Lake sturgeon (Acipenser fulvescens) spawn in the St. Marys River Rapids,Michigan

The St. Marys River connects Lake Superior to Lake Huron, comprising the international border between Michigan, United States, and Ontario, Canada. This Great Lakes connecting channel naturally encompasses various habitats including lakes, wetlands, islands, tributaries, side channels, and main channels. The St. Marys River Rapids are shallow rock areas with high flow velocities (>1 m/s) in the upper river adjacent to the navigation locks and electric power generating stations, while the Little Rapids are shallow, recently restored rocky areas with lower velocities located about 7 km downstream. The St. Marys River Rapids provide important spawning habitat for several native and introduced fishes, but spawning by lake sturgeon (Acipenser fulvescens) was not previously documented. We sampled for lake sturgeon eggs and larvae in both locations during June and July 2018–2019 using weekly benthic egg mat lifts and overnight D-frame larval fish drift nets. Viable lake sturgeon eggs (11 in 2018, 45 in 2019) were collected in the tailrace of a hydroelectric power facility adjacent to the St. Marys River Rapids. Larval lake sturgeon (21 in 2018, 1 in 2019) were collected in the same area as the eggs. Neither lake sturgeon eggs nor larvae were collected at Little Rapids in either year. Our results are the first documentation of successful lake sturgeon spawning and larval drift in the upper St. Marys River. While our observations showed spawning in a human-made tailrace area, the fate of larvae produced here is unknown and warrants further research.     

Proliferation of phytoplankton along a 500 km transect of the St. Lawrence River from its outflow at Lake Ontario

Observation of phytoplankton and water chemistry along the main channel of the St. Lawrence River was made at a high spatial resolution (every 12 km) in order to infer the factors that influence development of this phytoplankton community. The phytoplankton community in the main channel was collected over a 10-d period (mid July 2018) from the headwaters to near the beginning of the St. Lawrence River estuary. Total phosphorus concentration in river water increased with distance downstream (154–2,750 nM) and phytoplankton biomass (1.4–10.5 µg chl-a/L) was strongly correlated (r = 0.84, 46 d.f.) to the concentration of total phosphorus. Diatoms, chrysophytes and dinoflagellates dominated the phytoplankton community at the outlet of Lake Ontario and total chlorophyll-a concentrations increased three-fold with 500 km transit downstream from Lake Ontario; phycocyanin-rich Cyanobacteria showed the greatest proportional increase (227%). Total P concentrations observed in 1997 along this transect were identical to those observed in 2018; however, chl-a concentrations were much lower in 1997, a finding attributed to a greater filter feeding benthic organism impact on the standing crop of phytoplankton. Observations support the hypothesis that the phytoplankton community composition in this large river is strongly influenced by the headwater characteristics (Lake Ontario) and gradually influenced by entrainment of nutrient-rich tributary waters.     

Reduction in Sea Lamprey Hatching Success Due to Release of Sterilized Males

Male sea lampreys (Petromyzon marinus), sterilized by injection with bisazir, were released in Lake Superior tributaries from 1991 to 1996 and exclusively in the St. Marys River (the outflow from Lake Superior to Lake Huron) since 1997 as an alternative to chemical control. To determine effectiveness in reducing reproductive potential through the time of hatch, males were observed on nests and egg viability was determined in nests in selected Lake Superior tributaries and the St. Marys River. The proportions of sterilized males observed on nests were not significantly different than their estimated proportion in the population for all streams and years combined or for the St. Marys River alone. It was concluded that sterilized males survive, appear on the spawning grounds, and nest at near their estimated proportion in the population. There was a significant reduction in egg viability corresponding with release of sterilized males for all streams and years combined or for the St. Marys River alone. In the St. Marys River from 1993 to 2000, the percent reduction in egg viability was significantly correlated with the observed proportion of sterile males on nests. It was further concluded that sterilized males remain sterile through nesting and attract and mate with females. Reduction in reproductive potential in the St. Marys River due to both removal of females by traps and sterile-male-release ranged from 34 to 92% from 1993 to 2001 and averaged 64%. From 1999 to 2001, when the program stabilized, reductions ranged from 71 to 92% and averaged 81%. The current release of sterile males in the St. Marys River effectively reduced reproductive potential through the time of hatch and did so near theoretical levels based on numbers released, estimates of population size, and the assumptions of full sterility and competitiveness.     

Winter diets of round whitefish Prosopium cylindraceum in the St. Marys River

The round whitefish (Prosopium cylindraceum) is a coregonine native to numerous northern temperate lentic and lotic systems across North America. The St. Marys River, located between the United States and Canadian border, is one such system where the round whitefish supports a recreational fishery and is a prey source for piscivores. Round whitefish are generally known to prey upon benthic macroinvertebrates, but diets of round whitefish in the St. Marys River have not been characterized. We analyzed stomach contents from 107 round whitefish sampled from the St. Marys River during the winter months of 2020 and 2021 to describe their diets, examine their feeding strategies, and determine if they fed selectively. Ephemeropterans were the most important prey numerically, followed by megalopterans, trichopterans, and dipterans. The round whitefish population sampled from the St. Marys River exhibited a specialized feeding strategy that most often specialized on ephemeropterans. Patterns in the importance of prey types and feeding strategy were consistent between both years sampled. Selective feeding by round whitefish was examined using diet and environmental data from 2021 only, and we found that round whitefish selected both ephemeropterans and megalopterans, but avoided trichopterans and dipterans. Rather than being opportunistic invertivores, our results indicate round whitefish are specialized and selective feeders. Our findings can be used to inform conservation and management of round whitefish, as diets represent an integration of multiple ecological components such as prey availability, predator behavior, and habitat quality.     

SIZE‐FRACTIONATED PHYTOPLANKTON GROWTH AND MICROZOOPLANKTON GRAZING RATES IN THE UPPER ST. LAWRENCE RIVER

Chlorophyll‐a‐specific growth and grazing rates of phytoplankton in three size fractions (0.2 to 2 µm, 2 to 20 µm, and 20 to 153 µm) were determined using dilution assays (n = 38) that were conducted from May to December 2009 in the St. Lawrence River (discharge approx. 7135 m³ s^?1) from its headwaters at Lake Ontario to 180 km downstream. There was no discernible difference in phytoplankton growth or grazing rates as a function of river reach sampled. At water temperatures below 20°C specific rates of growth and grazing were closely matched (0.43 day^?1), suggesting tight coupling of phytoplankton grazing in the water column. However, specific phytoplankton growth rates exceeded specific grazing rates by 0.29 day^?1 when river water temperature exceeded 20°C. Nevertheless, the greater specific growth rate did not manifest in greater phytoplankton biomass with transit downstream suggesting the importance of grazer organisms on benthic surfaces that graze phytoplankton in this reach of a large river. Copyright © 2011 John Wiley & Sons, Ltd.     

Phytoplankton Distribution in Saginaw Bay

Phytoplankton cell counts were made on samples taken in Saginaw Bay during each of 11 cruises from April 1980 through November 1980. A spring assemblage numerically dominated by diatoms was followed by a brief period of dominance by green algae. Blue-green algae were numerically dominant from July through October when diatoms again became the dominant taxonomic group. Two regions of the bay were recognized based on the results of cluster analysis and principal component analysis of the average phytoplankton assemblage. The inner bay was typified by algal species with a Saginaw River origin and/or species typical of eutrophic waters in the Great Lakes. The outer region was typified in part by species of open Lake Huron. Wild Fowl Bay and the area to the southwest of Oak Point each have unique phytoplankton assemblages and are apparently not well integrated with the rest of the bay. On occasion, stations at or near the eastern side of the Saginaw Bay-Lake Huron interface have phytoplankton assemblages similar to inner bay and/or Wild Fowl Bay or Oak Point waters. Taken together, these findings indicate a possible strong nearshore effect on transport of Saginaw Bay populations to Lake Huron. The nearshore effect modifies the effect of Saginaw River on the phytoplankton of the Saginaw Bay-Lake Huron system.     

The Distribution of Diatoms Near a Thermal Bar in Lake Baikal

Studies of the spatial distribution of suspended matter and of diatoms across a thermal bar in Lake Baikal revealed that waters sinking at the thermal bar front (2 km off-shore) move to the bottom along the underwater slope, and may be traced to a depth of at least 700 m, 5 km off-shore. The distributions of 11 diatom species across the thermal bar were significantly different, reflecting their different ecological requirements. Maximum concentrations of Asterionella formosa, Nitzschia acicularis, Aulacoseira islandica occur near the shore. The distribution of Stephanodiscus hantzschii, a species characteristic of the Selenga River, suggests that riverine waters penetrate far into the lake along its eastern shore. Another species typical of the Selenga River, Stephanodiscus minutulus, was found both near the shore, and in the surface waters of the open lake. Endemic spring baikalian diatoms Aulacoseira baicalensis and Cyclotella baicalensis were found at highest concentrations in the deep waters far off-shore, beyond the thermal bar. Another endemic diatom, the autumn species Cyclotella minuta was evenly distributed over the open lake at all depths. The data obtained shed new light on the dynamics of water masses near thermal bars, and on the ecology of the diatom species studied.     

Nutrients Limiting Phytoplankton Production in Ice-Covered Lake St. Clair

Nutrient enrichment experiments on ice-bound phytoplankton populations at three stations in Lake St. Clair, of the St. Lawrence Great Lakes system, showed that silica was the primary nutrient limiting phytoplankton growth and photosynthesis in the Thames River plume, in mid winter. The addition of silica at concentrations of 150 μg L^?1 or greater relieved this limitation. Phosphate appeared to be a secondary limiting factor.Stations 1 and 2 below river outlets, draining rural and urban areas, showed variable results. Trace metal limitation was observed at station 1 on February 20, trace metal and vitamin limitation at station 2 in March. Possible limitation by phosphate was occasionally evidenced.     

Response of fish assemblages to restoration of rapids habitat in a Great Lakes connecting channel

Rapids habitats are critical spawning and nursery grounds for multiple Laurentian Great Lakes fishes of ecological importance such as lake sturgeon, walleye, and salmonids. However, river modifications have destroyed important rapids habitat in connecting channels by modifying flow profiles and removing large quantities of cobble and gravel that are preferred spawning substrates of several fish species. The conversion of rapids habitat to slow moving waters has altered fish assemblages and decreased the spawning success of lithophilic species. The St. Marys River is a Great Lakes connecting channel in which the majority of rapids habitat has been lost. However, rapids habitat was restored at the Little Rapids in 2016 to recover important spawning habitat in this river. During the restoration, flow and substrate were recovered to rapids habitat. We sampled the fish community (pre- and post-restoration), focusing on age-0 fishes in order to characterize the response of the fish assemblage to the restoration, particularly for species of importance (e.g. lake whitefish, walleye, Atlantic salmon). Following restoration, we observed a 40% increase in age-0 fish catch per unit effort, increased presence of rare species, and a shift in assemblage structure of age-0 fishes (higher relative abundance of Salmonidae, Cottidae, and Gasterosteidae). We also observed a “transition” period in 2017, in which the assemblage was markedly different from the pre- and post-restoration assemblages and was dominated by Catostomidae. Responses from target species were mixed, with increased Atlantic salmon abundance, first documented presence of walleye and no presence of lake sturgeon or Coregoninae.     

Spatial Pattern of Phytoplankton Based on the Morphology‐Based Functional Approach along a River–Floodplain Gradient

Current efforts to yield an appropriate method that would simplify the use of phytoplankton in the ecological evaluation of freshwaters resulted in different approaches based on clustering phytoplankton organisms. In this study, we applied the morphology‐based functional group (MBFG) concept to determine the spatial changes of phytoplankton in the natural riverine floodplain of the alluvial reaches of the Danube River along the horizontal gradient from the river towards the floodplain habitats. The obtained results showed that the magnitude of environmental changes depended on alternations in hydrological variables (hydropattern and water level) that influenced changes in the physical and chemical conditions. High‐intensity flood pulses caused environmental homogenizations and nitrate enrichment of the floodplain habitats. Phytoplankton dynamics were strongly associated with the environmental changes, and using the MBFG approach, two basic hydrological conditions were identified: inundation phase dominated by diatoms (GVI) and isolation phase dominated by filamentous cyanobacteria (GIII). Total diatom biomass decreased along the floodplain gradient with a diminishing of physical constraints, and site‐specific variables became more important in favouring diatom assemblages. The different response of cyanobacterial species to mixing regime was of particular significance for species successions during bloom period. Altogether, classifying very diverse diatoms (centrics and pennates and planktonic and benthic) and cyanobacterial taxa into single groups represents a weakness of the MBFG approach, which might make it impossible to reflect all the ecological differences governed by environmental constraints along river–floodplain gradients. Copyright © 2014 John Wiley & Sons, Ltd.     

Longitudinal Plankton Dynamics in the Rivers Rhine and Elbe

We compared the longitudinal plankton development in the two large rivers Rhine and Elbe by means of four Lagrangian sampling campaigns performed within the time span 2009–2011. The campaigns revealed low chlorophyll concentrations in the Rhine along a long river stretch (Rhine‐km 170 to 854) with maximum values below 5 µg L^?1 in 2010. In contrast, the Elbe (Elbe‐km 4 to 582) showed high and longitudinally increasing chlorophyll concentrations with maximal values of 174 µg L^?1 in 2009 and 123 µg L^?1 in 2011. Additional samples of the benthic bivalves along the river stretches revealed high densities of the filter feeders in the Rhine that could potentially explain losses of plankton production. Their densities in the Elbe were significantly lower, making important losses to benthic filter feeders unlikely. However, strong phytoplankton growth was observed during the sampling campaign in 2011 in the Rhine coinciding with a low discharge event. This resulted in an exceptionally high chlorophyll value of up to 244 µg L^?1 in the lower river sections, a value that was not reached in the last two decades of continuous water quality monitoring in the Rhine. Even though we cannot fully explain this phenomenon, it shows that phytoplankton has a high growth potential in the Rhine but is usually controlled by other mechanisms. Tributaries represented an additional and important source of plankton biomass and suspended substances in the Rhine, whereas they primarily diluted the plankton concentrations in the Elbe. Copyright © 2015 John Wiley & Sons, Ltd.     

Typology of a Great River Using Fish Assemblages: Implications for the Bioassessment of the Danube River

Matching habitat typology and ecological assemblages can be useful in environmental management. We examined whether a priori defined riverine sections correspond with distinct fish assemblage types along the >2000 km long course of the Danube River, Europe. We also tested whether different sampling methods (i.e. day and night inshore electric fishing and offshore benthic trawling) provide consistent typological results. Analysis of assemblage similarities, indicator species analysis, non‐metric multidimensional scaling (NMDS) and k‐means analyses indicated that fish assemblages of the a priori defined Upper‐, Middle and Lower‐Danubian sections differed slightly, but within class variability was high. Although indicator species analysis showed that the Upper‐Danube belongs to the barbel (Barbus barbus) zone and the Middle‐ and Lower Danube belong to the bream (Abramis spp) zone, indicator values of the character species were generally low. The NMDS analyses suggested a weak gradient in assemblage structure along the course of the river with relatively high variability between neighbouring sites. K‐means analyses revealed that many sampling sites were in a different class than the a priori defined sections, and classifications at other group numbers did not lead to better classification outcome. Overall, the results do not suggest clearly distinguishable assemblage types with distinct boundaries in the potamal section of a great river. Nevertheless, the division of the potamon to smaller sections may explain some variability in fish assemblage structure, and could be used for bioassessment purposes. The study also shows the importance of multihabitat and multigear surveys in the typological assessment of great rivers. Copyright © 2016 John Wiley & Sons, Ltd.     

Fish Assemblage Structure and Habitat Associations in a Large Western River System

Longitudinal gradients of fish assemblage and habitat structure were investigated in the Kootenai River of northern Idaho. A total of 43 500‐m river reaches was sampled repeatedly with several techniques (boat‐mounted electrofishing, hoop nets and benthic trawls) in the summers of 2012 and 2013. Differences in habitat and fish assemblage structure were apparent along the longitudinal gradient of the Kootenai River. Habitat characteristics (e.g. depth, substrate composition and water velocity) were related to fish assemblage structure in three different geomorphic river sections. Upper river sections were characterized by native salmonids (e.g. mountain whitefish Prosopium williamsoni), whereas native cyprinids (peamouth Mylocheilus caurinus, northern pikeminnow Ptychocheilus oregonensis) and non‐native fishes (pumpkinseed Lepomis gibbosus, yellow perch Perca flavescens) were common in the downstream section. Overall, a general pattern of species addition from upstream to downstream sections was discovered and is likely related to increased habitat complexity and additions of non‐native species in downstream sections. Assemblage structure of the upper sections were similar, but were both dissimilar to the lower section of the Kootenai River. Species‐specific hurdle regressions indicated the relationships among habitat characteristics and the predicted probability of occurrence and relative abundance varied by species. Understanding fish assemblage structure in relation to habitat could improve conservation efforts of rare fishes and improve management of coldwater river systems. Copyright © 2015 John Wiley & Sons, Ltd.     

Modeling Lampricide Transport in the St. Marys River

This paper describes use of an integrated chemical/oil spill computer model to study lampricide transport in the St. Marys River. The model is developed based on a depth-averaged two-dimensional advection-diffusion equation using a Lagrangian discrete parcel method. The hydrodynamics in the model is computed using a depth-averaged two-dimensional finite element model. The model is used to analyze the effectiveness of alternative lampricide application strategies. This analysis showed that releasing TFM from both the Great Lakes Power Plant and the Edison Sault Power Station is more effective than releasing from the Great Lakes Power Plant only, in terms of kill-per-dollar. However, the total cost for two-site releases are higher than single-site releases. The simulations also showed that the optimum duration of TFM release is between 14 and 16 hours. Simulations of bottom velocity distribution showed that the area over which the granular Bayluscide application could cover 70 to 90% of the sea lamprey (Petromyzon marinus) population in the St. Marys River, depending on the total river discharge.     

Adaptation of the Growth of the Diatom Fragilaria crotonensis (Kitton) and the Phytoplankton Assemblage of Lake Erie to Chromium Toxicity

Growth of the natural phytoplankton assemblages and the diatom Fragilaria crotonensis Kitton within the assemblage, in the presence of Cr(VI) from the control (0 μM) to 2.5 μM were measured for 40 days. Experiments were conducted in the summer and the winter. Chromium inhibited growth and this inhibition varied. Sensitivity was greater, at higher concentrations of Cr(VI), when the algae were exposed to the lower irradiation and temperature of winter, and varied with species. The toxicity effect was greater on F. crotonensis than the phytoplankton assemblage. At the highest concentration used, there was a shift in species of the assemblage from domination of diatoms to green algae.     

Assessment of fish mercury levels in the upper St. Lawrence River,Canada

The stretch of the St. Lawrence River near Cornwall, Ontario, Canada, between the Moses–Saunders power dam to the eastern outlet of Lake St. Francis in Québec, is currently listed as an Area of Concern (AOC), and has restrictive fish consumption advisories in place, largely due to high mercury levels. This study examined long-term temporal trends of mercury concentrations in northern pike, smallmouth bass, walleye and yellow perch from the St. Lawrence River, including the Cornwall AOC. In addition, differences in fish mercury concentrations among river sections were compared for each species using historical (1975–1979) and recent (2000–2011) data. Statistically significant declines in mercury concentrations were observed in all river sections for yellow perch (~ 40%), as well as in northern pike and walleye in at least one river section. For the river section encompassing the AOC, recent mercury concentrations are 33–59% lower than historical mercury concentrations for all four species. Further, a comparison of recent mercury concentrations between the AOC river section and other Ontario lakes/rivers suggests that AOC mercury values are within the 75th percentile of values for other Ontario water bodies in three of the four species considered. However, current fish mercury values for the AOC river section remain higher than one or more upstream river sections. These results indicate that recovery is still ongoing in this AOC.     

Life Cycle of a Mayfly Hexagenia Limbata in the St. Marys River Between Lakes Superior and Huron

Length-frequency distribution curves of Hexagenia limbata nymphs collected in May, August, and October 1974 and May 1975 in the St. Marys River between Lakes Superior and Huron were bimodal for each sampling period. These curves, combined with interpretation of nymphal emergence period and mean surface water temperatures, indicate that the population of Hexagenia nymphs in the St. Marys River is composed of two year classes or cohorts. One cohort emerges per season, 2 years after egg deposition.     

Field and Laboratory Studies of the Toxicity to Phytoplankton of Polychlorinated Biphenyls (PCBs) Desorbed from Fine Clays and Natural Suspended Particulates

Polychlorinated biphenyls (PCBs; Aroclor 1254) were adsorbed to natural (Hudson River and New York Bight) and commercial (illite) particles in the laboratory, then allowed to desorb for several hours into the surrounding aqueous medium in the presence of either of two laboratory strains of diatom species or a complete natural phytoplankton assemblage. Cell density, photosynthesis, and chlorophyll a concentration in the cultures were followed for 2 to 3 days. In two experiments, PCB-carrying natural particles were removed after desorption and prior to the introduction of algae. All incubations were carried out in the laboratory or in dialysis membrane bags suspended in the tidal channel of an estuarine marsh.Cultures containing 90 μg of illite-bound Aroclor 1254/L of water were severely damaged within 4 hours, by which time 72% of the PCBs had desorbed from particles and become available to the diatoms. Similarly, a natural phytoplankton community, incubated under natural conditions in the presence of 50 μg of Hudson River sediment-associated PCB/L of water, registered significant reductions of photosynthesis and chlorophyll a content for at least 3 days. When PCB-bearing New York Bight particles were removed from the medium prior to the introduction of algae, sufficient desorbed PCBs remained to reduce growth rates and chlorophyll a content of the culture. The latter experiment clearly demonstrates particle to water to cell transfer of desorbed PCBs.     

An assessment of water quality in two Great Lakes connecting channels

Compared to the Great Lakes, their connecting channels are relatively understudied and infrequently assessed. To address this gap, we conducted a spatially-explicit water quality assessment of two connecting channels, the St. Marys River and the Lake Huron-Lake Erie Corridor (HEC) in 2014–2016. We compared the condition of the channels to each other and to the up- and downriver Great Lakes with data from an assessment of the Great Lakes nearshore. In the absence of channel-specific thresholds, we assessed the condition of the area of each channel as good, fair, or poor by applying the most protective water quality thresholds for the downriver lake. Condition of the St. Marys River was rated mostly fair for total phosphorus (TP, 56% of the area) and mostly good (61% of the area) for chlorophyll a. Area-weighted mean concentrations of these parameters were intermediate to Lake Superior and Lake Huron. Unlike Lake Superior and Lake Huron, a large proportion (97%) of the area of the St. Marys River was in poor condition for water clarity based on Secchi depth. Area-weighted mean concentrations of TP and chlorophyll a in the HEC were more like Lake Huron than Lake Erie. For these indicators, most of the area of the HEC was rated good (81% and 86%, respectively). Interpretation of assessment results is complicated by variation in thresholds among and within lakes. Appropriate thresholds should align with assessment objectives and in the case of connecting channels be at least as protective as thresholds for the downriver lake.     

Compartmental Distribution of Organochlorine Contaminants in the Niagara River and the Western Basin of Lake Ontario

Ten chlorobenzenes, hexachlorobutadiene, and PCBs were measured in Niagara River water and suspended solids, and in western Lake Ontario sediments and benthic fauna. High levels of these contaminants were found on all fractions of the river suspended solids, but the larger particles contained much higher concentrations than the smaller particles. A portion of the CBs, HCBD, and PCBs present in the lake sediments was available to benthic organisms. A trend toward greater bioaccumulation for compounds having higher octanol-water partition coefficients was observed at all trophic levels.