Midwest Fish & Wildlife Conference 2018

AUTHORS: Daniel J. Dembkowski, Wisconsin Cooperative Fishery Research Unit; Ryan P. Koenigs, Wisconsin Department of Natural Resources; Daniel A. Isermann, USGS, Wisconsin Cooperative Fishery Research Unit

ABSTRACT: Fish populations in large interconnected systems, such as Lake Winnebago, can consist of different stocks that originate from distinct natal locations. Management and conservation initiatives including harvest regulations, stocking, and habitat restoration or protection efforts can substantially benefit from an understanding of natal origins and sources of recruitment. Trace element concentrations in fish otoliths (i.e., otolith microchemistry) and other calcified structures offer a unique tool for identifying natal origins and evaluating fish environmental history. However, for otolith microchemistry to be an effective tool, trace element concentrations within the environment must differ spatially. Therefore, our objective was to determine if trace element concentrations differ within (i.e., longitudinally) and among tributaries to the Lake Winnebago system. During June-July 2017, water samples were collected from 26 locations distributed among primary and secondary tributaries to the Lake Winnebago system (including locations within Lake Winnebago proper and lakes Butte des Morts, Poygan, and Winneconne) and analyzed for concentrations of barium, lithium, magnesium, manganese, and strontium. Preliminary results suggest that microelemental signatures vary among (and in some instances, within) tributaries, but further investigation is needed to determine if differences in microelemental signatures are sufficient to allow discrimination among sites and accurate assignment (e.g., of individual fish) to those locations based on microelemental concentration data. If spatial differences in microelemental signatures are sufficient to discriminate among tributaries, otolith microchemistry may be an effective tool to identify natal origins and sources of recruitment of important fishes in the Lake Winnebago system including Lake Sturgeon, Walleye, and Northern Pike.