The Source of Cobalt-60 and Migrations of Albacore off the West Coast of North America

Cobalt is an integral part of the vitamin Bl2 complex and an important cofactor in enzyme systems (Lowman et al. 1971; Reichle et al. 1970). It is, therefore, an element whose cycle in oceanic ecosystems is of interest. The artificial radionuclide cobalt-60 (60CO) has been observed in the livers of albacore, (Thunnus alalunga Bonnaterre) collected off the west coast of North America, Washington to Baja California (Pearcy and Osterberg 1968; Hodge et al. 1973), The albacore is a commercially important migratory species of tuna which normally inhabits the epipelagic subtropical and transitional waters of the Pacific, Atlantic, and Indian oceans. In the North Pacific, albacore may undertake transpacific migrations between Japan and the west coast of America (Clemens 1961; Otsu and Uchida 1963; Clemens and Craig 1965). While single-pass nuclear reactors were operated at Hanford, Wash., the Columbia River was an important source of artificial radionuclides in the Pacific Ocean off Oregon and Washington. Some radionuclides, formed by neutron activation of impurities in river water used to cool the reactors, were transported via the Columbia out into the ocean and were detectable in the plume water far at sea (Osterberg et al. 1965). Cobalt-60 was among the radionuclides carried by the Columbia River effluent (Gross and Nelson 1966). Fallout from nuclear detonations, however, was another source of 60CO (Lowman and Ting 1973; Hodge et al. 1973). Which of these sources was more significant in contaminating tuna is not known. We shall attempt to use the temporal and geographical variations in 60CO content of albacore livers to estimate the relative importance of the two sources and to provide information on migrations of albacore: