Surveying alternative cisco brood source collection sites in northern Lake Huron

Scott Koenigbauer (USFWS, scott_koenigbauer@fws.gov), Jose Bonilla-Gomez (USFWS), Ethan Buchinger (USFWS), Daniel Cunnane (USFWS), Chase Daiek (USFWS), Roger Gordon (USFWS), Amanda Ackiss (USGS), Andrew Honsey (USGS)

The restoration of cisco (Coregonus artedi) in Lake Huron is a formal management objective of the Lake Huron Committee (LHC) of the Great Lakes Fishery Commission (GLFC) (DesJardine et al., 1995). In recent decades, Lake Huron has undergone significant food web restructuring, including the collapse of non-native alewife (Alosa pseudoharengus) and reductions in rainbow smelt (Osmerus mordax) abundance (Riley et al., 2008; Riley and Roseman, 2013). These changes, likely corresponding with the proliferation of invasive Dreissena mussels (Barbiero et al., 2011) and altered predator-prey dynamics (He et al., 2016), may have vacated an ecological niche for native pelagic species such as cisco to reoccupy, if they were to reestablish natural reproduction in central Lake Huron (LHTC, 2007). Currently, extant Lake Huron cisco populations are largely restricted to northern regions and Georgian Bay (Dobiesz et al., 2005; Ebener, 2012). In 2008, Michigan Department of Natural Resources (MIDNR) assessed the feasibility of Lake Huron cisco reintroduction by collecting gametes from St. Mary’s River and rearing them in a hatchery (Johnson et al., 2017). Through two funded projects, the U.S. Fish and Wildlife Service (USFWS) Midwest Region Fisheries Program has supported a multi-agency effort to restore cisco in Central Lake Huron, including initial identification of spawning locations in northern Lake Huron, and collection from those locations to develop a captive brood line at the Jordan River National Fish Hatchery (JRNFH). Subsequently, cisco reintroduction through the JRNFH captive brood line and additional wild collections has been ongoing in Saginaw Bay, Lake Huron. For the Saginaw Bay cisco reintroduction program, LHC recommended a stocking target of 1.2 million fingerlings per year (±20%), divided into spring and fall releases (LHTC, 2023). To support this effort, wild cisco collections have occurred biennially since 2018, alternating between collection sites at Les Cheneaux Islands (Government Bay) and Drummond Island (Whitney Bay) (Figure 1). Collected gametes are used both to maintain captive brood lines at JRNFH, and to be reared and stocked directly into Saginaw Bay when captive brood lines cannot produce enough gametes to meet stocking goals. LHC stocking targets have been met through 2024, with over 7.4 million hatchery-reared cisco fingerlings stocked into Saginaw Bay (Bonilla-Gomez et al. 2025, in review). However, the captive brood lines are vulnerable to hatchery-associated disease, and future disease outbreaks may necessitate more frequent supplementation from the wild to meet production goals. Increased reliance on wild broodstock collections could place additional pressure on the limited spawning groups at Government and Whitney Bays. It is unknown how much fishing pressure these extant spawning populations can sustain, and therefore, increased frequency of gamete collections could prove deleterious to their stability. These source populations serve as critical genetic reservoirs (LHTC 2023), and protecting their integrity is essential. To mitigate the risk of overfishing, we propose identifying and evaluating potential additional wild cisco collection sites in northern Lake Huron including St. Mary’s River (46.391, -84.238), Harbor Island (46.047, -83.763), and Scammon Cove (45.942, -83.630) (Figure 1). St. Mary’s River was selected based on earlier MIDNR efforts to characterize cisco spawning grounds and collect gametes for hatchery rearing (Fielder 1998). Harbor Island and Scammon Cove were selected by analyzing USFWS fall gill net observations for catch per unit effort (CPUE; Appendix Figure 1). Critical aspects of successful cisco gamete collections include logistical suitability, local high relative abundance of spawning cisco (with identification of spawning grounds at fine scale), and biological suitability for stocking in Saginaw Bay. Establishing whether these aspects apply to new collection sites prior to attempting gamete collection is paramount to ensure stocking goals are met. Through targeted spawning surveys, we will assess the presence and abundance of spawning cisco at candidate sites. In addition, we will document key biological traits of cisco at these sites to evaluate their suitability as future brood sources for Saginaw Bay restoration. This approach aims to reduce the risk of overharvest at existing collection locations while enhancing the long-term success of the cisco restoration program. Results from this effort will directly inform the adaptive management of Lake Huron cisco restoration and help ensure the long-term viability of stocking efforts in Saginaw Bay. Further, characterizations of this adaptive strategy may inform coregonine restoration practices in other systems (Bunnell et al., 2024).