Otolith microchemistry reveals contribution of hatchery-origin Walleye in Lake Oahe, South Dakota

Document Type

Article

Publication Date

10-1-2025

Abstract

Objective: In Lake Oahe, South Dakota, recent stockings of fingerling Walleye Sander vitreus (every year from 2017 to 2019) have coincided with increased relative abundance of catchable-size Walleye. However, it is unknown if these fish originated from hatchery stockings or were produced naturally within Lake Oahe. Thus, we sought to use otolith microchemistry to delineate wild- versus hatchery-origin Walleye in Lake Oahe. Methods: In fall 2020, we collected age-0 through age-6 Walleye (n = 349) from Lake Oahe to determine fish origin during the standard gill-net survey. We used published water and otolith microchemical signatures to assign origin to collected adult Walleye. We then compared contribution of hatchery-origin fish to stocking years and locations in Lake Oahe. Additionally, we compared length at age of Walleye between both wild- and hatchery-origin fish. Results: Age-1 through age-3 Walleye represented year-classes in Lake Oahe that received Walleye stockings, and 11% (age 1, 2019 year-class, 300,000 Walleye stocked), 42% (age 2, 2018 year-class, 2,082,000 Walleye stocked), and 18% (age 3, 2017 year-class, 364,500 Walleye stocked) of the fish sampled within these age-classes were of hatchery origin. No fish were classified as hatchery origin from year-classes that did not receive Walleye stockings in Lake Oahe. Hatchery- versus wild-origin Walleye exhibited no appreciable difference in length at age for all stocked year-classes, though the stocked Walleye were consistently longer than naturally produced fish. Percent contribution for each sampling location ranged from 5% to 42% hatchery-origin Walleye. Conclusions: Otolith microchemistry provided a robust means to identify the contribution of stocked Walleye through age 3 in Lake Oahe. In general, greater stocking numbers corresponded to a higher percent contribution of hatchery-origin Walleye of a year-class. Hatchery-origin Walleye were found to contribute in higher proportion at sampling sites near stocking locations compared with sampling sites near the periphery of stocking locations. It appears that stocking fingerling Walleye has benefited lower Lake Oahe, and Walleye stocking should continue until Walleye natural recruitment becomes consistent and at a level suitable for sport fish harvest.

Publication Title

North American Journal of Fisheries Management

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