Otolith Microchemistry As a Tool to Discriminate Between River-Spawning Populations of Walleye (Sander vitreus) in Lake Erie

An ability to discriminate among local spawning populations (stocks) is necessary for fishery management agencies to quantify stock-specific contributions of recruits to the fishable population. Due to the known water strontium concentration [Sr] differences between Lake Erie tributaries, otolith [Sr] holds great potential to distinguish river-spawning stocks. However, use of this natural marker may be limited for populations whose young disperse from their natal river before the water’s elemental signature is retained in their otoliths. To better understand the potential of otolith microchemistry to discriminate between Lake Erie’s two largest river-spawning stocks (the Maumee and Sandusky rivers), we used laser ablation-inductively coupled plasma-mass spectrometry to analyze the otolith [Sr] from larval walleye collected during 1993-2013 (~20 larvae/site/year). Our analyses show that water and otolith [Sr] differed between the Maumee and Sandusky rivers, with [Sr] being significantly higher in the Sandusky River. Although otolith [Sr] increased with larval age, [Sr] differences between rivers were apparent even in otoliths from larvae as young as two days old. Given these findings, transport of larvae out of natal rivers at a young age should not preclude the use of otolith microchemistry to discriminate between important river-spawning stocks in Lake Erie.