Assessing the change in Lake Whitefish (Coregonus clupeaformis) maturity schedules from 1976-2013 in the Upper Great Lakes

Maturation schedules often vary within a given fish species, between individuals, and among different stocks within a population. These variations in maturation schedules can usually be linked to plastic or adaptive responses as a result of changes within the environment. This study assessed the change in Lake Whitefish maturity schedules in the U.S. waters of lakes Huron, Michigan, and Superior from 1976 to 2013 to better understand how maturity schedules have changed over time in order to help inform the future management of the Lake Whitefish fishery. To do this, I evaluated fishery independent and fishery dependent biological data from Lake Whitefish managers by performing a logistic regression using 'R' software's 'glm' function, which is a general linear model that produced estimates for length and age at 50% maturity. Results indicated that Lake Whitefish population maturation schedules varied through time, temporally, spatially, and sexually among populations in all three lakes. Females generally matured at older ages and longer lengths (5.0 years-old and 439 mm) than males (4.6 years-old and 419 mm). I found that the L50 for both sexes declined significantly in lakes Huron and Michigan after the year 1990, and both sexes in Lake Superior matured at larger lengths (F= 458 mm, M= 447 mm) for given ages than fish in lakes Huron and Michigan. These finding are likely a result of plastic responses due to ecological changes in the food web coupled with Lake Whitefish abundance. Continued monitoring of maturity schedules could help fishery managers to better understand how Lake Whitefish response mechanisms occur due to changes within the environment as a way to help inform future management decisions surrounding the harvest of Lake Whitefish.