MADISON, Wis. – The Wisconsin Department of Natural Resources (DNR) today announced the agency identified a potential issue with a disproportionate amount of female hatchery-reared extended growth walleye.
The DNR conducted a preliminary analysis of hatchery-reared extended growth walleye sex ratios in 2019, which led to more in-depth research in the fall of 2020, including additional walleye from both the Art Oehmke and Governor Thompson fish hatcheries for histological (studying of the tissues) sex determination.
Although sex was unable to be determined in all samples, these preliminary investigations indicated hatchery-reared extended growth walleye showed sex ratios favoring females. Surveys of naturally reproduced walleye generally show sex ratios closer to a one-to-one male to female or ratios skewed towards males. Currently, there is no evidence to suggest that skewed sex ratios exist in other hatchery-reared species.
DNR Investigating Cause
As a result of these findings, the DNR will conduct additional histological sex determination testing, a comprehensive review of hatchery practices, and an examination of more survey and past stocking data to better understand this issue and the extent of unbalanced sex ratios in hatchery grown walleye. An additional examination of naturally reproduced walleye sex ratios will also be conducted.
Although the cause of this sex ratio imbalance is unknown, DNR staff and other partners have initiated consultations with topic experts and have begun reviewing relevant studies. Additional examinations of hatchery extended growth walleye will be conducted at multiple facilities in 2021.
Since the Wisconsin Walleye Initiative began, over 800,000 hatchery-reared extended growth walleye have been stocked annually into waterbodies across the State. Before the initiative, most stocked walleye were either fry or small fingerlings. It is unknown whether an uneven sex ratio exists in hatchery-reared fry or small fingerling walleye, which the DNR will also investigate.
The DNR will continue to raise walleye while conducting its investigation. Results will be shared and posted to the DNR’s Wisconsin Walleye Initiative webpage after the investigation.