Effects of water temperature and barium concentration on otolith composition along a salinity gradient: Implications for migratory reconstructions

Abstract

Analysis of naturally occurring variation in otolith elemental composition has become a common approach for retrospectively determining migratory history in diadromous fishes. Environmental factors, such as temperature, salinity, and ambient water concentration, can independently, or in an interactive manner, affect elemental incorporation rates. Furthermore, the relative importance of kinetic and metabolic (or “vital”) effects on elemental incorporation remains unclear. In this study, a repeated measures design was used to: (1) quantify the effects of water temperature (9 °C, 12 °C, 15 °C) and freshwater Ba:Ca levels (low, intermediate, and high) on elemental partitioning and otolith composition (Mg:Ca, Sr:Ca, Ba:Ca) in juvenile Chinook salmon ( Oncorhynchus tshawytscha) along a salinity gradient (0, 5, 10, 14); and (2) estimate the lag time between physical exposure to chemically distinct water masses and changes in otolith composition. Additionally, relationships between elemental incorporation and somatic and otolith growth rates were evaluated across and within temperature treatments to identify potential rate effects. Otolith incorporation of Sr and Ba was positively related to water concentration whereas Mg incorporation was not. For Sr and Mg, there were significant interactions between temperature and salinity ( p ≤ 0.01). For Ba, there were complex interactions among temperature, water Ba:Ca values, and salinity ( p ≤ 0.01). In certain instances, interactive effects of temperature and salinity were large enough to confound interpretation of field data. Furthermore, there was evidence for negative effects of somatic growth rate on the incorporation of Ba that were consistent across temperatures ( r = − 0.32 to − 0.72). Observations were consistently contrary to expectations based on models of elemental incorporation for abiotic aragonite, highlighting the importance of vital effects and indicating that species-specific models of incorporation may be necessary. Changes in otolith composition were detected within 2–3 d of a change in water composition but otolith composition did not stabilize for 12–14 d, indicating that habitat transitions should be discernable in a short period of time but the otolith may not reflect ambient water levels for up to 2 weeks. These observations underscore the need to evaluate the effects of abiotic and biotic factors on otolith elemental incorporation in settings that mimic natural conditions to accurately interpret field data.