Introduction

Brian Wolff - "Geology of the Upper Colorado River basin related to otolith microchemistry"

Natural isotopic markers are increasing recognized as powerfull tools used to address complex animal behavior issues. Strontium isotope ratios (87Sr:86Sr, "Sr ratios") from fish otoliths ("ear stones") were used to determine if they could be used as natural markers to "fingerprint" origin locations of fishes that have been suspected of reservoir emigration. Otoliths are ideal for this type of analysis because they lay down daily increment layers, they passively incorporate various elements as new layers are formed, and once an layer is deposited it cannot be resorbed; thus, the chemical history of a fish is permanently retained throughout a fish's entire lifetime (Campana 1995). Strontium ratios are ideal markers because they are driven by underlying geology and do not undergo any biotic or abiotic fractionation, so the chemical signature of a fish is relecting its environment. Strontium-87 is formed by radioactive decay of Rubidium-87, so rocks with higher amounts of rubidium or older rocks should have higher Sr ratios. For my project I choose to examine if Sr ratios are correlated with the geology of their surrounding watersheds. For this analysis, I followed a methodology similar to that described by Barnett-Johnson et al. (2008).