DNR investigating unequal amount of stocked female walleyes from two hatcheries

The Wisconsin Department of Natural Resources (DNR) announced on March 17 the agency identified a potential issue with a disproportionate amount of female hatchery-reared extended growth walleyes.

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 walleyes 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 walleyes showed sex ratios favoring females. Surveys of naturally reproduced walleyes generally show sex ratios closer to a one-toone male to female or ratios skewed toward males. Currently, there is no evidence to suggest that skewed sex ratios exist in other hatchery-reared species.

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 walleyes. 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 walleyes will be conducted at multiple facilities in 2021.

Since the Wisconsin Walleye Initiative began, over 800,000 hatchery-reared extended growth walleyes have been stocked annually into waterbodies across the state. Before the initiative, most stocked walleyes Walleyes

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 walleyes while conducting its investigation. Results will be shared and posted to the DNR’s Wisconsin Walleye Initiative webpage (https://dnr.wisconsin.gov/topic/ Fishing/outreach/WalleyeInitiative. html) after the investigation.