first, relatively high 60 Co activities were seen off 

 the southern Oregon coast and somewhat lower 

 concentrations off northern Oregon and 

 Washington as well as off southern and Baja 

 California; second, 60 Co concentrations decreased 

 with time during the summer-fall period. Data 

 from other years corroborated these trends. 



Annual variations of 60 Co in albacore off the 

 Oregon coast (dots and solid line in Figure 2) indi- 

 cate that 60 Co concentrations increased from 1963 

 to 1964 then declined steadily until 1967, but in- 

 creased again in 1968. 



There are two possible sources of 60 Co for alba- 

 core in the northeastern Pacific. Until 1965, eight 

 Hanford reactors were a relatively constant source 

 of 60 Co entering the Columbia River (Gross and 

 Nelson 1966). In 1965, however, a sequence of 

 shutdowns of individual reactors began (Foster 

 1972). The other possible source of this isotope is 

 fallout from atmospheric tests of nuclear weapons 

 which also varied in time, but according to a dif- 

 ferent pattern (Lowman and Ting 1973; Hodge et 

 al. 1973). Inputs of 60 Co into the environment by 

 atmospheric tests that could directly effect the 

 activity levels in the North Pacific include over 

 100 U.S. and U.S.S.R. tests in 1961-62 and Lop 

 Nor, China, tests in 1964-65 (one test each year), 



1966 (three tests), 1967 (two tests), and 1968 (one 

 test) (U.S. Environmental Protection Agency 

 1960-72). 



The relatively constant input from the Hanford 

 plant fails to account for the low 60 Co values ob- 

 served in albacore during 1963 nor the increased 

 values in 1964 (Figure 2). Other evidence indicat- 

 ing that Hanford was not the major 60 Co source is 

 based on our knowledge of the migration of alba- 

 core into the Pacific Northwest fishery and their 

 subsequent movements. Albacore often first ap- 

 pear off the southern Oregon coast and move 

 northward and inshore as the summer progresses 

 (Powell et al. 1952; Keene 1974), sometimes along 

 the axis of the warm Columbia River plume wa- 

 ters (Pearcy 1973). Levels of 60 Co did not increase 

 with residence time of albacore in Oregon waters 

 or proximity to the Columbia River in northern 

 Oregon (Figure 1), as would be expected if Hanford 

 was the main 60 Co source. 



These trends are opposite of those noted in alba- 

 core livers for 65 Zn, a radionuclide that was known 

 to be associated with the Columbia River effluent, 

 but are similar to those of 54 Mn, a radionuclide 

 associated with atmospheric fallout (Pearcy and 

 Osterberg 1968). We conclude, therefore, that 

 most of the 60 Co we find in albacore livers was 



FIGURE 2.— Concentration of 60 Co in liv- 

 ers of albacore captured off Oregon and 

 Washington. Solid line indicates mean 

 values of our observations (dots); broken 

 line is a plot of 60 Co levels off southern and 

 Baja California as presented by Hodge et 

 al. (1973). Also indicated is the number of 

 Hanford reactors in operation and the 

 number of nuclear atmospheric tests 

 (bars = pre-1963 non-Chinese testing af- 

 fecting the North Pacific and post- 1963 

 testing at Lop Nor, China) which occurred 

 during our study period. 



o 

 U 

 O 



10 



No of 

 Reactors ^ 



— , , — -.-^ 



I 



en o 



O 

 Q. 



0! 



(110) Nuclear 

 Tests 



110 



105 



100 



co 



• (3) 



(I) 



(I) 



(2) 



(I) 



(2) 



1961- ' 1963 

 1962 



1964 ' 1965 



1966 ' 1967 

 YEAR 



1968 ' 1969 



1970 



868 



