Abstract
AbstractManganese is a commonly found constituent in fish otoliths, yet a direct correlation with ambient water concentrations as observed for other elements has proven elusive. There is compelling evidence that Mn uptake is related to the availability of reduced Mn (Mn2+) resulting from hypoxia (Limburg et al. 2015) but that fish growth rate also plays a role. We tested the latter possibility by examining otoliths from anadromous river herring (Alewife Alosa pseudoharengus and Blueback Herring A. aestivalis) in New York waters. A significant correlation was found between the ages at which shifts in otolith daily growth increments (assumed proportional to somatic growth) and shifts in otolith Mn:Ca ratios were detected. Furthermore, significant positive Spearman's rank correlations were observed between mean otolith daily growth and otolith Mn:Ca. Species‐ and site‐specific differences were evident, but significant positive correlations were found for these relationships within each species and at most sampling sites. Ambient water concentrations were weakly correlated with otolith Mn:Ca, suggesting that both exogenous and endogenous factors influence Mn:Ca in otoliths. Thus, while endogenous mechanisms (i.e., growth rate) likely influence Mn uptake, exogenous availability is the ultimate control.
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