 way, which greatly interfered with the initial trapping and 

 recapture operations. Rats of both sfiecies on six islets 

 were involved. Exposures of 3 to 7 mR d~^ were recorded 

 from rats on Runit and about 1 mR d~' on Enjebi are con- 

 trasted to zero readings in Igurin and Ananij rats. These 

 radiation levels detected by the rats' dosimeters appear to 

 correlate closely with the measurements obtained during 

 the cleanup operations (Table 7). 



The aborted PACE program (1972) had a principal 

 impact on Bijire with the removal and windrowing of plant 

 debris. The Polynesian rats used this increased cover, and 

 the sooty terns shifted their breeding colony to some of 

 the cleared habitat. From examination of stomachs, we 

 know that rats were preying or scavenging on the terns. 

 Numbers of Polynesian rats on the three-islet chain 

 (Aomon-Bijire-Lojwa) continued to be high during and fol- 

 lowing this period. 



When the final cleanup program was organized, Lojwa 

 was set up as a base facility (1977), and most of the land 

 area was scraped clean. Polynesian rats were pushed into 

 the fringe of remaining vegetation. As soon as living quar- 

 ters were constructed, rat infestations became chronic 

 problems. 



Garbage was disposed of in a pit across the bridge to 

 Bijire. Although periodic covering occurred, rats abounded. 

 We observed rats moving from distances of several hun- 

 dred meters to the dump, but no detailed marking and 

 movement studies were possible. 



The cleanup on Enjebi resulted in chaining and wind- 

 rowing much of the vegetation and subsequent removal of 

 contaminated soil and debris from many areas. The roof 

 rats, perhaps reduced in total numbers, were concentrated 



