Egg Hatchability and Egg Thiamine Concentrations in Lake Trout from the Northern Refuge of Lake Michigan

Abstract

AbstractThe Northern Refuge of Lake Michigan was established in 1985 under the auspices of the Great Lakes Fishery Commission as part of an intensely managed effort to restore a self‐sustaining Lake Trout Salvelinus namaycush population to the lake. Despite the stocking of millions of Lake Trout into the refuge and survival of these stocked fish to adulthood, signs of natural recruitment by Lake Trout in the refuge have been very sparse. To ascertain whether low egg viability or poor fry survival could be limiting natural recruitment by Lake Trout in the refuge, hatching rates of eggs taken from Lake Trout caught in the Northern Refuge during October 2019 were determined in the laboratory. Moreover, survival rates of the hatched‐out fry were determined along with the thiamine concentrations in the fry. In addition, thiamine concentrations in eggs of ovulating Lake Trout caught in the Northern Refuge during 2019–2021 were determined. Egg hatching rate in the laboratory averaged 93%. Survival rate of Lake Trout fry up to 5 weeks after hatching averaged 97%. Mean (SE) thiamine concentrations in eggs of Lake Trout caught in 2019, 2020, and 2021 were 19.1 (3.6), 5.9 (1.3), and 6.2 (0.4) nmol/g, respectively; these levels are well above the threshold concentration of 2.3 nmol/g, above which the likelihood of experiencing mortality due to thiamine deficiency complex (TDC) is low. Thiamine concentrations in the Lake Trout fry at the end of the laboratory experiment averaged 11.2 nmol/g, and abnormal behavior in the fry was not observed. We conclude that TDC does not appear to represent a major impediment to Lake Trout rehabilitation in the Northern Refuge at present, although TDC may have contributed to the lack of detectable natural recruitment in the past.