Exploitation of mixed-stock fisheries is a commonly recognized challenge in freshwater and marine environments, yet stock-based assessments are typically done by management units that have been spatially established assuming a single, as opposed to multiple, spawning populations. Such assessment information when presumed to be from a single stock can lead to overexploitation and even extirpation of local stocks, which may reduce population-level benefits accrued via ‘portfolio effects.’ Accurately quantifying mixing (i.e., movement) rates among stocks, together with the ability to identify source stock(s) of harvested fish and their relative contributions to harvest is an important aspect for the management of mixed-stock fisheries. Walleye is an ecologically and economically important native species in Lake Erie that exhibits a complex life history. Previous tagging studies suggest a high degree of spawning site fidelity (i.e., discrete spawning aggregations exist); however, a large percentage of western basin fish during non-spawning periods emigrate to the central and eastern basins of Lake Erie or Lake Huron and intermix with fish from other spawning locales. Recent attempts to use natural markers (e.g., genetics, otolith microchemistry) for walleye stock discrimination purposes have met with limited success in Lake Erie. Alternatively, electronic tagging (e.g., acoustic telemetry) provides a means for directly estimating stock-specific movements and a novel approach to stock discrimination. Specifically, we will examine whether fisheries during peak harvest months at a given location within Lake Erie are supported by a single stock (e.g., open-water reefs) or several stocks (e.g., open-water reefs, Maumee River, and Detroit River) by tagging walleye in a mixed-stock setting and estimating where tagged fish spawn post-release.
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