Knowledge of the distribution of ages of fish within a stock, and subsequently individual growth rates, allows managers the ability to calculate key metrics (i.e., recruitment, mortality, and stock growth rate) that greatly improve stock assessment models. Two remnant stocks of Lake Sturgeon Acipenser fulvescens exist near and within the Niagara River; one primarily occupying the headwaters of the river and the other primarily occupying the mouth of the river. Though initial efforts in the late 1990s collected data on the lower Niagara River stock, a long-term, comprehensive examination of age and growth is lacking and the age structure of the stock found at the headwaters has yet to be formally described to our knowledge. To ascertain the current age structure of these two stocks we sampled Lake Sturgeon in the lower Niagara River and at the headwaters of the Niagara River between 2012 and 2017 and took a portion of the leading pectoral fin spine of captured Lake Sturgeon for age estimation. Ages ranged between 4 and 42 years with females generally being older and larger than males. The median age appeared to increase from 14 to 18 years old throughout our study in both stocks. Lengths-at-age of both stocks were larger than those reported in other systems and growth rates appear to have increased over the past decade in the lower Niagara River. Despite efforts to improve age estimation accuracy, age estimates from fish whose ages were partly-known (derived from multiple age estimates from fish that were captured multiple times) demonstrated assigned ages may have greater error than expected. Additionally, a lack of young individuals confounded growth analyses. Although there was uncertainty in the assigned ages, this study still provides evidence of consistent recruitment in both stocks and, to our knowledge, the first characterization of the age structure of the Lake Sturgeon stock occupying the headwaters of the Niagara River.

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