Environmental History of Walleye Revealed Using Otolith Microchemistry

Natural river systems throughout the world have been extensively modified by humans. Channelization, impoundment, and other alterations disconnect rivers from floodplains and desynchronize ecological processes. The Missouri River contains the largest series of reservoirs in the United States. Although anthropogenic changes have dampened the river’s natural flood regime, disturbances still occur. Catastrophic flooding in 2011 initiated record discharges in all mainstem reservoirs. In response to flooding and potential entrainment, we used otolith microchemistry to investigate environmental history of Walleye Sander vitreus in four Missouri River reservoirs (Lakes Oahe, Sharpe, Francis Case, and Lewis and Clark). Otoliths form permanent elemental signatures in proportion to water column concentrations and deposit a growth record of concentric rings. Association of otolith biochronology with elemental composition may enable retrospective evaluation of environmental history and estimation of entrainment. Trace element ratios vary spatially in Missouri River tributaries, embayments, and mainstem environments and are positively associated with otolith signatures. As a result, trace elements distinguish juveniles and adults from unique environments, especially tributaries and mainstem locations. This study may advance Walleye management through development of a framework to evaluate intra- and inter-reservoir dispersal and predict entrainment in different hydrological regimes. 

Keywords:  Otolith microchemistry, Walleye