Recruitment dynamics of American eel (Anguilla rostrata L.) in lake Ontario systems

The upstream recruitment of American Eel into Lake Ontario involves multiple age-class juveniles, diversified habitats and environmental interactions. Understanding age structure of recruiting eel populations is essential for fish stock assessment and decision making for the rehabilitation of this species which has been listed as ‘Endangered’ under Ontario’s Endangered Species Act. A time series of juvenile American Eel ascending through the Saunders-Moses Hydroelectric Dam during 1975-2008 represented the temporal variability of recruitment and freshwater growth. Using R language-based MIX package, lognormal probability distribution with VBGM was constrained to discompose length frequency data into age composition. Pair-wise regression indicated a significant negative correlation between our index of eel recruitment and the average age of recruits. Daily passage of juveniles through the eel ladder varied from >26000 in 1983 to 40 in 2003 with, significant differences among years, months, and year-month interaction terms. Combined with five-year lag, eel recruitment index was strongly negatively associated with the December and February North Atlantic Oscillation Index, indicating that American Eel recruitment was impacted both by local temperature and climatic variations.