The Rusty Crayfish

By Clarke Garry

I still recall my excitement as a young boy (and collector of all things wild) the fun of tying a piece of chicken liver onto the end of a string and fishing for "crawdads" in a local lake near my home in Missouri. Little did I know that 50 years later I would still be collecting crayfish (albeit very different species, in a different way, and for a different purpose). Over the past few years students and I have collected several dozen crayfish from the Kinnickinnic Watershed while working on class projects. And I've picked up additional specimens in the course of the 1999 pilot macroinvertebrate inventory and more recently in the first year of a comprehensive two-year survey.

Most of the crayfish that we've collected from the Kinnickinnic River mainstem and the South Fork appear to be the expected Orconectes virilis, the most common crayfish in the state of Wisconsin and the northernmost distributed crayfish in North America (Hobbs and Jass 1988). This species has been collected from several locations in the lower Kinni from the reach just above the confluence of the Rocky Branch tributary below River Falls to a site within Kinnickinnic River State Park.

So the story is more-or-less predictable to this point. Then, last summer, when I had the opportunity to have Dr. Ray Bouchard of the Philadelphia Academy of Sciences look at a series of unidentified crayfish specimens from the Kinni, the last species I expected him to find was the rusty crayfish, Orconectes rusticus. Where finding a giant stonefly or the mayfly Isonychia in the Kinni (both less than common occurrences) would be considered promising events, finding the rusty crayfish is just the opposite. Gunderson (2001) refers to the species as a "nasty invader" and Hobbs and Jass (1988) summarize the rusty crayfish in Wisconsin as an ". . . exotic, aggressive, tolerant species that has been extremely successful in the variety of habitats into which it has been introduced."

The rusty crayfish is native to the Ohio River Basin and the states of Ohio, Kentucky, Tennessee, Indiana, and southern Illinois (Gunderson 2001). The range of O. rusticus in Wisconsin is disjunct, i.e., not connected to the region of native distribution (Hobbs and Jass 1988). These same authors indicate a modern range of O. rusticus across a large part of Wisconsin, except the Trempeleau-Black drainage basin, and they show no historical or literature-based data points for the Kinnickinnic Watershed. The prevailing hypotheses regarding movement of this species from native to non-native regions implicate human conveyance. These include bait transport by non-resident anglers, release of crayfish obtained from out-of-state biological supply houses for use in educational settings, and attempted development of populations of crayfish for commercial harvest (Gunderson 2001).

It has been appreciated for some time that the rusty crayfish has had detrimental effects on Wisconsin lakes, especially northern ones. Demonstrated impacts include: 1) displacement of native crayfish, 2) destruction of aquatic plant beds, and 3) heavy feeding by juveniles on benthic invertebrates (mayflies, stoneflies, midges, sideswimmers) (Gunderson 2001). In an intriguing study by Houghton and others (1998) the Prairie River in north-central Wisconsin was used to test the effect of the presence of O. rusticus on the density and diversity of aquatic invertebrates in a coldwater stream. The sections of the river chosen for analysis had three levels of rusty crayfish abundance: upper=not colonized, middle=intermediate colonization, and lower=high abundance. Interestingly, the upper section is classified as high-grade trout fishery (Class I). The lower section is considered a medium-grade trout fishery (Class II) as the river widens downstream, receives less groundwater influence, and is subjected to increased solar radiation. Following analysis of crayfish and macroinvertebrate populations, as well as multiple environmental factors, it was concluded that ". . . the decrease in benthic invertebrate density was brought about by the increasing abundance of rusty crayfish." An additional conclusion from this study, and one of pertinence to the Kinni, was that colder water temperatures were keeping rusty crayfish from the upper reaches of the studied river. Previous studies referred to by Houghton and others (1998) ". . . found that post-molting mortality in rusty crayfish increased dramatically when the temperature was held below 20°C (68°F), and rusty crayfish did not grow at temperatures below 14°C (57.2°F)."

Johnson's (1995, Fig. 2) record of 1993 summer temperatures (7/18/93 - 8/25/93) for the Kinnickinnic River at Quarry Road indicates an average water temperature of 14.4°C (57.9°F) for this period. And it appears that on only two days during that time did maximum water temperature rise above 20°C (68°F). Additional temperature data (Johnson 1995, Fig. 7) shows Lower Glen Park temperatures running approximately 4°F above example sites at Quarry Road and Cedar Street. Summer data (1 June-31 August) presented for the Quarry Road location in Schreiber (1998) for 1993 through 1997 indicates means ranging from 14.70°C (58.5°F) (1993) to 15.83°C (60.5°F) (1995). Data for the comparable period at the Below Rocky Branch location indicates means ranging from 16.51°C (61.7°F) (1997) to 17.88°C (64.2°F) (1995). To date specimens of the rusty crayfish have been found in the Kinni only the area of River Falls, between the Lower Dam and the confluence of Rocky Branch. It appears at this point that this region may be the most hospitable part of the river for O. rusticus. On a larger scale, considering the entire watershed, for most of the calendar year and a significant part of summer the habitat should be thermally unfavorable for this species.

Rusty crayfish feed on a variety of aquatic plants, benthic invertebrates, detritus, fish eggs, and small fish (Gunderson 2001). Crayfish in general serve as food for trout and other gamefish. Borger (1980) discussions fish preferences regarding crayfish and appropriate fly patterns. Gunderson (2001) reports that rusty crayfish drive native crayfish out of daytime hiding places. Also, as natives swim away from fish attack, they become vulnerable to fish predation, while rusty crayfish aggressively posture, making them less susceptible.

The presence of this introduced crayfish in the Kinnickinnic Watershed is an unfortunate outcome of human intrusion. At present the species appears to be confined to the reaches just below River Falls. The two impoundments in the City of River Falls have been shown to increase water temperatures for some distance downstream (Johnson 1995, Schreiber 1998) and this situation may be creating an environment, which is just suitable for survival of the rusty crayfish. An effort should be made to document and monitor the prevalence of this species in these areas and throughout the system. And here is but another reason to work to maintain and improve on temperature regimes of the Kinni.

References:

Borger, G. A. 1980. Naturals, A Guide to Food Organisms of the Trout. Stackpole Books, Harrisburg, Pennsylvania, 223 pp.

Gunderson, J. 2001. Rusty crayfish factsheet. Minnesota Sea Grant Program, University of Minnesota Duluth/University of Minnesota Extension Service, www.seagrant.umn.edu/exotics/rusty.html

Hobbs, H. H., III, and J. P. Jass. 1988. The Crayfishes and Shrimp of Wisconsin (Cambaridae, Palaemonidae). Milwaukee Public Museum, 177 pp.

Houghton, D. C., J. J. Dimick, and R. V. Frie. 1998. Probable displacement of riffle-dwelling invertebrates by the introduced rusty crayfish, Orconectes rusticus (Decapoda: Cambaridae), in a north-central Wisconsin stream. Great Lakes Entomologist 31:13-24.

Johnson, K. 1995. Urban stormwater impacts on a coldwater resource. Society of Environmental Toxicology and Chemistry, Vancouver, BC, 10 pp. + figures and tables.

Schreiber, K. 1998. Kinnickinnic River Priority Watershed Surface Water Resource Appraisal Draft Report. Wisconsin Department of Natural Resources, West Central Region, 26 pp.

Dr. Clarke Garry is a professor of biology at the University of Wisconsin-River Falls.