"Lake Michigan Steelhead: Where Were You Hatched?"

Lake Michigan steelhead, <i>Oncorhynchus mykiss</i>, are a mix of hatchery-produced and wild fish, the latter originating from many different natal tributaries within the lake basin. Mixed stock populations can complicate conservation and management due to unequal contributions from various stocks, thus making it necessary to understand the natal origins of such populations. We evaluated the use of otolith chemistry as an approach to identify the natal origin of Lake Michigan steelhead. Using laser-ablation inductively coupled plasma mass spectrometry, we analyzed the otoliths of juvenile steelhead collected in 2013 and 2014 from 46 Michigan and Wisconsin tributaries of Lake Michigan. We found distinct chemical signatures occurring between fish from different natal streams and hatcheries that could be used to predict natal origin with a high degree of accuracy. Strontium was found to be the most important trace element for discrimination, with highest natural values occurring in the Manistee River. Our results clearly demonstrate the utility of otolith chemistry and pave the way for future studies to determine the natal origins of adult steelhead, thus benefiting the management of both steelhead and their natal habitats.