Radionuclide Tracers Suggest Different Migratory Patterns in Two Groups of North Pacific Albacore (Thunnus alalunga)

The Fukushima Dai-ichi power station released radionuclides into the Pacific Ocean off eastern Japan in 2011, which provided an opportunity to examine migration routes and population structure of North Pacific albacore. Albacore samples collected (2011-2013) from two regions (North and South of 40° N) in the eastern Pacific were tested for radionuclides (¹³⁴Cs and ¹³⁷Cs) released from Fukushima. Pre-disaster control samples (2008) were also tested. Measurements thus far have shown almost no ¹³⁴Cs in Southern region albacore and a mix of presence/absence of ¹³⁴Cs and elevated ¹³⁷Cs in Northern region albacore. North albacore showed a positive correlation of ¹³⁴Cs and elevated ¹³⁷Cs with length, which indicated that the smaller individuals had not recently migrated from waters with ¹³⁴Cs such as eastern Japan or the North Pacific Transition Zone. The spatially variable concentrations of ¹³⁴Cs suggest latitudinal migratory differences and limited mixing of N/S albacore in the eastern Pacific. Albacore tissue contained radionuclide levels orders of magnitude less than FDA food standards. This work, in combination with other approaches (e.g., stable isotope analysis, tagging studies) suggests that North and South albacore may have different migratory histories.