Lakes In Northwestern Ontario Research Articles

Relationships among tissues, biofluids, and otolith selenium concentrations in wild female burbot (Lota lota).

In the Lake Koocanusa-Kootenai River system (Montana, USA and British Columbia, Canada), selenium (Se) contamination has become an international concern and is suspected to contribute to the observed burbot (Lota lota) population collapse. Due to our limited ability to sample burbot in Lake Koocanusa for monitoring studies, we used a reference population to develop tools to model tissue Se disposition for a focal species in systems with elevated Se. Total Se concentrations in otoliths, biofluids (blood and endolymph), and tissues (muscle, liver, and ovary) from burbot in reference lakes in northwestern Ontario, Canada, were measured to document tissue-to-tissue Se relationships and evaluate the potential for otoliths to retrace Se exposure in fish. Among burbot tissue, Se concentrations were the highest in the ovary (mean ± SD = 4.55 ± 2.23 μg g-1 dry mass [dm]), followed by the liver (2.69 ± 1.96 μg g-1 dm) and muscle (1.87 ± 1.14 μg g-1 dm), and decreased with body size (p < 0.05). In otoliths, Se was detected at low levels (<1 μg g-1 ). Selenium concentrations in burbot samples were positively correlated among muscle, ovary, liver, and endolymph tissues, but not for the most recent annually averaged or lifetime-averaged Se concentrations in otoliths. We hypothesize that Se concentrations were too low in this study to establish links between otoliths and other fish tissues and to detect significant lifetime variation in individuals, and that further validation using archived otoliths from burbot exposed to elevated Se levels in Lake Koocanusa-Kootenai River is needed to reconstruct exposure histories. However, intercompartmental models proved valuable for estimating Se concentrations in burbot tissues only available by means of lethal sampling (i.e., ovary), although additional work should confirm whether the established models are reliable to predict concentrations in Se-impaired systems as tissue distributions are likely to differ with increasing Se levels. Integr Environ Assess Manag 2023;00:1-11. © 2023 The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC).

Radio- and stable carbon isotope analysis reveals minimal assimilation of petrogenic carbon into an oligotrophic freshwater food web after experimental spills of diluted bitumen

Following an oil spill into water, bacteria can biodegrade petroleum hydrocarbons which could lead to petrogenic carbon assimilation by aquatic biota. We used changes in the isotope ratios of radio- (Δ14C) and stable (δ13C) carbon to examine the potential for assimilation of petrogenic carbon into a freshwater food web following experimental spills of diluted bitumen (dilbit) into a boreal lake in northwestern Ontario, Canada. Different volumes (1.5, 2.9, 5.5, 18, 42, 82, and 180 L) of Cold Lake Winter Blend (a heavy crude blend of bitumen and condensate) dilbit were applied to seven 10-m diameter littoral limnocorrals (approximate volume of 100 m3), and two additional limnocorrals had no added dilbit to serve as controls. Particulate organic matter (POM) and periphyton from oil-treated limnocorrals had lower δ13C (up to 3.2‰ and 2.1‰ for POM and periphyton, respectively) than the control at every sampled interval (3, 6 and 10 weeks for POM and 6, 8 and 10 weeks for periphyton). Dissolved organic and inorganic carbon (DOC and DIC, respectively) had lower Δ14C in the oil-treated limnocorrals relative to the control (up to 122‰ and 440‰ lower, respectively). Giant floater mussel (Pyganodon grandis) housed for 25 days in aquaria containing oil-contaminated water from the limnocorrals did not show significant changes in δ13C values of muscle tissue compared to mussels housed in control water. Overall, the changes in δ13C and Δ14C observed indicated small amounts (up to 11% in DIC) of oil carbon incorporation into the food web. The combined δ13C and Δ14C data provide evidence for minimal incorporation of dilbit into the food web of this oligotrophic lake, suggesting that microbial degradation and subsequent incorporation of oil C into the food web may play a relatively small role in the ultimate fate of oil in this type of ecosystem.

The Role of Climate and Lake Size in Regulating the Ice Phenology of Boreal Lakes

AbstractWe quantified the relationships between seasonal air temperatures and ice phenology for a 0.54 km2 boreal lake in Northwestern Ontario, Canada using a 50‐year time series (1970–2019). Significant temporal trends in the duration of ice cover (−4.0 days decade−1) occurred over the study period and both ice‐on and ice‐off dates were highly predictable from seasonal air temperatures. While temporal trends in ice‐off dates were not significant, ice‐on dates trended later by 2.2 days decade−1, and both ice‐off dates and the duration of ice‐cover became increasingly variable over the study period. For three consecutive winter seasons, we also evaluated regional variations of ice‐phenology and snow and ice‐thickness from 9 to 30 boreal lakes across a lake size gradient (0.02–26 km2) using ground based and satellite observations. Regional variation of ice‐on dates (30–45 days), ice‐off dates (10–21 days), and total duration of ice‐cover (22–38 days) between lakes displayed significant nonlinear relationships to lake size across all years. Regional variation of ice‐off dates was structured according to lake size, and appeared driven by relationships between lake size, snow thickness, and ice thickness. Multiple linear regression and generalized additive modeling approaches to predict ice‐on and ice‐off dates at the regional scale by integrating the effects of air temperature and lake size had similar performance, explaining &gt;90% of the variance of observed.

Relationship between water transparency and walleye (Sander vitreus) muscle glycolytic potential in northwestern Ontario lakes

Piscivorous predators at the apex of aquatic food webs are thought to exhibit foraging behaviours that depend on environmental conditions. Walleye (Sander vitreus), for example, is a freshwater predator that is most active under low light conditions. This study examined walleye resource use and swimming activity across lakes located in northwestern Ontario representing a gradient of water transparency. Muscle glycolytic potential, an index of swimming activity, was estimated by the activity of the enzyme lactate dehydrogenase (LDH). We show that walleye white muscle LDH activity increased with lake water transparency, but that this relationship is not determined by the use of nearshore resources, estimated from δ13C stable isotope signatures, or by prey abundance. On the other hand, walleye muscle LDH activity decreased with increasing prey size, and prey size was larger in lakes of low water transparency. These results support a positive relationship between water transparency and swimming activity in walleye, with prey size as an important factor contributing to this effect.

Distribution of Experimentally Added Selenium in a Boreal Lake Ecosystem.

Human activities have increased the release of selenium (Se) to aquatic environments, but information about the trophic transfer dynamics of Se in Canadian boreal lake systems is limited. In the present study, Se was added as selenite to limnocorrals (2-m-diameter, 3000-L in situ enclosures) in a boreal lake in northwestern Ontario to reach nominal concentrations of 1 and 10 µg Se/L in triplicate each for 77 d, and 3 additional limnocorrals were controls with no Se added. Total Se concentrations were determined in water, sediment, periphyton, benthic macroinvertebrates, zooplankton, and reproductively mature female fathead minnows (Pimephales promelas; added on day 33) collected throughout (and at the end of) the exposure period. Mean measured water Se concentrations in the control, 1-, and 10-µg/L treatments were 0.12, 1.0, and 8.9 µg/L. At the end of exposure (day 77), enrichment functions ranged from 7772 L/kg dry mass in the 8.9-µg/L treatment to 23495 L/kg dry mass in the 0.12-µg/L treatment, and trophic transfer factors for benthic macroinvertebrates ranged from 0.49 for Gammaridae to 2.3 for Chironomidae. Selenium accumulated in fathead minnow ovaries to concentrations near or above the current US Environmental Protection Agency criterion (15.1 µg/g dry mass for fish ovary/egg) in the 1.0- and 8.9-µg/L treatments, suggesting that, depending on aqueous Se speciation, such exposures have the potential to cause Se accumulation in fish to levels of concern in cold-water, boreal lake systems. Environ Toxicol Chem 2019;38:1954-1966. © 2019 SETAC.

GIS-based modeling of forest soil moisture regime classes: Using Rinker Lake in northwestern Ontario, Canada as a case study

There is a need to develop geospatial technological approaches to predict and map relative soil moisture (soil moisture regime) classes on forested landscapes. This is because soil moisture regime (SMR) maps are continuously being sought by forest managers for application in planning and operations. The aim of the study was to develop a GIS-based modeling approach to predict and map relative soil moisture classes on forested landscape. A rule-based geographic information system (GIS) modeling technique was developed to predict SMR classes (dry, fresh, moist and wet) using: 1) soil textural classes derived from Quaternary geology maps, and 2) water receiving areas derived from topographic attributes generated from 15 m digital elevation model. The rule-based GIS modeling approach produced a SMR map with an overall accuracy of about 65% relative to 54% generated from soil wetness index reclassification approach when compared to observed ground plot data. This novel geospatial technique could be easily applied by forest managers for enhanced forest resource inventory.

Tritium in fish from remote lakes in northwestern Ontario, Canada

Tritium is most commonly generated as a by-product of nuclear reactors. As such, environmental concentrations are typically only reported near regions of interest, and background concentrations in areas unaffected by anthropogenic disturbance are not well characterized. To provide information on background levels of tritium in the natural environment, tissue-free water tritium (TFWT) and organically-bound tritium (OBT) were measured in the flesh of 106 fish collected within three lakes located at the IISD-Experimental Lakes Area (ELA) in Ontario, Canada in 2014. For the three ELA lakes studied, water tritium (HTO) activity concentration was determined to be below reliably detectable levels (0.6 Bq/L). Fish TFWT was found to be below 0.7 Bq/L, similar to the surrounding water tritium activity concentration. Fish OBT activity concentrations, at below 5 Bq/L, were also very low. Fish size was significantly related to OBT activity in Lake Whitefish and White Sucker from Lake 302, but not in other lakes. Though we observed significant differences in potential tritium exposure to humans among lakes, the levels of tritium reported here are below the Canadian natural background radiation of 1.8 mSv/y. These results provide information on background levels of tritium in freshwater fishes in Canada.

Long-term Changes in the Fish Assemblage in Sandybeach Lake, Northern Ontario, Following the Introduction of Rainbow Smelt (&lt;i&gt;Osmerus mordax&lt;/i&gt;)

Rainbow Smelt (Osmerus mordax, Mitchill, 1814) has been widely introduced into lakes across North America and are reported to have an adverse effect on native fishes. In this study, we investigated the long-term changes to the pelagic fish assemblage in a northwestern Ontario lake (Sandybeach Lake) after Rainbow Smelt were introduced in the 1980s. We repeated an earlier summer, pelagic gill-netting survey of Sandybeach Lake and a nearby reference lake (Little Vermillion Lake) that does not contain Rainbow Smelt. Fishes throughout the water column were sampled with overnight sets of 5.2-m-deep, multi-mesh horizontal gill-nets. Compared with 1990 pelagic sampling, native fishes were significantly less abundant, less diverse, and largely absent from the deeper parts of Sandybeach Lake in 2012. Cisco (Coregonus artedi, Lesueur, 1818), Emerald Shiner (Notropis atherinoides Rafinesque, 1818), and Lake Whitefish (Coregonus clupeaformis, Mitchill, 1814) were notably absent in 2012. In contrast, Rainbow Smelt remained abundant at all depths sampled. A small number of ciscoes — including Shortjaw Cisco (Coregonus zenithicus (Jordan and Evermann, 1909)) — and Lake Whitefish were captured from benthic gill-nets. Based on the lack of ciscoes in pelagic gill-nets, the very old ages (mean 30 years) of the few individuals captured in benthic gill-nets, and a severely skewed sex ratio, it is highly likely that ciscoes will be extirpated from Sandybeach Lake. Although the composition of the pelagic fish assemblage differed between years, Cisco was still abundant in Little Vermillion Lake with the presence of young individuals indicating ongoing recruitment.

Morphological and genetic analyses identify a new record of a glacial relict: pygmy whitefish (Prosopium coulterii) from northwestern Ontario

The pygmy whitefish (Prosopium coulterii (Eigenmann and Eigenmann, 1892)) is a glacial relict species with a disjunct North American distribution that, apart from its most easterly known location in Lake Superior, is predominantly found in northern and western regions of Canada. Here we report on a new finding of pygmy whitefish from Winnange Lake in northwestern Ontario that extends the range of this species ∼320 km from its most easterly distribution in Lake Superior and almost 1500 km east of the closest previously known western localities. Genetic analyses confirmed that the fish from Winnange Lake were most closely related to the lineage that includes fish from Lake Superior and likely also originated via postglacial dispersal from a refugium in the upper Mississippi – Missouri river system.

Holocene paleoecology of a wild rice (Zizania sp.) lake in Northwestern Ontario, Canada

Whitefish Lake is a large (11-km-long), shallow, basin in Northwestern Ontario, Canada. The presence of extensive stands of wild rice (Zizania sp.) in combination with high archaeological site density suggests that this lake was ecologically important to regional precontact populations. Collection and analysis of sediment from Whitefish Lake was initiated in 2008 in order to reconstruct changes in lake depth, climate, and vegetation throughout the Holocene. In general, the upper 4.5 m of basinal sediment is composed of ~1.5+ m of varves, which is overlain by a 1.5-m-thick unit with ped-like structures, and ~1.5 m of lacustrine sediment. This sequence documents an early proglacial lake phase, followed by a dry interval before 4,300 (4,900 cal) BP when the lake was significantly shallower, and the establishment of the modern lake during the late Holocene. Plant microfossil (phytolith) evidence indicates that wild rice had colonized the basin ~5,300 (6,100 cal) BP as the lake level rose in response to climate change. Beginning ~4,000 (4,500 cal) BP, changes in elemental data suggest a sharp increase in lake productivity and a switch to anaerobic depositional conditions as the rate of organic sedimentation increased. Recent archaeological research confirms that wild rice was locally processed and consumed during the Middle and Late Woodland periods (~300 BC–AD 1700) although it was evidently growing in the lake well before this time.

Environment trumps predation and spatial factors in structuring cladoceran communities from Boreal Shield lakes

Understanding local and regional controls on communities is a major theme in ecology. Are communities mainly determined by local environmental gradients, local biotic interactions, and (or) dispersal processes? To address this, subfossil Cladocera were enumerated from the surface sediments of 50 remote Boreal Shield lakes in northwestern Ontario, Canada, to examine three ecologically relevant explanatory categories. Variation partitioning analyses were used to test and quantify the unique and shared effects of local abiotic measures, local predation factors, and spatial variables as predictors of community composition. Thirty-nine taxa were identified and communities were typically composed of pelagic taxa, such as Bosmina , daphniids, and Holopedium gibberum . Environmental variables (i.e., pH, lake surface area, specific conductivity, and lake water total aluminum concentration) explained uniquely 8.8% of the variation, which was 2.5 times greater than the unique contributions of predation or dispersal-related spatial variables. Predation and dispersal processes assumed lesser roles in structuring communities. Considering the extensive geographic scale of this study, our paleolimnological approach indicates that broad-scale dispersal limitation of cladocerans seems negligible for the many taxa examined here. Our findings further support the utility of cladocerans as key biological indicators to track environmental changes within Boreal Shield lakes.

Profundal-Pelagic Macrocrustacean Abundance in Boreal Lakes Before and After Experimental Clearcut Logging

A sampling program of 9 years revealed that the opossum shrimp Mysis relicta and the amphipod Diporeia hoyi were present in three boreal lakes in northwestern Ontario, Canada regardless of whether watershed forests were left completely intact, left as only a narrow buffer strip, or were nearly completely removed through experimental clearcutting. In fact, Diporeia were actually found to be more abundant in all lakes following logging. And the decline in Mysis abundance observed in one of the lakes occurred well before the initiation of timber removal. Consequently, it appears that these keystone, glacial-relic species of macrocrustaceans are not negatively impacted by clearcutting. This is in direct contrast to the hyper-sensitivity and extirpation of these same species which has been previously demonstrated in acidifying boreal lakes.

Water Quality Effects from an Aquaculture Operation in a Meromictic Iron Pit Lake in Northwestern Ontario, Canada

Abstract In 1989, aquaculture for the production of rainbow trout (Oncorhynchus mykiss) was started in the upper depths of the 180-m deep Caland pit lake formed after the flooding of the former Steeprock Iron Mine. After ten years of operation, water quality was shown to be affected by the fish farm as well as proximal waste and the surficial geology of the area. Meromictic conditions occurred in the pit lake with a dichotomy in water quality versus depth. A cluster of parameters (ammonia, total phosphorus, total Kjeldahl nitrogen, dissolved organic carbon, B, pH, dissolved oxygen) were either in higher concentrations in the mixolimnion or varied little throughout the entire water column, and a second cluster of parameters had higher levels below the chemocline (conductivity, alkalinity, dissolved inorganic carbon, total dissolved solids, nitrate, sulfate, Ca, Mg, hardness, Na, Cl, K, Fe, Mn, Sr, and silicon dioxide). Statistically significant variations in concentrations among many of these chemical parameters were observed between the two years of study, among depths, and among seasons. Nutrient loading from excess fish food and waste increased phosphorus and ammonia levels. The expansion of the fish farm also reduced the levels of dissolved oxygen in the lower depths of the pit lake, thus reducing the volume of usable water for aquaculture purposes. In the early 2000s the fish farm decreased production and those closed in 2006. Later data showed that nitrate and potassium had corresponding decreases in both the monimolimnion and the mixolimnion. Sulfate levels remained elevated.

Climate-related eutrophication of a small boreal lake in northwestern Ontario: a palaeolimnological perspective

A palaeolimnological investigation of changes in water quantity and quality in Lake 239, Experimental Lakes Area, in northwestern Ontario indicates marked changes in limnological conditions during the Holocene. Water quantity changes are based on the analysis of diatoms and inferences of lake-level changes from a nearshore sediment core. Changes in water quality are based on the analysis of diatom assemblages and associated quantitative inferences of total phosphorus (TP) from a deep central core, as well as changes in diatom accumulation rates, the proportion of chrysophyte scales to diatoms and changes to organic matter content. Lake levels at least 8 m lower than today were inferred from the nearshore core and were concurrent with an increase in nutrient-rich diatom assemblages, an increase in diatom accumulation and a decrease in the chrysophytes relative to diatoms in the central core. Fragilaria crotonensis and Aulacoseira subarctica were two of the dominant nutrient-rich taxa that contributed to an increase in diatom-inferred TP during the mid Holocene. Results from this study provide strong empirical evidence that water levels much lower than today can dramatically change trophic status, as occurred during the dry mid Holocene, and may provide a good analogue for understanding future impacts of climatic changes due to anthropogenic activities.

The post-release behaviour and fate of tournament-caught smallmouth bass after ‘fizzing’ to alleviate distended swim bladders

In recreational fishing, barotrauma occurs when fish that are angled from deep water are rapidly brought to the surface, causing a number of injuries and physiological alterations associated with gas expansion (such as distended swim bladders) that may impede swimming and prevent the fish from returning to depth. By deflating the swim bladder using a hypodermic needle (a process called “fizzing”) fish typically can return to depth. However, little is known about its consequences and efficacy on wild fish. At a competitive smallmouth bass ( Micropterus dolomieu) angling event on Rainy Lake in northwestern Ontario, we evaluated the effects of post-weigh in fizzing on the behaviour and short-term survival of three treatment groups after release: (i) barotrauma fish without fizzing ( N = 8); (ii) barotrauma fish that were fizzed ( N = 9); (iii) fish without signs of barotrauma that were fizzed ( N = 10) (sham control). Small external radio transmitters were affixed to the fish and tracked for 4 days. Fish were released at a common site and we assessed their dispersion at specific distances from the release site (50, 250, and 2000 m). All fish survived the 4-day monitoring period. No differences were observed in the time it took each group to disperse from the release site. Furthermore, there was no statistical evidence that fizzing influenced mean daily movements relative to controls, though a consistent trend was noted where fish that were fizzed displayed greater movement than non-fizzed fish with distended swim bladders. This study revealed that fizzing by trained experts is not detrimental to barotrauma fish. However, if done improperly there is risk to vital organs suggesting that there is merit in exploring other less invasive approaches to recompressing fish. Because our statistical power was generally low, further research is needed to determine whether fizzing should be encouraged or dissuaded to maintain the welfare status of the fish, decrease sublethal impairments, and reduce mortality.

Chemical Exposures: An Eye to the Sea

Gardening, choosing contraception, driving to work—we don’t typically think of these actions as having a high impact on fisheries, but they can. A session titled “From Kitchen Sinks to Ocean Basins: Emerging Chemical Contaminants and Human Health” at the February 2008 annual meeting of the American Association for the Advancement of Science detailed some recent findings showing that certain day-to-day activities can have big impacts on the oceans. Think of an oil spill like the 1989 Exxon Valdez incident, and you may visualize images of wildlife blanketed in black crude, struggling against acute poisoning and hypothermia. But John Incardona, a scientist with the National Oceanic and Atmospheric Administration (NOAA), was surprised that some spill compounds could cause far less obvious, though equally dramatic, effects. He found that polycyclic aromatic hydrocarbons (PAHs) caused heart defects in fish after the Exxon Valdez spill. He also found that PAHs had a similar adverse response in zebrafish, which is in many ways a better model of the human heart than the more commonly used mouse or rat. PAHs are also released during the combustion of wood, coal, and oil. “The emissions from a tailpipe include the PAHs created by burning but also aerosolized fuel that doesn’t get burned,” said Incardona. “In essence, the air is just like an aerosolized oil spill. And, if a physician knowingly gave an aerosolized cardiotoxicant to a patient with coronary artery disease or congestive heart failure, they would probably be sued for malpractice. But the air in big cities is doing just that to millions of people every day.” Untested synthetic chemicals emitted into waterways also could put fisheries at risk. Derek Muir, an environmental chemist with Environment Canada, wanted to find out if any of the 22,000 chemicals in medium to high levels of production today are as bioaccumulative or persistent as banned substances such as DDT and polychlorinated biphenyls. He developed a computer model that analyzed compounds’ structures and estimated levels of persistence using a database of known bioaccumulation rates. He found 400 chemicals that fit the persistence bill. Of those 400, 75% have never been described in the environmental literature, only 4% are regularly analyzed, and all have been in production for several decades. Other research focused on 17α-ethinyl-estradiol (EE2), a synthetic estrogen used in women’s birth control. EE2 passes through the female body and, later, wastewater treatment plants, often finding its way into fish when treated water is discharged into nearby rivers, streams, and oceans. Several studies in recent years have described the feminization of male fish in response to estrogenic exposures, but Karen Kidd, an ecotoxicologist with the University of New Brunswick, presented some of the first findings on how estrogens could affect an entire population. She exposed an isolated test lake in northwestern Ontario to 5 ng/L EE2, about average for streams and rivers receiving wastewater effluent. After one summer, male fish began releasing egg-forming proteins and had delayed sperm development, while females’ sexual development was significantly delayed. As a result, the fathead minnow in the lake stopped reproducing, and their population collapsed. That collapse had profound implications for larger predators such as lake trout, whose own population dropped 30% as a result. “These results are sobering because they show that estrogens can affect fish abundances both through direct toxicity or indirectly through the food chain because of the loss of their food supply,” said Kidd. EE2 can be easily broken down, however, and improvements to wastewater processing could mean less estrogen makes it into waterways. [For more on one possible improvement, see “Fe-TAML Takes On Estrogens in Effluent,” p. A159 this issue.] Finally, although the effects of many chemicals are known, the way they interact with other chemicals is not always clear. “We’ve got a pretty good handle on how to assess the health effects of single chemicals in toxicity trials,” said NOAA zoologist Nathaniel Scholz. “But the real world is more complex, and exposure to multiple chemicals in mixtures is the rule.” Using salmon as a test model, Scholz found that combinations of pesticides that run off into river waters frequently were synergistic, and certain combinations (such as diazinon plus malathion, both common pest control chemicals) can be lethal. This research is critical to the success of the multimillion-dollar effort to restore salmon habitat on the West Coast. As well, it may shed light on human health effects, because the human nervous system is similar to that of the salmon. “Pesticide residue typically occurs in the human food supply at very low levels, but pesticide mixtures are also very common,” Scholz said. “This creates the potential for synergistic interactions and enhanced toxicity to people.”

Severity of Barotrauma Influences the Physiological Status, Postrelease Behavior, and Fate of Tournament‐Caught Smallmouth Bass

AbstractMuch research on the fish physiological consequences of tournaments has been conducted to date and has provided anglers and tournament organizers with strategies for reducing stress and mortality. However, one aspect of tournaments that has received little attention is barotrauma. At a fall competitive angling event on Rainy Lake in northwestern Ontario, we evaluated the incidence of barotrauma among tournament‐caught smallmouth bass Micropterus dolomieu; we then tagged and released a subset of fish that had severe barotrauma indicators and compared physiology, postrelease behavior, and fate between these fish and those with negligible signs of barotrauma. Overall, 76% of fish had at least one sign of barotrauma (either hemorrhaging or swim bladder distention), but only 32% of fish had two or more indicators and were thus deemed to have severe barotrauma. When telemetered fish were released at a common site, we determined that fish with negligible signs of barotrauma evacuated the release site more rapidly than fish with severe barotrauma did. Some fish with barotrauma floundered at the surface when released, and one of these fish was subsequently hit and killed by a boat. At the end of the monitoring period, 20% of fish with severe barotrauma had died; two additional individuals (20%) that were still at the release site were moribund (failed to respond to diver stimuli). Conversely, we failed to observe any mortality in fish with negligible signs of barotrauma. All tournament fish had elevated levels of blood glucose and lactate. However, stress indices were higher in fish with barotrauma and tended to be highest among fish with barotrauma that died after release. This study revealed that the incidence of barotrauma in tournaments can be high; moreover, outside of a laboratory environment, a significant proportion of fish with severe barotrauma may die after release. Additional research is needed to determine the seasonal variation in incidence and consequences of barotrauma as well as the effectiveness of different depressurization techniques in the field that could be used during fishing tournaments.

Bioaccumulation of Toxaphene Congeners in the Lake Superior Food Web

The bioaccumulation and biotransformation of toxaphene was examined in the food webs of Lake Superior and Siskiwit Lake (Isle Royale) using congener specific analysis as well as stable isotope ratios of carbon and nitrogen to characterize food webs. Toxaphene concentrations (calculated using technical toxaphene) in lake trout ( Salvelinus namaycush) from the western basin of Lake Superior (N = 95) averaged (±SD) 889 ± 896 ng/g wet wt and 60 ± 34 ng/g wet wt in Siskiwit Lake. Major congeners in lake trout were B8-789 (P38), B8-2226 (P44), B9-1679 (P50), and B9-1025 (P62). Toxaphene concentrations were found to vary seasonally, especially in lower food web organisms in Lake Superior and to a lesser extent in Siskiwit Lake. Toxaphene concentrations declined significantly in lake herring ( Coregonus artedii), rainbow smelt ( Omerus mordax), and slimy sculpin ( Cottus cognatus) as well as in zooplankton (> 102 μm) and Mysis ( Mysis relicta) between May and October. The seasonal variation may reflect seasonal shifts in the species abundance within the zooplankton community. Trophic magnification factors (TMF) derived from regressions of toxaphene congener concentrations versus δ 15N were > 1 for most octa- and nonachlorobornanes in Lake Superior except B8-1413 (P26) and B9-715. Log bioaccumulation factors (BAFs) for toxaphene congeners in lake trout (ng/g lipid/ng/L dissolved) ranged from 4.54 to 9.7 and were significantly correlated with log octanol-water partition coefficients. TMFs observed for total toxaphene and congener B9-1679 in Lake Superior were similar to those in Arctic lakes, as well as to previous studies in the Great Lakes, which suggests that the bioaccumulation behavior of toxaphene is similar in pelagic food webs of large, cold water systems. However, toxaphene concentrations were lower in lake trout from Siskiwit Lake and lakes in northwestern Ontario than in Lake Superior possibly because of shorter food chains and greater reliance on zooplankton or other pelagic invertebrates.

Trophic Positions and Mercury Bioaccumulation in Rainbow Smelt (Osmerus mordax) and Native Forage Fishes in Northwestern Ontario Lakes

Rainbow smelt (Osmerus mordax) is a recent invader to the lakes of the Hudson Bay drainage in northwestern Ontario, Canada. In some systems, the invasion has been linked to an increase in mercury (Hg) concentration in native predatory fish. This increase may be due to the fact that rainbow smelt are trophically elevated and thus accumulate more Hg than native forage fish species. To test this hypothesis, we compared the trophic positions and Hg concentrations of rainbow smelt and native forage fish in a series of smelt-invaded and reference lakes in northwestern Ontario. A comparison of forage fish 15 N (an index of trophic position) between the smelt-invaded and reference lakes indicated that rainbow smelt moved into a trophic niche that was unoccupied prior to their arrival. Relationships between 15 N and body size and between Hg concentration and body size differed among the forage species. This indicates that the response of predator Hg concentrations to smelt invasion depends on both the species and size composition of their preversus post-invasion diet. At a standardized body mass of 10 g, rainbow smelt were significantly trophically elevated relative to most native forage species, but they did not have significantly higher muscle Hg concentrations. Relationships between Hg concentration and 15 N were weak, both within and among forage fish species. This study shows that trophic elevation on a fine scale (within the forage fish community) may not result in increased contaminant bioaccumulation. It further challenges the general assumptions of food web theory and contaminant bioaccumulation.

A hypolimnetic mass balance of mercury from a dimictic lake: Results from the METAALICUS project

The ability to determine the fate and transport of newly deposited mercury, from that of historically deposited mercury, was recently demonstrated by the Mercury Experiment To Assess Atmospheric Loading In Canada and the United States (METAALICUS). The METAALICUS project is a whole-watershed amendment study where different stable isotopes of mercury were applied to three watershed compartments totaling ∼53 Hectares: the upland, the wetland, and the surface of a dimictic lake in northwestern Ontario, Canada. Each compartment received approximately 5 times the annual background atmospheric deposition for the region. In the lake, the spike was divided into 9 bi-weekly injections administered over several hours through the wash of a trolling motor while circling the lake. The spike was added at dusk to limit photoreduction and evasion of elemental mercury. Results from two years of data show that new mercury is extremely particle reactive. Implications for the availability of newly deposited mercury for methylation, and a well-constrained mass balance of the hypolimnetic mercury cycle, will be presented.