Newman, R.M., 1999. Ruffe - A Problem or Just a Pest? University of Minnesota.

Reprinted with Permission from Aquatic Nuisance Species Digest (1999) 3(4): 37, 44-46

Ruffe - A Problem or Just a Pest?

The ruffe (Gymnocephalus cernuus L., formerly Acerina cernuua), a small perch-like fish native to Europe and Asia, was first found in North America in the St. Louis River Harbor, at the western end of Lake Superior, in 1986 (Pratt et al. 1992). They most likely arrived in ballast water from Europe, probably from somewhere in the Danube basin (Stepien et al. 1998). In Europe, ruffe, though often abundant, are of little sport and commercial value due to their small size (rarely larger than 25 cm or 10" and more commonly less than 15 cm) and spiny body. Ruffe are prolific and have a high reproductive potential; they may spawn two to six times during the year and females can produce from 10,000 to over 150,000 eggs during spawning. This high reproductive potential often results in abundant but "stunted" populations with smaller maximum sizes (Popova et al. 1998). 

Ruffe are benthic feeders (Ogle 1998), relying on small benthic invertebrates that live in lake and river bottoms. Chironomids are often a dominant component of the ruffe diet. Like perch and walleye, ruffe are well adapted to dark and turbid conditions such as those found in more eutrophic waters. Ruffe possess a well developed taptum lucidum, a layer of reflecting plates behind the retina, that enables them to feed in low light to dark conditions. In addition, ruffe have a highly developed lateral line system, including a network of sensory pores in the head, which also enables them to function under low or no light condition. Ruffe appear to avoid light and will move to deeper, darker waters in the day and return to shallow water at night (Ogle et al. 1995).

Should We Be Concerned?

When ruffe were first found in the Duluth Harbor there was great concern that they would increase rapidly and result in the demise of an important walleye fishery in the harbor then spread to the lower Great Lakes and affect important walleye and yellow perch fisheries in Lakes Michigan, Huron, and Erie. Evidence from Europe also suggested that ruffe would consume whitefish eggs (Adams and Tippett 1991) which could pose a problem for valuable North American whitefish populations in the Great Lakes. As expected, ruffe did increase and by 1991, estimated at over two million fish, became the most abundant species found in St. Louis River bottom trawl assessments (Bronte et al. 1998). While ruffe increased, abundances of other common forage fish such as perch, shiners, troutperch, and bullheads appeared to decrease (Jensen et al 1996).

Experimental and observational studies in Europe indicated that ruffe could out-compete European perch (Perca fluviatilus) and other fish (Bergman 1991, Bergman and Greenberg 1994) for benthic food resources, particularly in low light or poor water clarity conditions. However, some studies at the 1997 International Symposium on Ruffe (Gunderson 1998, Gunderson et al. 1998) suggested that ruffe would have fewer impacts than expected (e.g., Bronte et al. 1998) and projected the view that ruffe would be a nuisance but might not cause major disruptions to fish communities and invaded ecosystems as earlier predicted. Although a lab study indicated significant diet overlap between ruffe and perch and the potential for competition in the wild (Fullerton et al. 1998, see also Savino and Kolar 1996), Brazner et al. (1998) indicated that vegetated coastal habitats might provide native fish a refuge from ruffe. Bronte et al. (1998) suggested that declines in St. Louis River Harbor native fish communities following the establishment of ruffe reflected natural variation unrelated to the increasing abundance of ruffe and were not due to ruffe impacts alone. These results were interpreted by some to mean the ruffe would have little effect on native fish communities.

More recent research suggests that although ruffe may not have the impact of zebra mussels or Hydrilla, they do have the potential to affect native fish such as perch and may also have broader ecosystem-level effects. In research funded by Minnesota Sea Grant, Henson and Newman (in press) found that ruffe food consumption and digestion are less influenced by temperature than are perch, supporting other work that indicates that ruffe are temperature generalists (Bergman 1987, Holker and Thiel 1998). Ruffe can better locate, consume and process food at colder temperatures than perch. More importantly, however, Henson and Newman (in press) found that ruffe grow less efficiently than perch on a diet of macroinvertebrates. In other words, compared to perch, substantially more benthic prey items are required to support growth of an equal biomass of ruffe. Given the rapid increase of ruffe populations, they are likely affecting food resources available to native fishes.

Figure Figure 1. Trout Perch, Perch, and Ruffe (Gymnocephalus cernuus L., formerly Acerina cernuua).

The validity of these observations was further extended by a series of enclosure experiments conducted in a lake tributary to the St. Louis River. The four meter diameter enclosures extended from the water surface to the lake bottom. Each enclosure was stocked with varying densities of ruffe and perch. Because the enclosures were open to the natural sediments, they contained a natural array of benthic and planktonic forage species. These experiments clearly showed that ruffe would outcompete perch for food. Even when the effect of overall fish density was accounted for, perch growth was suppressed significantly in the presence of ruffe (Henson 1999, Henson et al. unpublished manuscript). Conversely, perch had little effect on ruffe growth. A combination of interference and resource competition appeared to be the cause of the suppressed perch growth rates. Ruffe generally consumed two to three times more food than perch in the same mesocosm. Furthermore, both overall fish density and presence of ruffe had significant effects on benthic prey density (Schuldt et al. 1999, Schuldt et al., unpublished manuscript). The effects on prey density were not extreme, however, given the relatively short duration of the experiments (5-6 weeks). Due to the higher foraging efficiency (Bergman 1987, Savino and Kolar 1996) but lower conversion efficiency of ruffe (Henson and Newman in press), and the explosive population growth and long term persistence of high density ruffe populations in natural systems (Bronte et al. 1998, Popova et al. 1998), it is likely that ruffe will have substantial long term effects on benthic food webs and native fish communities (see also Winfield et al. 1998).

Yet, it is likely that these effects will be difficult to detect in natural systems given natural variability in both benthic resources and fish populations. The difficulty is that these effects will likely be persistent and may be cumulative. Simulation models by Brenton (1998) of ruffe-perch interactions in the St. Louis River Estuary indicate that ruffe can suppress perch population abundance by 41% compared to baseline conditions without ruffe. If both species were constrained to one or few benthic prey for food, ruffe would always drive perch to extinction within 25 years. Although we must use caution when extrapolating from simulated populations, these results suggest that drastic effects on perch may take many years to appear, but at least under model conditions, ruffe ultimately may serious consequences for perch.

Can They Be Stopped or Controlled? 

When ruffe were first recognized in the St. Louis River system several options were considered for control. Chemical control was rejected because it would have a major effect on native fishes, it likely would not eradicate ruffe, and the size area would make chemical control prohibitively expensive (Busiahn 1997). It was decided that enhancing native predators, such as walleye and northern pike, via stocking and angling restrictions, would be the best approach. Unfortunately, the native predators did not consume many of the spiny ruffe in the early years of the program (Ogle et al. 1996) and the enhanced predator populations may have contributed to the declines of native fishes while the ruffe population continued to increase. Although walleye and northern pike predation on ruffe has slightly increased in recent years (Mayo et al. 1998), perhaps in part due to reduced availability of preferred prey, the levels of predation are too low to control the ruffe population (Mayo et al. 1998). It is now estimated that the ruffe infestation is at six million fish. Thus biological control with generalist predators does not appear to be an effective control measure.

Since the initial establishment of ruffe, some progress has been made on selective chemical controls. Although not highly specific to ruffe, several general piscicides are more toxic to ruffe than many native species and some degree of selective control can be achieved (Boogaard et al. 1996, Busiahn 1997). However, chemical control is expensive and often controversial (e.g., Buhsian 1997) and until highly selective toxicants are developed it is unlikely that chemical control will be used extensively, except perhaps for isolated limited infestations far outside the ruffe's current range.

One of the aims of the Ruffe Control Committee of the ANS Task Force, which was formed in 1992 to recommend actions to limit the spread and impact of ruffe, was to inhibit their spread from the St. Louis River and western Lake Superior to eastern Lake Superior and the other Great Lakes (Busiahn 1997). Chemical control and mechanical harvesting were proposed for the eastern-most areas colonized by ruffe. These measures proved controversial and were never substantially implemented, and ruffe slowly spread along the south shore of Lake Superior to Ontonagan, Michigan. In 1995, ruffe appeared in the Thunder Bay River at Alpena, Michigan on Lake Huron (Busiahn 1997), likely the result of ballast water transfer from Duluth Harbor (Busiahn 1997). Given that spread out of Lake Superior had now occurred, the goals were revised to prevent or delay further spread through the Great Lakes and to prevent spread to inland waters. Ruffe have not yet spread to inland waters, in part due to the extensive educational campaigns by Great Lakes states and provinces, particularly Minnesota. Continued education programs, backed by laws regulating transport and water transfers, should help delay or prevent spread to inland waters and other watersheds.

Although traditional mechanical, chemical, and biological control techniques have not been proven effective, recent research holds promise for inhibiting spread and possibly controlling populations. Maniak et al. (in review) have shown that ruffe are repelled by alarm odors released by injured ruffe. This alarm substance might be useful to exclude ruffe from particular areas, such as ballast water intakes, spawning grounds or passages to native fishes, other inland waters. Murphy et al. (1999) have determined that ruffe release a sex pheromone that might eventually be used to attract and trap ruffe in the wild. Flynn et al. (1998) have developed antibodies for ruffe sperm that might be capable of disrupting reproduction. Further work on these systems is required to determine if they can be used in natural field conditions.

Prospect

Ruffe are well established in the upper Great Lakes and will likely spread to the lower Great Lakes and inland waters. However, continued educational programs and legislation to prevent their transport and introduction to other water bodies will greatly prevent and slow their spread. Given their potential for serious ecological impacts and thus economic impacts, projected at $24 to $214 million annually (Leigh 1998), efforts to inhibit and delay their spread should not cease. Further research may turn up more feasible control measures in the interim and even a five or ten-year delay could be enough to develop effective controls that would prevent further range expansion. 

Raymond M. Newman is an Associate Professor at the Department of Fisheries and Wildlife, University of Minnesota, 1980 Folwell Avenue, St. Paul, MN 55108 U.S.A. rum@fw.umn.edu 

For more information visit the following web sites:
http://www.fw.umn.edu/research/ruffe/ 
http://www.ansc.purdue.edu/sgnis/www/ruffe.htm 
http://www.great-lakes.net/envt/exotic/ruffe.html  http://nas.er.usgs.gov/fishes/accounts/percidae/gy_cemn.html 

Literature Cited

Adams, C. E., and R. Tippett. 1991. Powan, Coregonus lavaretus (L.), ova predation by newly introduced ruffe, Gymnocephalus cernuus (L.), in Loch Lomond, Scotland. Aquaculture and Fisheries Management 22: 239-246.
Bergman, E. 1987. Temperature-dependent differences in foraging ability of two percids, Perca fluviatilis and Gymnocephalus cernuus. Environmental Biology of Fishes 19:45-53.

Bergman, E. 1991. Changes in abundance of two percids, Perca fluviatilis and Gymnocephalus cernuus, along a productivity gradient: relations to feeding strategies and competitive abilities. Canadian Journal of Fisheries and Aquatic Sciences 48:536-545. 

Bergman, E., and L. A. Greenberg. 1994. Competition between a planktivore, a benthivore, and a species with ontogenetic diet shifts. Ecology 75:1233-1245. 

Boogaard, M.A., T.D. Bills, J.H. Selgeby, and D.A. Johnson. 1996. Evaluation of piscicides for control of Eurasian ruffe (Gymnocephalus cernuus). North American Journal of Fisheries Management. 16: 600-607.

Brazner, J. C., D. K. Tanner, D. A. Jensen, and A. Lemke. 1998. Relative abundance and
distribution of ruffe (Gymnocephalus cernuus) in a Lake Superior coastal wetland fish assemblage. Journal of Great Lakes Research 24: 293-303. 

Brenton, B.D. 1998. Simulating the effects of invasive ruffe on walleye and yellow perch population dynamics in Great Lakes waters. M.S. Thesis, University of Michigan, Ann Arbor. 103 pp.

Bronte, C. R., L. M. Evrard, W. P. Brown, K. R. Mayo, and A. J. Edwards. 1998. Fish community changes in the St. Louis River estuary, Lake Superior, 1989-1996: Is it ruffe or population dynamics? Journal of Great Lakes Research 24: 309-318.

Busiahn, T. R. 1997. Ruffe control: A case study of an aquatic nuisance species control program. Pages 69-86 in F. M. Ditri (eds). Zebra Mussels and Aquatic Nuisance Species. Ann Arbor Press, Inc, Chelsea, MI. 

Flynn, K., P. Schoff, and J. Holy. 1998. Localization of ruffe testicular antigens by a panel of antibodies Journal of Great Lakes Research 24: 379-382. 

Fullerton, A. H., G. A. Lamberti, D. M. Lodge, and M. A. Berg. 1998. Prey preferences of Eurasian ruffe and yellow perch: comparison of laboratory results with composition of Great Lakes benthos. Journal of Great Lakes Research 24:319-328.
Gunderson, J. 1998. Overview of the International Ruffe Symposium, Aquatic Nuisance Secies Digest 2: 34-35. 

Gunderson, J. L., M. R. Klepinger, C. R. Bronte, and J. E. Marsden. 1998. Overview of the International Symposium on Eurasian Ruffe (Gymnocephalus cernuus) Biology,
Impacts, and Control. Journal of Great Lakes Research 24: 165-169. Henson, F.G. 1999. Competition between ruffe (Gymnocephalus cernuus) and yellow perch (Perca flavescens) and the influence of temperature on growth and gastric evacuation of ruffe. MS Thesis, University of Minnesota, St. Paul, MN.

Henson, F.G. and R.M. Newman. In press. Effect of temperature on growth at ration and gastric evacuation rate of ruffe (Gymnocephalus cernuus). Transactions of the American Fisheries Society.

Hölker, F., and R. Thiel. 1998. Biology of ruffe (Gymnocephalus cernuus (L.)) a review of selected aspects from European literature. Journal of Great Lakes Research 24: 186 204. 

Leigh, P. 1998. Benefits and costs of the ruffe control program for the Great Lakes fish ery. Journal of Great Lakes Research 24: 351-360. 

Maniak, P.J., R.D. Lossing, and P.W. Sorensen. In review. Injured Eurasian ruffe, Gymnocephalus cernuus, release an alarm pheromone which may prove useful in their control, Journal of Great Lakes Research. 

Mayo, K. R., J. H. Selgeby, and M. E. McDonald. 1998. A bioenergetics modeling evaluation of top-down control of ruffe in the St. Louis River, western Lake Superior. Journal of Great Lakes Research 24: 329-342.

Murphy, C.A., P.J. Maniak, and P.W. Sorensen. 1999. Functional and biochemical characterization of a novel sex pheromone in the Eurasian ruffe, Gymnocephalus cernuus. Ninth International Zebra Mussel and Aquatic Nuisance Species Conference, Duluth, Minnesota, April 1999. 

Ogle, D. H. 1998. A synopsis of the biology and life history of ruffe. Journal of Great Lakes Research 24: 170-185. Ogle, D. H., J. H. Selgeby, R. M. Newman, and M. G. Henry. 1995. Diet and feeding periodicity of ruffe in the St. Louis River Estuary, Lake Superior. Transactions of the American Fisheries Society 124:356-369.

Ogle, D.H., J. H. Selgeby, J. F. Savino, R. M. Newman, and M. G. Henry. 1996. Predation on ruffe by native fishes of the St. Louis River Estuary, Lake Superior, 1989-1991. North American Journal of Fisheries Management 16:115-123.

Popova, O. A., Y. S. Reshetnikov, V. I. Kiyashko, Y. Y. Dgebuadze, and V. N. Mikheev. 1998. Ruffe from the former USSR Variability within the largest part of its natural
range. Journal of Great Lakes Research 24: 263-284.

Pratt, D. M., W. H. Blust, and J. H. Selgeby. 1992. Ruffe, Gymnocephalus cernuus: newly introduced in North America. Can. J. Fish. Aquat. Sci. 49: 1616-1618. 

Savino, J. F., and C. S. Kolar. 1996. Competition between nonindigenous ruffe and native yellow perch in laboratory studies. Transactions of the American Fisheries Society 125:562-571. 

Schuldt, J.A., C. Richards, and R.M. Newman. 1999. Effects of Eurasian ruffe on food resources and native yellow perch in experimental mesocoms. Bulletin of the North American Benthological Society 16(l): 163.

Stepien, C. A., A. K. Dillon, and M. D. Chandler. 1998. Genetic identity, phylogeography, and systematics of ruffe Gymnocephalus in the North American Great Lakes and Eurasia. Journal of Great Lakes Research 24: 361-378. 

Winfield, I. J., R. Rosch, M. Appelberg, A. Kinnerback, and M. Rask. 1998. Recent introductions of the ruffe (Gymnocephalus cernuus) to Coregonus and Perca lakes in Europe and an analysis of their natural distributions in Sweden and Finland. Journal of Great Lakes Research 24: 235-248.

Contact: Raymond Newman, University of Minnesota, Department of Fisheries and Wildlife, 1980 Folwell Avenue, St. Paul, MN 55108-6124
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