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USGS2018

Food‐web structure and ecosystem function in the Laurentian Great Lakes—Toward a conceptual model

The relationship between food‐web structure (i.e., trophic connections, including diet, trophic position, and habitat use, and the strength of these connections) and ecosystem functions (i.e., biological, geochemical, and physical processes in an ecosystem, including decomposition, production, nutrient cycling, and nutrient and energy flows among community members) determines how an ecosystem responds to perturbations, and thus is key to understanding the adaptive capacity of a system (i.e., ability to respond to perturbation without loss of essential functions). Given nearly ubiquitous changing environmental conditions and anthropogenic impacts on global lake ecosystems, understanding the adaptive capacity of food webs supporting important resources, such as commercial, recreational, and subsistence fisheries, is vital to ecological and economic stability. Herein, we describe a conceptual framework that can be used to explore food‐web structure and associated ecosystem functions in large lakes. We define three previously recognised broad habitat compartments that constitute large lake food webs (nearshore, pelagic, and profundal). We then consider, at three levels, how energy and nutrients flow: (a) into each basal resource compartment; (b) within each compartment; and (c) among multiple compartments (coupling). Flexible shifts in food‐web structures (e.g., via consumers altering their diet or habitat) that sustain these flows in the face of perturbations provide evidence for adaptive capacity. We demonstrate the conceptual framework through a synthesis of food‐web structure and ecosystem function in the Laurentian Great Lakes, with emphasis on the upper trophic levels (i.e., fishes). Our synthesis showed evidence of notable adaptive capacity. For example, fishes increased benthic coupling in response to invasion by mussels and round gobies. However, we also found evidence of loss of adaptive capacity through species extirpations (e.g., widespread collapse in the abundance and diversity of ciscoes, Coregonus spp., except in Lake Superior). In large freshwater lakes, fishery managers have traditionally taken a top‐down approach, focusing on stocking and harvest policy. By contrast, water quality managers have focused on nutrient effects on chemical composition and lower trophic levels of the ecosystem. The synthesised conceptual model provides resource managers a tool to more systematically interpret how lower food‐web dynamics influence harvestable fish populations, and vice versa, and to act accordingly such that sustainable resource practices can be achieved. We identify key gaps in knowledge that impede a fuller understanding of the adaptive capacities of large lakes. In general, we found a greater uncertainty in our understanding of processes influencing energy and nutrient flow within and among habitats than flows into the system.

Great Lakes↗

USGS2011

Nutrient inputs to the Laurentian Great Lakes by source and watershed estimated using SPARROW watershed models

Nutrient input to the Laurentian Great Lakes continues to cause problems with eutrophication. To reduce the extent and severity of these problems, target nutrient loads were established and Total Maximum Daily Loads are being developed for many tributaries. Without detailed loading information it is difficult to determine if the targets are being met and how to prioritize rehabilitation efforts. To help address these issues, SPAtially Referenced Regressions On Watershed attributes (SPARROW) models were developed for estimating loads and sources of phosphorus (P) and nitrogen (N) from the United States (U.S.) portion of the Great Lakes, Upper Mississippi, Ohio, and Red River Basins. Results indicated that recent U.S. loadings to Lakes Michigan and Ontario are similar to those in the 1980s, whereas loadings to Lakes Superior, Huron, and Erie decreased. Highest loads were from tributaries with the largest watersheds, whereas highest yields were from areas with intense agriculture and large point sources of nutrients. Tributaries were ranked based on their relative loads and yields to each lake. Input from agricultural areas was a significant source of nutrients, contributing ∼33-44% of the P and ∼33-58% of the N, except for areas around Superior with little agriculture. Point sources were also significant, contributing ∼14-44% of the P and 13-34% of the N. Watersheds around Lake Erie contributed nutrients at the highest rate (similar to intensively farmed areas in the Midwest) because they have the largest nutrient inputs and highest delivery ratio.

Laurentian Great Lakes↗

USGS2014

A scientific basis for restoring fish spawning habitat in the St. Clair and Detroit Rivers of the Laurentian Great Lakes

Loss of functional habitat in riverine systems is a global fisheries issue. Few studies, however, describe the decision-making approach taken to abate loss of fish spawning habitat. Numerous habitat restoration efforts are underway and documentation of successful restoration techniques for spawning habitat of desirable fish species in large rivers connecting the Laurentian Great Lakes are reported here. In 2003, to compensate for the loss of fish spawning habitat in the St. Clair and Detroit Rivers that connect the Great Lakes Huron and Erie, an international partnership of state, federal, and academic scientists began restoring fish spawning habitat in both of these rivers. Using an adaptive management approach, we created 1,100 m 2 of productive fish spawning habitat near Belle Isle in the Detroit River in 2004; 3,300 m 2 of fish spawning habitat near Fighting Island in the Detroit River in 2008; and 4,000 m 2 of fish spawning habitat in the Middle Channel of the St. Clair River in 2012. Here, we describe the adaptive-feedback management approach that we used to guide our decision making during all phases of spawning habitat restoration, including problem identification, team building, hypothesis development, strategy development, prioritization of physical and biological imperatives, project implementation, habitat construction, monitoring of fish use of the constructed spawning habitats, and communication of research results. Numerous scientific and economic lessons learned from 10 years of planning, building, and assessing fish use of these three fish spawning habitat restoration projects are summarized in this article.

Detroit River, St. Clair River↗

USGS2013

Morphometric variation among spawning cisco aggregations in the Laurentian Great Lakes: are historic forms still present?

Cisco (Coregonus artedi Leseur, formerly lake herring Leucichthys artedi Leseur) populations in each of the Laurentian Great Lakes collapsed between the late 1920s and early 1960s following a multitude of stressors, and never recovered in Lakes Michigan, Erie and Ontario. Prior to their collapse, Koelz (1929) studied Leucichthys spp. in the Great Lakes basin and provided a description of their diversity. Three cisco morphotypes were described; a ‘slim terete’morphotype (L. artedi artedi), a ‘deep compressed’ morphotype (L. artedi albus), and a deep-bodied form resembling tullibee in western Canadian lakes (L. artedi manitoulinus). Based on body measurements of 159 individuals (Koelz 1929), we used discriminant function analysis (DFA) to discriminate historic morphotypes. Shapes of historic morphotypes were found to vary significantly (Pillai’s trace = 1.16, P < 0.0001). The final DFA model used nine body measurements and correctly classified 90% of the historic cisco. Important discriminating measurements included body depth, eye diameter, and dorsal fin base and height. Between October-November of 2007-2011, we sampled cisco from 16 Great Lakes sites collecting digital photographs of over 1, 700 individuals. We applied the DFA model to their body measurements and classified each individual to a morphotype. Contemporary cisco from Lakes Superior, Ontario and Michigan were predominantly classified as artedi, while the most common classifications from northern Lake Huron were albus and manitoulinus. Finding historic morphotypes is encouraging because it suggests that the morphological variation present prior to their collapse still exists. We conclude that contemporary cisco having shapes matching the missing historic morphotypes in the lower lakes warrant special consideration as potential donor populations in reestablishment efforts.

Lake Michigan;Lake Erie;Lake Ontario;Lake Huron;La↗

USGS1991

Compsopogon cf. coeruleus , a benthic red alga (Rhodophyta) new to the Laurentian Great Lakes

We found Compsopogon cf. coeruleus for the first time in the Laurentian Great Lakes, growing on limestone rocks at a depth of 21&ensp;m on Six Fathom Bank in central Lake Huron. It is the first freshwater red alga to be found in the Great Lakes and the only red alga ever found on an offshore reef in the Great Lakes. However, because this alga usually inhabits water 10–28 °C and has not survived freezing winter temperatures elsewhere, it may not be a permanent member of the flora.

Canadian Journal of Botany↗

USGS2018

Ecosystem classification and mapping of the Laurentian Great Lakes

Owing to the enormity and complexity of the Laurentian Great Lakes, an ecosystem classification is needed to better understand, protect, and manage this largest freshwater ecosystem in the world. Using a combination of statistical analyses, published knowledge, and expert opinion, we identified key driving variables and their ecologically relevant thresholds and delineated and mapped aquatic systems for the entire Great Lakes. We identified and mapped 77 aquatic ecological units (AEUs) that depict unique combinations of depth, thermal regime, hydraulic, and landscape classifiers. Those 77 AEU types were distributed across 1997 polygons (patches) ranging from 1 to >48 000 km 2 in area and were most diverse in the nearshore (35 types), followed by the coastal margin (26), and then the offshore (16). Our classification and mapping of ecological units captures gradients that characterize types of aquatic systems in the Great Lakes and provides a geospatial accounting framework for resource inventory, status and trend assessment; research for ecosystem questions; and management and policy-making.

Laurentian Great Lakes↗

USGS2025

Integrating acoustic telemetry research into management: successes and challenges in the Laurentian Great Lakes

In the Laurentian Great Lakes, the application of acoustic telemetry to track fish movements has evolved into an important part of multijurisdictional management. Nevertheless, barriers remain in translating telemetry research into management or conservation actions. Here, we synthesize acoustic telemetry literature within the Great Lakes basin to explore factors that have contributed to successes and failures of integrating research with the needs of decision-making processes. Collaboration between researchers and managers, facilitated by consistent opportunities for stakeholder engagement, stood out as one of the most effective means of integration. For example, 79% (95 of 127) of articles published (up to 2023) included co-authorship by both government and academic organizations. Case studies on lake sturgeon ( Acipenser fulvescens ), walleye ( Sander vitreus ), and sea lamprey ( Petromyzon marinus ) further highlight how telemetry has informed management through collaborative engagement among researchers, stakeholders, and managers, as well as ongoing challenges. By exploring facets of acoustic telemetry research and connections to conservation and fisheries concerns, we identify pathways to reduce knowledge–action gaps widely applicable within and outside of the Great Lakes.

Laurentian Great Lakes↗

USGS2026

Decreased water transparency of nearshore Laurentian Great Lakes habitats is driven by increased dissolved organic carbon.

Little is understood of lake browning (due to increased dissolved organic carbon; DOC) in large lakes such as the Laurentian Great Lakes. Lake browning can alter whole lake ecosystems, including decreasing exposure to damaging ultraviolet radiation (UV-B) which is strongly and selectively attenuated by DOC more so than photosynthetically active radiation (PAR). We compared the changes in UV-B and PAR transparency to DOC data collected during the ice-free seasons from 62 nearshore sites in four of the five Great Lakes from 2002 to 2022 using linear mixed effects regression models based on backwards selected Bayesian information criteria. Regionally, DOC significantly increased from 2002 to 2022 by 0.5% per year on average. DOC strongly and inversely explained the variability of UV-B and PAR transparencies, as did seasons and offshore influence on these habitats. We provide regional evidence of lake browning within the nearshore habitats of the Great Lakes as a strong contrast to the well-documented increased offshore water transparency associated with the spread of invasive dreissenid mussels.

Great Lakes↗

USGS2026

Availability of dark daytime refuge may limit mysid abundance in the Laurentian Great Lakes

The zooplankton Mysis diluviana is a major component of the Laurentian Great Lakes food web and has recently declined in abundance in both lakes Michigan and Huron. Drivers of these declines are not well understood. Here, we explore the hypothesis that recent increases in water clarity have contributed to the decline of M. diluviana (mysids) by limiting the availability of daytime dark refuge from visual predators. Using Secchi depth data from 1996 to 2021, we estimate that dark refuge has decreased substantially in lakes Michigan and Huron where mysids have declined, but dark refuge has remained more stable in lakes Ontario and Superior where mysid populations did not decline. Results from a 2021 uncrewed surface vessel hydroacoustic survey and lake-wide, net-based sampling in lakes Michigan and Huron revealed significantly more mysids in areas with dark refuge, such as Lake Michigan’s northern basin. Conversely, Lake Huron contains sparse dark refuge consistent with low mysid densities in that lake. Higher water clarity leading to increased predation may be a primary driver of mysid declines in the Great Lakes.

Laurentian Great Lakes↗

USGS2023

A science and management partnership to restore coregonine diversity to the Laurentian Great Lakes

Similar to many freshwater ecosystems, the Laurentian Great Lakes of North America have undergone numerous anthropogenic stressors resulting in considerable loss of biodiversity and habitat. Among Great Lakes fishes, the coregonine sub-family has endured the most extensive declines, including extinction of several species ( Coregonus johannae, C. alpenae , and C. kiyi orientalis ) and at least 10 instances of local extirpations of other species ( C. nigripinnis, C. reighardi, C. zenithicus, C. hoyi , and C. artedi ) across all 5 lakes, much of which occurred prior to the 1960s owing to overfishing, interactions with non-indigenous species, and habitat loss. Despite these declines, no federal-, provincial-, or state-mandated actions were ever implemented to conserve coregonine diversity, potentially because so much of the coregonine declines occurred prior to the enactment of federal conservation legislation. Possible explanations for inaction since enactment of that legislation include insufficient data on biological vulnerability or threats, unresolved taxonomy, and limited support from the fishery management agencies and their stakeholders prior to the 2000s. In recent decades, however, several fishery management agencies have undertaken efforts to re-introduce coregonine diversity. These efforts helped lead to development of a science-based framework to restore coregonines that was universally endorsed by fishery managers representing eight U.S. states, four U.S. tribal organizations, and the province of ON, Canada, in May 2018. The basin-wide framework is based on principles of conservation biology and adaptive management. We describe details of its key steps, including planning, restoring, and evaluating, while also describing recent implementation efforts to develop methods, improve available resources, and enhance coordination across the basin. Although our paper describes a regional effort to restore native coregonines, our adaptive-management approach could be used by other multi-agency stakeholders seeking to conserve or restore native fishes.

Laurentian Great Lakes↗

USGS1972

Factors of ecologic succession in oligotrophic fish communities of the Laurentian Great Lakes

Oligotrophic fish communities of the Great Lakes have undergone successive disruptions since the mid-1800s. Major contributing factors have been intensive selective fisheries, extreme modification of the drainage, invasion of marine species, and progressive physical–chemical changes of the lake environments. Lake Ontario was the first to be affected as its basin was settled and industrialized earliest, and it was the first to be connected by canals to the mid-Atlantic where the alewife ( Alosa pseudoharengus ) and sea lamprey ( Petromyzon marinus ) which ultimately became established in the Great Lakes were abundant. Oligotrophic fish communities were successively disrupted in Lakes Erie, Huron, Michigan, and Superior as the affects of population growth, industrialization, and marine invaders spread upward in the Laurentian drainage.The degree and sequence of response of families offish and species within families differed for each factor, but the sequence of change among families and species has been the same in response to each factor as it affected various lakes at different times. The ultimate result of the disruption of fish communities has been a reduction of productivity of oligotrophic species that ranges from extreme in Lake Ontario to moderate in Lake Superior, and which has reached a state of instability and rapid change in the upper three Great Lakes by the rnid-1900s similar to the situation in Lake Ontario in the mid-1800s. Since oligotrophic species (primarily salmonines, coregonines, and deepwater cottids) are the only kinds of fish that fully occupied the entire volume of the deepwater Great Lakes (Ontario, Huron, Michigan, and Superior), the fish biomass of these lakes has been reduced as various species declined or disappeared. In Lake Erie, which is shallow, and in the shallow bays of the deep lakes, oligotrophic species were replaced by mesotrophic species, primarily percids, which have successively increased and declined. All oligotrophic species are greatly reduced or extinct in lakes Ontario and Erie, and are in various stages of decline in lakes Huron, Michigan, and Superior, from greatest to least, respectively. The percids appear to be near the end of their sequence of succession in lakes Erie, Ontario, and Huron (primarily Saginaw Bay) where only the yellow perch ( Perca flavescens ) remains abundant. The yellow perch appears to be on the brink of decline in Lake Erie, which has been more severely influenced by water quality change than the other lakes.

Journal of the Fisheries Research Board of Canada↗

USGS2004

The Late Cambrian SPICE (δ13C) event and the Sauk II-Sauk III regression: new evidence from Laurentian basins in Utah, Iowa, and Newfoundland

Carbon isotope data from Upper Cambrian sections in three Laurentian basins in northern Utah, central Iowa, and western Newfoundland record a large positive ??13C excursion (SPICE event) of up to + 5???. Peak ??13C ratios are well dated by trilobite collections to the middle of the Steptoean Stage (Dunderbergia Zone) and occur during maximum regression associated with formation of the Sauk II-Sauk III subsequence boundary on the North American craton. Maximum regression was marked by an influx of quartz sand into carbonate-platform settings in all three widely separated basins. In northern Utah, this quartz sand formed a thick sequence known as the Worm Creek Quartzite, which marks a conspicuous interruption of carbonate deposition during the Middle to Late Cambrian in the region. In western Newfoundland, the thickness of the quartz sand unit is much reduced but still marks a brief shutdown of the carbonate factory that is unique to the Cambrian shelf succession of the area. In the central Iowa area of the cratonic interior, an upward-shallowing carbonate succession culminates in cross-stratified trilobite grainstones at the peak of the SPICE in Dunderbergia Zone time, and the lowest point on the relative-sea-level curve is associated with the occurrence of coarse quartz sand derived from the encroaching shoreface. Although it is difficult to determine precisely the departure from baseline ??13C that marks the beginning of the SPICE excursion in the stratigraphic successions analyzed, our results are consistent with a rise and subsequent fall in ??13C tracking a major regressive-transgressive event recorded across northern Laurentia. The correlation of a major ??13C excursion with regression is similar to that described for the Late Ordovician, for which the pattern has been attributed to either increased carbonate relative to terrigenous weathering rates as ice sheets covered up organic-matter-containing silicates at high latitudes or high productivity and organic-carbon burial driven by oceanic overturn. The lack of known Steptoean-age ice sheets that could have affected the ratio of carbonate to silicate weathering rates suggests that organic-carbon burial was the likely cause of the SPICE event. We suggest that increased weathering and erosion rates during relative sea-level fall (Sauk II-III) increased the burial fraction of organic carbon in an expanded region of fine-grained siliciclastic deposits in shelf and upper slope environments during the Steptoean. ?? 2004, SEPM (Society for Sedimentary Geology).

Journal of Sedimentary Research↗

USGS2008

Restoring piscivorous fish populations in the Laurentian Great Lakes causes seabird dietary change

Ecosystem change often affects the structure of aquatic communities thereby regulating how much and by what pathways energy and critical nutrients flow through food webs. The availability of energy and essential nutrients to top predators such as seabirds that rely on resources near the water's surface will be affected by changes in pelagic prey abundance. Here, we present results from analysis of a 25-year data set documenting dietary change in a predatory seabird from the Laurentian Great Lakes. We reveal significant declines in trophic position and alterations in energy and nutrient flow over time. Temporal changes in seabird diet tracked decreases in pelagic prey fish abundance. As pelagic prey abundance declined, birds consumed less aquatic prey and more terrestrial food. This pattern was consistent across all five large lake ecosystems. Declines in prey fish abundance may have primarily been the result of predation by stocked piscivorous fishes, but other lake-specific factors were likely also important. Natural resource management activities can have unintended consequences for nontarget ecosystem components. Reductions in pelagic prey abundance have reduced the capacity of the Great Lakes to support the energetic requirements of surface-feeding seabirds. In an environment characterized by increasingly limited pelagic fish resources, they are being offered a Hobsonian choice: switch to less nutritious terrestrial prey or go hungry. ?? 2008 by the Ecological Society of America.

Ecology↗

USGS2002

Comparison of 5 benthic samplers to collect burrowing mayfly nymphs ( Hexagenia spp.:Ephemeroptera:Ephemeridae) in sediments of the Laurentian Great Lakes

The recent return of burrowing mayfly nymphs ( Hexagenia spp.) to western Lake Erie of the Laurentian Great Lakes has prompted a need to find a sampler to obtain the most accurate (i.e., highest mean density) and precise (i.e., lowest mean variance) abundance estimates of nymphs. The abundance of burrowing nymphs is important because it is being used as a measure of ecosystem health to determine management goals for fisheries and pollution abatement programs for waters in both North America and Europe. We compared efficiencies of 5 benthic grab samplers (Ponar, Ekman, petite Ponar, Petersen, and orange-peel) to collect nymphs from sediments of western Lake Erie and Lake St. Clair. Samplers were used at one site with soft substrates in both lakes in 1997 (Ponar, Ekman, petite Ponar, and Petersen) and 1998 (Ponar and Ekman), and at one site with soft and one site with hard substrates in Lake St. Clair in 1999 (Ponar and orange-peel). In addition, the Ponar, Ekman, and Petersen samplers were used at one site with soft substrates of western Lake Erie in 2000 to examine the causes of differences among samplers. The Ponar was more accurate than the other samplers; it collected the highest densities of nymphs for 31 of 32 date and site comparisons. In soft substrates, the order of decreasing overall densities was: Ponar>Petersen>petite Ponar>Ekman in western Lake Erie and Ponar>Petersen> Ekman>petite Ponar in Lake St. Clair in 1997, Ponar>Ekman in both lakes in 1998, and Ponar>orange-peel in Lake St. Clair in 1999. In hard substrates, the Ponar was more accurate than the orange-peel in Lake St. Clair in 1999. Precision of the Ponar was generally greater than the Ekman, petite Ponar, and Petersen but similar to the orange-peel. Higher densities of nymphs obtained with the Ponar than other grabs are attributed to its relatively heavy weight, which allows it to sample deeper in sediments than the Ekman and petite Ponar. Also, the Ponar has a screened top, which allows it to minimize hydraulic shock waves more than the Petersen, and uniform sides, which allow it to sample nymphs more uniformly through sediments than the orange-peel. We recommend that future estimates of burrowing mayfly densities be obtained with a standard Ponar sampler similar to the one used in our study because it will yield the most accurate and precise measurements of burrowing mayfly nymphs such as Hexagenia spp.

Journal of the North American Benthological Societ↗

USGS2017

Climatic-change implications from long-term (1823-1994) ice records for the Laurentian Great Lakes

Long-term ice records (1823-1994) from six sites in different parts of the Laurentian Great Lakes region were used to show the type and general timing of climatic changes throughout the region. The general timing of both freeze-up and ice loss varies and is driven by local air temperatures, adjacent water bodies and mixing, and site morphometry. Grand Traverse Bay and Buffalo Harbor represent deeper-water environments affected by mixing of off-shore waters; Chequamegon Bay, Memnominee, Lake Mendota, and Toronto Harbor represent relatively shallow-water, protected environments. Freeze-up dates gradually become later and ice-loss dates gradually earlier from the start of records to the 1890s in both environments, marking the end of the 'Little Ice Age.' After this, freeze-up dates remained relatively constant suggesting little change in early-winter air temperatures during the 20th century. Ice-loss dates at Grand Traverse Bay and Buffalo Harbor (but not at the other sites) became earlier during the 1940s and 1970s and became later during the 1960s. The global warming of the 1980s was marked by a trend toward earlier ice-loss dates in both environments.

Great Lakes↗

USGS2019

Interactive mapping of nonindigenous species in the Laurentian Great Lakes

Nonindigenous species pose significant risks to the health and integrity of ecosystems around the world. Tracking and communicating the spread of these species has been of interest to ecologists and environmental managers for many years, particularly in the bi-national Laurentian Great Lakes of North America. In this paper, we introduce the Great Lakes Aquatic Nonindigenous Species Information System (GLANSIS) Map Explorer. The Map Explorer provides access to records of documented nonindigenous species and their spatial distributions. Users may view the distributions of well-known nonindigenous species (such as zebra mussels) as well as perform custom queries. Additional map layers allow users to compare the distribution of nonindigenous species to environmental conditions. This tool serves to communicate knowledge to diverse stakeholder groups and to enable further in-depth research on nonindigenous species.

Laurentian Great Lakes↗

USGS2021

Are Cisco and Lake Whitefish competitors? An analysis of historical fisheries in Michigan waters of the Upper Laurentian Great Lakes

Historically, Cisco Coregonus artedi and Lake Whitefish Coregonus clupeaformis were abundant throughout the Laurentian Great Lakes, but overharvest, habitat degradation, and interactions with exotic species caused most populations to collapse by the mid-1900s. Strict commercial fishery regulations and improved environmental and ecological conditions allowed Cisco to partially recover only in Lake Superior, whereas Lake Whitefish recovered in all the upper Great Lakes (Superior, Michigan, and Huron). The differential responses of Cisco and Lake Whitefish to improved environmental and ecological conditions in lakes Michigan and Huron have led to questions about potential negative interactions between these species. To provide context for fishery managers, we tested for positive and negative correlations between historical (1929–1970) Cisco and Lake Whitefish commercial gill net catch per effort (CPE; kg/km of net) at a variety of spatial scales in Michigan waters of the upper Great Lakes. The three best-fit spatial models—LAKEWIDE, REGIONAL 10, and SIMPLE—all had similar levels of support (scaled second-order Akaike Information Criterion < 3.0), and we used these models to determine whether there was a significant correlation between Cisco and Lake Whitefish CPE (positive and negative). There was either no correlation between Cisco and Lake Whitefish CPE or a positive correlation for most (12 of 13) pairwise (Cisco–Lake Whitefish) comparisons. We identified no strong positive or negative correlations in the lakewide (LAKEWIDE) or reduced (SIMPLE) models. In the regional model (REGIONAL 10), we identified strong and positive correlations between Cisco and Lake Whitefish CPE in two regions (ρ = 0.59–0.71) and a weak negative correlation in one region (ρ = −0.45). Collectively, our findings suggest that Cisco and Lake Whitefish CPE were largely independent of each other; thus, these species likely did not interact to the detriment of one another in Michigan waters of the upper Great Lakes during 1929–1970.

Michigan↗

USGS2021

How many Ciscoes are needed for stocking in the Laurentian Great Lakes?

Historically, Cisco Coregonus artedi and deepwater ciscoes Coregonus spp. were the most abundant and ecologically important fish species in the Laurentian Great Lakes, but anthropogenic influences caused nearly all populations to collapse by the 1970s. Fishery managers have begun exploring the feasibility of restoring populations throughout the basin, but questions regarding hatchery propagation and stocking remain. We used historical and contemporary stock-recruit parameters previously estimated for Ciscoes in Wisconsin waters of Lake Superior, with estimates of age-1 Cisco rearing habitat (broadly defined as total ha ≤ 80 m depth) and natural mortality, to estimate how many fry (5.5 months post-hatch), fall fingerling (7.5 months post-hatch), and age-1 (at least 12 months post-hatch) hatchery-reared Ciscoes are needed for stocking in the Great Lakes to mimic recruitment rates in Lake Superior, a lake that has undergone some recovery. Estimated stocking densities suggested that basin-wide stocking would require at least 0.641-billion fry, 0.469-billion fall fingerlings, or 0.343-billion age-1 fish for a simultaneous restoration effort targeting historically important Cisco spawning and rearing areas in Lakes Huron, Michigan, Erie, Ontario, and Saint Clair. Numbers required for basin-wide stocking were considerably greater than current or planned coregonine production capacity, thus simultaneous stocking in the Great Lakes is likely not feasible. Provided current habitat conditions do not preclude Cisco restoration, managers could maximize the effectiveness of available production capacity by concentrating stocking efforts in historically important spawning and rearing areas, similar to the current stocking effort in Saginaw Bay, Lake Huron. Other historically important Cisco spawning and rearing areas within each lake (listed in no particular order) include: (1) Thunder Bay in Lake Huron, (2) Green Bay in Lake Michigan, (3) the islands near Sandusky, Ohio, in western Lake Erie, and (4) the area near Hamilton, Ontario, and Bay of Quinte in Lake Ontario. Our study focused entirely on Ciscoes but may provide a framework for describing future stocking needs for deepwater ciscoes.

Great Lakes↗