Can hatchery-origin coregonines be used to identify potential spawning habitats in Lake Ontario?

Alex Gatch (USGS, agatch@usgs.gov), Dimitry Gorsky (USFWS), Brian Weidel (USGS), Nicole Berry (USGS), Brian O'Malley (USGS), Mike Connerton (NYSDEC), Tim Johnson (OMNR), Adam Fridman (USGS), Jason Haag (USGS), Marc Chalupnicki (USGS), Gregg Mackey (USGS)

Lake Ontario, bloater (Coregonus hoyi) populations declined from the late 1800s-1900s and ultimately were extirpated from the lake by 1983 (Weidel et al. 2022). Few records exist to document critical habitats used by bloater before their extirpation (Goodyear et al. 1982; Stone 1947). In particular, spawning grounds of bloater were not fully described for Lake Ontario, likely because spawning takes place offshore from January-February (Koelz, 1929) when Lake Ontario would have been inaccessible to early commercial fishers. Reintroduction efforts in Lake Ontario have been ongoing since 2011 with experimental stocking of Lake Michigan lineage bloater (Weidel et al. 2022). These stocking efforts were largely under the assumption that the conditions in Lake Ontario were still suitable to foster a wild reproducing population of bloater, however, the lack of information about historic habitat use of this species makes it difficult to test this assumption. To date, no wild bloater have been collected in Lake Ontario (See caveat below), suggesting that reproductive success may be limited by environmental conditions.             Identifying critical habitats for species of low abundance can be achieved using remote sensing (Gatch et al. 2023; Withers et al. 2021). For example, acoustic telemetry has been used with other coregonine species to identify fine scale spawning site selection in Lake Ontario (Gatch et al. 2023). Acoustic-tagging of bloater could also be used to identify potential spawning areas used by hatchery-origin bloater in Lake Ontario. However, no wild bloater are available to capture and tag in Lake Ontario, and of the few (3 years old) held at the USGS Tunison Lab (TLAS) could be used as surrogates to locate spawning habitats. Although hatchery-reared individuals would be naive to wild conditions, some evidence exists that hatchery-origin individuals display similar behaviors to wild conspecifics when released (Binder et al. 2023, 2016; Goetz et al. 2022). For example, lean and siscowet ecotype lake trout (Salvelinus namaycush) reared for 9-years in a laboratory were tagged and released into Lake Superior and both ecotypes resumed behaviors of their wild ecotype (e.g., depth distributions and temperature preferences), suggesting that some behaviors are heritable (Goetz et al. 2022). Furthermore, since no wild bloater remain in Lake Ontario to influence hatchery-origin behaviors, spawning habitat selection should be similar between hatchery-origin individuals regardless of age (i.e., released at age-1 or age-4). Recent studies in Lake Ontario have described the spawning habitats and locations used by cisco (Coregonus artedi; Brown et al. 2022; Paufve et al. 2022; Gatch et al. 2023; Weidel et al. 2023), which allows for the testing of the hypothesis that hatchery-origin and wild conspecifics will select for similar spawning habitats. By tagging hatchery-origin adult cisco reared at TLAS and releasing into Lake Ontario, we can determine whether spawning site selection is similar to wild populations (Gatch et al. 2023). Additionally, tagged cisco may help inform bloater restoration. For example, one confirmed bloater/cisco hybrid (2023) and two additional putative hybrids were captured in Lake Ontario suggesting hatchery-reared bloater (a deep spawner) may co-occur with cisco (a shallow spawner) during spawning months (Amanda Ackiss Pers. Comm.). If naive hatchery-origin bloater are mixing with spawning wild cisco populations in Lake Ontario, managers may find this information useful for decisions around continued stocking. We propose to acoustic-tag and release hatchery-origin bloater and cisco in Lake Ontario to 1) identify potential bloater spawning areas, 2) determine if hatchery-origin adult cisco display similar behaviors to wild conspecifics, and 3) elucidate if hatchery-reared bloater have spatial-temporal overlap with cisco during spawning seasons. Identifying bloater spawning habitats in Lake Ontario will allow for continued research to evaluate if spawning habitat is an impediment to bloater reintroduction efforts. Additionally, tagging hatchery-reared cisco and comparing spawning site selection to wild conspecifics will validate the method of using hatchery-reared individuals as surrogates to locate spawning sites. A better understanding of how surrogates might be used to find spawning locations may also be helpful for other imperiled species with low or extirpated populations. Finally, a better understanding of bloater and cisco mixing during spawning seasons may be useful for understanding spatial habitat use and potential hybridization of the two species in Lake Ontario.