Hamilton Harbour Research Articles

Application of telemetry-based fish habitat models to predict spatial habitat availability and inform ecological restoration.

Conservation decisions surrounding which fish habitats managers choose to protect and restore are informed by fish habitat models. As acoustic telemetry has allowed for improvements in our ability to directly measure fish positions year-round, so too have there been opportunities to refine and apply fish habitat models. In an area with considerable anthropogenic disturbance, Hamilton Harbour in the Laurentian Great Lakes, we used telemetry-based fish habitat models to identify key habitat variables, compare habitat associations among seasons, and spatially identify the presence distribution of six fish species. Using environmental data and telemetry-based presence-absence from 2016 to 2022, random forest models were developed for each species across seasons. Habitat variables with the highest relative importance across species included fetch, water depth, and percentage cover of submerged aquatic vegetation. The presence probability of each species was spatially predicted for each season within Hamilton Harbour. Generally, species showed a spatial range expansion with greater presence probability in the fall and winter to include parts of the harbor further offshore, and a range contraction in the spring and summer toward the nearshore, sheltered areas, with summer having the most limited habitat availability. Greater habitat suitability was predicted in western Hamilton Harbour for the majority of species, whereas the east end was less suitable and may benefit from habitat restoration. These types of fish habitat models are highly flexible and can be used with a variety of data, not just telemetry, and should be considered as an additional tool for fish habitat and fisheries managers alike.

From Man vs. Nature to Environment vs. Budget - The Shifting Battles in the History of Pollution and Toxicity in Hamilton Harbour

Hamilton Harbour is the principle port serving South Western Ontario and the Niagara Peninsula region with two of Canada’s largest steel manufacturers occupying the waterfront. As early as the 1860s fishery inspectors in Hamilton noted that fish tasted of coal, and that there were dead ducks and small animals that were coated in oil from refineries. In the 1950s the Hamilton Harbour was deemed unfit for recreational use and, even today, has yet to be delisted from the International Joint Commission’s Area of Concerns designations list. Giglia’s article seeks to add to the growing scholarship on the environmental history of Ontario. She analyzes historical sources of pollution and shows how they have affected Hamilton Harbor’s ecology. Furthermore, Giglia weighs the efforts and effectiveness of specific groups in their attempt to delist the Hamilton Harbour from the Area of Concerns designation list.

Distribution and trophodynamics of substituted diphenylamine antioxidants and benzotriazole UV stabilizers in a freshwater ecosystem and the adjacent riparian environment.

Substituted diphenylamine antioxidants (SDPAs) and benzotriazole UV stabilizers (BZT-UVs) are industrial additives of emerging environmental concern. However, little is known about their environmental fate and bioaccumulation. This study investigated the concentrations of SDPAs and BZT-UVs in the water, sediment and biota samples in the freshwater ecosystem and adjacent riparian environment using Hamilton Harbour in the Great Lakes of North America as a study site. The bioaccumulation factors and trophodynamics of these contaminants were studied using field-collected samples. Eight target SDPAs and two BZT-UVs (2-(2H-benzotriazol-2-yl)-4,6-bis(1-methyl-1-phenylethyl)phenol (UV234) and 2-(2H-benzotriazol-2-yl)-4,6-di-tert-pentylphenol (UV328)) were frequently detected in the sediment, water and biota samples. UV328 showed significantly greater concentrations in water (0.28-2.8 ng L-1) and sediment (8.3-48 ng g-1, dry weight) than other target contaminants, implying greater contamination of UV328 in Hamilton Harbour. SDPAs exhibited trophic dilution in species living in the water, whereas UV234 was biomagnified in the same samples. No clear trophodynamic trend was found for UV328 for water-respiring species. Air-breathing invertebrates had higher concentrations of both SDPAs and BZT-UVs than water-respiring invertebrates, and biomagnification was observed particularly for adult dragonflies. These results suggest that the trophodynamics of SDPAs and BZT-UVs vary depending on whether the food web is terrestrial or aquatic. Future research should investigate the occurrence and partitioning of SDPAs and BZT-UVs in the air-water interface and evaluate the toxicities of these contaminants in air-breathing species.

Diversity of movement patterns of Longnose Gar tracked in coastal waters of western Lake Ontario

AbstractUnderstanding the spatial ecology of fish is critical for effective conservation and management. Gar (Lepisosteidae spp.) are an ancient lineage of freshwater fishes that have long been thought of as having high site fidelity with limited large-scale movements. We acoustically tagged Longnose Gar (L. osseus) in a large freshwater embayment (Hamilton Harbour) and tracked the movements of 12 individuals within this system and throughout the coastal waters of Lake Ontario for up to 4 years. Three distinct movement patterns were observed: migrants (N = 7), which moved throughout much of western Lake Ontario and had a maximum displacement of 184 km (linear distance); residents (N = 3), which remained in or near the original tagging location (an industrial slip with year-round warmwater outfall); and sporadic migrants (N = 2), which showed both migratory and resident behavioural patterns in different years. Seasonally, gar were most active during the summer and then fall, with more restricted home ranges and movements during winter suggestive of more quiescent behaviour. This study represents the first use of acoustic telemetry to track Longnose Gar movements year-round in a large lake and confirmed that a majority of tracked fishes make large-scale movements in Lake Ontario. Such results reframe the presumption that gar are more resident fishes with restricted space use.

Life outside the fishbowl: Tracking an introduced population of goldfish (Carassius auratus) in an embayment on the Laurentian Great Lakes

Invasive species are a key threat to biodiversity in freshwater ecosystems; and, as such, their management can be an important part of ecosystem restoration and conservation. In Hamilton Harbour, an impaired Lake Ontario embayment, invasive species are an important threat. In the early 2000s, an increase in invasive goldfish (Carassius auratus) was identified during monitoring surveys. This population of goldfish was studied via acoustic telemetry to gain knowledge about its biology to support management control options. Hamilton Harbour goldfish exhibited seasonal patterns in site and depth use, and clear preferences for over-wintering and spawning areas. Goldfish were largely resident to Hamilton Harbour with the exception of one individual. To predict when goldfish would move into spawning areas, we examined goldfish presence, abundance, and temperature at a fish-barrier connected to the harbour and developed models to predict goldfish presence based on Cumulative Growing Degree Days (CGDD) and Day of Year (DOY). Goldfish were captured in large numbers (>100 day−1) at the fishway when CGDD > 25.0 and DOY > 100; therefore, we predicted that our tagged fish would move to spawning areas when these thresholds were reached. Both models accurately predicted when tagged fish moved to spawning areas which largely occurred when water temperatures were lower (≥ 9.7 °C) than thresholds previously identified in the literature (i.e., 15.0 °C − 22.0 °C). This suggested that pre-spawn/staging behaviour was detected using telemetry driven by factors including water temperature. Results from this work will inform control strategies for goldfish, including active removal during aggregation prior to spawning.

Spatial heterogeneity in water quality across the northern nearshore regions of the Laurentian Great Lakes

We provide the first comprehensive analysis of spatial heterogeneity in water quality across the Canadian nearshore regions of the Laurentian Great Lakes (LGL) with periodic sampling in the ice-free seasons from 2000 to 2019 for 24 water quality variables from 52 nearshore sites. We asked: (1) What is the extent, range, and magnitude of spatial heterogeneity in water quality conditions across the nearshore of the Canadian Great Lakes? and (2) How do features of anthropogenic development, sub-basin characteristics, anticipated coastal circulation, and weather influence water quality conditions in the nearshore of the Canadian Great Lakes? Principal Components Analysis explained 42% of the variation in water quality across the Canadian Great Lakes, with high spatial heterogeneity both within and among lakes, ranging from oligotrophic conditions in Lake Superior to eutrophic conditions in Lake Erie. Lakes Erie and Ontario generally had higher concentrations of chloride, chlorophyll a, and nutrients while higher silicate concentrations were observed in Lake Superior. Consistent patterns of degraded water quality were observed in Areas of Concern, such as Hamilton Harbour, Bay of Quinte, Nipigon Bay, and near Thunder Bay. Across the nearshore of the Canadian Great Lakes, regions with warmer air temperatures, in addition to urbanized and agricultural landscapes, were associated with deteriorated water quality. Our study highlights the importance of improving management practices across urban and agricultural landscapes, particularly in consideration of climatic change cumulatively degrading water quality conditions in the highly biologically, culturally, and socioeconomically important nearshore regions of the LGL.

In vitro assessment of the genotoxicity and immunotoxicity of treated and untreated municipal effluents and receiving waters in freshwater organisms

Municipal wastewater effluent is one of the largest sources of pollution entering surface waters in the Laurentian Great Lakes. Exposure to wastewater effluent has been associated with impaired immune systems and induction of genotoxicity to aquatic animals. Due to habitat degradation and environmental pollution linked to industrial development and population growth, several regions of the Great Lakes have been designated Areas of Concern (AOCs). In this study, we assessed the effect of extracts of sewage influent, (treated) effluent and receiving surface waters from the Hamilton Harbour AOC and the Toronto and Region AOC (Ontario, Canada) on the phagocytic immune response of rainbow trout (Oncorhynchus mykiss) kidney leukocytes and the genotoxicity (DNA strand breaks) of these extracts on freshwater mussel (Eurynia dilatata) hemocytes. We identified and quantified numerous chemicals present in the various samples extracted for exposure. In freshwater mussels, extracts from Hamilton Harbour AOC induced DNA damage with the most frequency (12 out of 28 samples) regardless of sample type, reflecting past and present industrial activities. In contrast, extracts from Toronto and Region AOC induced DNA damage infrequently (2 out of 32 (summer) and 5 out of 32 (fall) samples, respectively) and from different WWTPs at different times. None of the extracts induced any significant effect on phagocytosis of rainbow trout kidney leukocytes. The present study indicates that despite overall improvements to effluent quality, treatment of influent by WWTPs may not result in a corresponding improvement of the genotoxicity of effluents. In vitro bioassays are useful and cost-effective rapid-screening tools for preliminary assessments of contamination of aquatic ecosystems.

Analysis of bacterioplankton genes in an impaired Great Lakes harbour reveals seasonal metabolic shifts and a previously undetected cyanobacterium.

Hamilton Harbour is an impaired embayment of Lake Ontario that experiences seasonal algal blooms despite decades of remedial efforts. To study the harbour's cyanobacterial and heterotrophic bacterial communities, we extracted and sequenced community DNA from surface water samples collected biweekly from different sites during summer and fall. Assembled contigs were annotated at the phylum level, and Cyanobacteria were further characterized at order and species levels. Actinobacteria were most abundant in early summer, while Cyanobacteria were dominant in mid-summer. Microcystis aeruginosa and Limnoraphis robusta were most abundant throughout the sampling period, expanding the documented diversity of Cyanobacteria in Hamilton Harbour. Functional annotations were performed using the MG-RAST pipeline and SEED database, revealing that genes for photosynthesis, nitrogen metabolism, and aromatic compound metabolism varied in relative abundances over the season, while phosphorus metabolism was consistent, suggesting that these genes remained essential despite fluctuating environmental conditions and community succession. We observed seasonal shifts from anoxygenic to oxygenic phototrophy, and from ammonia assimilation to nitrogen fixation, coupled with decreasing heterotrophic bacteria and increasing Cyanobacteria relative abundances. Our data contribute important insights into bacterial taxa and functional potentials in Hamilton Harbour, revealing seasonal and spatial dynamics that can be used to inform ongoing remediation efforts.

Phytoplankton metabolite profiles from two Lake Ontario Areas of Concern reveal differences associated with taxonomic community composition

Water quality and phytoplankton community composition are important factors that can indicate freshwater ecosystem health. We combined water quality, phytoplankton community, and metabolomic data from algae and water sampled from two embayments in Lake Ontario, Hamilton Harbour and the Bay of Quinte, over ten weeks from August to October in the year 2020. Metabolomics was performed using liquid chromatography tandem mass spectroscopy (LC-MS/MS) to identify changes in intracellular metabolites within algae communities over time, and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) was used to characterize putative isomers of extracellular metabolites at sub-ppb mass accuracy. Results from this study indicate that Hamilton Harbour and the Bay of Quinte are two very different ecosystems with respect to water quality, phytoplankton metabolites, and phytoplankton community composition. Community composition is strongly driven by conductivity and nitrates in Hamilton Harbour, while the opposite is true in the Bay of Quinte. Metabolites including α-aminobutyric acid and glycine were found in larger abundance within algal communities at both locations, while taurine was more predominant in algal communities from the Bay of Quinte. These metabolic profiles could reflect the different communities of phytoplankton, and be alternative indicators of algal bloom growth.

Spatial ecology of non-native common carp (Cyprinus carpio) in Lake Ontario with implications for management.

The online version contains supplementary material available at 10.1007/s00027-022-00917-9.

Fish community structure varies by location and presence of artificial islands: a case study in Hamilton Harbour, Lake Ontario

Artificial islands and reefs have been used in the Laurentian Great Lakes for over 40 years as a means of improving aquatic habitat; but research on their efficacy has primarily focused on their ability to increase the abundance of specific sportfish, top predators, or other keystone species. To understand the importance of islands in structuring the whole fish community, we took a holistic approach and analysed the effect of islands, location, and the interaction effect between the two in structuring fish communities in Hamilton Harbour, Lake Ontario using a 30-year electrofishing dataset. The effect of islands varied by location within the harbour, with some species showing a preference for islands in some locations while avoiding them in others. Island communities also tended to have significantly different species compositions, with higher index of biotic integrity scores and species richness, greater numbers of pollution intolerant fishes, centrarchids, and fewer generalist species. However, these results paled in comparison to the level of inter-annual variation in the fish community of the harbour, which has changed markedly over the 30-year time span. Taken together, our results highlight that while island creation can influence the fish community, the type and magnitude of effect will vary based on their distance to other suitable habitats (i.e., location within the system) and the design of the island itself. Further, the noted inter-annual variability emphasizes the importance of considering long time scales (> 10–20 years) when exploring fish community responses to habitat creation. Collectively, these results will help the design of more effective management strategies for restoring fish communities.

Long-term and seasonal nitrate trends illustrate potential prevention of large cyanobacterial biomass by sediment oxidation in Hamilton Harbour, Lake Ontario

Several studies have shown that large, experimental additions of nitrate (NO3) to eutrophic systems can mitigate large populations of nuisance cyanobacteria and that high NO3 concentrations can oxidize anoxic sediments. These studies are consistent with observations from numerous aquatic systems across a broad trophic range showing development of reduced surficial sediments precedes the formation of large cyanobacteria populations. We use 50+ years of data to explore whether high NO3 concentrations may have been instrumental both in the absence of large populations of cyanobacteria in eutrophic Hamilton Harbour, Lake Ontario in the 1970s when total phosphorus (TP) and total nitrogen (TN) concentrations were high, and in delaying large populations until August and September in recent decades despite much lower TP and TN. Our results indicate that large cyanobacteria population events do not occur at the central station in July-September when epilimnetic NO3 > 2.2 mg N L−1. The results further suggest that remedial improvements to wastewater treatment plant oxidation capacity may have been inadvertently responsible for high NO3 concentrations > 2.2 mg N L−1 and thus for mitigating large cyanobacteria populations. This also implies that large cyanobacteria populations may form earlier in the summer if NO3 concentrations are lowered.

Impacts of wastewater treatment plants on benthic macroinvertebrate communities in summer and winter

Treated effluent from municipal wastewater treatment plants (WWTPs) is a major source of contamination that can impact population size, community structure, and biodiversity of aquatic organisms. However, because the majority of field research occurs during warmer periods of the year, the impacts of wastewater effluent on aquatic communities during winter has largely been neglected. In this study, we assessed the impacts of wastewater effluent on aquatic benthic macroinvertebrate (benthos) communities along the effluent gradients of two WWTPs discharging into Hamilton Harbour, Canada, during summer and winter using artificial substrates incubated for 8 weeks. At the larger of the two plants, benthic macroinvertebrate abundance was higher and diversity was lower at sites downstream of the outfall compared to upstream sites in both seasons. Whereas at the smaller plant, the opposite was observed, abundance increased and diversity decreased with distance from the outfall in both seasons. While the impacts of wastewater on benthic communities were largely similar between seasons, we did detect several general seasonal trends – family diversity of macroinvertebrates was lower during winter at both WWTPs and total abundance was also lower during winter, but only significantly so at the smaller WWTP. Further, benthic macroinvertebrate community composition differed significantly along the effluent gradients, with sites closest and farthest from the outfall being the most dissimilar. Our contrasting results between the WWTPs demonstrate that plants, with different treatment capabilities and effluent-receiving environments (industrial/urban versus wetland), can dictate how wastewater effluent impacts benthic macroinvertebrate communities.

Automated Coastal Ice Mapping with SAR Can Inform Winter Fish Ecology in the Laurentian Great Lakes

Many freshwater lakes in the temperate zone undergo annual freeze-thaw cycles. Climate change has disrupted these patterns and altered habitat for many species including ecologically, economically, and culturally valuable fish species. To understand the relationship between ice cover and aquatic species, suitable data can be derived from remote sensing. We developed a novel ice classification method with minimal user input using freely available Sentinel-1 data and an adjacent and time-coincident validation dataset. Using image object segmentation and a random forest classifier, ice conditions were classified correctly with >85% overall accuracy. Our ice mapping efforts coincided with a telemetry dataset of tagged Walleye (Sander vitreus) and Northern Pike (Esox lucius) in Hamilton Harbor in western Lake Ontario. Between years with low and high ice covers (2017 and 2019, respectively), we found Walleye appeared to reduce their area of movement when the harbor was covered in ice. Our ice mapping tool can provide a quick and consistent method for agencies to adopt for freshwater resource management as well as provide ice cover information in coastal areas that are important overwintering habitat for many fishes.

Ecological responses to elevated water temperatures across invasive populations of the round goby (Neogobius melanostomus) in the Great Lakes basin

Climate warming is expected to alter the distribution, abundance, and impact of non-native species in aquatic ecosystems. In laboratory experiments, we measured the maximum feeding rate and critical thermal maximum (CTmax) of an invasive Eurasian fish, the round goby (Neogobius melanostomus), acclimated to a range of temperatures (18–28 °C) reflecting current and projected future thermal conditions for the nearshore Great Lakes. Fish were collected from four distinct populations along a latitudinal gradient from the western basin of Lake Erie to Hamilton Harbour (Lake Ontario) and the upper St. Lawrence River. Thermal tolerance increased with acclimation temperature for populations in Lakes Erie and Ontario. However, the St. Lawrence River populations had lower acclimation capacity and exhibited an unexpected decline in CTmax at the highest acclimation temperature. Maximum feeding rates peaked at 18–24 °C and declined with temperatures above 24 °C. Northern populations in the basin appear poorly adapted to elevated temperatures such that their performance and impact could be reduced by climate warming. Thermal response data from latitudinally distributed populations are needed to inform invasive species risk assessment.

A comparison of passive and active gear in fish community assessments in summer versus winter

Fish populations and communities are monitored using a variety of sampling gears, each with their own inherent biases. Gear biases can arise from a number of factors, such as fish species characteristics (e.g., body shape/size, physiology, and behaviour), species habitat requirements, as well as the abiotic characteristics of sites sampled. Such factors and their effects on gear selectivity are also heavily influenced by seasonality. Consequently, understanding the effects of seasonal changes on gear selectivity is of vital importance, especially during the winter—a season seldom studied in freshwater systems. Here, we compared the selectivity, efficiency, and degree of biodiversity in fish communities sampled using three gear types: minnow traps, Windermere traps, and electrofishing during summer and winter in Hamilton Harbour, ON, Canada. Catch per unit effort was similar among gear types in the summer, whereas in the winter, minnow traps captured the most fish. Electrofishing samples were the most species rich and species diverse, but only during the summer. Additionally, sampling efficiency and the number of different species encountered was highest when all gear types were used in combination, followed by electrofishing alone, Windermere traps alone, and minnow traps alone in both seasons. Each gear type differed in its selectivity for certain species, which was further influenced by seasonality. This resulted in the fish communities caught within each gear type being dissimilar from one another. Our study highlights the importance of understanding gear type selectivity, particularly under different climatic conditions, and outlines the importance of incorporating multiple gear types in ecological assessments of fish populations and communities.

Spatiotemporal trends of polychlorinated biphenyls (PCBs) in surface and suspended sediments from the Lake Ontario Canadian nearshore 1994–2018: A fish consumption advisory perspective

Spatiotemporal trends for polychlorinated biphenyls (PCBs) were examined in surface and suspended sediments collected between 1994 and 2018 from over twenty nearshore stations on the Canadian side of Lake Ontario and the St. Lawrence River. In 2018, PCB concentrations ranged over an order-of-magnitude in surface (<10 ng/g−357 ng/g) and suspended sediments (<10 ng/g–330 ng/g), illustrating the presence of legacy hotspots as well as diffuse urban inputs. PCB concentrations in both surface and suspended sediments were consistently highest in Hamilton Harbour, but were also elevated at other stations around the perimeter of the Niagara basin as well as near Trenton and Kingston, Ontario. Generally, higher PCB concentrations were found in surface sediment relative to paired suspended sediment samples suggesting temporal improvements in nearshore sediment quality. However, many stations demonstrated temporal variability in PCB concentrations, a likely factor in the lack of an overall nearshore declining trend. Given that PCBs are listed as a consumption-limiting contaminant for all fish sampling blocks in the Canadian waters of Lake Ontario and are responsible for 78% of restricted advisories, sediment quality benchmarks that account for bioaccumulation potential should be considered over toxicologically-derived guidelines to gauge severity of PCB contamination of nearshore sediments. Relatively higher TOC-normalized PCB concentrations in the western end of Lake Ontario suggests additional research on PCB bioavailability from nearshore sediment would be beneficial in understanding basinwide trends of PCBs in fish, and that an adaptive approach to sediment management may be needed in the context of consumption advisories.

A probabilistic assessment of the impairment status of Areas of Concern in the Laurentian Great Lakes: How far are we from delisting the Hamilton Harbour, Lake Ontario, Canada?

Environmental policy analysis aims to identify the important drivers of degradation, elucidate sources of controversy, and put the necessary risk assessment tools in place to prepare for the unexpected. It is thus critical to develop risk assessment frameworks that ensure both continuity in the decision-making process, but also iterative adjustments to accommodate the non-stationarity of open environmental systems or the intrinsic uncertainty reflecting our incomplete knowledge. In this context, we reappraise the idea of probabilistic water quality criteria as a pragmatic way to accommodate the frequently experienced situation when the prevailing conditions may not always be favourable, even if the central tendency of the system is on par with what is defined as an acceptable ecosystem state. Our case study is the Hamilton Harbour, a large embayment located at the western end of Lake Ontario, with a long history of environmental pollution problems. Based on a probabilistic framework, our basic objective is to provide a comprehensive assessment of the current state of eutrophication and fish contamination in the system. Notwithstanding the significant improvements brought about by the remedial measures in the area, our analysis shows that the system continues to experience excessively high exceedance frequencies of the water quality goals, as well as of the consumption advisory PCB benchmarks of eight sport fish species examined. Specifically, 95.6% of the measured TP concentrations exceeded the proposed threshold level of 20 μg L−1, while 43.9% of the measured values exceeded the proposed chlorophyll a targeted value of 10 μg L−1. Likewise, the recent THg exceedance frequencies of the advisory benchmark were consistently very low, except from freshwater drum, but we still found high frequency violations of the advisory PCB benchmark across all fish species examined. These results clearly suggest that the Hamilton Harbour is still a long way off from being delisted as an Area of Concern. While our modelling analysis does not negate -in principle- the optimism that the goal of restoring environmental health of the system is achievable, it cautions that there are many “ecological unknowns” that may determine the degree and timing of restoration. The present framework encapsulates one of the founding concepts of the Hamilton Harbour remediation, whereby management strategies and quality goals heavily rely on continuous research and monitoring and dynamically adapt to the contemporary changes of the ecological conditions.

A Bayesian assessment of tumour prevalence in brown bullhead and white sucker from the Canadian waters of the Great Lakes

Liver and skin tumours in brown bullhead (Ameiurus nebulosus) and white sucker (Catostomus commersoni) have been associated with contamination of the aquatic environment. In this study, we present a Bayesian hierarchical logistic-Bernoulli framework that considers the role of fish covariates (e.g., age, total weight, gonad weight, liver weight, fork length) on tumour prevalence to identify the presence of “hot-spots” around the Canadian waters of the Great Lakes, where high fish tumour frequencies are registered. We developed methods to discern the degree of impairment that are either based on the comparison of tumour frequencies in contaminated (or impacted) sites against those predicted in their corresponding reference areas, or the assessment of the prevailing conditions in impaired sites independently, without the need to establish baseline conditions for comparison purposes. Our modelling study predicts low frequencies of neoplastic tumours in all the impacted locations. In contrast, the same comparisons with the preneoplastic lesions provided evidence of distinct differences between impacted and reference sites in Jackfish Bay, St. Mary’s River, Niagara River, Hamilton Harbour, and Bay of Quinte. We also found weak to moderately strong relationships between tumour occurrence and fish physical characteristics that varied considerably in terms of their strength and nature (sign) among the different locations. Our study concludes that the prevalence of neoplastic tumours appears to have reached acceptable levels around the Great Lakes, but the distinctly higher levels of preneoplasms in several impacted locations underscore the need to improve our understanding of the lesions that may lead to carcinogenesis.

Intense variability of dissolved oxygen and temperature in the internal swash zone of Hamilton Harbour, Lake Ontario

ABSTRACT The thermocline of large, stratified lakes is constantly sloshing along the sloping bed, creating a spatially variable internal swash zone. Temperature and dissolved oxygen vary rapidly here, potentially impacting fish habitat on timescales of hours. Large spatial differences in the time-dependent variance of temperature around Hamilton Harbour, Lake Ontario, Canada, were partly controlled by basin shape and bathymetry. The temporal variability was nearly twice as large at sites along the mildly sloping, narrow, upwind end of the basin relative to those at a similar depth at the steeper, broad, downwind end. Because the thermocline and oxycline were coincident, the same physical mechanisms resulted in a dissolved oxygen variance also twice as great at the mild slope compared to the steeper slope. Frequent hypoxic events occurred throughout the internal swash zone, drastically reducing the availability of fish habitat for anoxia-intolerant species. In the dynamic littoral zone, weekly measurements would overlook the acute temporal variability of temperature and dissolved oxygen. Here, we demonstrate that field observations and 3-dimensional (3D) hydrodynamic modelling can predict how basin morphometry affects internal seiche dynamics and spatial variability of internal swash zones.