Contrasting seasonality of 137Cs concentrations in two stream animals that share a trophic niche.

Understanding the seasonality of ¹³⁷Cs concentrations in aquatic animals is crucial for reviving local inland fisheries. The seasonality of ¹³⁷Cs concentrations in animals is expected to vary, even if focal species consume similarly contaminated foods because the ¹³⁷Cs excretion rate is species-specific, and ¹³⁷Cs uptake by foraging autochthonous food resources also vary among seasons. Here, we conducted a seasonal monitoring survey of dissolved ¹³⁷Cs concentrations as an indicator of the contamination level of food resources and measured ¹³⁷Cs concentrations in two carnivorous aquatic animals (Palaemon paucidens and Rhinogobius sp.) that share a trophic niche in a stream connected to a dam reservoir. The dissolved ¹³⁷Cs concentration had clear seasonality—high in summer and low in winter. The ¹³⁷Cs concentrations in the animals revealed a different seasonal pattern—it peaked in October in P. paucidens and peaked in February in Rhinogobius. Overall, the ¹³⁷Cs concentration was relatively higher in P. paucidens than in Rhinogobius , suggesting that P. paucidens has a lower excretion rate than Rhinogobius. Consequently, the seasonality of the ¹³⁷Cs concentration in P. paucidens showed temporal changes similar to those of the dissolved ¹³⁷Cs concentration, which were likely affected by ¹³⁷Cs uptake through foraging, whereas that in Rhinogobius was controlled by ¹³⁷Cs excretion. This study shows that the seasonality of ¹³⁷Cs concentration can differ between sympatric animals that share a trophic niche. Accumulating knowledge and comparing the seasonality of ¹³⁷Cs concentrations in fisheries species based on the balance between uptake and excretion will be valuable to determine the appropriate seasons to obtain less-contaminated products. [Display omitted] • Two sympatric species that belong to different phyla was compared. • Stable carbon and nitrogen ratios showed that the two species share a trophic niche. • Dissolved ¹³⁷Cs concentration peaked in summer and dropped in winter. • The two species showed different seasonality of ¹³⁷Cs concentrations. • ¹³⁷Cs seasonality varies with interspecific variations of excretion rates in animals. [ABSTRACT FROM AUTHOR]