Development of conceptual early life history models and evaluation of sampling techniques in support of long-term monitoring for cisco and lake whitefish

Ralph Tingley (USGS, rtingley@usgs.gov), Cory Brant (USGS), David Bunnell (USGS), robin DeBruyne (USGS), Kevin Donner (Little Traverse Bay Band of Odawa Indians), Erin Dunlop (OMNRF), Andrew Honsey (USGS), Jory Jonas (MIDNR), Kevin McDonnell (USFWS), Andrew Muir (GLFC), Ed Roseman (USGS), Jason Smith (Sault Ste Marie Tribe of Chippewa Indians), Daniel Tule (USGS), Brian Weidel (USGS)

Recruitment is set early during life (<2 years of age) for many fish populations (Hjort 1914, Houde 1987). From fertilization to juvenile stages, fishes are susceptible to abiotic and biotic factors that directly or indirectly influence growth, condition, and survival (Ludsin et al. 2014, Pritt et al. 2014). The mechanistic processes influencing recruitment, their interactions,and the timing at which they are most influential remains unclear for many fishes. By improving understanding of early life history (ELH) ecology and recruitment constraints, we can improve monitoring and support more informed management decisions. Long-term ELH monitoring programs that inform management are limited for cisco (Coregonus artedi) across the Great Lakes. In Lake Superior, cisco year-class strength is assessed using an age-1 index generated via a spring bottom trawl (Vinson et al. 2022). This index has been low since 2009, raising concern that a recruitment bottleneck is occurring during the first year of life, the exact mechanism(s) of which is unknown. In the other Great Lakes, cisco recruitment indices from fishery independent sources are not established, perhaps owing to low prioritization of reduced or near extirpated populations since the mid-20th century (Berst and Spangler 1973, Christie 1973, Hartman 1973, Lawrie and Rahrer 1973, Wells and McLain 1973). As cisco populations recover in some lakes and as restoration programs progress, agencies are beginning to apply established sampling techniques from Lake Superior to other systems. Efforts to date have yielded limited success. For example, spring bottom trawling in Lake Michigan that mirrors efforts in Lake Superior has failed to recover yearling cisco, even in locations where adult densities are highest (e.g., Grand Traverse Bay, Claramunt et al. 2019). For lake whitefish (Coregonus clupeaformis), several short-term monitoring studies aimed at exploring constraints on early life stages have occurred since the 1970s (e.g Freeberg et al. 1990, Hoyle et al. 2011), but long-term ERL surveys that are used to inform management are limited. In a recent review paper, Ebener et al. (2021) highlight the development of sampling protocols to index lake whitefish recruitment as a primary management need and note that biotic and biotic factors influencing ELH survival and recruitment remains understudied. Recent work by the Ontario Ministry of Northern Development, Mines, Natural Resources and Forestry (MNDMNRF) that compares current (2017-2021) larval densities to a historic larval dataset (1970s and 1980s), along with expanded annual monitoring in several regions of Lake Huron by MNDMNRFand the US Fish and Wildlife Service, are steps towards improving understanding of current recruitment constraints and could form the basis of new or expanded larval monitoring efforts. In recent years, numerous studies in the Great Lakes, its connecting waterways, and its tributaries have evaluated cisco and lake whitefish spawning habitat and ELH habitat use from embryonic to early juvenile stages (Brown et al. 2022, Paufve et al. 2022, Pothoven and Olds 2022, Amidon et al. 2021, Ransom et al. 2021,Roseman et al. 2021, Schaefer et al. 2021, Lucke et al. 2020, McKenna et al. 2020, Tucker et al. 2018, Roseman et al. 2012). Despite a diversity of objectives, study areas, and sampling techniques, two prominent themes appear in many of these publications. First, year-class strength for both species is likely set early in their life history, although the exact timing is unclear. Second, there is a critical need to develop standardized monitoring initiatives to answer questions regarding habitat use and recruitment bottlenecks and to inform effective long-term indices that are comparable across systems. In addition to published research, an increasing number of recent or ongoing surveys focus on coregonid early life stages and may prove useful in understanding ELH ecology and evaluating sampling techniques. For example, a beach-seining initiative targeting age-0 juvenile lake whitefish (and collecting some age-0 cisco) that was established by the Sault Tribe of Chippewa Indians and expanded by the Little Traverse Bay Band of Odawa Indians in Lake Michigan has been in place for nine years and now covers new areas of Lakes Huron, Michigan and Superior with numerous sampling techniques being implemented. In Lake Huron and the Saint Marys River, an informal review of Spring 2022 ELH coregonid sampling efforts indicates that six agencies and tribes are implementing at least one sampling program, but each effort varies in some aspect of habitat and life stage sampled, study design, and sampling gear. In Lake Ontario and Lake Erie, new techniques to sample coregonine embryos and emerging larvae are being implemented and early results offer an opportunity to critically consider their applicability to long-term monitoring. Further, new genetic analyses provide increasingly affordable opportunities to distinguish among coregonid species and between populations at early life stages. Findings from these and other efforts can be used with published extant data and expert knowledge to inform conceptual models for cisco and lake whitefish that describe habitat use for ELH stages as well as the key abiotic or biotic factors that influence stage-specific survival and growth. Development of these conceptual models should highlight knowledge gaps and provide insight regarding which sampling techniques will provide the most reliable indices of recruitment for each species. Given the recent increase in publications, expanded monitoring, and the clear management need to develop recruitment indices for cisco and lake whitefish in most of the Great Lakes, we argue the timing is ripe to bring together biologists, managers, and partners for an in-person workshop to generate 1) conceptual models of lake whitefish and cisco ELH habitat use and key drivers of vital rates at each stage, 2) recommendations of best sampling practices to target key life stages and habitat types, and 3) a prioritized list of research needs to reduce uncertainty in habitat use and recruitment constraints.