Examining the potential for unrepresentative sampling during cisco Coregonus artedi gamete collections for the Saginaw Bay restoration effort

Andrew Honsey (USGS, ahonsey@usgs.gov), Kevin McDonnell (USFWS), Wendylee Stott (DFO), Roger Gordon (USFWS), Todd Hayden (USGS) Dave Fielder (MIDNR), Chris Olds (USDA)

Great Lakes cisco populations declined during the 19th and 20th centuries due to factors such as overfishing, habitat degradation, and interactions with invasive species (Van Oosten 1930; Crowder 1980; Myers et al. 2009; George 2019). Cisco are now considered extirpated from Lake Erie, and populations are fragmented and dramatically reduced relative to historical baselines in the other Great Lakes (although some populations appear to be recovering; Stockwell et al. 2009; Claraumunt et al. 2019). In response to these declines and given recent ecosystem shifts that favor coregonines (e.g., declines in invasive species and nutrient loading; Smith 1980; Dolan and Chapra 2012; Bunnell et al. 2014; Madenjian et al. 2015), Great Lakes managers have prioritized the restoration of cisco and other coregonines to promote diverse prey fish communities and sustainable fisheries (Bronte et al. 2017). Coregonine restoration efforts are underway, including a reintroduction program for cisco in Saginaw Bay, Lake Huron. The cisco restoration effort in Saginaw Bay stems from recommendations from the Lake Huron Technical Committee (LHTC), as described in their rehabilitation guide for cisco (LHTC 2007). Specifically, the LHTC recommended to the Lake Huron Committee (LHC) that successful cisco restoration in Saginaw Bay and the main basin of Lake Huron would require the return of spawning stocks to Saginaw Bay. The LHC and LHTC concurred that a stocking and assessment program was the best option for cisco recovery, and, after considerable discussion, the LHC directed that restoration stocking events proceed first with gametes sourced from northern Lake Huron, in the Les Cheneaux Islands and Drummond Island region. Gametes have been collected from Les Cheneaux and Whitney Bay (Drummond Island) since 2016 using shortset, small mesh gillnets set in 2-20 m of water. Sampling for these events occurs during the early portion of spawning season and ends when roughly 100 pairs of fish are collected. If genotypes and/or phenotypes of cisco spawners vary across the spawning season within an aggregation, it is possible that this collection approach results in unrepresentative and incomplete samples of the diversity present in those aggregations. Moreover, this approach limits our understanding of the length of the cisco spawning season in northern Lake Huron. We propose to (1) investigate whether the gamete collection protocols used for the Saginaw Bay cisco restoration effort representatively sample the genetic and phenotypic diversity of the source population(s), and (2) estimate the duration of the cisco spawning period in northern Lake Huron. To do this, we will use new and existing data to examine genetic and phenotypic diversity throughout the spawning period. Results from this work will be relevant to management decisions related to cisco gamete collections and broodstock development. This work also complements ongoing efforts to genotype existing brood fish.