Louis River Research Articles

A Collapsible Trap for Capturing Ruffe

Abstract A modified version of the Windermere trap was designed, constructed, and tested for its effectiveness in capturing ruffe Gymnocephalus cernuus. The inexpensive, lightweight, collapsible trap was easily deployed and retrieved from a small boat. Field tests conducted at the St. Louis River estuary in western Lake Superior in spring 1995 and 1996 indicated that the trap was effective in capturing ruffe. Proportions of ruffe in trap and bottom trawl catches were similar in 1995 and 1996. This trap could be a useful tool in surveillance, monitoring, or control programs for ruffe or similar species, either to augment existing sampling programs or especially in situations where gillnetting or bottom trawling are not feasible.

Effects of laboratory test conditions on the toxicity of silver to aquatic organisms

AbstractThe effects of various chemical manipulations of test water on acute toxicity of silver to fathead minnows (Pimephales promelas) were investigated. Increases in hardness and organic carbon substantially reduced toxicity. Toxicity was also inversely related to pH and alkalinity when these parameters were jointly changed by addition of strong acid or base. The addition of 2 meq/L sodium sulfate had no significant effects, but the addition of 0.2 meq/L sodium chloride increased toxicity, perhaps related to the formation of the dissolved AgCl0 complex. We also evaluated the effects of static versus flow‐through test conditions, feeding during exposure, and aging of test solutions before exposure on the acute toxicity of silver to fathead minnows and Daphnia magna. Static conditions and feeding reduced toxicity, likely as a result of accretion of organic carbon. Aging of test solutions had little effect. For both juvenile fathead minnows and D. magna, silver was much less toxic in water from the St. Louis River than in our normal laboratory water, presumably because of the much higher organic carbon content of the river water. This study identified some aspects of test conditions that are important in assessing the risk of silver to aquatic biota, but improved assessments will require information for more conditions, species, and endpoints. More importantly, if toxicity test results are to be extrapolated among waters with different chemistries, adequate characterization of the chemical speciation of silver and a better understanding of the mechanisms of silver toxicity and its relationship to silver speciation and other chemical factors are needed.

A Bioenergetics Modeling Evaluation of Top-down Control of Ruffe in the St. Louis River, Western Lake Superior

Ruffe ( Gymnocephalus cernuus), were accidentally introduced into the St. Louis River estuary, western Lake Superior, in the mid 1980s and it was feared that they might affect native fish through predation on eggs and competition for forage and habitat. In an effort to control the abundance of ruffe and limit dispersal, a top-down control strategy using predators was implemented in 1989. We used bioenergetics modeling to examine the efficacy of top-down control in the St. Louis Riverfront 1991 to 1994. Five predators––northern pike ( Esox lucius), walleye ( Stizostedion vitreum vitreum), small-mouth bass ( Micropterus dolomieui), brown bullhead ( Ictalurus nebulosus), and yellow perch ( Perca flavescens)––were modeled to determine their consumption of ruffe and four other native prey species––spottail shiner ( Notropis hudsonius), emerald shiner ( Notropis atherinoides), yellow perch ( Perca flavescens), and black crappie ( Pomoxis nigromaculatus). Although predators ate as much as 47% of the ruffe biomass in 1 year, they were not able to halt the increase in ruffe abundance. The St. Louis River is an open system that allows predators to move freely out of the system, and the biomass of managed predators did not increase. A selectivity index showed all five predators selected the native prey and avoided ruffe. The St. Louis River has several predator and prey species creating many complex predator-prey interactions; and top-down control of ruffe by the predators examined in this study did not occur.

Fish Community Changes in the St. Louis River Estuary, Lake Superior, 1989–1996: Is It Ruffe or Population Dynamics?

Ruffe ( Gymnocephalus cernuus) have been implicated in density declines of native species through egg predation and competition for food in some European waters where they were introduced. Density estimates for ruffe and principal native fishes in the St. Louis River estuary (western Lake Superior) were developed for 1989 to 1996 to measure changes in the fish community in response to an unintentional introduction of ruffe. During the study, ruffe density increased and the densities of several native species decreased. The reductions of native stocks to the natural population dynamics of the same species from Chequamegon Bay, Lake Superior (an area with very few ruffe) were developed, where there was a 24-year record of density. Using these data, short- and long-term variations in catch and correlations among species within years were compared, and species-specific distributions were developed of observed trends in abundance of native fishes in Chequamegon Bay indexed by the slopes of densities across years. From these distributions and our observed trend-line slopes from the St. Louis River, probabilities of measuring negative change at the magnitude observed in the St. Louis River were estimated. Compared with trends in Chequamegon Bay, there was a high probability of obtaining the negative slopes measured for most species, which suggests natural population dynamics could explain, the declines rather than interactions with ruffe. Variable recruitment, which was not related to ruffe density, and associated density-dependent changes in mortality likely were responsible for density declines of native species.

Reproduction and Early Life History of Ruffe ( Gymnocephalus cernuus) in the St. Louis River, a Lake Superior Tributary

Reproduction and early life history of ruffe ( Gymnocephalus ceriums) was investigated during April to July in 1993 and 1994 in the St. Louis River, a western Lake Superior tributary. This study was conducted to assist fishery managers in determining possible interactions among the early life stages of ruffe and other North American percids, and in obtaining information useful in developing control methods targeted at the early life stages of ruffe. Ruffe had a prolonged spawning period that extended from late April to late June with peak spawning in mid to late May when water temperatures were between 12 and 14°C. The majority of ruffe protolarva were captured 1 to 2 weeks after egg deposition between mid May and late June and most were captured in water 0.5-m deep. Onshore-offshore movements were not observed, but diel vertical movements of larval ruffe were observed on several occasions. The greatest chance of ballast water transport of pelagic larval ruffe is between mid May and July. Information on reproduction and early life history in this report will assist fishery mangers in development of ruffe control methods, and assist Great Lakes shipping in ballast water management to prevent the spread of ruffe.

Overview of the International Symposium on Eurasian Ruffe ( Gymnocephalus cernuus) Biology, Impacts, and Control

This special topic section is dedicated to ruffe (Gymnocephalus cernuus), a small but aggressive fish native to Europe and Asia. Ruffe were introduced into the St. Louis River, the largest U. S. tributary to Lake Superior, in the early 1980s, probably in the freshwater ballast of ocean-going vessels. The port of Duluth-Superior is located in the St. Louis River estuary in western Lake Superior, and is the largest inland port in the United States. At the time of their discovery in 1987, the available literature suggested that ruffe mature quickly, have a high reproductive capacity, spawn over an extended period, and adapt to a wide variety of environments. This potential for rapid population growth, coupled with the threat of competition for food and space with native fishes, and predation on their eggs (Ogle, this volume), was perceived to pose a serious threat to fisheries in the Great Lakes as well as across North America. True to those early predictions, ruffe became the most abundant fish (based on trawl samples) in the 13,000-acre St. Louis River estuary within 5 years (Bronte et al., this volume). They quickly spread on their own nearly 200 miles along the south shore of Lake Superior by 1994. Ruffe were found in Thunder Bay, Ontario in Canadian waters of Lake Superior in 1991 and in Thunder Bay, Lake Huron (near Alpena, Michigan) in 1995, most likely having been transported via ballast water of ships leaving the Port of DuluthSuperior. Populations at both these locations are small but appear to be reproducing. The International Symposium on the Biology and Management of Ruffe was organized to address the potential threats ruffe pose to North American fisheries. Scientists in diverse disciplines from Eurasia and North America were brought together in an attempt to examine all aspects of the North American invasion of ruffe, and to highlight the effects of similar introductions in Europe and Asia.

Maternal Transfer of Organochlorines to Eggs of Walleye ( Stizostedion vitreum) in Lake Manitoba and Western Lake Superior

Gravid walleye were sampled from Lake Manitoba and western Lake Superior (St. Louis River) to measure the concentrations of organochlorine contaminants (OCs) in eggs and muscle and to assess the influence of maternal age and size on the transfer of OCs from mother to egg. Concentrations of most OCs in Lake Superior walleye eggs were 1 to 3 orders of magnitude greater than in Lake Manitoba eggs. Toxaphene (mean concentration (wet weight) ± 1 SE, 1580 ± 462 ng/g) and polychlorinated biphenyls (PCBs) (240 ± 24 ng/g) were the predominant OCs in Lake Superior walleye eggs, whereas DDT and metabolites (eggs 16 ± 1.5 ng/g, muscle 2.1 ± 0.36 ng/g) and PCBs (eggs 9.2 ± 0.83 ng/g, muscle 2.0 ± 2.4 ng/g) were the most common OCs in Lake Manitoba walleye eggs and female muscle. Egg size (dry mass) and the concentration of most OCs in Lake Manitoba walleye eggs were positively correlated with female length and age. This relationship was strongest for more hydrophobic OCs (e.g., PCBs) but was not significant for less hydrophobic OCs (e.g., hexachlorocyclohexanes (HCHs)). Neither egg size nor egg OC concentration of Lake Superior walleye were significantly correlated with female length or age. There was no relationship between OC concentrations in muscle tissue and female length or age of Lake Manitoba walleye. OC concentrations in Lake Manitoba walleye eggs were not correlated with concentrations in the muscle tissue of the mothers, suggesting that OCs in walleye eggs are derived from various tissues. A positive relationship between the egg:muscle ratio of PCB concentrations and the egg:muscle ratio oflipid in freshwater fish suggests that the maternal transfer of PCBs in freshwater fish is related to the relative amounts of lipid in the eggs and mother. The transfer of hydrophobic OCs from mother to eggs in freshwater fish appears to vary within and among fish species and with the hydrophobicity of the OC.

Relative Abundance and Distribution of Ruffe ( Gymnocephalus cernuus) in a Lake Superior Coastal Wetland Fish Assemblage

Fish assemblages from Allouez Bay Wetland in the St. Louis River estuary were sampled with fyke-nets from May to October, 1995, to characterize typical use patterns in different seasons and microhabitats. The relative abundance and distribution of ruffe ( Gymnocephalus cernuus) in these habitats was of interest because their recent invasion into the Great Lakes has the potential to disrupt native fish assemblages. A total of 15,867 fish comprised of 34 species were captured in 2,300 h of netting. The majority offish over the whole study were caught in the outer marsh (63%, 9,957 individuals), and seasonally during late June (7,384 individuals/4 net-nights) and early May (2,281 individuals). Yellow perch ( Perca flavescens), brown bullhead ( Ameiurus nebulosus), emerald shiner ( Notropis atherinoides), and silver redhorse ( Moxostoma anisurum) were the most abundant species, comprising 85 percent of the total catch. Ruffe was the seventh most abundant species captured (294 individuals), comprising only two percent of the total catch. They were the fifth most abundant species in the outer marsh, but only thirteenth most abundant in the inner marsh. Ninety-one percent of all ruffe (268 individuals) were caught in the outer marsh. Of the 75 species by life-stage combinations derived by classifying all individuals captured into one of 3 life stage categories (YOY, yearling, and adult), yearling ruffe were the twelfth most abundant, adult ruffe were sixteenth, and YOY ruffe were twenty-seventh. While ruffe have been the most abundant fish captured in bottom trawls in St. Louis River estuary during the 1990s, our results indicate the invasion of ruffe in shallow, heavily vegetated areas like those in Allouez Bay has been much less successful. Our results also suggest further degradation of coastal wetlands and other vegetated habitats would eliminate significant refugia from ruffe competition and could lead to increased dominance of ruffe in shallow water habitats in the Great Lakes.

Reproductive characteristics of the ruffe, <I>Gymnocephalus cernuus</I>, in the St. Louis River estuary on western Lake Superior: a histological examination of the ovaries over one annual cycle

Reproductive characteristics of the ruffe, <I>Gymnocephalus cernuus</I>, in the St. Louis River estuary on western Lake Superior: a histological examination of the ovaries over one annual cycle

Predation on Ruffe by Native Fishes of the St. Louis River Estuary, Lake Superior, 1989–1991

Abstract The ruffe Gymnocephalus cernuus, an exotic Eurasian percid, recently became established in the St. Louis River estuary, Lake Superior, after accidental introduction. Management actions (catch regulations and stockings) were enacted in 1989 to increase the density of top-level predators in the estuary, and thus to increase predation on ruffe. We conducted a field and laboratory study to determine if, and to what extent, native piscivores consume ruffe. Stomachs of 3,669 predators were examined in 1989–1991. Ruffe occurred in 6.7% of burbot Lota lota, 5.8% of bullheads Ictalurus spp., 4.7% of smallmouth bass Micropterus dolomieu, 2.6% of northern pike Esox lucius, 2.6% of black crappies Pomoxis nigromaculatus, and 1.3% of yellow perch Perca flavescens (4.5% after 1989) captured during the 3-year study. No ruffe were found in 967 stomachs of walleyes Stizostedion vitreum examined. Ruffe were 22.7%, of the diet (by weight) of bullheads (during the only year bullheads were captured) and 0.1–17.9% of t...

Effects of Temperature on Hatching and Development of Ruffe ( Gymnocephalus cernuus)

The ruffe ( Gymnocephalus cernuus) was introduced into the estuary of the St. Louis River at the western end of Lake Superior in about 1986 and is now the numerically dominant trawl-caught fish in this ecosystem. To learn more about the early life history of this new North America species, we incubated ruffe embryos at 6, 11, 16, and 21°C. In this way we determined the effects of temperature on hatching success, rates of development, the times from fertilization to hatching, and from fertilization to swim-up stage. After cooling from 13–16°C and subsequent incubation at 6°C few embryos hatched and no normal larvae were produced. At 11, 16, and 21°C, hatching success ranged from 49–58%, and 66% of those that hatched survived to swim-up. The mean time from fertilization to hatching was 29, 11,6, and 4 days at 6, 11, 16, and 21°C, respectively. The time from fertilization to swim-up was 26, 14, and 9 days at 11, 16, and 21°C, respectively. We believe the information provided will be of value to those interested in the basic environmental biology of this new species to North America, and to those natural resource managers responsible for waters where this species is or will become present. This new information will aid natural resource managers in planning chemical control strategies so as to avoid scheduling treatment when the ruffe's resistant egg stage may be extant; and also in aiding them to know when greater caution should be enforced so as to avoid extending their range through entrainment of the vulnerable swim-up larvae, e.g., during ships ballasting, with the possible consequence of transport to new sites of invasion.

Diet and Feeding Periodicity of Ruffe in the St. Louis River Estuary, Lake Superior

Abstract Ruffe Gymnocephalus cernuus, a percid native to Europe and Asia, is established in the Lake Superior drainage and could have negative impacts on native fish through competition for forage and predation on fish eggs. We investigated the diet of ruffes in the 4,654-ha St. Louis River estuary in May–October 1989–1990 and the feeding periodicity of ruffes in two adjacent habitats during five 24-h periods in summers 1990–1991. Ruffes were primarily benthophagous. Age-0 ruffes fed mostly on cladocerans and copepods in early summer and midge larvae (Chironomidae) in late summer and fall. Adult ruffes less than 12 cm fed mostly on midges and other macrobenthos but also consumed large numbers of microcrustaceans. Adult ruffes 12 cm and larger fed mostly on midges, burrowing mayflies Hexagenia spp., and caddisflies (Trichoptera). Ruffes consumed few fish eggs. Adult ruffes in deeper waters and all age-0 ruffes fed throughout the day as indicated by weight patterns of stomach contents. However, adult ruffes...

Growth-Temperature Relation for Young-Of-The-Year Ruffe

The ruffe ( Gymnocephalus cernuus) was accidentally introduced into the Great Lakes basin from Eurasia and has established a breeding population in the St. Louis River, a major tributary to western Lake Superior. We captured young-of-the-year ruffe in the St. Louis River; acclimated groups of 90-91 fish to test temperatures of 7, 10, 15, 20, and 25°C; and fed them ad libitum for 42 days at those temperatures. Ruffe grew at all five temperatures, but the optimum temperature for growth was about 21°C. Because the optimum temperature for growth of walleye ( Stizostedion vitreum), sauger ( Stizoste-dion canadense), and yellow perch ( Perca flavescens) is about 22°C, ruffe will probably attempt to share their thermal habitat. A recent survey of the St. Louis River revealed that yellow perch and small forage fish declined sharply as ruffe abundance increased. A similar decline in yellow perch abundance in Lakes Michigan, Huron, and Erie would seriously affect the fisheries in these lakes.

Ruffe, Gymnocephalus cernuus: Newly Introduced in North America

The Eurasian ruffe, Gymnocephalus cernuus, was collected from the lower St. Louis River, Lake Superior's westernmost tributary, in late summer 1987. This is the first known occurrence of the ruffe in North America. The likely vector for this species was ballast water of a transoceanic vessel dumped into the international port of Duluth-Superior located on the lower end of the St. Louis River. The ruffe is increasing in abundance and expanding its range into other tributaries and nearshore areas of Lake Superior.

Morphology of Ruffe (Gymnocephalus cernuus) Protolarvae from the St. Louis River, Lake Superior

ABSTRACT We describe hatching and the morphological and meristic characteristics of 2.5–5.6 mm long ruffe protolarvae (Gymnocephalus cernuus). Eggs and sperm from St. Louis River ruffe were mixed, producing fertilized eggs that were 0.9–1.2 mm in diameter. Newly hatched protolarvae were 2.5–3.2 mm long. They had 14–15 preanal and 23–24 postanal myomeres, a continuous finfold of even width, unpigmented eyes, and a large anterior oil globule in the yolk sac, and the head deflected over the yolk sac. Pectoral fin buds appeared on the dorsal side of the yolk sac 5 hours after hatching. Two-day-old protolarvae had fully pigmented eyes, and the head was free from the yolk sac. Three-day-old protolarvae were 3.9–4.3 mm long and possessed opercula, gills, pectoral fins, and a functional jaw. Feeding and swimming began about one week after hatching when the yolk sac was almost completely absorbed. Protolarvae grew rapidly at 20–22°C and were 4.9–5.6 mm long after 13 days. Newly hatched ruffe protolarvae are distinguished from other Lake Superior percids by having the fewest preanal myomeres (14–15), the head deflected over the yolk sac, continuous finfold of even width, and a total length of less than 4.0 mm.

Larval identification of the ruffe, Gymnocephalus cernuus (Linnaeus) (Percidae: Percini), in the St. Louis River Estuary, Lake Superior drainage basin, Minnesota

A reproducing population of the Eurasian percid Gymnocephalus cernuus was discovered in the St. Louis River, Lake Superior basin, near Duluth, Minnesota. This study is the first documented evidence of the species occurrence and reproduction in North America. Larvae resemble typical percids and are described with emphasis on meristic, morphometric, and pigmentary characters. Ruffe are distinguished from all native North American percids by the presence of a slightly concave head becoming attenuated at larger length intervals, a pointed snout with teeth on the maxillary and premaxillary by the time a length of 11 mm is reached, a large dorsally pigmented swim bladder, a serrated preopercle, and few postanal myomeres (usually 18–22). In particular, ruffe superficially resemble johnny darters as yolk-sac larvae, and walleye, yellow perch, and logperch at lengths greater than 10 mm, but can be distinguished by the previously mentioned characteristics and a deep shoulder depth and a narrow caudal peduncle.

Notes: Lymphocystis in a Walleye Population

Lymphocystis disease occurs commonly in populations of walleye Stizostedion vitreum; however, it has not been considered fatal to infected fish. From 1980 to 1985. adult walleyes with and without lymphocystis were marked during the spawning period and monitored for return rates to the St. Louis River, Wisconsin, the next year. Lymphocystis virus infected 18% of 12,918 walleyes marked during spring spawning. Return rates at spawning 1 year later were significantly higher (P < 0.0001) for walleyes not infected at time of tagging than for fish infected when tagged. Lymphocystis may cause mortality in this walleye population.

Use of Volatile Chloroorganics as a Measure of the Rehabilitation of the St. Louis River and Bay

A major source of chloroorganic discharge into the St. Louis River system is a pulp mill located 33 km upstream from Lake Superior. The effect of diverting the pulp mill effluent to an advanced secondary treatment plant, located 33 km downstream, was examined using a “chloroform monitoring technique.” Chloroform, formed during the bleaching of pulp, was used as a tracer substance to follow the movement of the chloroorganic effluent plume originating from the pulp mill. The treatment plant was shown to be only partially effective in removing chloroorganics, indicating that the point source of chloroorganic discharge into the St. Louis River system has only been relocated.

Derivation of site‐specific water quality criteria for cadmium and the St. Louis River Basin, Duluth, Minnesota

AbstractSeveral freshwater aquatic species were exposed to cadmium in site and laboratory water to evaluate a protocol recommended by the U.S. Environmental Protection Agency for deriving site‐specific water quality criteria. The recalculation, indicator species and resident species procedures of this protocol were used to modify the national cadmium criteria. These procedures were used to account for differences in species sensitivity and in the biological availability and/or toxicity of cadmium due to physical and/or chemical characteristics of the site water.The site‐specific maximum concentration derived from the recalculation procedure was slightly lower (1.3 as compared with 2.2 μg/L) than the national criterion. The maximum concentration derived from the indicator species procedure was 7.0 μg/L and was calculated by using a water effect ratio from tests conducted in both site and laboratory water. Acute tests with several species demonstrated that cadmium was less toxic in site water than in laboratory water. The site‐specific maximum concentration derived from the resident species procedure (from eight species exposed to cadmium in site water) was 1.9 μg/L. The 30‐d average concentrations were the same as the maximum concentrations in the procedures in which the national acute/chronic ratio was used in the calculation. These concentrations were much lower when the site‐specific acute/chronic ratio was applied.Acute tests conducted monthly in site water showed that cadmium toxicity varied by more than a factor of 3 over the year. This indicates the need for considering seasonal changes in physical and chemical characteristics of the site water when deriving criteria to protect aquatic life.

A Floristic Study of a Developing Plant Community on Minnesota Point, Minnesota

Minnesota Point, a sand bar about seven miles long south of Duluth, Minn., separates Lake Superior from Superior Bay which connects with St. Louis River Bay. It is opposed by Wisconsin Point three miles long, originally a part of the same sand bar through underwater connections. Between these two Points, is the Superior entrance channel, the natural outlet of St. Louis and Nemadji Rivers. The Duluth entrance channel is artificial. The highest elevation of the dunes and ridges is about twenty-four feet above the lake level. Its natural width has varied from less than two hundred to five hundred yards. At present it is considerably wider in places along Superior Bay shore due to sand-fills made by dredging the navigation channel. On one of these sand-fills the present study was made. The sand-fill adjoining Oatka Beach Addition along Minnesota Avenue between 40th and 43rd streets, about 3.5 miles from the north end of the Point, was made during the summer of 1935 by the United States Engineering Department. It comprises an area of 29.7 acres. The sediment consists of sand and silt. The general elevation of the sand-fill is only a few inches above the bay level. On the bay side of the sand-fill in the fall of 1935, there were many shallow ponds and depressions which became modified during subsequent years by sinking of the soil, erosion by wave action and by the developing vegetation into a marsh, one to two feet deep. The northwest corner of the sand-fill became an island, cut off by a shallow channel diagonally through the marsh. During the summer of 1938 with unusually high water level, the west shore was eroded by wave action while deposition took place along the north and south shores. Thus, at present, it is somewhat narrower and longer than originally.