INVESTIGATION OF GREAT LAKES LAKE WHITEFISH EGG FERTILITY AND HEALTH

Author

Michael L. DiefenbachFollow

Date of Award

11-2025

Degree Type

Thesis

Degree Name

Master of Science

Department

Biology

Program

Biology (MS)

First Advisor/Chairperson

Dr. Jill Leonard

Abstract

Lake whitefish (Coregonus clupeaformis) recruitment in the Great Lakes has declined, and it remains unclear whether early failure at fertilization and during embryo development varies among spawning stocks. I tested whether fertilization differs among locations and which biological covariates best explain any patterns. Over two years, I spawned 67 wild pairs from four sites (Fox River, Whitefish Bay, northern Lake Huron, and Little Traverse Bay) using a standardized split-clutch design comparing untreated eggs with iodophor-disinfected eggs. Embryos were incubated under controlled conditions; I quantified fertilization and eye-up and screened adults, gametes, and eggs for bacterial pathogens. Fertilization differed significantly by site, with Little Traverse Bay consistently lowest. Iodophor applied after fertilization during water hardening left fertilization unchanged, but reduced eye-up, indicating a developmental cost. Regression identified visually scored egg quality at spawn as the dominant predictor, with female condition (Wr) showing a modest positive association and location still influencing outcomes. Pathogens did not explain site differences once egg quality and other traits were considered. Together, the results show that spawning locale (a proxy for population) influenced early outcomes, and that when and how eggs were collected strongly affected success. These findings support site-specific broodstock timing, routine egg-quality scoring, careful optimization of iodophor exposure, and continued disease surveillance in older stocks.

Recommended Citation

Diefenbach, Michael L., "INVESTIGATION OF GREAT LAKES LAKE WHITEFISH EGG FERTILITY AND HEALTH" (2025). All NMU Master's Theses. 905.
https://commons.nmu.edu/theses/905

Access Type

NMU Users Only

Justification for Restricting Access

The author requests an embargo of 12 months to allow submission of the thesis chapters as peer-reviewed manuscripts and to honor existing data-sharing agreements with collaborating agencies and Tribal partners. Public release prior to publication could jeopardize journal consideration.