Continued assessment of Cisco reintroduction in Saginaw Bay, Lake Huron

Jose Bonilla-Gomez (USFWS, jose_bonillagomez@fws.gov), Scott Koenigbauer (USFWS), Ethan Buchinger (USFWS), Daniel Cunnane (USFWS), Chase Daiek (USFWS), Amanda Ackiss (USGS), David Fielder (MI-DNR), Roger Gordon (USFWS), Timothy O’Brien (USGS), Andrew Honsey (USGS), Darryl Hondorp (USGS)

There is a growing need to evaluate whether hatchery-reared Cisco (Coregonus artedi) survive following stocking and are successfully recovering in the Great Lakes (Claramunt et al., 2019; Rook et al., 2021; Bunnell et al., 2024; Fielder and McDonnell, 2024; Koeberle et al., 2023; Kraus et al., 2024), and whether they home to appropriate spawning sites (Gatch et al., 2023). While early stocking efforts have shown promise, cisco restoration remains constrained by limited understanding of Cisco spawning behavior, habitat use, and recruitment success (Gatch et al., 2023; Koeberle et al., 2025). Cisco remain functionally absent from the western main basin of Lake Huron and restoring them “to a significant level” (DesJardine, 1995) remains an unmet objective for Lake Huron management agencies (Riley and Ebener, 2020). In response, the Lake Huron Technical Committee (LHTC) developed a Cisco recovery guide in 2007 under the direction of the Lake Huron Committee (LHTC, 2007). Historically, Saginaw Bay (SB) was an important spawning area and supported the largest Cisco fishery in Lake Huron (Berst and Spangler, 1973; Baldwin et al., 2009). To evaluate restoration strategies, age-0 fingerling Cisco have been stocked annually in Saginaw Bay since 2018, with stocking planned through 2027 using gametes from northern Lake Huron populations. Oxytetracycline (OTC) marks were applied prior to stocking to distinguish spring and fall release cohorts. Early life-history monitoring, post-stocking survival assessment, and spawning monitoring were identified as essential components of program evaluation (LHTC, 2023). Post-stocking evaluations began in 2019 and have continued through 2024. To date, a total of 67 adult Cisco have been captured (mean length = 348.2 ± 51.7 mm; mean weight = 481.3 ± 181.2 g), including 65 of hatchery origin and two of wild origin (Bonilla-Gomez et al., 2025 in review). OTC marks and genetic analyses confirmed species identification and identified release cohorts. Among recaptured hatchery fish, 86.2% originated from spring releases and 13.8% from fall releases. Wild fish accounted for 3.0% of the total catch. These findings suggest that hatchery-reared Cisco can survive to maturity and return to SB during the spawning season. In 2024, monitoring efforts detected evidence of natural reproduction for the first time. Genetic analysis of over 500 coregonine larvae from SB, collected in daytime larval tows across 240 sites and beach seines in six beaches, identified two larvae (matched >84%) assigned to the Les Cheneaux Islands Cisco strain. In addition, to evaluate spawning in SB, a USGS-led study funded by CRF in 2023 sought evidence of Cisco spawning activity. The subproject objective was to determine spatial extent and timing of spawning by coregonines, including Cisco, in SB. Gangs of metal-ring egg traps (Weidel et al. 2023) set at 24 locations in SB and retrieved weekly or biweekly were used to quantify spawning activity during the period 6 Nov-18 Dec 2024. Coregonine eggs (N = 421) were sampled at 20 of 24 (83%) stations with peak egg deposition occurring between 20 Nov and 11 Dec, which suggested that egg trapping was a viable method for indexing spawning activity by Lake Whitefish and Cisco. Collection of 4 non-whitefish coregonine eggs during the period 02-12 Dec also provided the first potential evidence of Cisco reproduction in SB since the collapse of the historical spawning stock (Hondorp et al., in prep). The 2024 results support ongoing restoration efforts and indicate natural reproduction is possible. However, continued monitoring of larval production, juvenile survival, and adult spawning remains essential to assess success and inform future strategies. A stochastic population model indicates that Cisco reintroduction in Saginaw Bay is feasible, with a 75-95% chance of success if stocking continues for at least 10 years. Simulations highlight adult and age-0 survival as key drivers of long-term viability (Fielder and McDonnell, 2024). We are requesting funds to build on prior efforts and continue Cisco monitoring and evaluation in Saginaw Bay during FY26. Our focus will be to assess whether Cisco spawning in the bay results in viable eggs that hatch successfully in spring and to track larval distribution and movement.