Isoscape development

Our ability to reconstruct natal origin and freshwater movement patterns of fishes in the California Central Valley depends primarily on how well we have mapped the system, and how unique each habitat is. Building on the seminal work carried out by Drs Rachel Johnson and Peter Weber, we are attempting to better understand strontium isotopic gradients within the Central Valley - spatial and temporal heterogeneity and implications for movement reconstructions using otolith chemistry.

We are building an online, publicly accessibly database of "knowns" (juvenile salmon collected prior to outmigration from their natal tributary; coded wire tagged adults and juveniles from various hatcheries; water samples; bivalve shells - see images, right), examining variation in isotopic signals through space and time, then building isoscape maps using Spatial Statistical Modeling on Stream Networks to predict values for unsampled locations or time periods. 

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Early version of the California strontium isotope, inferred by water samples, salmon otoliths (caged, tagged, or collected while still in their natal river), and clam shells.