Stock-Specific Growth Rates of Lake Herring, Coregonus artedi, in Western Lake Superior

Abstract

We constructed environmental growth histories, termed biochronologies, for lake herring, Coregonus artedi, from four areas of western Lake Superior using scale samples from historical collections. We created chronologies using a linear growth model (LGM) to describe individual somatic growth as the sum of both intrinsic and environmental factors. We built a master chronology using all possible scale samples age five or younger, then examined subsets of the data according to collection site (Bayfield Wisconsin, Black Bay Ontario, French River Minnesota, and Thunder Bay Ontario). The LGM best fit the site-specific data, indicating statistically different stock-specific growth rates. These differences were primarily due to environmental growth, as age effects were similar across sites. We show that the LGM is a useful tool for identifying lake herring stocks in western Lake Superior, a situation where genetic stock identification techniques have been unsuccessful. Our findings demonstrate that the stocks at these four sites are growing at different rates and therefore require different management strategies according to the unit stock concept. Further refinement of these chronologies and coupling with abundance data may allow managers to determine the degree of stock rehabilitation.