Resolving the cisco complex of Lake Superior using morphological and genetic tools

Owen Gorman (USGS, otgorman@usgs.gov), Amanda Ackiss (USGS), Sophia Dabrowski (USGS), Randy Eschenroder (GLFC), Thomas Pratt (DFO)

Here we seek additional funding to follow-up a previous GLRI-funded project, “Morphologic, geographic and genetic variation among Lake Superior ciscoes.” Our goal was to conduct a comprehensive description of the morphological and genetic diversity of the Lake Superior cisco complex and to provide keys to facilitate identification of forms in field and laboratory settings (Gorman et al. 2022a). We addressed this goal by conducting a comprehensive morphological description of all known cisco forms by life stage and geographic region in combination with a genetic assessment to determine whether these forms are morphologically and genetically distinct. The project was launched at the start of the Covid-19 pandemic, which complicated work schedules and precluded plans to collect fish from sites where rare forms have been previously collected. Because fresh collections of rare ciscoes were not possible, we relied on samples of opportunity: gillnet samples collected in the early 2000s in Canadian waters, gillnet samples collected by a commercial fisherman for TNC in 2018-2020 as part of a GLRI-funded project (“Kiyi reproductive phenology in Lake Superior”), and from USGS annual bottom trawls from 2007-2019. Despite these challenges, we completed detailed morphometric measurements for 2017 fish representing common forms (Coregonus artedi, C. hoyi, C. kiyi), rare forms (C. zenithicus, C. nigripinnis and C. reighardi), and undescribed forms. Of these, 1454 fish were genetically analyzed and 744 fish were aged from otoliths. In May 2022, we gave a presentation at the JASM conference that summarized our findings to date (Gorman et al. 2022b). Thus far, we have identified four morphologically and genetically distinct cisco forms in Lake Superior: artedi, hoyi, kiyi, and reighardi, but zenithicus and nigripinnis remain unresolved forms. Leveraging our data with another GLRI-funded project currently led by co-PI Ackiss (Stott & Ackiss 2021), we also found that Lake Superior reighardi was genetically identical to the extinct Lake Michigan reighardi and extinct Lake Michigan zenithicus was a genetically unique group. Overall, we found considerable morphological and genetic variation in cisco forms which may be due to geographic/demic population structure. Our findings raise questions about the status of Lake Superior ciscoes and their evolutionary origins. Of particular interest is the affirmation that reighardi exists in Lake Superior and is a broadly distributed rare form that is genetically identical to the extinct form in Lake Michigan. We seek an additional year of funding to complete key objectives in our previous proposal that were unmet because of the Covid-19 pandemic, i.e., inability to sample fish for our study. Our proposed work matches Priority 5, Adding knowledge and understanding of the Lake Superior Coregonine community as a “reference” lake and Priority 6, Additional years of funding for previously funded projects. A better understanding of the diversity of ciscoes in Lake Superior will benefit restoration efforts by identifying appropriate forms for restoration and providing a framework for a functional cisco complex in a Great Lake.