The U.S. Geological Survey, Voyageurs National Park, South Dakota State University, and Missouri Department of Conservation conducted a cooperative study to measure ratios of strontium to calcium (Sr:Ca) in cross sections of pectoral fin rays obtained from lake sturgeon (Acipenser fulvescens) captured in lakes and rivers of Namakan Reservoir in Minnesota and Ontario. We measured Sr:Ca ratios in cross sections of 37 pectoral fin rays collected from 10 locations (5 rivers and 5 lakes) in Namakan Reservoir as part of a larger study to investigate whether relations between Sr:Ca in water and pectoral fin rays were significant and useful for determining migratory histories of lake sturgeon in Namakan Reservoir. Pectoral fin rays were removed nonlethally at the time of capture from lake sturgeon captured during surveys collected from 2007-09. Cross sections of collected pectoral fin rays were analyzed using laser ablation inductively-coupled plasma mass spectrometry at the University of Massachusetts at Amherst. Laser ablation transects started in the center of the fin ray cross section near the origin, which represents growth from birth through the first year of life. Laser ablation transects advanced outward toward the edge of the fin ray cross section, which represents the most recent growth of the lake sturgeon. Laser ablation analyses occurred November 2-6, 2015. Photographs of ablated pectoral fin ray cross sections were taken using a digital camera mounted to a microscope.