Exploiting the sensory physiology of migratory fishes to guide them away from hazards like hydroelectric turbines is of interest to regulatory agencies and hydropower operators to achieve conservation and management goals. Here we describe a river-scale experiment where out-migrating adult American eel (Anguilla rostrata) were tracked downstream via acoustic telemetry as they encountered a 216 m long floating LED light array on the St. Lawrence River. Eel (N = 51) spatial responses to light were compared to eels detected on control (no light) nights with the expectation that light would cause eels to deflect laterally along the light array toward the river-right shore. Eels generally swam near the surface at night, and 39.5% of eels that encountered the light altered their downstream trajectories consistent with lateral deflection, although those responses were relatively modest. However, 76.7% of eels demonstrated diving responses of >= 4 m, consistent with seeking darker passage under the light field. Although we observed some degree of light avoidance, additional research is needed to optimize use of light for effective behavioral guidance in large rivers.

This publication is a user guide for an archive of morphological data recorded by various authors from North American ciscoes of the Coregonus artedi species complex (subfamily Coregoninae). The archive is accessible from the Great Lakes Fishery Commission’s (GLFC) server, is open access, and contains data for the Laurentian Great Lakes; Lake Nipigon, Ontario; and Great Slave Lake, Northwest Territories. The archive comprises morphometrics and meristics (together metrics) for 6,700 individual Cisco of which 1,400 are accompanied by images. In addition, the archive contains metrics presented as arrays by W. N. Koelz, Coregonid fishes of the Great Lakes, Bulletin of the U.S. Bureau of Fisheries 43(2):297-643, which were based on 10,000 individuals. Spreadsheets in the Metrics folder of the archive are divided broadly into Contemporary and Historical subfolders and the Contemporary subfolder is further divided into Cisco Monograph and Extra Monograph subfolders to encourage statistical assessment of findings in GLFC Miscellaneous Publication 2023. The Images folder is organized into subfolders by lake. Tables in this user guide allow for quick determination of the availability of data by lake, subspecies, author, and year.

Hydroelectric dams and their turbine infrastructure threaten out‐migrating anguillid eels en route to marine spawning grounds. For decades, invested parties have attempted to guide eels away from turbines and toward safe passage routes. A subset of this work (hereafter behavioral guidance) has involved exploiting sensory biology (e.g., sight and hearing) to divert eels from areas of danger toward safe passage, including collection facilities for trap and transport. Here, we narratively review these efforts and interpret available information through an applied lens. We collated relevant literature and organized it based on behavioral guidance modalities of light, sound, hydrodynamics, and electricity. Combined (multimodal) approaches were categorized under the primary behavioral stimulus. With further research, light could have some degree of potential as a standalone method, but field evidence indicates it is more practically effective when paired with physical barriers. Sound alone may not be sufficient, but flume evidence indicates it can also increase the effectiveness of physical barriers. Current evidence to support manipulation of hydrodynamics as a means to alter eel behavior is limited, and responses may vary considerably according to the nature of the manipulation. Electrical fields can be hazardous to downstream‐swimming eels, though they generally do elicit behavioral effects. Given our current understanding, it is apparent that multimodal approaches, particularly light and sound to augment physical barriers, are likely the most realistic for achieving reliable and effective behavioral guidance. Future research could refine knowledge in this area. It is important to continue to scale promising methods to the field to assess practical relevance.

Lake sturgeon Acipenser fulvescens remain a species of conservation concern in Lake Superior with a rehabilitation goal of maintaining spawning populations that are self-sustaining throughout their native range. The Lake Sturgeon Index Survey was developed to address rehabilitation research needs, determine rehabilitation progress, and monitor lake-wide and tributary-specific recruitment. Sampling with standardized gill nets occurred off the mouth of 19 known lake sturgeon spawning tributaries during 2011, 2016, and 2021. A target of 0.5 geometric mean catch per unit effort (CPUE) for cohort ages 4-8 was used as a quantitative recruitment indicator to determine progress towards Lake Superior's Fish Community Objectives. In 2021, CPUE of the age 4-8 cohort met the target at the Bad, Ontonagon, Batchawana, Goulais, Michipicoten, and Pic/White rivers (7 of 19 locations), but was below target at the St. Louis, Montreal, North and South Entry Sturgeon, Pigeon, Kaministiquia, Black Sturgeon/Wolf, Nipigon, Gravel, Prairie, and Tahquamenon rivers. The Index Survey sampling design meets assessment needs by concentrating sampling effort near tributary mouths and by assessing recruitment over the age 4-8 cohort. Power analysis indicated that detecting a 50% change in CPUE was not likely at individual tributaries except Goulais River, but could detect recruitment changes when aggregated lake-wide. The Index Survey allows fishery managers to quantitatively measure recruitment for individual populations to inform evaluation or modification of rehabilitation efforts in a timely manner and help determine where rehabilitation efforts and funding should be focused.

Lake Superior is the least anthropogenically impacted of the Laurentian Great Lakes ecosystems, yet dramatic changes to the fish community are evident. Previous published works chronicled those changes and the efforts to rehabilitate the fish community through the year 2000. Here, we review through the year 2022, where post-rehabilitation stability was driven by lean lake trout (Salvelinus namaycush namaycush) as the most abundant piscivore in nearshore waters, siscowet lake trout (Salvelinus namaycush siscowet) as the most abundant piscivore in offshore waters, and a healthy, intact assemblage of native prey species, which created ecological redundancies and helped stabilize the food web. Stocking of non-native salmonines was reduced 74%, and populations of Chinook salmon (Oncorhynchus tshawytscha) and coho salmon (Oncorhynchus kisutch) were maintained through natural reproduction. Despite reduced stocking, yield from recreational fisheries was stable. Likewise, developments in population modeling led to evaluations and refinement of management strategies that helped create stability for lake trout, lake whitefish (Coregonus clupeaformis), and cisco (Coregonus artedi) fisheries. With lake trout rehabilitation achieved, focus shifted toward rehabilitation of native brook trout (Salvelinus fontinalis), lake sturgeon (Acipenser fulvescens), and walleye (Sander vitreus). Despite continued control efforts, sea lamprey (Petromyzon marinus) abundance increased considerably, and estimates of fish killed by lampreys averaged 2.65 million kg annually. Environmental changes have benefited sea lampreys and fostered thermal habitats more suitable to non-native organisms, posing new challenges for managers and researchers. Nevertheless, the post-rehabilitation stability in the contemporary fish community will help provide resilience to future perturbations in the ecosystem.

Integrated Pest Management (IPM) provides a powerful framework for addressing threats to human well-being caused by nuisance species including invasives. We examined the hypothesis that adaptive management could erode barriers to IPM implementation by developing a decision-analytic adaptive management framework for invasive sea lamprey (Petromyzon marinus) IPM in the Laurentian Great Lakes of North America. The framework addressed objectives associated with coordinating multiple sea lamprey control actions at the regional scale and objectives associated with internal validity of control actions. We reduced the scope of possible management actions by orders of magnitude to the set of 6432 alternatives expected to be both socially acceptable and technically feasible. Using utility theory, we identified the management actions that optimized expected utility for all possible objective weighting schemes that considered tradeoffs between maximizing learning about control tactic efficacy and minimizing cost to the IPM program. Sensitivity analyses revealed that assumptions about the social acceptability of deploying electric weirs to control invasive sea lamprey influenced selection of the optimal control action, suggesting that resolving this source of uncertainty through iterative application of the framework may lead to improved sea lamprey control outcomes. Overall, we found that adaptive management enabled learning processes useful for overcoming barriers to IPM of invasive sea lamprey. It formalized learning about sea lamprey control tactic efficacy as an objective of the IPM institution, questioned previously held assumptions about what constitutes a viable control strategy, and enabled a management experiment with temporal and spatial replication.

ABSTRACT Young American eels ( Anguilla rostrata ) undergo a remarkable migration from oceanic spawning grounds to continental growth habitats. Impaired river connectivity can prevent facultatively catadromous eels from completing their upstream migration. The effects of barriers on the upstream migration dynamics of this endangered species remain poorly understood. This study evaluated the timing of juvenile eel migration and the spatial distribution and size/age structure of migrating eels within the tidal and hydropower‐regulated Wolastoq | Saint John River in Canada. Upstream eel migration in this river is restricted by the Mactaquac Dam and Generating Station, located 150 km upstream of the sea. Approximately 36,000 eels were caught with fyke nets at various locations between the river mouth and the Mactaquac Dam, measured for length, and a subsample ( n = 401) was aged via sagittal otolith readings. While glass eels (not fully pigmented juvenile eels) were observed up to 90 km upstream, approximately 20 km beyond the point of saltwater intrusion, eels arriving at the Mactaquac Dam were exclusively fully pigmented, with 80% being continental age 1+ or 2+. The mean length of juvenile eels increased with distance upstream. These results indicate that upstream eel migration in the Wolastoq | Saint John River can take multiple years and involves phases of juvenile residency. Our study provides important insights into juvenile eel migration in large rivers and implications for effective management of passage success at barriers such as hydropower dams.

Movement patterns and habitat use of yellow‐phase American eels Anguilla rostrata in the Wolastoq/Saint John River were examined using acoustic telemetry. Tracking 72 tagged yellow‐phase eels from late summer 2021 to autumn 2023 revealed overall restricted longitudinal movements (mean linear range ± standard deviation [SD] 6.4 ± 10.9 km) and high site fidelity. However, two eels exhibited small‐scale (20–25 km) seasonal movements within freshwater habitats and one eel undertook large‐scale (~83 km) seasonal movements between estuarine habitats in winter and freshwater habitats in summer. Tracking 24 yellow‐phase eels equipped with depth sensors indicated that depth use correlated with diel period, season and fish length, with eels occupying shallower habitats at night, presumably for foraging, and deeper habitats during the day, likely for shelter. Sixteen tagged eels presumably matured to the silver phase and initiated out‐migration in late summer. These eels moved rapidly through freshwater (mean ± SD 11.9 ± 8.8 km/day) but slowed considerably on reaching estuarine habitats (1.3 ± 1.3 km/day). These findings highlight the diversity of movement strategies in yellow‐phase eels and provide new insights into the transition to the migratory silver phase.

The upstream migration of juvenile American eels (Anguilla rostrata) is frequently obstructed by dams and other in-stream barriers, leading to habitat loss and fragmentation, factors that are believed to contribute to the species' population decline. While fishways can help restore access to upstream habitats, their effective design and implementation require reliable estimates of the number of eels arriving at migration barriers. The Mactaquac Dam and Generating Station (672 MW) is the lowermost barrier on the Wolastoq|Saint John River in Canada and currently does not provide an eel-specific fish passage. To inform the design and required capacity of a potential future eel passage at this site, this study provides mark-recapture-based estimates of the number of American eels arriving in the tailrace during three consecutive upstream migration seasons (2021-2023). During the peak migration period from late June to early August, a total of 30,144 juvenile eels were captured, tagged with visible implant elastomer tags, and released in the spillway bays of the dam over multiple sampling occasions spanning 30 to 42 days. Data were analyzed using POPAN Jolly-Seber models and resulted in population estimates ranging from approximately 150,000 individuals in 2021 and 2022 to approximately 950,000 in 2023. Although confidence intervals were relatively wide, these results highlight the importance of an upstream passage system for eels at this dam, provide guidance for future research and management, and demonstrate the potential for long-term monitoring at a future eel ladder to support local stock assessment.

Characterizing the diversity of migration behaviors from the individual to the population level is essential for understanding how organisms respond to environmental variation and how these responses affect survival and habitat use. Lake sturgeon (Acipenser fulvescens) is a species of special concern in the Laurentian Great Lakes that are long-lived and generally classified as intermittent, adfluvial spawners. Observations of lake sturgeon movements at ecologically relevant spatiotemporal scales have shown that migration behavior often varies among individuals within the same population. However, studies on individual populations, particularly when focused only on a part of the life cycle (e.g., often spawning), provide just a partial understanding of the species’ full migratory scope and processes underlying expression of different migratory behaviors. To better understand lake sturgeon migratory diversity, we characterized and compared migratory behaviors of six lake sturgeon populations occupying environments that varied in habitat availability and connectivity in different Laurentian Great Lakes. Sequence analysis combined with agglomerative hierarchical clustering and visual inspection of daily location data were used to identify distinct lake sturgeon migratory behaviors present in each population. Seven distinct migratory behaviors were identified based on differential patterns of lake and river use that encompass spawning and other seasonal periods. Behaviors were categorized as annual spring river, intermittent spring river, intermittent two-step, annual summer river, annual winter river, and annual interlake migrants along with river residents. The presence and frequency of migratory behaviors varied substantially among populations. Our study demonstrated that migratory diversity is a general feature of lake sturgeon life history that may be partially shaped by habitat availability and connectivity. Given these results, we propose a conceptual model that links habitat availability and connectivity to migratory diversity and predict a positive association between them. This updated framework provides a cohesive basis for understanding lake sturgeon migratory behavior across variable ecological contexts in the Laurentian Great Lakes and will help promote future research to refute or refine the model.

The importance of connectivity for freshwater organisms is widely recognised, yet in-stream barriers associated with population declines and increased risk of extinction remain globally ubiquitous. Despite their negative consequences, these barriers can protect aquatic communities by limiting the spread of invasive species, leading to conflicting management goals in some regions. Selective fish passage is a solution for the conflicting goals of passing native, desirable species while restricting the spread of invasives. Approaches that can target groups of species sharing similar attributes (i.e. guilds) are likely to be more efficient than those that target species individually, particularly in taxonomically diverse systems. We explored the guild structure of 220 Great Lakes freshwater fishes based on morphological, phenological, physiological and behavioural attributes associated with passage and movement. We identified five distinct guilds as well as the attributes most important for defining these groupings: maximum total length, trophic level, relative eye size, spawning temperature, spawning season, presence/absence of ampullary electroreceptors and the presence/absence of hearing specialisations. The approaches outlined in this work can be generalised to enhance selective fish passage in aquatic ecosystems worldwide.

The Laurentian Great Lakes (LGL) formed following the retreat of the Wisconsin glaciation 15-9 ka and provided a vast volume of freshwater habitat for coregonines, which included a diverse endemic complex of ciscoes. However, anthropogenic impacts in the 19th and 20th centuries resulted in declines and losses of ciscoes, leaving only Lake Superior with a relatively intact complex that still dominates its prey fish community. In the 1920s, W. Koelz described six putative cisco species from Lake Superior: Coregonus artedi , C. hoyi , C. kiyi , C. zenithicus, C. reighardi , and C. nigripinnis . Of these, artedi , hoyi and kiyi remain extant and abundant in Lake Superior, zenithicus is considered extirpated throughout the LGL except in Lake Superior, and reighardi and nigripinnis are considered extinct and had been synonymized as zenithicus in Lake Superior. Using an integration of morphological and genetic approaches, we present results reaffirming the presence of artedi , hoyi , and kiyi, and new evidence for the presence of reighardi , a species thought to be extinct. Our analysis did not elucidate the presence of zenithicus and nigripinnis , leaving their status unresolved. The principal morphological characters that discriminate artedi, hoyi, kiyi, and reighardi are related to habitat and trophic (ecological) specialization and foster niche segregation: eye size, gill raker length, and gill raker spacing, the same as those that foster niche segregation in subarctic European whitefishes. The discovery of reighardi is expected to stimulate new interest in the development of conservation and restoration plans for rare and imperiled cisco species in the LGL and other freshwater lakes throughout the Northern Hemisphere, and our integrated morphological and genetic approach can benefit these efforts by providing insights for the evolution, diversity, and ecology of ciscoes. ### Competing Interest Statement The authors have declared no competing interest.

In the Laurentian Great Lakes, the issue of barrier removal is complicated by the presence of non‐native species below barriers. A fish tracking study was conducted to guide efforts for barrier remediation decisions for the restoration of fish populations with a focus on Walleye (Scander vitreus) and Lake Sturgeon (Acipenser fulvescens) in the Black Sturgeon River, a river system fragmented by a dam which blocks access of fishes to the majority of a large, otherwise barrier‐free watershed. Data from 3 years of spawning migrations (2018–2020) indicated that the Walleye population in Black Bay likely consists of both river (65%) and lake spawners (27%), with the remaining individuals spawning in the bay or river in different years. Walleye and Lake Sturgeon showed consistent differences in the extent to which individuals migrated upstream in the river during the spawning season, despite expectations that both species would spawn at the base of the dam when prevented from further migration. The dam was presumably a barrier to migration for Lake Sturgeon, as nearly all Lake Sturgeon that entered the river migrated to the base of the dam. In contrast, few Walleye entering the river during the spawning season migrated to the dam annually. These findings suggest that Walleye and Lake Sturgeon may not benefit equally, at least in the short term, from barrier remediation or dam removal.

ObjectiveThis purpose of this paper is to describe the characteristics of recovered Lake Trout Salvelinus namaycush populations in Lake Superior by describing its population dynamics, ecology, and recent research and management activities since 1993, when Lake Trout were declared rehabilitated.MethodsData from commercial fisheries, recreational fisheries, agency stocking reports, and natural resource agency fishery-independent survey data along with published research findings on lean Lake Trout in Lake Superior between 1993 and 2022 were synthesized and reported.ResultCurrently, Lake Trout populations are self-sustaining and lightly exploited with only a few areas with elevated total mortality rates. The total annual mortality has been far below the target maximum range of 42-45%. Furthermore, stocking of hatchery Lake Trout is no longer necessary.ConclusionWe have learned from research and management experience that the regulatory role of Lake Trout in the Great Lakes is critical to proper ecosystem function. Thus, continued commitment from natural resource agencies to cooperate and implement effective management actions is required to preserve the accomplishments of lakewide recovery of Lake Trout populations. Impact statement The Lake Trout is the keystone predator in deepwater areas of the Great Lakes, and its successful recovery in Lake Superior has restored ecosystem stability and valued fisheries. This paper synthesizes information that describes the status of a highly managed species after restoration objectives have been achieved and maintained.

American Eel (Anguilla rostrata) undertake extensive migrations from their rearing grounds to spawn in the Sargasso Sea, and historically the upper St. Lawrence River and Lake Ontario provided an important source for large, fecund female eel. Following declines in the Lake Ontario population, glass eel were translocated from eastern Canada from 2006 to 2010. From 2016 to 2018, large, presumably translocated yellow eel (N = 230) with the potential to begin maturing and out-migrating within their year of capture were collected in spring and fall and tagged with acoustic transmitters. Eel were released into eastern Lake Ontario and tracked to better understand their movement patterns prior to and during migration, and the timing of migration. Most eels successfully migrated out of Lake Ontario (64%). Timing of migration was consistent regardless of year or tagging season and primarily occurred in late summer or fall, with cooling water temperatures and decreasing sky illumination associated with initiation for fall tagged eel. Eels were mostly detected in eastern Lake Ontario and those in western Lake Ontario were mostly detected in shallow waters (< 20 m) close to shore. Eels were detected on fewer receivers in the winter, suggesting reduced movements during this season. Finally, larger individuals spent less time in the system, particularly when tagged in the fall. These findings confirm that translocated eels can migrate out of Lake Ontario; however, the weeks when migration occurred were more aligned with timing in their natal range (i.e., eastern Canada) than with naturally recruited eels from Lake Ontario. This temporal mismatch requires further consideration, since it may influence arrival times of translocated eel to the spawning grounds and their recruitment potential. These results can be used to inform future assessments of eel translocation efficacy and can also aid in the design of future tracking studies to more completely explore the downstream migration success of eel translocated into the highly productive waters of Lake Ontario.

In-stream barriers pose threats to fishes, including habitat loss, constraints on migration, and reduced connectivity between populations. Despite many negative consequences, barriers can serve to protect native species by limiting the spread of invasive species. For example, in the Laurentian Great Lakes, physical barriers have long been used to control invasive sea lamprey (Petromyzon marinus) populations by limiting access to potential upstream spawning and rearing habitat. Selective fish passage systems could solve this management trade-off, termed the “connectivity conundrum”, but must efficiently pass multiple native or desirable species while blocking invasive species. Designing such fish passage systems requires an understanding of the attribute dimensions of the fish community, specifically, the phenology, morphology, physiology, and behaviour of each species. Here, we describe the first comprehensive collection of sortable attributes associated with fish passage. The integrated database consists of 21 biological attributes that influence the movement and passage of 220 species in the Great Lakes, including native species, established non-native species, and unestablished but potentially invasive fishes. Data coverage varies with species, taxonomic orders, and attribute dimensions. Behavioural attributes were typically underrepresented in the literature, and the ecology of potential invaders was not well understood. The synthesis described herein is a critical step towards a holistic approach to fish passage design and may help to inform management actions related to population connectivity. The database is openly accessible online and is expected to be updated periodically.

Lake Sturgeon (Acipenser fulvescens) is a species of conservation concern throughout North America, and healthy populations are rare. Earlier sampling efforts identified the Goulais Bay population in Lake Superior as a potentially healthy population after three years of sampling. With seven additional years of sampling, we updated the earlier analysis and developed a matrix population model to conduct a pop-ulation viability analysis (PVA). We identified a non-linear relationship between cohort strength and May river discharge rate which was incorporated into the population model to evaluate the influence of future discharge scenarios on population persistence. Population size was estimated, with an open-population mark-recapture model, at approximately 5,200 juvenile Lake Sturgeon. This estimate equates to approx-imately 440 mature females and 625 mature males in the population. A population of this size has a prob-ability of extinction of 4 % and 18 % over 250 and 1000 years under status quo conditions. If the May river discharge were to decrease in the future, which may represent the most likely scenario under future cli-mate conditions, our model predicts an increased risk of population extirpation. This indicates that increased management actions may be required to ensure this population remains resilient. Crown Copyright (c) 2022 Published by Elsevier B.V. on behalf of International Association for Great Lakes Research. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/ licenses/by-nc-nd/4.0/).

Background While Pace of Life Syndrome predicts behavioural differences between individuals with differential growth and survival, testing these predictions in nature is challenging due to difficulties with measuring individual behaviour in the field. However, recent advances in acoustic telemetry technology have facilitated measurements of individual behaviour at scales not previously possible in aquatic ecosystems. Methods Using a Walleye ( Sander vitreus ) population inhabiting Black Bay, Lake Superior, we examine whether life history characteristics differ between more and less mobile individuals as predicted by Pace of Life Syndrome. We tracked the movement of 192 individuals from 2016 to 2019 using an acoustic telemetry study, relating patterns in annual migratory behaviour to individual growth, and seasonal changes in optimal thermal-optical habitat. Results We observed two consistent movement patterns in our study population—migratory individuals left Black Bay during late summer to early fall before returning to the bay, whereas residents remained within the bay year-round. The average maximum length of migrant Walleye was 5.5 cm longer than residents, and the sex ratios of Walleye caught during fall surveys was increasingly female-biased towards the mouth of Black Bay, suggesting that a majority of migrants were females. Further, Walleye occupancy outside of Black Bay was positively associated with increasing thermal-optical habitat. Conclusions Walleye in Black Bay appear to conform to Pace of Life Syndrome, with migrant individuals gaining increased fitness through increased maximum size, which, given size-dependent fecundity in this species, likely results in greater reproductive success (via greater egg deposition vs. non-migrants). Further, apparent environmental (thermal) controls on migration suggest that migratory Walleye (more so than residents) may be more sensitive to changing environmental conditions (e.g., warming climate) than residents.

The common carp (Cyprinus carpio) is a non-native fish species in many parts of the world which has negative impacts on freshwater environments including plant loss, re-suspended sediment, and altered nutrient flux. Eradication of common carp can be extremely difficult and conventional management efforts have focused on control or containment, achieved with barriers that decrease or eliminate access to specific habitats. Here, we examined biological traits of common carp that can be exploited with barriers to control populations and minimize ecological impacts; however, an important consideration during barrier design and implementation are impacts on non-target, native species (i.e., selective fragmentation). Phenology, such as differences in reproductive timing, could be used to operate barriers to minimize impacts on some native species. Sensory ability could also be exploited in cases where common carp is more sensitive to electrical, acoustic, visual and/or chemical stimuli. Differences in morphology of common carp compared to native species could contribute to barrier design (e.g., 5.0 cm spacing in vertical bars screens), whereby larger common carp are excluded but many native species can pass. Behaviour, such as common carp jumping, can also be exploited to separate carp from native species with modified barriers. We explore cases of each trait being used through diverse case studies: phenology (Sea Lamprey Control Program); sensory capability (carbon-dioxide deterrents); morphology (vertical bar screens); and behaviour (the Williams’ cage). The approach taken here with common carp can be applied to other aquatic non-native species to assess the potential for barriers to reduce associated negative impacts on native fish species with selective fragmentation.