Predicting Lake Whitefish (Coregonus clupeaformis) Year-Class Strength to Improve Pre-Recruitment Indices in the Upper Great Lakes, USA

Over the past century, lake whitefish recruitment has been highly variable due to changes in climate, food resources, and population abundance. To evaluate how variability in year-class formation at age-0 relates to future recruitment of whitefish, we studied the observed recruitment of adults (individuals ≥ 432mm length) from the 2005 and 2006 year- classes in Lake Michigan’s commercial fishery. The abundances of these year-classes were calculated using number of larvae caught per seine haul (1000m³ ± SE) during peak emergence. The 2005 year-class was considered weak (16.6 ± 24.8), while the 2006 year-class was considered strong (373.7 ± 28.3). Relative abundance of these year-classes was determined by sampling commercial harvest from 2008 through 2012. The 2006 year-class maintained high levels of recruitment into the commercial fishery, as related to larval density, suggesting that a direct relationship between larval abundance and recruitment exists. However, the abundance of adult fish that were recruited from the 2005 year-class was variable, indicating that other factors were influencing whitefish growth and survival post larval stage. Understanding the ecological factors that influence year-class strength during pre-recruit years will provide managers with the tools to more efficiently manage this highly valued Great Lakes fishery into the future.