Validation of Sr isotopes in otoliths by laser ablation multicollector inductively coupled plasma mass spectrometry (LA-MC-ICPMS): opening avenues in fisheries science applications

Advances in probe-based mass spectrometry allow for high spatial resolution of elemental and isotopic signatures in fish otoliths that can be used to address fundamental questions in fisheries ecology. Analyses of Chinook salmon (Oncorhynchus tshawytscha) otoliths from two river populations yield identical Sr-87/Sr-86 ratios using laser ablation multicollector inductively coupled plasma mass spectrometry (LA-MC-ICPMS) and thermal ionization mass spectrometry (TIMS). Results were obtained from freshwater otoliths with low Sr concentrations (300-800 ppm) using high spatial resolution (50 mu m) corresponding to temporal histories of similar to 12 days fish growth. Low natural variation in Sr-87/Sr-86 among otoliths from the same rivers allows for conservative estimates of external precision of techniques. Thus, we demonstrate that Sr isotope ratios obtained by LA-MC-ICPMS can be accurate and precise, bypassing the time-intensive sample preparation required by microdrilling and TIMS. This technique opens the use of Sr isotopes for broader ecological questions requiring large sample sizes to characterize nursery habitats, metapopulation dynamics, and stock discrimination similar to studies that focus on elemental concentrations, thereby providing a more robust tool for some freshwater and diadromous fishes.