Tracing Origins of Invasive Piscivores Using Strontium Isotope Ratios (87Sr/86Sr) In Otoliths

We examined the utility of strontium isotope ratios (⁸⁷Sr/⁸⁶Sr) in fish otoliths to determine the origins of invasive piscivores throughout the Upper Colorado River Basin.  Our objectives were to examine the distinctiveness of ⁸⁷Sr/⁸⁶Sr from fishes in different reservoirs, and temporal and interspecific variability of these ratios within reservoirs.  Fishes were collected from 14 reservoirs and their downstream rivers. Otoliths were analyzed using a laser ablation multicollector inductively coupled plasma mass spectrometer (LA-MC-ICP-MS).  Model selection with Akaike’s Information Criterion (AIC) was used to rank the relative importance of reservoir location, species, and temporal effects on ⁸⁷Sr/⁸⁶Sr in otoliths.  Strontium isotope ratios were nearly unique across all reservoirs, consistent among species within reservoirs, and temporally stable across many years.  We were able to track the movements of unknown history river-caught fish from the “fingerprint” of their likely reservoir of origin in their otoliths. Fish escapement from reservoirs could be determined with annual resolution using LA-MC-ICP-MS, providing insights into processes that increase escapement risk such as dam operations and climatic conditions.  This research showed that invasive piscivore escapement from reservoirs appears to be common throughout the Upper Colorado River Basin and should be a concern for fisheries managers in that region.