Quantifying 87Sr/86Sr temporal stability and spatial heterogeneity for use in tracking fish movement

The specificity and accuracy of inferred fish origin and movement relies on describing spatial heterogeneity and temporal stability of environmental signatures. But the cost and logistics of sample collection often precludes the complete quantification of environmental signature temporal stability and spatial heterogeneity. We used repeated sampling and a novel approach (Bayesian ridge regression, BRR) to quantify the temporal stability and spatial heterogeneity of ⁸⁷Sr/⁸⁶Sr, respectively. We explained 86% of observed variation in ⁸⁷Sr/⁸⁶Sr using a BRR model and estimated ⁸⁷Sr/⁸⁶Sr throughout the Upper North Platte River Basin with high accuracy (±0.00106). Year to year variation in ⁸⁷Sr/⁸⁶Sr signatures ranged from 0.00007 to 0.00073 (SD), while seasonal variation ranged from 0.00091 to 0.00134 (SD). We then assessed the specificity and discussed the accuracy of inferring movement using three scenarios of described spatial heterogeneity. Our results indicate reliable inference of fish movement requires comprehensive quantification of spatial heterogeneity and temporal variation in environmental signatures.