Evaluating genetic and phenotypic similarity of extant Cisco populations in coastal inland lakes to historic and contemporary Lake Michigan populations

Amanda Ackiss (USGS, aackiss@usgs.gov), Cory Brant (USGS), Jory Jonas (MIDNR), Jared Homola (MSU), Ralph Tingley (USGS), Ann Ropp (USGS), Matt Herbert (TNC)

Several recent research projects are producing data that will inform the delineation of historic and contemporary Cisco spatial units ahead of an assessment requested by the Lake Michigan Technical Committee (anticipated 2026). This includes work to genotype historic spawning Lake Michigan Cisco populations by PIs Ackiss and Brant (FY25 GLRI Proposal “Describing historic Cisco population structure in Lake Michigan with scale samples from 1930-1974”) and completed and proposed work examining genotypes and phenotypes of contemporary Lake Michigan drowned river mouth Cisco populations by PI Tingley (Tingley et al. in revision; Tingley et al. FY26 GLRI Proposal “Assessing the likelihood of spatially distinct cisco (Coregonus artedi) spawning aggregations outside of Grand Traverse Bay, Lake Michigan”). PIs Brant and Tingley are also evaluating morphological diversity in historic Lake Michigan Cisco specimens archived at the University of Michigan’s Museum of Zoology. Preliminary results of our FY25 GLRI project reveal greater historical diversity in Lake Michigan than exists today. We propose to expand the study of historic and contemporary Lake Michigan Cisco diversity into adjacent coastal lakes, which could contain phylogenetic or phenotypic remnants of lost Lake Michigan Cisco stocks. We identified coastal lakes that contain stable, present, or suspected present Cisco populations that can be used for genetic and phenotypic comparisons to historic Lake Michigan populations (2024 MIDNR status; Latta 1995). Several of these were recently connected to Lake Michigan, such as Elk Lake and North/South Lake Leelanau, which were severed by dam construction in the 1850s. In regions without coastal lakes containing Cisco populations, we identified Cisco lakes historically associated with rivers - Mary and Louise Lakes on the Menominee River, which drains into Green Bay; Little Paw Paw Lake, which had historic connections to the St. Joseph River system; and Elkhart Lake in Wisconsin near the Sheboygan River, which was shown to have a Great Lakes-associated lineage in a previous genetic analysis (Ackiss et al. 2021). Our proposed work leverages datasets currently being generated to elucidate the changes that have occurred to Lake Michigan Cisco diversity over the past century. In addition, many previously collected tissue and scale samples from coastal lakes are already available to use. New efforts include field work in partnership with MIDNR monitoring efforts to collect Cisco from lakes where samples do not exist or where high-quality samples for more robust genetic data are desired, and museum travel to expand existing historic Lake Michigan morphometric datasets. These data will improve our understanding of the phylogenetic and morphological relationships of nearby coastal and river-associated Cisco populations to the once highly diverse Lake Michigan Cisco populations. Adjacent lakes may contain remnant genetic or phenotypic diversity that was lost during the collapse of Lake Michigan Cisco populations, which could expand the toolbox of restoration options for managers, in support of the Coregonine Restoration Framework.