Effect of metabolic rate on time-lags change in otolith microchemistry - An experimental approach using Salmo trutta.

Abstract

Over decades ecologists have long been interested in relevant techniques to track the field movement patterns of fish. Elemental composition of otolith represents a permanent record of the growing habitats experienced by the fish throughout its entire lifetime that is increasingly used in the literature. The lack of a predictive and mechanistic understanding of the individual kinematics underlying ion incorporation/depletion still limits our fine-scale temporal interpretation of the chemical signal recorded in the otolith. In particular, the rate at which elements are incorporated into otoliths is hypothesized to depend on fish physiology. However, to date, time-lags have mostly been quantified at a population scale. Here, we report results from controlled experiments (translocation and artificially enriched environment) on individual trace element incorporation/depletion rates in Salmo trutta (Salmonidae). We reported significant lags (i.e. weeks to months) between changes in water chemistry and subsequent change in otolith composition and highlighted substantial inter-individual variations in the timing and magnitude of Sr/Ca and Ba/Ca responses. These differences are partially linked to the energetic status (i.e. metabolic rate) of the individuals. It, therefore, appears that individuals with the highest metabolic rate are more likely to record detailed (i.e. brief) temporal changes than individuals having lower metabolic values. The time taken for environmental changes to be reflected in the growing otolith thus can no longer be assumed to remain a constant within populations. Results from the current study are a step towards fine reconstructing environmental histories in dynamic environments.