Analysis of Cisco (Coregonus artedi) Populations in Eastern Lake Ontari

The Cisco (Coregonus artedi) is a cold-water planktivorous fish species that has undergone significant declines within Lake Ontario as a result of over-exploitation and other anthropogenic impacts. The goal of this project was to expand upon the current scientific knowledge base for Cisco within Eastern Lake Ontario [ELO] by providing an up-to-date assessment of the current status of this population. This thesis focusses on two distinct topics, each related to a distinct natural history characteristic of the ELO Cisco population that could represent a factor limiting population recovery in this region: fisheries-induced alterations to life-history traits, and fluctuations in year-class strength. In order to identify whether fisheries-induced change has occurred in this population, I compared the size-at-age and maturation of the ELO population both before [1926-1928] and after [1992-2016] the collapse of the fishery. The modern population had larger body sizes at a given age compared to the historical group, as well as a lower age-at-maturity [size-at-maturity remained similar]. It appears as though Cisco within the historical population may have been experiencing fisheries-induced selection in size-at-age, with potential recovery of this trait occurring in the modern population after a reduction in fishing pressure. This suggests that Cisco have a high capacity for adaptation through either phenotypic plasticity or evolutionary change. To assess patterns in year-class strength [YCS] within the ELO population, I used a residual catch-curve method to first calculate relative YCS, and then used linear models to correlate any fluctuations in YCS with environmental variables [temperature, ice cover, wind velocity]. The ELO population of Cisco demonstrated high variability in YCS, and only the timing of first consistent ice cover appeared to be correlated with these fluctuations. The environmental conditions influencing YCS in Lake Ontario may be different from those acting in other Great Lakes, highlighting the importance of local assessment. Advancing our knowledge of Cisco life-history within Lake Ontario provides important insights into the current condition of this population, which could have potential implications for future rehabilitation in this region.