Temperature and growth effects on otolith elemental chemistry of larval Pacific cod, Gadus macrocephalus

Variation in otolith elemental composition is used to investigate movements of teleost fishes based on observations that otolith elemental composition reflects variation in water chemistry. Various environmental (e.g., temperature, salinity, and water concentration) and biological (e.g., growth, diet, and ontogeny) factors can influence otolith elemental incorporation although the relative influence of these factors remains poorly understood for most species. Therefore, we examined the effects of temperature and growth rate on the otolith elemental composition of larval Pacific cod, Gadus macrocephalus. The larvae were progeny of wild Pacific cod collected from spawning grounds near Kodiak Island, Alaska. Immediately after hatching, larvae were acclimated to 2 degrees C, 5 degrees C, and 8 degrees C and reared for 38-51 days. Otolith concentrations of Li, Mg, Ca, Mn, Zn, Sr, and Ba were measured using laser ablation-inductively coupled plasma mass spectrometry. Li and Zn otolith concentrations were near detection limits and excluded from subsequent analyses. The effects of temperature on otolith partition coefficients (D(Me)) varied among elements. D(Mg) showed no relationship with temperature whereas D(Sr) and D(Ba) decreased with increasing temperature. It is possible that, for larval Pacific cod, kinetic effects are more important in the incorporation of Sr and Ba whereas metabolic effects may play a larger role in the incorporation of Mg. There was no evidence for an effect of somatic growth rate or otolith precipitation rate on D(Me) for any of the elements, which indicates that individual growth variation is unlikely to lead to misinterpretation of field-collected data. Understanding variable relationships among otolith elemental signatures, environmental conditions, and fish physiology can improve the accuracy of interpretations of field data, particularly in marine systems where spatial variation in element concentrations are typically lower than freshwater environments.