Tracking the Dead Zone: Use of Otolith Chemistry to Identify Interactions of Fishes with 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 we 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.  Additionally, we present an analytic framework that quantifies properties of the fleeting nature of hypoxia.  This research suggests a potential means to identify individual fish exposure to hypoxia, over entire lifetimes.  With further testing and understanding, in the future fish may be able to be used as “mobile monitors” of hypoxic conditions.