Use of radiocarbon from nuclear fallout as a dated marker in the otoliths of haddock Melanogrammus aeglefinus

Radiocarbon (¹⁴C) activity in the world's oceans roughly doubled between 1950 and 1970 as a result of the atmospheric testing of nuclear weapons. Through comparison with the ¹⁴C time series reconstructed from nearby corals, Kalish (1993) used the ¹⁴C activity of fish otolith cores as a means of confirming the annulus-based age estimates for those fish. Here I report the first pre- and post-bomb ¹⁴C chronology based only on young fish otoliths, thus avoiding all assumptions concerning the age and date of uptake into the otolith, and any requirement for reference coral chronologies. On the basis of accelerator mass spectrometry (AMS) assays, the ¹⁴C activity of 103 young haddock Melanogrammus aeglefinus otoliths collected off the eastern coast of Canada increased sharply between 1958 and 1965 and remained elevated thereafter, in phase with published ¹⁴C chronologies for bivalves and corals in the North Atlantic. Assays at the ¹⁴C content of the extracted otolith core of old haddock served as a dated marker of the year of hatch, thus providing an absolute age determination for individual fish which was accurate to within 1 to 2 yr. Internationally accepted criteria for annulus interpretation in haddock otoliths appear to be accurate to an age of at least 10 yr, and to within 2 to 3 yr for haddock up to an age of 22 yr.