Continental-scale variation in otolith geochemistry of juvenile American shad (Alosa sapidissima)

Abstract

Abstract:We assembled a comprehensive atlas of geochemical signatures in juvenile American shad (Alosa sapidissima) to discriminate natal river origins on a large spatial scale and at a high spatial resolution. Otoliths and (or) water samples were collected from 20 major spawning rivers from Florida to Quebec and were analyzed for elemental (Mg:Ca, Mn:Ca, Sr:Ca, and Ba:Ca) and isotope ( 87 Sr: 86 Sr and d 18 O) ratios. We examined correlations between water chemistry and otolith composition for five rivers where both were sampled. While Sr:Ca, Ba:Ca, 87 Sr: 86 Sr, and d 18 O values in otoliths reflected those ratios in ambient waters, Mg:Ca and Mn:Ca ratios in otoliths varied independently of water chemistry. Geochemical signatures were highly distinct among rivers, with an average classification accuracy of 93% using only those variables where otolith values were accurately predicted from water chemistry data. The study represents the largest assembled database of otolith signatures from the entire native range of a species, encompassing approximately 2700 km of coastline and 19 degrees of latitude and including all major extant spawning populations. This database will allow reliable estimates of natal origins of migrating ocean-phase American shad from the 2004 annual cohort in the future.

Assessment of otolith chemistry for identifying source environment of fishes in the lower Illinois River, Illinois

“…Significant correlations between water and otolith signatures for these three naturally occurring chemical markers are consistent with results of prior studies (Patterson et al, 1993;Wells et al, 2003;Walther and Thorrold, 2008). Observed differences in water and otolith  18 O between the Illinois River and its floodplain lakes are likely due primarily to the greater opportunity for evaporative fractionation (Hoefs, 2004) to be expressed in floodplain lakes as a result of their longer water residence times relative to the Illinois River.…”

Influence of constant and periodic experimental hypoxic stress on Atlantic croaker otolith chemistry

“…The stressful periodic hypoxia decreased otolith Mg:Ca as would be expected if Mg is under endogenous control, but otolith Ba:Ca also decreased. In many euryhaline species, otolith Ba:Ca typically displays positive relationships with ambient dissolved Ba, as observed in both controlled lab experiments (Bath et al 2000, Elsdon & Gillanders 2002, 2003, 2004, 2005, Bath Martin & Thorrold 2005, Walther & Thorrold 2006, Miller 2009, and field studies (Dorval et al 2007, Walther & Thorrold 2008, Mohan et al 2012). Some studies have found an effect of somatic/otolith growth on otolith Ba:Ca (Walther et al 2010, Miller 2011 Interestingly, the periodic hypoxia treatment did result in significant Sex × Treatment interactions for otolith Sr:Ca and Na:Ca ratios and also decreased both otolith Ba:Ca and Mg:Ca ratios, perhaps because alternating between hypoxic and normoxic conditions is more physiologically stressful than remaining in constant hypoxic conditions.…”

A review of ecogeochemistry approaches to estimating movements of marine animals

“…Walther and coworkers initially identified unique geochemical signatures in otoliths of young-of-the-year American shad (Alosa sapidissima) from a total of 20 rivers along the east coast of the United States (Walther and Thorrold 2008). They then used river-specific values in d 18 O, 87 Sr : 86 Sr, Sr : Ca, and Ba : Ca in the core region of adult otoliths to determine natal origins of ocean-phase subadults collected in the Gulf of Maine (Walther and Thorrold 2010).…”