Lake Saint-Pierre Research Articles

Establishing perennial strips in a cultivated floodplain for habitat restoration: monitoring over 4 years and success drivers

Floodplains, one of the most biologically diverse and productive ecosystems, are under threat from intensive crop production. Implementing perennial strips alongside agricultural ditches and streams could reduce negative impacts of intensive agriculture and restore wildlife habitats in cultivated floodplains. To successfully set up perennial strips, it is important to understand the parameters that drive their establishment. Here we assessed the establishment success of reed canarygrass (RCG; Phalaris arundinacea) strips in the lake Saint Pierre (LSP) floodplain, Québec, Canada by monitoring RCG biomass and vegetation height over 4 years and identify the factors driving its establishment. A total of 26 RCG strips across six municipalities of LSP were monitored. Biomass and vegetation height of RCG increased over time to reach an average of 5048 kg/ha in year 4 and 104 cm in year 3 in established strips. The RCG established successfully in 62% of surveyed plots and three environmental parameters explained 61% of this success. Establishment of RCG was most successful when a first rain came right after seeding (<3 days). High clay content and low elevation were associated with establishment failures. Overall, our results highlight the ability of RCG strips to restore dense perennial vegetation cover in cultivated floodplain, thereby providing suitable habitat for fish spawning during spring floods. This study provides significant insight into the drivers of establishment of perennial grass strips in highly constrained cultivated areas such as floodplains.

Anisakid nematode larvae in freshwater fishes in the St. Lawrence River (Québec, Canada)

Anisakid nematodes were observed in freshwater and anadromous fishes in the St. Lawrence River, Québec, Canada. Fish were caught at different locations across a 250 km gradient in the St. Lawrence ecosystem covering freshwater and estuarine habitats. Depending on the sampling sites, nematode prevalence ranged from 30% to 58% for sauger (Sander canadensis) and was 43% for Atlantic tomcod (Microgadus tomcod). For walleye (Sander vitreus), parasites were found only in a fluvial Lake (Lake Saint-Pierre) of the St. Lawrence River, with a prevalence of 23%. In all sampling sites, mean abundance of nematodes in the flesh was higher in sauger than in walleye. Presence of nematodes was significantly correlated with fish total length for walleye, sauger and Atlantic tomcod. Sealworm, Phocanema decipiens s.s., and whaleworm, Anisakis simplex s.s., were found and identified by molecular analysis in sauger and walleye in a fluvial lake (Lake Saint-Pierre), the fluvial estuary and the upper estuary of the St. Lawrence River, while Atlantic tomcod were found infected in a freshwater river tributary (Sainte-Anne River) during spawning.This is the first record of Ph. decipiens s.s. in a non-anadromous freshwater fish. The presence of sealworm and whaleworm in walleye and sauger is attributed to their forays into the brackish waters of the fluvial estuary and suggest large scale migrations between the brackish and the fresh waters of the St. Lawrence River.

The “right‐to‐farm” in Lac Saint‐Pierre (Québec, Canada) floodplains: Are problem‐framing processes able to foster conservation conflict resolution?

AbstractUsing qualitative data, we investigate the impact of the problem‐framing process on stakeholder mobilization for fish habitat restoration and its influence on transforming agricultural practices in floodplains. Problem‐framing involves defining and delineating a problem to suggest practical and measurable solutions for addressing it. We are examining how the conservation conflict changes over time in Lac Saint‐Pierre (LSP), part of the St. Lawrence River Basin in Québec, Canada. Such conflicts arise when there are differing perspectives, interests, or actions regarding conservation goals and objectives. In recent decades, the LSP floodplain has undergone significant changes, particularly the conversion of perennial crops to intensive annual crops, which are deemed incompatible with the ecological needs of yellow perch. This species has experienced a notable decline in LSP since the 1990s, prompting Québec authorities to impose a moratorium on yellow perch fishing in 2012 to safeguard stocks. This moratorium has catalyzed efforts at the policy level to restore its habitat. However, it has also engendered tensions between agricultural activities and conservation endeavors aimed at restoring yellow perch habitat, constituting the conservation conflict under investigation. To investigate this issue, we adopt a post‐normal science approach characterized by reflexivity, inclusivity, and transparency in addressing epistemological and ontological uncertainties among LSP stakeholders. Our findings offer insights into stakeholders' perspectives on the problem‐framing process and its outcomes, highlighting both supportive actions enhancing the effectiveness of certain strategies among LSP stakeholders and barriers hindering their mobilization. These results underscore the importance of incorporating diverse stakeholder perspectives during the problem‐framing process to enhance the robustness of the science–policy interface.

Conflicting perspectives on ecosystem conservation in a cultivated floodplain: The role of science and the challenge of pluralism in decision‐making in Lac Saint‐Pierre (Quebec, Canada)

AbstractBy generating and explaining facts, science holds an important role in environmental policy decision‐making. However, scientific knowledge is often framed as objective and neutral in policy debates, which can be challenged by stakeholders who have a different view of the issue. To counter this situation, we propose a novel scientific approach to analyze problems that are highly contested and seem difficult to resolve, that is, wicked problems. Our study combined post‐normal science and environmental justice perspectives to shed light on a wicked problem—the largely unsuccessful efforts to rehabilitate yellow perch stocks in Lac Saint‐Pierre (LSP), Quebec, Canada. The combination of these two perspectives allows us to investigate the causes of the decrease of yellow perch stocks and the social and institutional barriers to rehabilitation—which can only be overcome if the injustice perceived by different stakeholders is overcome. Our study presents an approach that addresses uncertainties, integrates various knowledge forms, reassesses decision‐making procedures, and highlights inequalities within a specified territory. The research also underlines the importance of the qualitative dimension in the development of knowledge and the need to address equity in the development of environmental policies.

Using remote sensing to assess how intensive agriculture impacts the turbidity of a fluvial lake floodplain

Lake St-Pierre is set in the largest floodplain in the province of Quebec, Canada, and is a rich ecosystem of great ecological importance. However, Lake St-Pierre has seen its ecological integrity deteriorate in recent decades, largely due to the development of agriculture in and around its floodplain. This study uses a simple turbidity retrieval model (NIR and RED reflectances from Sentinel-2) to quantify the impact of land use on water turbidity within the lake floodplain during the 2019 and 2020 spring flood. Using a linear mixed effect model, we assessed how land use (wet meadows, cultivated grasslands, soybean, corn fields) impacts turbidity retrieved from Sentinel-2. Water turbidity was found to increase with the level of agricultural perturbations. During the severe and long 2019 flood, the turbidity was 5% higher over cultivated grassland fields, 35% higher over soybean fields and 70% higher over corn fields, compared to wet meadows. For 2020, a comparatively drier year, the corresponding impacts were 9% for cultivated grassland fields, 65% for soybean fields and 93% for corn fields. However, land use only explained 4% (2019) and 5% (2020) of the water turbidity spatiotemporal variance, which was instead mostly driven by the sediment load coming from upstream watersheds. Our results indicate that, despite complex processes driving water mass movements in the floodplain, intensive farming practices lead to higher water turbidity compared to natural lands. This study provides evidence that intensive agriculture impacts the water quality in a critical moment for the long-term health of the Lake St-Pierre.

Multiresidue method for the fast and efficient analysis of current-use pesticides in streambed sediments using pressurized liquid extraction

A multiresidue method for the fast and efficient analysis of current-use pesticides in streambed sediments is reported. The method employs pressurized liquid extraction (PLE) for the automated extraction of pesticide residues from small quantities (5 g) of lyophilized sediment samples. Various PLE parameters, including the extraction solutions and oven temperature, were optimized for thirty diverse current-use pesticides (CUPs) known to be commonly applied to corn and soybean monoculture crops. Following extraction, samples were analyzed with a fast and simplified quantitative multiresidue analytical method using ultra high-performance liquid chromatography tandem mass spectrometry (UHPLC-MS/MS) with online solid phase extraction (SPE) on a hydrophilic-lipophilic balance (HLB) column. Validation of the method demonstrated acceptable recoveries (avg 41.4 %) comparable with other multiresidue methods for sediments, reliable intraday (<13 %) and interday (<24 %) repeatability, reasonable matrix effects (avg −54 %), and low LODs (avg 0.53 ng g−1 dw) and LOQs (avg 2.18 ng g−1 dw) given the complexity of the sediment matrix. The method was applied to 119 streambed sediment samples collected from agriculture-adjacent headwater streams near Lac Saint-Pierre in Québec, Canada to demonstrate the utility of the method. Fourteen of the thirty target analytes were detected within the samples, including nine herbicides, two insecticides, and three fungicides. To the best of our knowledge, an equally simple and efficient multiresidue method for the quantitative analysis of diverse CUPs in streambed sediments using PLE and UHPLC-MS/MS with online SPE has not yet been reported in the literature. This method helps to reduce labour and material inputs, avoids excessive sample manipulation, and allows for fast quantitative analysis of trace pesticide residues in streambed sediments, with the potential for application to other contaminants of emerging concern.

Data on phenological changes of benthic primary producers from Lake Saint-Pierre (1982-2019), Lake Müggelsee (2000-2021), Limnotron warming experiments and a literature synthesis

Data on phenological changes of benthic primary producers from Lake Saint-Pierre (1982-2019), Lake Müggelsee (2000-2021), Limnotron warming experiments and a literature synthesis

Significance of chemical affinity on metal subcellular distribution in yellow perch (Perca flavescens) livers from Lake Saint-Pierre (QUEBEC, Canada)

The subcellular partitioning approach provides useful information on the location of metals within cells and is often used on organisms with high levels of bioaccumulation to establish relationships between the internal concentration and the potential toxicity of metals. Relatively little is known about the subcellular partitioning of metals in wild fish with low bioaccumulation levels in comparison with those from higher contaminated areas. This study aims to examine the subcellular partitioning of various metals considering their chemical affinity and essentiality at relatively low contamination levels. Class A (Y, Sr), class B (Cu, Cd, MeHg), and borderline (Fe, Mn) metal concentrations were measured in livers and subcellular fractions of yellow perch (n = 21) collected in Lake Saint-Pierre, QC, Canada. The results showed that all metals, apart from MeHg, were distributed among subcellular fractions according to their chemical affinity. More than 60% of Y, Sr, Fe, and Mn were found in the metal-sensitive fractions. Cd and Cu were largely associated with the metallothionein-like proteins and peptides (60% and 67% respectively) whereas MeHg was found mainly in the metal-sensitive fractions (86%). In addition, the difference between the subcellular distribution of Cu and other essential metals like Fe and Mn denotes that, although the essentiality of some metals is a determinant of their subcellular distribution, the chemical affinity of metals is also a key driver. The similarity of the subcellular partitioning results with previous studies on yellow perch and other fish species from higher contaminated areas supports the idea that metals are distributed in the cellular environment according to their chemical properties regardless of the bioaccumulation gradient.

Monitoring Water Turbidity in a Temperate Floodplain Using UAV: Potential and Challenges

The Lake Saint-Pierre (LSP) is a wide (≈300 km2) and shallow (≈3 m) lake created through a widening of the St. Lawrence River. Each spring, freshet makes it the largest floodplain in the province of Quebec. Agricultural practices in the littoral increase the water turbidity, which deteriorate the habitat’s quality of many fish species. However, measuring spatio-temporal turbidity patterns in the LSP floodplain remain difficult because turbidity is highly variable in space and time. This study aims to evaluate the potential to use an Unmanned Aerial Vehicle (UAV) to measure the water turbidity in the LSP’s floodplain. The results show that the UAV can efficiently measure the variation of turbidity in the LSP with a RMSE of 28.22 FNU. We also compared the turbidity retrieved from UAV with those retrieved from Sentinel-2 observations. The results show that the two models are comparable, even if Sentinel-2 yields better results. However, challenges remain when using UAV for turbidity monitoring, such as software limitations for mosaics creation over large water bodies. Nevertheless, the high spatial and temporal information can provide insights into the complex water turbidity patterns which characterize floodplains. The method could help land use management to improve the water quality of these ecosystems.

Pesticides Inhibit Retinoic Acid Catabolism in PLHC-1 and ZFL Fish Hepatic Cell Lines.

The population of yellow perch (Perca flavescens) in lake Saint-Pierre (QC, Canada) has been dramatically declining since 1995 without any sign of recovery. Previous studies have shown disrupted retinoid (vitamin A) metabolic pathways in these fish, possibly due to the influence of pesticides. Our study aimed to evaluate the impact of some herbicides and neonicotinoids on retinoic acid catabolism in the fish hepatic cell lines PLHC-1 and ZFL. We hypothesized that pesticides accelerate the catabolism of retinoic acid through oxidative stress that exacerbates the oxidation of retinoic acid. Results obtained with talarozole, a specific CYP26A1 inhibitor, and ketoconazole, a generalist inhibitor of cytochrome-P450 enzymes, revealed that CYP26A1 is mainly responsible for retinoic acid catabolism in ZFL but not PLHC-1 cells. The impacts of pesticides on retinoic acid catabolism were evaluated by incubating the cells with all-trans-retinoic acid and two herbicides, atrazine and glyphosate, or three neonicotinoids, clothianidin, imidacloprid, and thiamethoxam. Intracellular thiols and lipid peroxidation were measured following pesticide exposure. The possible causal relation between oxidative stress and the perturbation of retinoic acid catabolism was investigated using the antioxidant N-acetylcysteine. The data revealed that pesticides inhibit retinoic acid catabolism, with the involvement of oxidative stress in the case of atrazine, imidacloprid, and thiamethoxam but not with clothianidin and glyphosate. Pesticides also affected the isomerization of all-trans-retinoic acid over time, leading to an increased proportion of active isomers. These results hint at a possible perturbation of retinoic acid catabolism in fish living in pesticide-contaminated waters, as suggested by several in vivo studies. Such a disruption of retinoid metabolism is worrying, given the numerous physiological pathways driven by retinoids.

Hydrological control of a floodplain subsidy to littoral riverine fish

Ecological subsidies have been hypothesized to be key factors affecting the dynamics of the recipient ecosystems. We assessed the impact of the flood regime on the assimilation of a trophic subsidy produced in the floodplain of a large fluvial lake, Lake Saint-Pierre (Quebec, Canada) on five invertivore littoral fish species (yellow perch (Perca flavescens), pumpkinseed (Lepomis gibbosus), bridle shiner (Notropis bifrenatus), golden shiner (Notemigonus crysoleucas), and banded killifish (Fundulus diaphanus)). We hypothesized that the incorporation of floodplain-derived carbon into fish biomass and individual fitness would increase in years with higher magnitude and longer duration floods. Studying four consecutive years with contrasting spring-flood events, we used a stable isotope mixing model to estimate floodplain contribution, and linear mixed models to analyze the impact of hydrology on floodplain contribution and fish body condition. Floodplain and main river’s invertebrates exhibited statistically distinct isotopic ratios (t test: p value &lt; 0.001). Floodplain contribution and body condition were positively correlated with flooding intensity and duration for all species. Body condition was positively correlated with the assimilation of floodplain-subsidy for golden shiner and banded killifish. Our study identified flooding intensity as a main driver influencing the assimilation of floodplain-derived carbon by littoral fish and their fitness in a large river ecosystem.

Biological markers to establish a relationship between the health status of the St. Lawrence River yellow perch (Perca flavescens) with a gradient of anthropogenic disturbances

Since the mid-1990s, the decline of the yellow perch population of Lake Saint-Pierre (hereinafter LSP) in Quebec, Canada has been the subject of several research programs. The combined effect of habitat deterioration, the presence of invasive species, and poor water quality negatively affected the yellow perch population in this lake. In 2013, we sampled yellow perch (larvae, juveniles and adults) at six sites along the St. Lawrence River representing a gradient of increasing human influences from upstream to downstream and measured several biomarkers including retinoid compounds (vitamin A). In the most contaminated sites (LSP, north and south shores), we found that retinoid stores were decreased in all three stages of development. To corroborate these results and to test other biomarkers, we once again sampled yellow perch (adults only) from the same sites. Results from our 2014 and 2015 samplings confirmed that LSP yellow perch appeared to be at a disadvantage compared to fish from upstream populations. Individuals from LSP have lower acetylcholinesterase (AChE) activity as well as lower retinoid levels in liver and plasma. These fish were also marked by lower levels of antioxidants such as lycopene and vitamin E. A discriminant analysis of this set of results confirmed that the yellow perch of the LSP could be easily discriminated from those of the other sites (2014 and 2015) on the basis of liver retinoid and, to a lesser extent, of the liver tocopherol and protein concentration of the muscle, as well as AChE activity and DROH (all-trans-3,4-dehydroretinol) measured in plasma.

How intensive agricultural practices and flow regulation are threatening fish spawning habitats and their connectivity in the St. Lawrence River floodplain, Canada

Hydrological and land use changes for human purposes, have resulted in the increased fragmentation of river landscapes and the loss of aquatic habitats, leading to profound changes in fish diversity and productivity. In the fluvial Lake Saint-Pierre (St. Lawrence River, Canada), we studied how agricultural practices and water-flow regulation have impacted the area and connectivity of spawning habitats of northern pike (Esox lucius). Northern pike spawning and nursery habitats were modelled over a 49-year period (1965–2013) to estimate effective spawning area under four contrasting hydrological conditions. Simulations coupled with land cover analyses revealed that natural flow conditions historically favourable for fish reproduction (high and stable water flows) have been lost due to human activities. The highest potential for reproduction and habitat connectivity have been lost due to (1) intensive agriculture and ploughing of natural vegetation in the upper floodplain that overlaps suitable spawning areas for northern pike, and (2) flow regulation that has lowered and shortened spring floods and dried spawning grounds more frequently. To restore the St. Lawrence River functions, we propose to reconvert the portion of the floodplains that is vital to fish, but is currently used by intensive agriculture, into natural wetlands or perennial crops and to restore a more natural flow regime by extending the duration of floods between spawning and nursery periods. The highest priority for habitat restoration should target the most effective and recurrent spawning habitats, ditch and stream networks, and connected managed wetlands.

Linking fisheries to land use: How anthropogenic inputs from the watershed shape fish habitat quality

Aquatic ecosystems are increasingly threatened by anthropogenic stressors, both at local and larger scales. For instance, runoff from intensively cultivated areas leads to higher nutrient and sediment concentrations deteriorating water quality, which potentially trigger trophic state changes. Unfortunately, we have a poor understanding of the complex relationships linking water quality degradation and different ecosystem components. Here we analyze the long-term cascading effects of several anthropogenic stressors on both submerged aquatic vegetation (SAV) and the key traits of an exploited yellow perch (Perca flavescens, YP) population from the watershed of Lake Saint-Pierre — the largest fluvial lake of the St. Lawrence River (Québec, Canada). Lake Saint-Pierre drains one of the most impacted watersheds in Eastern Canada and had sustained a YP fishery (worth up to 10 M$ CAN/year) until the population collapsed in the mid-1990s. SAV abundance has declined since the 1980s, partially overlapping with the YP collapse. Within a structural equation modeling framework, we tested the links between changes in both SAV abundance and the YP fishery with abiotic stressors acting at both local and larger scales. Our results show that both SAV and YP declines are causally associated with anthropogenic nutrient and sediment loadings from the watershed. The decline of YP landings is also explained by a reduction in SAV abundance and YP juvenile growth, mainly caused by a sharp decrease in water transparency over the last decades. These results suggest a causal association between environmental degradation due to nutrients and sediments and different components of the trophic aquatic network. Such an integrative approach is crucial for the development of management strategies that consider cultivated lands and aquatic systems as a continuum rather than separate compartments. SAV restoration is thus a critical feature contributing to water depuration and promoting the recovery of fish populations threatened by habitat degradation.

The pitchfork or the fishhook: a multi-stakeholder perspective towards intensive farming in floodplains

When conservation conflicts occur, the recognition of a plurality of perspectives among the stakeholders makes it possible to better understand the divergences and convergences between the parties. In this research, Q methodology was used to explore different stakeholder views on management issues surrounding intensive farming in the floodplain of Lac Saint-Pierre (Quebec, Canada), a UNESCO biosphere reserve and a RAMSAR conservation site. In recent decades, Lac Saint-Pierre has undergone many changes in its floodplain, notably through the conversion of perennial crops to more intensive annual crops considered incompatible with aquatic life by the conservation community and current agri-environmental laws. This research highlighted three perspectives related to the standing of intensive farming in Lac Saint-Pierre’s floodplain: pro-conservation, pro-agriculture and conflict between agriculture and conservation in the floodplains. This research illustrates the socio-ecological complexity behind intensive farming in floodplains and the need for representativeness of the main perspectives during negotiations between the parties.

Measuring Recreation Benefit Loss under Climate Change with Revealed and Stated Behavior Data: The Case of Lac Saint-Pierre World Biosphere Reserve (Québec, Canada).

Based on a case study carried out on the Lac Saint-Pierre (LSP) World Biosphere Reserve (Québec, Canada), this paper estimates ecosystem service loss, more precisely the loss related to cultural and recreational activities of the LSP due to the fall of its water level under the pressure of climate change. We measure two dimensions of this loss. As a first step, the extrapolation of our representative survey reports $100 million annual loss in terms of recreation revenue due to the trip reduction to LSP, which is about 60% of current level. Subsequently, the travel-cost data and the contingent behavior data are combined in a revealed and stated behavior panel random-effect estimation, which reports an additional loss measured by consumer surplus that visitors can obtain from their trips up to $232 million, signifying 42% of reduction in their current value.

Mercury and selenium distribution in key tissues and early life stages of Yellow Perch (Perca flavescens)

Whereas early life stages are usually considered as particularly sensitive to both organic and inorganic contaminants, field studies assessing contaminant bioaccumulation in these stages are scarce. Selenium (Se) is thought to counteract Hg toxic effects when it is found at Se:Hg molar ratios above 1. However, the variation of this ratio in key fish tissues of different early life stages is mostly unknown. The present study therefore aimed to assess Hg and Se content in gravid female tissues (gonads, muscle, liver, gut, and brain) and different life stages (egg masses, newly hatched larvae (NHL), larvae and juvenile) of Yellow Perch (YP) in a large fluvial lake (Lake Saint-Pierre, Québec, Canada). Se:Hg molar ratios were measured for each compartment in order to fill associated knowledge gaps. Total Hg (THg) and methylmercury (MeHg) concentration varied between tissue according to the following trend: Muscle > Liver > Gut > Brain > Gonads. During YP early life stages, MeHg values increased according to an ontogenetic pattern (mg/kg dw) (mean ± SEM): Egg masses (0.01 ± 0.002) < NHL (0.015 ± 0.001) < Larvae (0.14 ± 0.01) < Juveniles (0.18 ± 0.01). Se concentrations in different YP tissues showed the following trend (mg/kg dw) (mean ± SEM): Gut (3.6 ± 0.1) > Liver (2.5 ± 0.1) > Gonads (1.92 ± 0.06) > Brain (1.26 ± 0.03) > Muscle (1.23 ± 0.06). In YP early life stages, Se concentrations were highest in NHL (3.0 ± 0.2), and then decreased as follows: Egg masses (2.8 ± 0.1) > Larvae (1.37 ± 0.04) > Juveniles (0.93 ± 0.05). Se:Hg molar ratios varied considerably and were systematically above 1. This is the first study to simultaneously report Hg and Se bioaccumulation through fish life cycle.

Seasonality of a Floodplain Subsidy to the Fish Community of a Large Temperate River

This study examines the temporal and spatial variability of the floodplain trophic contribution to the fish community of Lake Saint-Pierre, a large (≈ 300 km2), shallow (≈ 3 m) widening of the St. Lawrence River (Quebec, Canada). We hypothesized that floodplain contribution to fish diet would be maximal during the early growing period following the seasonal flood and at sites located closest to the floodplain. Carbon stable isotope ratios (δ13C) of invertebrates and 35 fish species were analyzed at the beginning and at the end of two growing seasons, at increasing distances from the floodplain. Floodplain contribution, in the form of exported aquatic invertebrates, was estimated at the fish community (littoral versus main river), species and individual fish level, using a stable isotopic mixing model and a linear mixed model selection. As hypothesized, fish captured in the early part of the growing season near the floodplain benefitted from the largest floodplain contribution, which decreased during the late growing season. In addition, floodplain contribution differed among fish species, being higher in small or immature littoral species (northern pike, yellow perch, blackchin and golden shiners) than for larger taxa inhabiting the main river channel (shorthead redhorse, white sucker and channel catfish). Our study revealed that floodplain production during the early growing season represents a key food resource to a large portion of the riverine food web, thus highlighting the essential role of the floodplain in human-altered temperate rivers.

The fish or the egg: Maternal transfer and subcellular partitioning of mercury and selenium in Yellow Perch (Perca flavescens)

Mercury (Hg) is a trace element of particular concern since it is ubiquitous in the environment and because its methylated form (MeHg) readily bioaccumulates and biomagnifies in food webs. This latter process leads to elevated Hg concentrations in fish and may thus induce toxicity. Maternal transfer of bioaccumulated contaminants to offspring is a suggested mechanism of impaired reproductive success in fish. The purpose of this study was to assess the toxicity potential of Hg during maternal transfer in Yellow Perch from Lake Saint-Pierre (Quebec, Canada) using a subcellular partitioning approach. We also evaluated potential protective effects of selenium, as this element has been shown to alleviate Hg toxicity through sequestration. A customized subcellular partitioning protocol was used to separate liver and gonad of Yellow Perch into various subcellular fractions. Results show that, in the liver, MeHg was primarily (51%) associated to the subcellular fraction containing cytosolic enzymes. Furthermore, 23% and 15% of MeHg was found in hepatic and gonadal mitochondria, respectively, suggesting that Yellow Perch is not effectively detoxifying this metal. There was also a strong relationship (R2 = 0.73) between MeHg bioaccumulation in the liver and MeHg concentrations in gonadal mitochondria, which corroborates the potential risk linked to MeHg maternal transfer. On the other hand, we also found that selenium might have a protective effect on Hg toxicity at a subcellular level. In fact, Se:Hg molar ratios in subcellular fractions were systematically above 1 in all tissues and fractions examined, which corresponds to the suggested protective threshold. This study provides the first assessment of subcellular Se:Hg molar ratios in fish. Since early developmental stages in aquatic biota are particularly sensitive to Hg, this study represents a step forward in understanding the likelihood for toxic effects in wild fish through maternal transfer.

RNA-sequencing to assess the health of wild yellow perch (Perca flavescens) populations from the St. Lawrence River, Canada

This study aimed to better understand in situ cumulative effects of anthropogenic stressors on the health of St. Lawrence River (QC, Canada) yellow perch populations using high-throughput transcriptomics and a multi-biological level approach. Fish were collected in the upstream fluvial Lake Saint-François (LSF) with low degree of environmental perturbations; Lake Saint-Louis (LSL) considered having a moderate degree of anthropogenic stressors, and Lake Saint-Pierre (LSP) a sector where the perch population has been severely declining. Morphometric results indicated that fish from the downstream LSP showed lower body condition compared to LSF and LSL. Liver transcriptomic responses were assessed by RNA-sequencing. Two hundred and eighty genes were over-transcribed in LSP perch while 200 genes were under-transcribed compared to LSF and LSL. In LSP fish, genes transcripts related to reproduction, retinol, iron, thyroid hormones, oxidative stress, lipid metabolism and immune functions were among the most abundant suggesting that multiple metabolic and physiological pathways were impacted by environmental stressors at this site. Inhibition of liver superoxide dismutase, catalase and glutathione S-transferase activities were also observed at the cellular level. Overall, identified impacted biological pathways in perch from LSP may help understand the precarious state of this population and identify the factors inhibiting its recovery.