Otolith microchemistry as a tool to discriminate between river-spawning populations of walleye (Sander vitreus) in Lake Erie

Abstract

Effective management of Lake Erie’s walleye (Sander vitreus) fisheries depends on an ability to understand the relative contributions of recruits from local spawning populations (stocks) to the fishable population. To achieve this goal, one must first find a means to discriminate between stocks so that the natal origins of older individuals (i.e., juveniles, adults) can be determined. Natural markers such as the microchemical composition of otoliths (calcified ear stones used for equilibrium and hearing) show great potential to differentiate between individuals originating in different spawning locations with unique water chemistries. However, this technique may be limited for river- or reef-spawning fishes whose young can quickly disperse from their natal site within a matter of days, before the natal-site signature is retained in the otoliths. To better understand the potential value of otolith microchemistry as a tool to discriminate between Lake Erie’s two largest river-spawning stocks, we determined if young larval walleye retain in their otoliths the unique elemental signature that is characteristic of water in their natal (riverine) environment. Towards this end, we used Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS) to analyze the otolith strontium concentration [Sr] of larvae collected from the Sandusky and Maumee Rivers during 1993-1995 and 2011-2012 (n=20 larvae/site/year), and daily ring counts in otoliths were used to age larvae. Our analyses show that otolith [Sr] differed between larvae produced in the Maumee versus Sandusky River, with [Sr] being significantly higher in the Sandusky. Although [Sr] increased with the fish age, differences between rivers were apparent even in otoliths from larvae as young as two days old. Given these findings, otolith microchemistry holds great potential to discriminate between Maumee and Sandusky River spawning stocks, even during years in which larvae are transported out of the river at a young age.