Developing evaluation methods for stocked cisco in Lake Erie

Robin DeBruyne (USGS, rdebruyne@usgs.gov), Zachary Amidon (University of Toledo), Justin Chiotti (FWS), Ann Gorman (Ohio DNR), Phillipa Kohn (TNC), Christine Mayer (University of Toledo), Jason Robinson (NYSDEC), Ed Roseman (USGS), Joseph Schmitt (USGS), Wendy Stott (DFO), Eric Weimer (Ohio DNR), Pascal Wilkins (NYSDEC)

Cisco are extirpated in Lake Erie but will be stocked in 2025 into New York waters as spring yearlings. Evaluating the success of these stocked fish is a CRF priority, which could be done through assessment of survival of stocked cisco or finding evidence of successful reproduction. Standard gillnet and trawl assessments conducted by Lake Erie partner agencies will be used to evaluate survival of yearling and older stocked cisco. To prepare for the latter, establishing sampling locations and methods for long-term assessment of age-0 coregonines (e.g., lake whitefish and ideally cisco as soon as 2027) is needed, beyond project-specific, short-term sampling previously conducted in Lake Erie (Schaefer et al. 2021; Amidon et al. 2021a; DeBruyne et al. in press). Larval surveys can assess reproductive success of stocked cisco, confirming that stocked fish survived to become reproductively mature and congregate in sufficient numbers to successfully spawn. Assumptions can be made regarding the spawning site selection of the stocked fish based on historical records (Schaeffer et al. 2021), but it is not known if re-introduced cisco will migrate from eastern basin to western basin to spawn in fall or remain in the eastern basin to spawn. Lake whitefish are known to use spawning grounds throughout the west basin (Goodyear et al. 1982; Amidon et al. 2021b) and in the central and eastern basins (Chiotti et al. 2024; DeBruyne et al. in press; T. MacDougall, unpublished data). The life history parallels between these two coregonine species, established lake whitefish and re-introduced cisco, provides a unique opportunity to develop early life history assessment strategies for cisco prior to likely detection of reproduction in Lake Erie. We will draw on sampling methods already used in lakes Michigan, Huron, Superior, and Ontario to assess age-0 cisco during spring or summer, as well as methods that we have already undertaken to sample lake whitefish eggs and larvae in Lake Erie. Previous and current studies in lakes Huron, Michigan, and Ontario have also sampled both cisco and lake whitefish where the two species co-exist (Brown et al. 2023, McKenna et al. 2020, Brant et al. 2024, Cubbage et al. 2024). Hence, our assumption is that the gears and locations used for these surveys will serve as pre-stocking assessment for cisco early life stages in the future. By initiating a survey design in Lake Erie prior to expected natural reproduction of stocked cisco, we can design, evaluate, and optimize the survey and locations that capture and track lake whitefish around Lake Erie. Furthermore, we expect cisco and lake whitefish to use similar spawning areas, based on 1) overlap in historical spawning grounds (Schaeffer et al. 2021) and 2) overlap between observed contemporary lake whitefish spawning areas with historical cisco spawning grounds (Amidon et al. 2021b; Chiotti et al. 2024). Furthermore, expanding the sampling to include the western basin is critical because a majority of contemporary lake whitefish spawning occurs in the western basin, although we expect that adults and age-0 fish migrate to the central and eastern basins to avoid the higher water temperatures and potential thermal stress associated with the western basin. The post-pelagic age-0 distribution, habitat selection, and survival is a knowledge gap for coregonines in Lake Erie (Amidon et al. 2021a). This sampling will be exploratory in this first sampling season regarding the locations and the gear, with the goal of understanding why gears are effective only in some locations to track coregonines and if the gears show the same catch patterns.