*Corresponding author.

Transcription

1 J. Great Lakes Res. 24(2): Internat. Assoc. Great Lakes Res., 1998 Overview of the International Symposium on Eurasian Ruffe (Gymnocephalus cernuus) Biology, Impacts, and Control Jeffrey L. Gunderson* Minnesota Sea Grant 208 Washburn Hall University of Minnesota Duluth, Minnesota Michael R. Klepinger Michigan Sea Grant 334 Natural Resources Building East Lansing, Michigan Charles R. Bronte U. S. Geological Survey, Biological Resources Division Great Lakes Science Center, Lake Superior Biological Station 2800 Lakeshore Drive East Ashland, Wisconsin J. Ellen Marsden School of Natural Resources, Aiken Center University of Vermont Burlington, Vermont 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 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 Duluth- Superior. 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. *Corresponding author. jgunderson@extension.umn.edu

2 The symposium, sponsored by the Minnesota and Michigan Sea Grant College programs, featured 48 oral and poster presentations and was held in Ann Arbor, Michigan, during March The symposium was part of an outreach education project funded by the National Oceanic and Atmospheric Administration's Sea Grant College Program and abstracts are available from Minnesota or Michigan Sea Grant. The symposium was designed to (1) promote the transfer of research information from the U.S., Europe, and Asia to researchers, educators, fisheries managers, sport and commercial fishermen, and the public, and (2) facilitate cost-effective management decisions by enhancing the current understanding of ruffe and its implications for North America fisheries. The symposium was divided into five primary sessions: (1) research syntheses from selected Eurasian locations; (2) biology, reproduction, and physiology; (3) ecology, genetics, distribution, and impacts; (4) control and management; and lastly (5) economic impacts. Papers in each of these broad topic areas are presented in this special section on ruffe. All of the papers published in this special section were presented at The International Symposium on the Biology and Management of Ruffe, with the exception of Lappalainen and Kjellman, Lehto-nen and Urho, and Selgeby, which were contributed afterward. Syntheses of information on ruffe from different parts of Europe and Asia were provided at the symposium by five invited researchers, selected by solicitation of proposals. These individuals and their papers were: Colin Adams from Scotland (Adams and Maitland), Franz Holker from Germany (Holker and Thiel), Vladimir Kovac from Slovakia (Kovac), Viktor Mikheev from Russia (Popova et al.), and Ian Winfield from England (Winfield et al.). These synthesis papers brought forward research results that may not have been translated into English, that had not been published in easily available scientific journals, or that were new information. These five papers, together with Lappalainen and Kjellman (Finland) and Lehtonen and Urho (Finland) and the overview of available published literature by Ogle (all in this volume), provide an excellent summary of ruffe biology, life history, impacts, and management in Eurasia. The remaining 11 papers in this ruffe special section report results of North American ruffe research. Examination of ruffe biology, reproduction, and physiology confirm that ruffe are remarkably well-suited as a successful invader species. Ruffe mature at an early age, spawn more than once during a season, feed on a wide assortment of prey under a variety of conditions, and tend to discourage and avoid predators. Ruffe also tolerate a wide variety of substrates, salinities, and temperatures, lentic and lotic environments, and oligotrophic to eutrophic conditions (Adams and Maitland, Holker and Thiel, Kovac, Lehtonen and Orho, Ogle, Popova et al., Winfield et al. this volume). Following their unintentional introduction, ruffe quickly became extremely abundant in the St. Louis River, USA (Bronte et al., Ogle this volume), Loch Lomond, Scotland (Adams and Maitland this volume), Bassenthwaite Lake, England, and Lake Constance, on the borders of Germany, Austria, and Switzerland (Winfield et al. this volume). Significant negative impacts on native species were expected when ruffe quickly became one of the most abundant fish in these waters. The species of primary concern, because of their economic value and perceived risk from competition or predation, were yellow perch (Perca flavescens), Eurasian perch (Perca fluviatilis, a species very similar to yellow perch), walleye (Stizostedion vitreum), and whitefishes (Coregonus spp). Surprisingly, a number of papers suggested that no negative impacts were detected for these native fish species in the waters invaded by ruffe (Bronte et al., Adams and Maitland, Winfield et al. this volume). In the St. Louis River, population declines of native fishes were more likely the result of natural population dynamics, rather than interactions with ruffe (Bronte et al). In Loch Lomond, unpredictable changes in trophic pathways outside the fish community occurred (Adams and Maitland). Ruffe invasion of all these waters is recent (ruffe were first noticed in Loch Lomond in 1982, the St. Louis River in 1986, Lake Constance in 1987, and Bassenthwaite Lake in 1991) and may not offer the time scale needed to assess long-term impacts on native fishes. Still, it is remarkable that no immediate impacts on other fish were apparent when ruffe rapidly became the dominant fish. As one of the symposium participants commented "there is no free lunch," and intuitively, it would seem that as biomass of ruffe increased, the number or biomass of native fish would decrease correspondingly. Since that has not happened, it may be that ruffe have occupied an "open niche." What appears as a "free lunch" program for ruffe requires further investigation.

3 An examination of how ruffe relate to ecologically similar Eurasian species reveals that ruffe naturally coexist with Eurasian perch, pikeperch (Stizostedion lucioperca), and Coregonus spp. in many lakes in Sweden, Finland (Winfield et al. this volume), and Russia (Popova et al. this volume). Winfield et al. (this volume) presented data that showed Eurasian perch are found in significantly more lakes than ruffe in both Sweden (presence in 94% vs 30% of sampled lakes) and Finland (presence in 93% vs 60% of sampled lakes). Ruffe are generally more abundant in eutrophic lakes than in oligotrophic lakes, unless severely eutrophic conditions cause low hypolimnetic oxygen levels (Lehtonen and Urho, and Winfield et al. this volume). Even when co-occurring, yellow perch and ruffe appear to be somewhat spatially segregated. In contrast to yellow perch, ruffe do not spawn in vegetation (Holker and Thiel this volume) and were not found in vegetated sites in the St. Louis River estuary (Brazner et al. this volume). Generally, ruffe are more hypolimnetic and benthic, whereas yellow perch are more epilimnetic and littoral; however, diel and seasonal overlaps occur between these species (Ogle this volume). Ruffe are considered nocturnal and have a well-developed cephalic lateral line that allows them to feed effectively, even in complete darkness, whereas yellow perch are diurnal. Brown et al. (this volume) concluded that competition for food between larvae of ruffe and yellow perch is unlikely, because yellow perch hatch earlier than ruffe and move to offshore pelagic waters before ruffe hatch. When ruffe hatch they occupy pelagic nearshore areas, and later become benthic. Winfield et al. (this volume) expressed concern that egg predation by ruffe in Lake Constance, Loch Lomond, and Bassenthwaite Lake could pose a significant threat to powan (Coregonus lavaretus) reproduction. Popova et al. (this volume) reported predation on whitefish (Coregonus spp.) eggs in Russian waters, and Selgeby (this volume) noted ruffe predation on lake herring (Coregonus artedii) eggs in Lake Superior. Although many fish eat fish eggs without affecting recruitment of the prey species, there is concern regarding predation on the fall/winter incubating eggs of Coregonus spp. because ruffe attain high densities and feed more actively in cold water than other fish (Holker and Thiel this volume). Egg predation by ruffe was insignificant, however, in the St. Louis River (Ogle this volume), in the Danube River (Коvác this volume), and in Bassenthwaite Lake (Winfield et al. this volume). During the symposium it was suggested that the extent of egg predation may be related to water clarity, although this was subsequently challenged based on observations in German waters (F. Hőlker pers. comm.). Fullerton et al. (this volume) conducted laboratory studies on yellow perch and ruffe feeding preferences for a wide variety of benthic invertebrates. They concluded that ruffe and yellow perch will likely consume similar food resources where they co-occur. They found that ruffe and yellow perch preferred soft-bodied macroinvertebrate taxa which was consistent with ruffe stomach content analysis in the St. Louis River, Lake Superior. They also sampled Lake Michigan benthic communities and compiled data on benthic invertebrates from other Great Lakes. They concluded that all the Great Lakes contain prey suitable for ruffe, but the presence of zebra mussels may mediate the impacts of ruffe on benthic invertebrates by serving as a complex substrate upon which ruffe forage less efficiently. They also note that the presence of zebra mussels can increase some invertebrate taxa which are vulnerable to ruffe predation. We must be cautious in extrapolating negative interactions from laboratory studies to impacts in the wild. Diet overlap has been shown for many coexisting Eurasian species (Popova et al., Kovác, Holker and Thiel, Ogle this volume), but documented negative impacts in wild populations as a direct result of diet overlap are scarce (Ogle this volume). For diet overlap to result in competition (and negative impacts), food resources must be limited. Laboratory studies of ruffe biology, feeding, behavior, and interaction with native species add considerably to the scientific literature and help us look for similar interactions in the wild, but they should be used cautiously to predict impacts in ruffeinvaded waters. Even small reductions in important Great Lakes species would have large economic effects. Leigh (this volume) examined the benefits and costs associated with a proposed Great Lakes ruffe control program. Leigh found that a decision not to institute an 11 year, $12 million ruffe control program could result in substantial net economic losses. Leigh analyzed three possible scenarios. Under the "minimum impact" scenario (a projected decrease of 10% in yellow perch populations, and a 1% decrease in both walleye and lake whitefish (Coregonus clu-peaformis)), annual reductions in commercial and U.S.

4 sport fishery benefits reach nearly $24 million. Annual "moderate" and "maximum" reductions reach nearly $120 million and $215 million respectively. Leigh acknowledges that many underlying assumptions are speculative. Nevertheless, Leigh's cost benefit analysis provides a valuable economic framework for evaluating ruffe management decisions. Control of ruffe that invade new waters is a clear priority for research, and five papers in this special section address ruffe control. Mayo et al. (this volume) found that an attempt to control ruffe by stocking predators in the St. Louis River was unsuccessful, as predators selected native species and avoided ruffe. Also, predators never achieved the desired increase in abundance, probably because the St. Louis River is open to Lake Superior, which allowed them to disperse. Popova et al. (this volume), however, indicated that increased predators offered some measure of control in a Russian lake. The St. Louis River estuary experience should, therefore, not discourage future efforts at top-down control by predators, but such efforts will have to consider the results presented by Mayo et al. The sensitivity of ruffe to various piscicides has been documented, but the effectiveness of the piscicides depends on the ruffe's ability to detect and avoid these chemicals (Dawson and Boogaard this volume). Dawson and Boogard found that lethal concentrations of most formulations, including the most selective toxicant TFM, tended to repel ruffe. Antimycin and nicosamide did not repel ruffe, but delayed-release and sinking formulations (antimycin and Bayluscide granules) caused increased swimming and surfacing by ruffe. Additional studies are needed before delayed-release formulations of antimycin and Bayluscide could be recommended for treating localized ruffe populations. Flynn et al. (this volume) examined molecular methods of ruffe control, and attempted to identify antigens that would disrupt ruffe reproduction. Monoclonal antibodies were produced by injecting mice with ruffe sperm and testicular tissue, and four groups of testicular antigens were identified. The antibodies specific to the sperm surface show the most promise as a tool with which to disrupt reproduction at fertilization. Much more research is needed, however, before molecular disruption of reproduction could be considered as a viable control option. Brown et al. (this volume) examined spawning and the early life history of ruffe as they relate to the risk of ballast water transfer of pelagic larval ruffe. They found that ruffe spawned in the St. Louis River from early May until mid-june. They concluded that the greatest possibility for ballast water transport of ruffe occurs during a period from mid- May to July when larval ruffe are pelagic, but suggested that an extended spawning and hatching interval could expand this time period. Ruffe sometimes undergo diel vertical movements, but these movements are not consistent enough to suggest a specific time of day that would significantly reduce the risk of ballast water entrainment of larval ruffe during their pelagic period. An understanding of the sources and routes of ruffe introductions may facilitate limiting their spread. Stepien et al. (this volume) used mitochondrial DNA analysis to compare ruffe from Eurasia to ruffe from the Great Lakes. They found that the Great Lakes were invaded by ruffe originating most likely in the Black Sea. Ruffe from the Danube River, a tributary to the Black Sea, were identical to ruffe from the St. Louis River, Lake Superior. They also determined that ruffe from Thunder Bay, Lake Huron were identical to those from the St. Louis River, which suggests a range expansion (most likely via ballast transport) rather than an independent Eurasian introduction. Stepien et al. (this volume) also reported genetic differences between ruffe from the Danube River in Slovakia and ruffe from the Baltic region of Europe that are large enough to suggest that they may be separate species. They found that Baltic ruffe and Danube River ruffe appear as genetically distinct from each other as other closely-related species (G. cernuus, G. baloni, G. schraetser) are from each other. Further work will be required to confirm these findings. The general conclusion from the International Symposium on the Biology and Management of Ruffe and this special section is that ruffe may not be as great a threat to yellow perch, walleye, and Coregonus spp. in the Great Lakes as was first thought. Even so, we must not become complacent and dismiss the potential for as yet unrealized impacts of ruffe on the Great Lakes ecosystem. The high population density and expansive spatial occupation of invading ruffe may be more disruptive than in fish communities which co-evolved with ruffe. Also, absence of effects of ruffe on Eurasian species does

5 not preclude effects on ecologically similar North American species. Researchers and managers must remain alert to changes in fish communities that may be attributable to ruffe and actions should be taken to prevent the spread of ruffe to other North American waters