Courtnie L. Ghere ^1* Michael C. Quist ¹ Ryan S. Hardy ² Malte Willmes ³ Levi Lewis ⁴ Sean M. Wilson ² Troy W. Smith ²

• ¹ College of Natural Resources, University of Idaho, Moscow, United States
• ² Idaho Department of Fish and Game (IDFG), Boise, Idaho, United States
• ³ Norwegian Institute for Nature Research (NINA), Trondheim, Sør-Trøndelag, Norway
• ⁴ University of California, Davis, Davis, California, United States

White Sturgeon Acipenser transmontanus in the Kootenai River basin is listed as endangered in the United States and Canada. Declines have been mainly attributed to poor recruitment exacerbated by the environmental effects of Libby Dam in Montana. Reduced primary production downstream of Libby Dam has been identified as one factor limiting growth of White Sturgeon, thereby limiting natural reproduction through delayed sexual maturity. However, estimating changes in growth over time without knowledge of fish location (i.e., Kootenai River vs. Kootenay Lake) is difficult. The objective of this project was to use microchemistry analysis to describe the movement of White Sturgeon within the Kootenai River basin. Water samples (n = 27) and White Sturgeon fin rays (n = 162) collected in the Kootenai River basin were measured for strontium isotope ( 87 Sr: 86 Sr) ratios using laser ablation multicollector inductively coupled plasma mass spectrometry. All water samples and a subset of fin rays (n = 8) were also analyzed for trace elements (e.g., Sr, Ba, Mg). Fin ray annuli were measured and tested using knowledge of known age; known locations from physical capture events were assigned to age at capture. Strontium isotope analysis was unable to detect differences in the Kootenai River and Kootenay Lake using water or fin ray samples. The Kootenai River and Kootenay Lake were distinguishable using trace element data from water samples, but not fin rays. The discrepancy with trace elements appears to be associated with the physiology of fin ray growth. Although this study did not meet its original objective of describing the movement of White Sturgeon in the Kootenai River basin from fin ray microchemistry, our results provide insight into the potential influence of physiology on microchemistry analysis. In particular, fin ray microchemistry of slow-growing fishes may be possible in freshwater systems with further investigation into the physiological processes associated with growth and the incorporation of elements into calcified structures.