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Examining the potential of otolith chemistry to determine natal origins of wild Lake Michigan Chinook salmon

Previous research has demonstrated a large movement of hatchery-reared Chinook salmon (Oncorhynchus tshawytscha) from Lake Huron to Lake Michigan, suggesting the potential for wild fish to exhibit similar movement patterns. We assessed the feasibility of using otolith microchemistry to estimate the natal source composition of wild Chinook salmon in Lake Michigan and evaluate interbasin movement. Otolith pairs were extracted from juvenile and adult fish collected in 2015 and 2016 from Great Lakes tributaries. Otoliths were analyzed using laser ablation inductively coupled plasma mass spectrometry to determine trace element concentrations, and four multivariate classification algorithms were evaluated for classification accuracy. Juvenile data reclassified to their natal regions with up to 89% success on a basin level, with a random forest approach performing the best among all models. Assigning adults to their natal origins resulted in more success on a basin-wide scale (74% to 88%) compared with a regional scale (32% to 51%), but success was still below juvenile reclassification accuracy. Our findings suggest that otolith microchemistry can be used to estimate wild Chinook salmon interbasin movement and that classification accuracy can be improved by matching juvenile and adult year classes in our assessment samples. Ultimately, we intend to use these models to assess the effects of wild Chinook salmon interbasin movement on Lake Michigan predatory demand and evaluate the risks of various stocking alternatives.