A complete otolith-based bomb radiocarbon chronology for the Baltic Sea and its use in the age validation of regional fishes

A complete bomb radiocarbon (14C) chronology — covering an 80-year period (1938–2018) and reflecting thermonuclear testing in the 1950s and 1960s — was established using known-date otolith material to trace the signal in the Baltic Sea and to establish a tool in validating the age of regional fishes. Of particular interest were Baltic herring (Clupea harengus) and sprat (Sprattus sprattus) that are estimated to live >20 years in the Baltic Sea, a longevity that is ∼2× greater than determined for other locations. The new 14C chronology was used to validate age estimates up to 22 years for herring and 18 years for sprat, although there was evidence of 14C emissions from nuclear facilities, as well as deficiencies from other environmental factors. This work confirmed the accuracy of high-confidence age reading protocols used for decades and is a first step in establishing a valid basis for observed growth differences between northernsouthern Baltic Sea populations. An exploration of 14C in otoliths of coastal Baltic pike (Esox lucius), pikeperch (Sander lucioperca), and Baltic cod (Gadus morhua) lend support for broader use of bomb 14C dating on marine and freshwater organisms of the Baltic Sea basin.