Date of Report: December 1999

Date of Next Status Report: December 2000

Date of Workprogram Approval: July 1, 1999

Project Completion Date: June 30, 2001

LCMR Work Program 1999

I. PROJECT TITLE: Freshwater Mussel Resources in the St. Croix River

Project Managers: Daniel J. Hornbach and Mark C. Hove

Affiliation: Macalester College

Mailing Address: Dept. Biology, 1600 Grand Ave. St. Paul, MN 55105

Telephone Number: 651-696-6101 E-mail: Hornbach@macalester.edu Fax: 651-696-6443

Webpage Address: http://www.macalester.edu/~hornbach

Total Biennial Project Budget:

$ LCMR:	$58,000	$ Match:	$750
-$ LCMR Amount	$18,000	-$ Match Amount	$750
=$ LCMR Balance:	$40,000	=$ Match Balance:	$ 0

NF05 Freshwater Mussel Resources in the St. Croix River $58,000

Appropriation Language: Freshwater Mussel Resources in the St. Croix River $29,000 the first year and $29,000 the second year are from the trust fund to the commissioner of natural resources for an agreement with Macalester College to continue refugia studies and assess populations for freshwater mussels.

B. Status of Match Requirement: None

II. PROGRESS SUMMARY AND RESULTS:

The results of this project will help to improve the management and conservation of freshwater mussels by: 1) continuing a mussel relocation and refugia study begun in 1997 in association with the University of Minnesota; and 2) by continuing a monitoring program of freshwater mussel resources in the St. Croix River begun in 1990. Refugia may be important in protecting native mussels from invasive species such as zebra mussels. The continued monitoring of a refuge project begun in 1997 will provide information on the long-term impact of mussel relocations and thus provide insight into the efficacy of this conservation measure. This summer we collected, measured, and weighed each mussel from the reference and relocation sites at Wild River State Park. Mortality was low, around 10%, and mortality and growth did not differ between relocated mussels and resident mussels, or between sites. Additionally, we were happily surprised to collect empty shells of the federally endangered winged mapleleaf at Wild River State Park. This species has never been collected above St. Croix Falls.

While the distribution of various mussel species has been established in the St. Croix River, the long-term stability of these populations has not been examined. Repeated quantitative sampling is required to assess changes in populations of mussels. We have quantitatively sampled seven locations in the St. Croix River at least once since 1990. This summer we resampled three of these locations: Wild River State Park, Franconia, and Prescott. Comparison of this year's data with previous work shows that the communities at Wild River State Park and Prescott are relatively stable, whereas the diversity and abundance of mussels at Franconia have declined significantly. Also, a significant increase in lower quality, fine sediments was recorded at all three sites. We will study the four remaining locations in 2000 to examine temporal changes in populations. Data collected from both projects are being provided to a variety of resource agencies and placed on the Macalester College website.

III. PROGRESS SUMMARY:

The results of this project will help to improve the management and conservation of freshwater mussels by: 1) continuing a mussel relocation and refugia study begun in 1997 in association with the University of Minnesota; and 2) by continuing a monitoring program of freshwater mussel resources in the St. Croix River begun in 1990. Refugia may be important in protecting native mussels from invasive species such as zebra mussels. The continued monitoring of a refuge project begun in 1997 will provide information on the long-term impact of mussel relocations and thus provide insight into the efficacy of this conservation measure. While the distribution of various mussel species has been established in the St. Croix River, the long-term stability of these populations has not been examined. Repeated quantitative sampling is required to assess changes in populations of mussels. We have quantitatively sampled seven locations in the St. Croix River at least once since 1990. As part of this project we resampled three of these locations in 1999. We will study the four remaining locations in 2000 to examine temporal changes in populations. Data collected from these two projects are being provided to a variety of resource agencies and placed on the Macalester College website.

IV. OUTLINE OF PROJECT RESULTS:

Result 1 - Relocation and refugia study

LCMR Budget: $13,610 Match: $375

Balance: $8000 Match Balance: $0

Project Activities in Result 1. We returned to study areas setup in the summer of 1997. These two areas are located on the St. Croix River near Wild River State Park (near Almelund and Sunrise, Minnesota). At both reference and relocation sites we recovered mussels, marked unmarked mussels, and assessed growth and survivorship. Data analysis revealed mortality was low, and mortality and growth did not differ between relocated mussels and resident mussels, or between sites. Data collected from this project are being provided to a variety of resource agencies and placed on the Macalester College website.

Result 2 - Monitoring mussel populations in the St. Croix River

LCMR Budget: $44,390 Match: $375

Balance: $32,000 Match Balance: $0

Project Activities in Result 2. We returned to three of seven locations on the St. Croix River where we have quantitatively sampled the mussel community in the past. At these sites we collected at least 100 0.25 m^2 samples of the substrate and removed all of the mussels by sieving. We identified and measured the length of each mussel collected. From these measurements we estimated population density, community diversity, and age structure of the mussel populations. We compared this year's data with previously collected data and observed that the communities at Wild River State Park and Prescott are relatively stable, whereas the diversity and abundance of mussels at Franconia have declined significantly. There has been a significant increase in lower quality, fine sediments at all three sites. Data collected from this project are being provided to a variety of resource agencies and placed on our Macalester College website.

V. DISSEMINATION

We are disseminating the results of the project in a number of ways. As indicated in the outline of project results, we have presented the results from work completed in 1999 at the St. Croix River Rendezvous meeting. We have also presented the results at the PEW Midstates Science and Mathematics Consortium, St. Louis, Missouri. Results from work completed in 2000 will be presented at the St. Croix River Rendezvous meeting in 2000. The St. Croix River Rendezvous meetings are attended by a wide variety of stake-holders. These include individuals from Minnesota state agencies, a number of federal agencies including the Fish and Wildlife Service and the National Park Service. In addition, individuals from academia and the general public often attend these meetings. We also plan to submit the results of this work for publication in refereed scientific journals. All data collected will be provided to the Minnesota DNR for inclusion in their Heritage database. Additionally, any mussels collected as voucher specimens will be deposited in the Bell Museum, University of Minnesota. As indicated in the outline of project results, We will have a student develop a webpage describing the results of this project. We presently have the outlines of a webpage available at http://www.macalester.edu/~hornbach.

VI. CONTEXT

A. Significance: Freshwater mussels are among the most endangered organisms on earth (Abramovitz, 1996). Recently the state of Minnesota has acknowledged the threats posed to this group of organisms by increasing the number species of mussels recognized as endangered or threatened. The major reasons for listing of a species as threatened or endangered are reduction in the geographical distribution of a species or a reduction in the population size of a species. Most of the work that has been completed on the mussel fauna of Minnesota has been distributional in nature: describing which species are found in various lakes and streams. Little work has been done to quantify the population sizes of mussels and those few studies that have been conducted generally lack a temporal component. To better manage mussel resources an indication of the change in populations over time is required. Also information on changes in age-structure and species composition is crucial in developing adequate management strategies for this resource.

The St. Croix River is designated as a Wild and Scenic River. One of the most important resources in the St. Croix River are its freshwater mussels. Recent studies indicate freshwater mussels are the most imperiled group of organisms in the United States (Master et al. 1998). At least 40 species of mussels live in the St. Croix River. Two of these species are on the federal endangered species list and 14 species are state endangered or threatened in Minnesota. Many of the state-listed species have been placed on this list because of limited distribution and declining populations. The St. Croix River provides a refuge for many of these threatened species since population levels remain high. There have been a number of projects that managers must evaluate that may influence mussel habitats in the St. Croix watershed. These include the Stillwater Bridge project, NSP powerline projects, water release from the reservoir above the dam at St. Croix Falls, Wisconsin and a number of smaller less public projects (gas pipelines, video cables, emergency fire hydrants, etc.). Resource managers must have both data upon which to base recommendations and mitigation options in order to effectively manage natural resources.

The decline in freshwater mussels is being accelerated by the introduction of the exotic species especially the zebra mussel, Dreissena polymorpha. Zebra mussels have recently been found in small numbers in the lower portion of the St. Croix River, but there is no evidence of a self-sustaining population of zebra mussels in the St. Croix River at the present time. A number of agencies are examining techniques to protect the native mussel fauna from the zebra mussel invasion. There have been few studies that have examined the efficacy of relocation of mussels into refugia as a conservation strategy for these organisms (Cope and Waller, 1995). Of these relatively few studies, most have followed the growth and survivorship over a fairly short time period (1-2 years). We began an examination of the efficacy of relocation strategies in the summer of 1997 as part of an LCMR program. This project was completed in the summer of 1998 with only a single year of data being provided. To more fully understand the long-term success of this relocation experiment we propose to continue monitoring the mussels that were relocated in 1997 through 2000. Since mussels are long-lived and slow growing, this longer time horizon is needed to provide insight for management activities.

In addition, this project will have a significant educational component for it will involve undergraduate students in an applied scientific project and presentation of the results.

B. Time: This project began on July 1, 1999 and the final report will be provided to the LCMR on June 30, 2000. Both activities in this project have the potential to be on-going projects. The relocation project could be continued beyond 2000, assuming low mortality and low out-migration of mussels. Certainly there is a need for a continued long-term mussel monitoring program on the St. Croix River. It is possible that I will request additional funds from the LCMR to continue these projects in the future.

C. Budget Context: There are a number of agencies that have supplied past funding for a variety of projects that have provided baseline data upon which to base the current project. The relocation activity was funded from 1997-1999 through the LCMR to the University of Minnesota ($21,795). Our monitoring program is based on comparing population sizes assessed in 1999 and 2000 with past estimates. The past estimates have been obtained from 1990 to the present. Sponsors that have supported this past research include the MN DNR Non-game Wildlife program, the US Environmental Protection Agency, the US Fish and Wildlife Service, the US National Park Service, and the WI DNR. Additional support has been provided by the Blandin Foundation, Howard Hughes Medical Institute, and Macalester College. Often the population assessments were made as part of a larger project and it is difficult to estimate the amount of the awards used specifically for population assessments.

1. Budget:

VII. COOPERATION: We are cooperating with the Minnesota DNR, the WI DNR, the US Fish and Wildlife Service, and the National Park Service. All of these agencies have responsibility for overseeing the mussel resources of inland waters. We are required to obtain scientific collecting permits from all of these agencies. In addition, the National Park Service and the states (WI and MN) have the responsibility of managing the mussel resources in the St. Croix River. We will be providing these agencies with all of the data we collect. Also, we will be cooperating with Dr. Diane Waller of the Biological Survey of the USGS. Dr. Waller is conducting a relocation project at another location in the St. Croix River, using the same methodology that we are using. We are collaborating to publish the results of these studies. None of these individuals or agencies will receive LCMR project dollars.

VIII. LOCATION: Minnesota counties - Washington, Chisago

IX. Reporting Requirements: Periodic work program progress reports will be submitted not later than December 1999 and December 2000. A final work program report and associated products will be submitted by June 30, 2001.

Attachment A - Deliverable Products and Related Budget

3 students first summer, 4 students second summer

Work-study award for 1 student during the academic year

X. Research Projects:

I. Abstract

This project has two major activities: the evaluation of in situ refugia as a means to mitigate negative impacts on freshwater mussels, and to continue a long-term monitoring project of mussel communities in the St. Croix River. The mussel refugia activity will include continuing a relocation experiment that began in 1997. This activity includes translocating mussels from one location to another and then examining the growth and survivorship of both relocated and resident mussels. This summer we collected, measured, and weighed each mussel from the reference and relocation sites at Wild River State Park. Mortality was low, around 10%, and mortality and growth did not differ between relocated mussels and resident mussels, or between sites. The long-term monitoring activity includes returning to seven locations on the St. Croix River that have been quantitatively sampled at least once since 1990. This activity involves assessing population density and age-structure of these populations, and mussel community structure. This project will also examine physical factors that may account for variation in density (e.g. water depth, velocity and substrate size). This summer we resampled three of these locations: Wild River State Park, Franconia, and Prescott. Comparison of this year's data with previous work shows that the communities at Wild River State Park and Prescott are relatively stable, whereas the diversity and abundance of mussels at Franconia have declined significantly. Also, a significant increase in lower quality, fine sediments was recorded at all three sites. We will study the four remaining locations in 2000 to examine temporal changes in populations

II. Background and hypothesis

Freshwater mussels (Family Unionidae) are widely distributed throughout the United States. There are 44 species of freshwater mussels currently on the federally endangered species list (Abramovitz,1996). Despite this fact there is little known concerning the factors that control the distribution of these organisms, especially in flowing water systems. Certainly factors such as surface geology, stream size, water quality, substrate type, water flow, and food availability, among others, are important in determining the community structure and population dynamics of freshwater mussels (Strayer, 1983). Not only are unionids important because of their diversity in flowing water systems, but based on the river continuum concept (Vannote et al.,1980) large filter-feeders (such as mussels) are also extremely significant components of larger river systems. They are one of the few organisms able to process the fine particulate organic matter that makes up a significant portion of the energy basis for these reaches of river systems. The recent introduction of the zebra mussel (Dreissena polymorpha) from Europe is likely to affect adversely populations of native mussels (Family Unionidae). There is the potential for both direct and indirect influence of Dreissena on the biodiversity of unionids.

Despite the importance of unionids in flowing water systems in North America, little is known about the population dynamics of these organisms. Mussel are relatively long-lived (10-80+ years) and have a unique reproductive cycle (McMahan, 1991). Males release sperm into the water and are taken in through the incurrent siphon by the female. Fertilization of the eggs occur and zygotes are brooded in the water tubes of the gills by the female. Various species become sexually mature at different ages (3-9 years). Female unionids often produce a large number of eggs (500,000 - 1 million; Burky, 1983). The zygotes develop into glochidia larvae that are discharged into the water column. The discharged larvae attach to the fish host where they remain for varying periods of time (estimates range from 10-90 days for various species). The glochidia transform to juveniles and drop off their fish host. The juveniles, upon settling on suitable habitat attach by a byssal thread, which prevents their being swept away in water currents.

Given the elaborate life cycle, and the great longevity of these organisms, understanding the population dynamics requires a long-term commitment to develop a historical data set of population size. To address this lack of data, I have begun what I hope will be a long-term project to follow the population dynamics of mussels in the St. Croix River. This river has a diverse assemblage of unionids in fairly high density (Doolittle, 1988; Hornbach, 1997). There are 40 species of mussels that have been recorded from the St. Croix River (Hornbach 1997) with individual locations often having as many as 20 species present. There are two federally endangered species (Lampsilis higginsi and Quadrula fragosa) in the river, and for the winged mapleleaf mussel (Quadrula fragosa) the St. Croix River contains the only known extant population (Hornbach et al. 1996). Historically this species was found in at least 13 states but is now restricted to two locations, one in the St. Croix River. Additionally there are 14 species of mussel in the St. Croix River that the state of Minnesota has declared endangered or threatened. Many of these state-listed species are considered imperiled because of an historical reduction in the distribution and abundance of these organisms. However, the St. Croix River appears to be a refuge for many of these species with healthy reproducing populations. Proper management of this rare aquatic resource should be a priority. Unfortunately, many of the past studies on the St. Croix River have utilized qualitative sampling and this can provide biased population and community estimates compared to quantitative estimates (Hornbach and Deneka, 1996).

As mentioned above, freshwater mussels are among the most endangered organisms in North America. Historically, declines in mussel density and changes in community structure have been attributed to habitat degradation and alteration (Fuller, 1974; Cummings and Mayer, 1991; McMahon, 1991; Williams et al., 1993; Layzer et al., 1993). Currently, many researchers believe that the introduction of the zebra mussel from Europe in the late 1980s may prove to be even more devastating that past impacts on native mussels (Nalepa, 1994; Schloesser & Nalepa, 1994; Ricciardi et al, 1995). With these impacts there have been a number of efforts to examine techniques to protect native mussel populations. Few studies, however, have adequately examined relocation as a viable means of protecting populations from either zebra mussels or as a mitigation technique associated with human influences on river habitats (Cope and Waller, 1995). Among the most obvious locations to relocate threatened mussels, are areas that harbor rich and diverse mussel assemblages including, if possible, the species that are being relocated. However, if mussels are being moved into a dense mussel bed, the question arises concerning the impact of increasing the mussel density in the relocation area. I propose to continue a relocation study that was begun in the river in the summer of 1997. In this study we are examining the influence of mussel relocation on both the relocated mussels and on the mussels that existed in the location to which mussels were relocated.

In summary, the two major questions we are examining are:

1. How temporally stable are mussel populations? That is how much "natural" variation is found in mussel population density, community composition and age-structure in the St. Croix River?

2. How effective is in-situ relocation as an effective means to protect native mussels? What is the impact of relocation on the relocated mussels and on the mussel populations that receive the relocated mussels? Is there a negative effect of increasing mussel density in areas receiving relocated mussels?

III. Description of methodology

To examine the changes in mussel population density, age-structure, and community structure over time, we will return to seven locations in the St. Croix River that we have sampled in the past (Figure 1).

Figure 1. Seven mussel communities studied in the St. Croix River.

At each of these locations stratified quantitative sampling will be used at each station. At each of the seven sampling locations, ten sampling sites will be examined. Five of these sites will be from the middle of the channel and five near the shore. At each of these ten sampling sites, ten 0.25 m^2 quadrats will be taken with SCUBA. The entire contents (mussels and substrate) will be removed from the quadrat and sieved to ensure that all sizes of mussels are collected. Mussels will be identified and their shells measured (length, width, and height). In my previous work, I found that this sampling regime of taking approximately 100 0.25-m^2 quadrats is sufficient to characterize the mussel community at a location (Hornbach and Deneka, 1996).

From the quantitative samples, measures of community structure, age-distribution, and population density will be ascertained and compared to previous sampling data. In addition, at each site we will examine those factors likely to have a major impact on the distribution and abundance of unionids. Changes in these factors could be used to explain any observed differences in mussel population density, or community or age structure. These factors include water depth, location in the river, flow rates, and substrate type. Water depth will be determined with a sonar unit, location in the river with a GPS unit, and flow rate with a Marsh-McBirney Model 201D flowmeter. Substrate type will be determined by wet sieving the substrate that is taken with the mussel samples through four sieves and then weighing each fraction (Lewis, 1984).

At the present time, no self-sustaining populations of zebra mussels have been identified in the St. Croix River. There have been isolated individuals found attached to native mussels or small clumps of zebra mussels attached to boat hauls in the river below Stillwater. We will inspect all native mussels that we collect for the presence of zebra mussels. Care will be taken to disinfect our sampling boat and gear as we move from location to location in the river. We will also plan the research to begin sampling upstream and then to move downstream, to minimize the potential of moving zebra mussels into areas not previously infected.

To examine the efficacy of in-situ mussel relocations as a conservation technique, we will continue with the study design approved by the LCMR for implementation in 1997/98. This design included designating a site in the St. Croix River near the confluence with the Sunrise River as a "reference" site and a site near Wild River State Park as a "relocation" site. At each site a 5 m x 5 m grid has been demarcated on the bottom of the river. At each grid we randomly selected five 1 m x 1 m quadrats and assigned them to one of the following treatments:

Control - in 1997 these quadrats were not disturbed

Quadrula pustulosa - in 1997 each of these quadrats received an additional 10 Quadrula pustulosa.

Lampsilis cardium - in 1997 each of these quadrats received an additional 10 Lampsilis cardium.

Elliptio dilatata - in 1997 each of these quadrats received an additional 10 Elliptio dilatata.

Double density - in 1997 each of these quadrats received double the "normal" density. This was calculated by taking 10 0.25 m^2 quadrats outside the relocation grid and averaging the number of mussels collected. This amounted to adding 78 mussels to each of the double density treatment areas.

For all quadrats (except controls in 1997) we removed all mussels, identified them, measured their shell length and weighed them. We also etched a unique number on the shell of each mussel we collected. Mussels were replaced in the quadrats from which they were removed. At the reference site the Q. pustulosa, L. cardium and E. dilatata were collected from around the relocation grid while at the relocation area these species were taken from the reference site and move to the relocation area. Thus these 3 species are the "test" or relocated mussels. Figure 2 gives an overview of the relocation design. For the 10 0.25 m^2 quadrats taken to estimate the population density, we removed all of the sediment and wet sieved it through four sieves, weighing each fraction (Lewis, 1984) in order to determine sediment size.

In 1998, we revisited the relocation site, and removed all mussels from each quadrat, identified the mussel, measured its shell length, and weighed it. If the mussel was from a control quadrat or did not have an identification number we etched a number on the shell. All of the mussels were returned to the quadrat from which they were sampled. In addition, we searched around the grid to locate missing mussels. Another 10 0.25 m^2 were taken outside the relocation grid to assess changes in population density and substrate size.

In this study, we resampled these relocation grids using the same methods described for 1998. This will allow for the examination of changes in mussel mortality and growth in the various treatments. Analysis of variance will be used to assess differences in growth and survivorship and similar analysis will be used to detect differences in mortality among treatments (SAS Institute, 1994).

Figure 2. Study design in mussel relocation project.

IV. Description of results

Result 1 - Relocation and refugia study

In 1997 we marked and measured 1270 mussels at the reference site and 1272 mussels at the relocation site (Figure 2). In 1998 we recovered 1023 (80.6%) and 979 (76.9%) at the reference and relocation sites, respectively. At the reference site 120 mussels collected were dead, representing 9.4% mortality of the originally marked mussels, while the mortality at the relocation site was 5.0% (64 dead mussels). There was no difference in the number of mussels found alive, dead or missing among the four treatments (double density treatment, or the addition of the 3 test species - Quadrula pustulosa, Elliptio dilatata, Lampsilis cardium) nor were there differences between locations. It was noted that there were a large number of new mussels found in many of the test quadrats. At the reference site 814 new, unmarked mussels were found, while the number at the relocation site was 625. These preliminary analyses indicate that mussels are quite mobile, and that survivorship after handling is quite high. The survivorship of mussels (50 mussels of each - Quadrula pustulosa, Elliptio dilatata, Lampsilis cardium ) moved to the relocation site while not statistically different from that of the mussels maintained at the reference site was somewhat lower (Table 1).

Table 1. One-year mortality of relocated mussels from the reference and relocation sites.

	Elliptio dilatata			Lampsilis cardium			Quadrula pustulosa
Site	#recovered	% dead		#recovered	% dead		#recovered	% dead
Reference	38	12		36	8		36	8
Relocation	36	8		36	2		32	8

In 1999 we collected mussels from the reference and relocation sites at Wild River State Park. 2150 mussels were handled at the reference site and 1900 mussels at the relocation site. We measured and weighed 1950 live mussels at the reference site, of these 1550 (79%) had been labeled during a previous year. At the relocation site we measured and weighed 1700 live mussels, 1300 (76%) of these had been labeled during a previous year. Individual mussels grew less in 1999 than in 1998, and there does not appear to be a significant difference between the two sites. There were a large number of new mussels found in many of the test quadrats (approximately 400 individuals at both the reference and relocation sites). As we observed in 1998 it appears as though several mussels moved into the study grids.

Table 2. Two-year mortality of relocated mussels from the reference and relocation sites.

	Elliptio dilatata			Lampsilis cardium			Quadrula pustulosa
Site	#recovered	% dead		#recovered	% dead		#recovered	% dead
Reference	35	16		38	16		33	16
Relocation	31	10		25	4		26	16

While conducting work on this project we made an important discovery. Winged mapleleaf (Quadrula fragosa) shells were collected at the relocation site. This federally endangered species has never been observed in the upper Saint Croix River and presence of the shells could have a substantial impact on whether or not to relocate this species from the lower St. Croix River. The USFWS provided us with support to conduct a survey for live winged mapleleaf in the area. Although no live winged mapleleaf were collected, two additional shells were collected.

Result 2 - Monitoring mussel populations in the St. Croix River

This summer we collected 100 quadrats at Wild River State Park, Franconia, and Prescott. Mean mussel species richness at Wild River State Park decreased between 1993 and 1999 but the change is not statistically significant (Figure 3).

Figure 3. Mussel species richness at Wild River State Park between 1993-1999.

Mussel density at this site did not change significantly between 1993, 1996, and 1999 (Figure 4), but sediment size has shifted significantly to more coarse and back to less coarse between 1993 and 1996, and 1996 and 1999 respectively (Figure 5).

Figure 4. Mussel density at Wild River State Park between 1993-1999.

Figure 5. Sediment size at Wild River State Park between 1993-1999.

At Franconia we observed greater changes in the mussel community and sediment size. Species richness dropped significantly in 1999 to nearly one mussel per quadrat (Figure 6).

Figure 6. Mussel density at Franconia between 1991-1999.

Mussel density also decreased significantly (Figure 7) and there was a significant increase in the amount of fine sediment in the riverbed (Figure 8).

Figure 7. Mussel density at Franconia between 1991-1999.

Figure 8. Sediment size at Franconia between 1991-1999.

The mussel community at Prescott did not change significantly from 1994 to 1999 but there was a significant shift to finer particles in the substrate. Although mussel density and species richness decreased between 1994 and 1999 it was not statistically significant (figures 9 and 10). As was observed at Wild River State Park and Franconia there was a significant shift to finer substrate particles at Prescott (Figure 11).

Figure 9. Mussel density at Prescott between 1994-1999.

Figure 10. Mussel species richness at Prescott between 1994-1999.

Figure 11. Sediment size at Prescott between 1994-1999. (Standard error bars too small to visualize on graph.)

In addition to native mussels a few zebra mussels were collected from the study area at Prescott. In our study grids we found two empty zebra mussel shells and one live zebra mussel attached to an empty native mussel shell. Outside of the study grids we observed two native mussels each with a live zebra mussel on their shells.

Literature cited:

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Burky, A.J. 1983. Physiological ecology of freshwater bivalves, pp. 281-327. In Russell-Hunter, W.D. [ed]. The Mollusca, Vol. 6. Ecology. Academic Press, New York.

Cope, W.G. And D. Waller. 1995. Evaluation of freshwater mussel relocation as a conservation and management strategy. Regulated Rivers 11: 147-155.

Cummings, K.S. and C.A. Mayer. 1992. Field Guide to Freshwater Mussels of the Midwest. Illinois Natural History Survey, Manual 5. Champaign, IL. 194 p.

Doolittle, T.C.J. 1988. Distribution and relative abundance of freshwater mussels in the St. Croix National Scenic Riverway. Cable Natural History Museum, Ashland, WI.

Fuller, S.L.H. 1974. Clams and mussels (Mollusca: Bivalvia), p 215-273. In: C.W. Hart, Jr. and S.L.H. Fuller, (eds.) Pollution Ecology of Freshwater Invertebrates. Academic Press, New York, NY.

Hornbach, D.J. 1997. Bivalves in the St. Croix River: a report for the Water Resources Management Plan, St. Croix National Scenic Riverway, National Park Service, pp. E1-E50. In K.L. Holmberg, J. Perry, R.S. Ferrin and D.L. Sharrow, Water Resources Management Plan, St. Croix National Scenic Riverway, Minnesota and Wisconsin. February 1997.

Hornbach, D.J., J.G. March, T. Deneka, N.H. Troelstrup, and J.A. Perry. 1996. Factors influencing the distribution and abundance of the endangered winged mapleleaf mussel, Quadrula fragosa in the St. Croix River, Minnesota and Wisconsin. American Midland Naturalist 136: 278-286.

Hornbach, D.J. and T. Deneka. 1996. A comparison of a qualitative and a quantitative collection method for examining freshwater mussel assemblages. Journal of North American Benthological Society 15: 587-596.

Layzer, J.B., M.E. Gordon, and R.M. Anderson. 1993. Mussels: the forgotten fauna of regulated rivers: a case study of the Caney Fork River. Regulated Rivers: Research and Management 8: 63-71.

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Master, L. L., S. R. Flack, and B. A. Stein, eds. 1998. Rivers of life: critical watersheds for protecting freshwater biodiversity. The Nature Conservancy, Arlington, Virginia. 71 pp.

McMahon, R.F. 1991. Mollusca: Bivalvia, p. 315-399. In (J.H. Thorp and A.P. Covich, eds.) Ecology and Classification of North American Freshwater Invertebrates. Academic Press, Inc. New York, NY.

Nalepa, T.F. 1994. Decline of native unionid bivalves in Lake St. Clair after infestation by the zebra mussel, Dreissena polymorpha. Canadian Journal of Fisheries and Aquatic Sciences 51: 2227-2233.

Ricciardi, A., F.G. Whoriskey, and J.B. Rasmussen. 1995. Predicting the intensity and impact of Dreissena infestation on native unionid bivalves from Dreissena field density. Canadian Journal of Fisheries and Aquatic Sciences 52: 1449-1461.

SAS Institute. 1994. JMP Statistics and Graphics Guide. Version 3 of JMP. SAS Institute, Inc., Cary, NC.

Schloesser, D.W. and T.F. Nalepa. 1994. Dramatic decline of unionid bivalves in western Lake Erie after infestation by the zebra mussel Dreissena polymorpha. Canadian Journal of Fisheries and Aquatic Sciences 51: 2234-2242.

Williams, J.D., M.L. Warren, Jr., K.S. Cummings, J.L. Harris, and R.J. Neves. 1993. Conservation status of freshwater mussels of the United States and Canada. Fisheries 18(9): 6-22.

V. Timetable

July 1999-Sept. 1999 - Sample Relocation Site, sample three population monitoring locations (Wild River State Park, Franconia, Prescott)

Sept. 1999-Dec. 1999 - Analyze data, prepare interim report, present results at St. Croix River Rendezvous

July 2000-Sept. 2000 - Sample Relocation Site, sample four population monitoring locations (Interstate Park, Osceola, Lakeland, Bayport)

Sept. 2000-Dec. 2000 - Analyze data, prepare interim report, present results at St. Croix River Rendezvous

June 2001 - Final report to LCMR

VI. Budget

In addition Macalester College will provide summer housing for students, and Dan Hornbach will oversee the project and spend approximately 5% of his time on this grant. This time being supported by Macalester College.