In Search of the Dead Zone: Use of Otoliths for Tracking Exposure to Hypoxia

Otolith chemistry is often useful for tracking provenance of fishes, as well as examining migration histories.  Whereas elements such as strontium and barium correlate well with salinity and temperature, experiments that examine manganese uptake as a function of these parameters have found no such correlation.  Instead, dissolved manganese is available as a redox product, and as such, is indicative of low-oxygen conditions.  Here I present evidence for that mechanism in a range of habitats from marine to freshwater, across species, and also present ancillary proxies that support the mechanism as well.  The implication of this research is that there is now a way to identify individual fish exposure to hypoxia (dead zones), over its entire lifetime.