Lake Trout Research Articles

Improving nutritional intakes and reducing metal(loid) exposures from wild fish broth among Inuit pregnant women.

Recipes made with local country foods are central to Inuit culture and nutrition. Recipes are recommended for their different health benefits, such as a wild fish broth recipe that is said to help the baby's growth during pregnancy and with lactation. However, some country foods can have high concentrations of potentially toxic metal(loid)s such as mercury (Hg), arsenic (As) or cadmium (Cd), and it is unknown to what extent these are transferred to the broth. During pregnancy, there are higher risks of developing iron (Fe) and calcium (Ca) deficiencies. A simple way to optimize the nutrient content of recipes is by adding other ingredients like seaweed, bivalves (mussels and clams) or a Lucky Iron Fish® known to be rich in these nutrients. Using an experimental approach, nutrient (essential elements and fatty acids) and metal(loid) transfer to broth were studied by measuring their concentrations in ingredients and broth. Most fish, seaweeds and bivalves were important sources (>20% of the daily intakes) of nutrients required for healthy pregnancies. Several nutrients were transferred to the broth by these ingredients, but only fish broth was an important source of nutrients. The Lucky Iron Fish was a potential source of iron when preconditioned. Total Hg concentrations were elevated in lake trout muscles and cheeks (up to 4.5μg/g ww; >90% in methylated form) but were not a concern in other fish species. Few metal(loid)s were transferred to the broth, except arsenic (As). Total As concentrations were high in some raw seaweeds and most broths, but the less toxic organic forms were mainly found. Overall, wild fish broths were relatively low in nutrients and toxic forms of metal(loid)s. Adding local ingredients such as seaweed and bivalves could increase nutrient intake from fish broth if consumed as a whole.

Burbot Population Dynamics in Northern Lake Michigan, 2001–2023, and Predation on Newly Stocked Lake Trout by Burbot

ABSTRACTAlthough the worldwide status of burbot (Lota lota) across its Holarctic distribution has recently been assessed, adverse effects of dreissenid mussels on burbot abundance in waters invaded by mussels have not been investigated. We analyzed data from an annual spring gillnet survey to characterize burbot population dynamics in northern Lake Michigan during 2001–2023. Adult burbot abundance in northern Lake Michigan trended neither significantly upward nor downward during 2001–2023. Thus, expansion of the quagga mussel (Dreissena rostriformis bugensis) population into deeper waters of Lake Michigan during 2003–2008 had no detectable negative effects on burbot abundance. Burbot continued to feed on lake trout (Salvelinus namaycush) stocked in the Northern Refuge of Lake Michigan through 2023, which supported a hypothesis that the burbot population potentially impeded lake trout restoration in the refuge.

Acute and Subchronic Toxicity of 6PPD-Quinone to Early Life Stage Lake Trout (Salvelinus namaycush).

N-(1,3-Dimethylbutyl)-N'-phenyl-p-phenylenediamine-quinone (6PPD-Q) is a rubber-tire derivative which leaches into surface waters from roadway runoff, from tire particles and has been identified as a possible driver of urban runoff mortality syndrome in coho salmon. Sensitivity to this toxicant is highly variable across fish species and life stages. With environmental concentrations meeting or exceeding toxicity thresholds in sensitive fishes, the potential for ecologically relevant effects is significant. There is currently no data regarding the sensitivity of lake trout (Salvelinus namaycush) to 6PPD-Q. As early life stages of fishes are typically more sensitive than adults, the goal of this study was to evaluate the acute and subchronic toxicity of 6PPD-Q to early life stage lake trout. Alevins exposed from hatch until 45 days posthatch (dph) to time-weighted average 6PPD-Q concentrations ranging from 0.22 to 13.5 μg/L exhibited a 45 day median lethal dose (LC50) of 0.39 μg/L. Deformities throughout growth were observed, with a unique pooling of blood observed in the caudal fin and eye. A subsequent acute study with exogenously feeding lake trout fry determined a 96 h LC50 of 0.50 μg/L. From this study we can conclude that lake trout alevins and exogenously feeding fry are sensitive to 6PPD-Q, which underscores the relevance of this chemical to inland freshwater ecosystems.

Widespread admixture blurs population structure and confounds Lake Trout (Salvelinus namaycush) conservation even in the genomic era

Intraspecific variation is important for species’ long-term persistence in changing environments. Conservation strategies targeting intraspecific variation often rely on the identification of management or policy units below the species level based on biological differences among populations. To identify management units, this paper examines intraspecific divergence of Lake Trout (Salvelinus namaycush) in Great Slave Lake (GSL), Canada, using low-coverage whole-genome sequencing data. Specifically, we evaluate genetic differentiation and assess the relationship with morphological, mitochondrial, and putatively adaptive divergence. We show that at least three and up to five genetically distinct Lake Trout populations co-occur in GSL and exhibit differences in spatial distribution and body size, with signatures of selection. However, admixture was widespread (60% of the fish) and population structure was shallow (average FST = 0.022). These findings highlight that, even in the era of whole genome sequencing, identifying discrete management units to implement conservation efforts and policy can remain challenging in systems where gene flow among genetically and ecologically distinct populations is ubiquitous. To give more recognition to this complexity, management efforts should also focus on the area where adaptive variation is evident, and evolutionary acts are at play, to better protect species’ resilience and adaptive potential in some natural systems.

Calibrating acceleration transmitters to quantify the seasonal energetic costs of activity in lake trout.

Bioenergetics models are powerful tools used to address a range of questions in fish biology. However, these models are rarely informed by free-swimming activity data, introducing error. To quantify the costs of activity in free-swimming fish, calibrations produced from standardized laboratory trials can be applied to estimate energy expenditure from sensor data for specific tags and species. Using swim tunnel respirometry, we calibrated acceleration sensor-equipped transmitting tags to estimate the aerobic metabolic rates (ṀO2) of lake trout (Salvelinus namaycush) at three environmentally relevant temperatures. Aerobic and swim performance were also assessed. Like other calibrations, we found strong relationships between ṀO2 and acceleration or swimming speed, and jackknife validations and data simulations suggest that our models accurately predict metabolic costs of activity in adult lake trout (~5% algebraic error and ~20% absolute error). Aerobic and swim performance metrics were similar to those reported in other studies, but their critical swimming speed was lower than expected. Additionally, lake trout exhibited a wide aerobic scope, suggesting that the avoidance of waters ≥15°C may be related to selection for optimal growing temperatures. The ability to quantify the free-swimming energetic costs of activity will advance our understanding of lake trout ecology and may yield improvements to bioenergetics model.

Stable isotopes reveal trophic ontogeny in Cisco (Coregonus artedi).

Cisco (Coregonus artedi) are a widespread, cold-water zooplanktivore native to North America. Although Cisco are generally referred to as an "obligate zooplanktivore," there is some evidence that the species exhibits considerable variability in trophic niche. Here, we assessed how Cisco body size relates to trophic position, that is, trophic ontogeny. We analysed 13C and 15N isotopes from Cisco ranging from 127 to 271 mm in body length (n = 66) from Trout Lake, Vilas County, Wisconsin, USA. 15N isotopes showed smaller Cisco had a trophic position of ~3, which steadily increased to ~3.5 for larger Cisco. Further, 13C isotope signatures showed Cisco transitioned to be more pelagically reliant (lower 13C signatures). Using gillnet catch data, we found that larger Cisco were using deeper habitats than smaller Cisco. Our results support that Cisco have significant variability in trophic niche even though they are traditionally thought of as an obligate planktivore. Overall, we emphasize that researchers should be cautious when generalizing Cisco trophic function, particularly when considering the broader food web.

A transferable approach for quantifying benthic fish sizes and densities in annotated underwater images

Abstract Benthic fishes are a common target of scientific monitoring but are difficult to quantify because of their close association to bottom habitats that are hard to access. Advances in image‐acquisition technologies, machine vision and deep learning have made capturing and quantifying fishes with cameras increasingly feasible. We present a method and open‐source software called ‘FishScale’ to estimate benthic fish lengths, numeric abundance and biomass density in underwater environments assessed with down‐looking monocular images. ‘FishScale’ estimates fish abundances and size frequencies from near‐nadir monocular images where fish have already been semantically segmented. The software accounts for lens distortion, underwater magnification effects and fish body curvature to automatically estimate fish lengths and the areas of images where they were captured. Numeric and biomass density are estimated through a deterministic machine vision algorithm that requires a user‐provided length‐weight relationship for species of interest and calibration images. Results from validation studies show that lengths and weights can be estimated with high accuracy and precision for round goby (Neogobius melanostomus) captured in distorted action camera images, and from large‐bodied lake trout (Salvelinus namaycush) imaged with a machine vision camera. The real‐world utility of the approach is demonstrated in a case study estimating round goby abundances and size frequencies along a 10.7‐km transect surveyed with an autonomous underwater vehicle in Lake Michigan, USA. Our validation studies demonstrate that the approach estimates benthic and benthopelagic fish lengths and weights with little bias and good accuracy and precision for species with much different body shapes and sizes. The method is applicable to data collected using a variety of nadir imaging approaches with widespread applications to fisheries monitoring and quantification of any species or object for which nadir images and working distances between the camera and feature of interest are available.

Modeling future dissolved oxygen and temperature profiles in small temperate lake trout lakes

Modeling future dissolved oxygen and temperature profiles in small temperate lake trout lakes

Food web structure of the Lake Superior fish community in 2021–2022

The trophic linkages and ecological requirements of the Lake Superior fish community have not been assessed on a whole lake scale in over a decade. Here, we investigated the trophic dynamics across multiple species and habitat zones of Lake Superior. From April to October of 2021 and 2022, a total of five piscivore, four planktivore, and six benthivore species were collected by region and length class during bottom-trawl, standard gillnet, commercial cisco gillnet, and recreational angler surveys. To assess trophic linkages, stomach contents were measured to estimate biomass consumed and a multivariate analysis was used to assess diet composition by species, length, and region. We found a high degree of interconnectedness in the Lake Superior food web, with Mysis as a critical diet item for most fishes. Native piscivore diets varied by region and with ontogeny. Lake charr were important habitat couplers in the lake, exhibiting a diverse diet and opportunistic foraging strategy. Conversely, Pacific salmon were more restricted in their foraging. Planktivores and benthivores primarily consumed Mysis, with less reliance on Diporeia compared to previous studies. Lake whitefish and cisco were the exception to this pattern, with broader bathymetric depth distributions represented in their diets. We found the food web to be supported by a predominantly native species assemblage, with redundancies at all trophic levels

Developing a predictive model to identify Sea Lamprey parasitism on Lake Trout using biologgers

AbstractObjectiveSea Lamprey Petromyzon marinus remain problematic for Lake Trout Salvelinus namaycush restoration in the Laurentian Great Lakes. Fisheries assessments would benefit from knowledge of spatial–temporal patterns of Sea Lamprey parasitism on Lake Trout; however, such patterns are challenging to estimate from wounding rates on caught Lake Trout. Electronic tags have been used to identify distinct fish behaviors (e.g., foraging or spawning) using measurements of acceleration or heart rate. We hypothesized that Sea Lamprey attachment would elicit changes in the heart rate and swimming behavior of Lake Trout. Here, we determined whether tagging devices could record these changes and whether we could accurately predict lamprey attachment on Lake Trout using these recordings.MethodsAdult Lake Trout (n = 34) were implanted with acceleration and heart rate tags and then were subjected to Sea Lamprey parasitism within a laboratory setting. Approximately 70 different acceleration and heart rate metrics were collected and tried as predictors of lamprey attachment. The top variables were used to train random forest models and then tried on test data sets. The accuracy of these models was then validated using a jackknife approach.ResultMetrics related to body orientation and heart rate were identified as the best predictors of Sea Lamprey attachment. The best models predicted lamprey attachments with high accuracy; however, individual‐level jackknife tests resulted in less accurate cross‐individual prediction and regularly predicted false negatives. These findings may be related to individual variance in the Lake Trout response to attachment, but there was evidence that the shifting of tags after implantation impacted predictive performance, which could be remedied with adjustments during implantation.ConclusionsOur study highlights the potential to use tagging devices for quantifying Sea Lamprey attachments on Lake Trout in the wild. Further development appears necessary; however, once improved, these predictive models have the potential to generate field‐based estimates of Sea Lamprey attack rates on Lake Trout.

The influence of food web structure and foraging behaviour on visual system traits in a predatory freshwater fish

Lake trout (Salvelinus namaycush Walbaum, 1792) forages across macrohabitats (offshore vs nearshore) that likely pose different challenges to the visual system. We examined how differential foraging between macrohabitats challenges the visual system by sampling lake trout from four lakes with differing food web structures (e.g., presence/absence of cisco/smallmouth bass) and evaluating the association between nearshore energy use and visual traits. We found that lake trout foraging more nearshore had relatively larger eyes (corrected for body size) and larger optic tectum size only in lakes with the large pelagic cisco prey absent, while there was no association with these visual traits when cisco was present. Eye shape was not influenced by nearshore foraging. Our results suggest that nearshore foraging challenges the visual system more than offshore foraging but that this may be dependent on important food web structural attributes.

The potential of oviduct tags and fine-scale acoustic telemetry to reveal the timing and location of spawning in Arctic salmonids (Salvelinus spp.).

Identifying and characterizing spawning locations are paramount for the protection of critical fish habitats but can be challenging, particularly in remote locations. Using the underexplored oviduct-tagging technique, we aimed to identify the timing and location of spawning for wild Arctic char (Salvelinus alpinus) and lake trout (Salvelinus namaycush) in two high-Arctic lakes in Nunavut. Specifically, Innovasea V7 acoustic telemetry transmitters were inserted into the oviducts of 13 Arctic char and 4 lake trout, and the timing and location of tag expulsion were determined using a fine-scale positioning system. Twenty Arctic char and 20 lake trout were also tagged with abdominal V16 transmitters, and 10 of them were paired with the oviduct tags, to further study the behavior of individual fish during the spawning season. Oviduct tags from four Arctic char and one lake trout could be used to assess the timing and location of spawning. Spawning anadromous Arctic char drastically reduced their activity and remained proximate to their presumed spawning location immediately before and for months after spawning. In contrast, a non-anadromous (i.e., freshwater resident) Arctic char and a lake trout showed little to no reduction in activity around presumed spawning events. Because of the highlighted sedentary behavior of inferred spawning anadromous Arctic char implanted with both abdominal and oviduct tags, we could also infer potential spawning based on the behavior of individuals equipped only with abdominal tags. Spawning areas identified via telemetry also aligned well with Inuit knowledge of those lakes. This is the first field study to use acoustic oviduct and abdominal tags coupled with a fine-scale positioning system. Despite a limited success rate of ejection, the study reveals the strong potential of the method to study spawning habitat and timing, particularly in remote areas.

Stable isotope analysis of western Lake Superior predatory fishes, part one: Trophic niche overlap

Characterizing food web interactions between introduced and native fish predators is important to quantify niche overlap, assess predator–prey balance, and support fisheries management. Lake Superior provides an ideal setting to investigate potential trophic overlap between native top predators, lake trout (Salvelinus namaycush) and walleye (Sander vitreus), and a diverse assemblage of introduced salmonids. Angler-caught fish were used to measure trophic position and niche overlap between predatory fishes in the western arm of Lake Superior based on carbon and nitrogen stable isotope ratios (δ13C, δ15N). Within a species, we did not find consistent differences in either δ13C or δ15N values by sex, collection year, capture location, or length. Among species, the range in δ15N values was >5 ‰, indicating that these species occupy ∼2 trophic positions, with dietary reliance ranging from primarily invertebrates to primarily fish, whereas the range in δ13C values indicated dietary reliance on a mix of pelagic and benthic prey. Combined, the δ13C and δ15N values revealed siscowet lake trout as the apex predator having a distinct trophic niche, while walleye and lean lake trout were intermediate trophic position predators with overlapping isotopic niches, and introduced salmonids were the lowest trophic position predators with overlapping trophic niches. Overlapping trophic niches indicated similar resource reliance and habitat occupancy among native lake trout and walleye, as well as among introduced salmonids, but less so between native and introduced predators.

Comparative QSAR and q-RASAR modeling for aquatic toxicity of organic chemicals to three trout species: O. Clarkii, S. Namaycush, and S. Fontinalis

Oncorhynchus clarkii, Salvelinus fontinalis, and Salvelinus namaycush are vital trout species in North America, crucial for maintaining ecological balance, economic stability, and human health. These species thrive in cold, unpolluted waters and are highly vulnerable to contaminants. Given the rapid proliferation of industrial organic chemicals, traditional in vivo toxicity testing methods are inadequate to ensure timely and comprehensive risk assessments. Therefore, we employed in silico tools, namely Quantitative Structure-Activity Relationship (QSAR) and Quantitative Read-Across Structure-Activity Relationship (q-RASAR), to efficiently predict the aquatic toxicity of chemicals. Utilizing acute median lethal concentration (LC50) data from the US EPA’s ToxValDB, we developed the first-ever species-specific QSAR and q-RASAR models. The q-RASAR models outperformed traditional QSAR models by achieving higher internal and external statistical quality for each species. Key toxicity-determining descriptors included electrotopological state indices, autocorrelation descriptors, and similarity-based RASAR descriptors. For O. clarkii, the presence of chlorine atoms and rotatable bonds significantly influenced toxicity. S. fontinalis toxicity was strongly affected by polarizability, and van der Waals volumes, while S. namaycush showed sensitivity to weak hydrogen bond acceptors and topological complexity. The models predicted the toxicity of 1172 external compounds, identifying the most and least toxic chemicals for each species. This study not only offers the first comprehensive q-RASAR models for predicting trout species-specific toxicity but also provides novel insights into species-specific toxicological modes of action. The results contribute significantly to chemical screening and prioritization in aquatic risk assessments, effectively filling critical data gaps and advancing predictive modeling techniques.

Food web structure across basins in Lake Erie, a large freshwater ecosystem

Understanding spatial variation of aquatic food web structure and how ecosystem boundaries should be delineated is important. Here, we investigated the spatial variation in food web structure within Lake Erie across its three basins using δ13C and δ15N. Fish and lower trophic level composition were similar but differences in food web structure were observed between basins. The food web in the central basin had the smallest δ13C and δ15N range and total area based on stable isotope values by the aquatic community, likely due to chronic epibenthic hypoxia in the summer that affects fish habitat and resources. The largest δ15N range was in the east, driven by the high trophic position of lake trout present in this deepest basin. The western basin had the largest mean distance to the centroid (CD) of all three basins, indicating a large trophic diversity, probably due to high nutrient loadings and productivity. This research revealed spatial variability of food web structure in large lake ecosystems and the importance of considering smaller sub-units, such as basin, in large lakes.

Lake Trout (Salvelinus namaycush) origin, behavior, and habitat residency in Sherbrooke Lake, Nova Scotia, Canada

Lake Trout (Salvelinus namaycush) origin, behavior, and habitat residency in Sherbrooke Lake, Nova Scotia, Canada

Consumption of non-native rainbow smelt (Osmerus mordax) is associated with changes in the heart morphology of wild lake trout (Salvelinus namaycush)

The heart is an essential organ for survival and reproduction across all animals. In particular, salmonine fishes display vast variability in heart morphology across and even within populations, which often reflects their functional requirements for cardiac output and aerobic capacity. However, changes in heart morphology are not always adaptive, and other factors such as diet can influence heart morphology. A growing concern is the consumption of the thiamine (vitamin B1)-degrading enzyme thiaminase found in some prey species such as rainbow smelt ( Osmerus mordax (Mitchell, 1814)). Here, we investigate the association between rainbow smelt consumption and heart morphology in wild lake trout ( Salvelinus namaycush (Walbaum in Artedi, 1792)) found in the Sudbury Basin (Ontario, Canada). We found that rainbow smelt consumption is associated with increases in ventricular mass, reductions in ventricular fluid content, and alterations in the allometry of myocardia. We discuss the potential impacts of these changes in heart morphology for the conservation of the species.

Modeling regional occupancy of fishes using acoustic telemetry: a model comparison framework applied to lake trout

Acoustic telemetry is a common tool used in fisheries management to estimate fish space use (i.e., occupancy) from a local habitat scale to entire systems. Numerous analytical models have been developed to estimate different aspects of fish movement from telemetry datasets, yet evaluations of model performance and comparisons among models are limited. Here, we develop a framework to evaluate model estimates of regional occupancy in large and fragmented systems using an acoustic receiver array in Lake Champlain. We simulated the tracks of 100 acoustically tagged fish using a random walk function and created detection events based on receiver positions and distance-based detection probability. Regional occupancy for the simulated data was estimated by six movement models that ranged in analytical complexity, and results were compared to the true distributions for each simulated track to evaluate model error. The six movement models included: (1) a basic residency index using detections alone; (2) a residency index using last-observation-carried-forward; (3) a centers of activity model; (4) linear and non-linear interpolations (i.e., least-cost paths); and (5 and 6) two dynamic Brownian bridge movement models generated using separate packages in R. We developed a model selection process to compare model performance and select the optimal analysis based on simulation error. This process showed significant differences in model performance among the six movement models based on model error. Overall, the model generating least-cost paths using linear and non-linear interpolations consistently provided the most accurate regional occupancy estimates. Based on these simulation results, we applied this model to a case study that evaluated patterns in the regional distribution of stocked lake trout (Salvelinus namaycush) in Lake Champlain, which demonstrated distinct regional occupancy of two stocked lake trout groups. These results demonstrate potential for large variability in interpretation of acoustic telemetry data for describing regional fish distribution dependent on the analytical method used.

An Invasive Predator Substantially Alters Energy Flux Without Changing Food Web Functional State or Stability

ABSTRACTUnderstanding how invasive species affect the stability and function of ecosystems is critical for conservation. Here, we quantified the effect of an actively suppressed invasive species on the Yellowstone Lake ecosystem using a food web energetics approach. We compared energy flux, functional state, and stability of four food web states: a pre‐invasion network and three post‐invasion networks undergoing active invasive species suppression, namely, initial invasion, expansion, and decline. Invasion caused ≥ 25% change (±) in energy flux for most consumers, and total flux increased twofold post‐invasion. Flux to the species of conservation concern, Yellowstone cutthroat trout (Oncorhynchus virginalis bouvieri), was 2.8 times less post‐invasion versus pre‐invasion, whereas invasive lake trout (Salvelinus namaycush) flux was up to 17.3 times higher compared to the initial invasion network. The dominant functional state and food web stability did not change post‐invasion, likely due to introduction of a generalist predator and the stabilizing effect of suppression. Lake trout invasion in Yellowstone Lake caused large changes to energy flux, shifting dominant fluxes away from the species of conservation concern, despite not changing functional state or stability. We demonstrate that changes in energy flux may signal invasions in ecosystems, but functional state or stability may not necessarily reflect the magnitude of invasion influences. For invaded fish communities, a better understanding of how the invasive species control the food web beyond just the direct influence on prey can be achieved by investigating energy flux, functional state, and food web stability. Furthermore, evaluating the effect of suppression beyond the invasive species can demonstrate the far‐reaching value of suppression management actions for conservation.

Lake Superior fish community and fisheries, 2001–2022: An era of stability

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.