derived from fallout, even off the coast of Oregon 

 where the influence of the Columbia River plume 

 should be the greatest. 



Since radioactivity originating from fallout is 

 higher in the open ocean than in coastal waters 

 where upwelling occurs (Pillai et al. 1964; Folsom 

 and Young 1965; Gross et al. 1965), the spatial- 

 temporal trends evident in Figure 1 may be 

 explained by the residence time of albacore in 

 coastal waters. Highest levels of 60 Co are expected 

 in oceanic waters off southern Oregon in June and 

 July; lower levels are expected later in the season 

 after albacore have migrated northward and 

 shoreward and have resided in coastal waters, 

 provided that the biological half-life of 60 Co in 

 tuna livers is short enough. The decrease in 60 Co 

 levels in albacore (Figure 1) is much more rapid 

 than would be expected from natural radioactive 

 decay of 5.26 yr. Biological turnover must be rapid 

 in order to produce a short effective half-life. 



Hodge et al. (1973) related the levels of 60 Co in 

 albacore to fallout deposition and found that 

 maximum uptake of 60 Co by albacore lagged nuc- 

 lear atmospheric detonations by 1-2 yr. Annual 

 changes of 60 Co concentrations observed off Ore- 

 gon (Figure 2) show a similar delayed response, 

 but the peak activity levels in albacore occurred a 

 year earlier than the peaks seen by Hodge et al. 

 ( 1973) off southern California (dashed line, Figure 

 2). The main atmospheric input by nuclear deto- 

 nations occurred in 1961-62. Our main peak of 

 60 Co in albacore occurred in 1964, and that re- 

 ported by Hodge et al. occurred in 1965, indicating 

 a delay of about 2 and 3 yr respectively after 

 testing before the uptake is observed in albacore. 

 This not only suggests that the source of 60 Co in 

 albacore is from atmospheric fallout, but that the 

 availability of the radionuclide was different be- 

 tween the albacore caught off California and those 

 caught off Oregon, perhaps because of differences 

 in distributions and migratory patterns than 

 those described by Clemens (1961). 



Laurs and Lynn (1977) presented data that 

 confirm this suggestion. Based on recapture of 

 tagged albacore and length-frequency distribu- 

 tions, they concluded that the albacore population 

 found off Oregon is different from that found off 

 southern and Baja California. They further 

 suggest that albacore which migrate into Oregon 

 waters may come from a portion of the offshore 

 population which is located north of the 35th 

 parallel, while those that move into the California 

 waters are located south of the 35th parallel. 



The bomb detonations at Lop Nor (lat. 40°N) 

 gave the heaviest fallout input into the North 

 Pacific at about this latitude. Due to the circula- 

 tion in the North Pacific (Sverdrup et al. 1942), it 

 appears quite possible that albacore which were 

 associated with waters north of lat. 35°N may 

 have experienced high levels of 60 Co up to a year 

 before the tuna associated with waters to the 

 south. Circulation in the North Pacific and the 

 latitudinal differences in the location of the two 

 portions of the albacore population appear to be a 

 plausible explanation for the difference of 1 yr in 

 activity peaks between albacore caught off Oregon 

 by us and those off southern and Baja California 

 by Hodge et al. (1973). 



Acknowledgments 



This research was supported by the U.S. Energy 

 Research and Development Administration (con- 

 tract E(45-l)-2227, task agreement 12), RLO- 

 2227-T12-69. We thank N. H. Cutshall, T. R. 

 Folsom, R. M. Laurs, and V. F. Hodge for their 

 comments on the manuscript. 



Literature Cited 

 Clemens, h. b. 



1961. The migration, age, and growth of Pacific albacore 

 (Thunnus germo), 1951-1958. Calif. Dep. Fish Game, 

 Fish Bull. 115, 128 p. 

 CLEMENS, H. B., AND W. L. CRAIG. 



1965. An analysis of California's albacore fishery. Calif. 

 Dep. Fish Game, Fish Bull. 128, 301 p. 

 FOLSOM, T. R., AND D. R. YOUNG. 



1965. Silver-llOm and cobalt-60 in oceanic and coastal 

 organisms. Nature (Lond.) 206:803-806. 



Foster, r. F. 



1972. The history of Hanford and its contribution of 

 radionuclides to the Columbia River. In A. T. Pruter and 

 D. L. Alverson (editors), The Columbia River estuary and 

 adjacent ocean waters, p. 3-18. Univ. Wash. Press, Seat- 

 tle. 



Gross, M. G., C. a. Barnes, and g. k. Riel. 



1965. Radioactivity of the Columbia River effluent. Sci- 

 ence (Wash., D.C.) 149:1088-1090. 



Gross, M. G., and J. L. nelson. 



1966. Sediment movement on the continental shelf near 

 Washington and Oregon. Science (Wash., D.C.) 

 154:879-885. 



Hodge, v. f., t. r. folsom, and D. R. Young. 



1973. Retention of fall-out constituents in upper layers of 

 the Pacifiic Ocean as estimated from studies of a tuna 

 population. /^Radioactive contamination of the marine 

 environment, p. 263-276. Int. At. Energy Agency, Vienna. 



KEENE, D. F. 



1974. Tactics of Pacific Northwest albacore fisherman - 

 1968, 1969, 1970. Ph.D. Thesis, Oregon State Univ., 

 Corvallis, 102 p. 



869 



