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Completed Project: Cisco Restoration in Lake Ontario

Ellen George, Matt Hare, Rudstam, Darran Crabtree (TNC), Brian Lantry (USGS) (Funded by New York Sea Grant with contributions from TNC, USGS and USFWS)

Cisco was once a commercially and ecologically important fish in Lake Ontario, before declining in the late 1800’s and early 1900’s due to overfishing, habitat degradation, and impacts from invasive species. Currently, interest in restoring cisco populations in Lake Ontario is growing, as it forms an important part of the native food web and supports native predators such as Atlantic salmon and lake trout. Unfortunately, little is known about the status of cisco in Lake Ontario, as critical information such as the distribution and number of spawning populations, the structure and connectedness between these populations and their level of genetic diversity is unknown. This study aimed to address several of these major knowledge gaps facing cisco restoration in Lake Ontario. First, we evaluated the extent of cisco spawning in the eastern basin by sampling historical spawning sites and areas of suitable habitat with egg collection mats. We were able to confirm cisco spawning in two previously unknown locations; in Henderson Harbor and near Fox and Grenadier Islands. Second, we compared microsatellite diversity of several aggregations of cisco in the eastern basin to assess population structure, genetic diversity, potential legacy effects of a historical genetic bottleneck, and estimate the effective population size (Ne)­ of the Lake Ontario cisco population. Finally, we developed a panel of three nuclear RFLP markers to identify cisco-lake whitefish hybrids. The presence of remnant and/or expanded spawning populations beyond the areas previously known is encouraging for the capacity of cisco populations to recover in Lake Ontario. Lake Ontario cisco have not experienced a detectable genetic bottleneck despite their numerical decline. Cisco genetic diversity is comparable to that found in lake whitefish, and a large effective population size suggests that genetic drift is not currently a risk factor. We found a low rate of hybridization in a sample of coregonine larvae from Chaumont Bay in 2014. However, the majority of adult fish visually identified as possible hybrids were demonstrated with the RFLP marker panel to be a mixture of F1 and backcrosses, suggesting that hybrids survive to adulthood and may reproduce. Ellen George completed her PhD in 2019.