Statewide Assessment of Freshwater Mussels in Iowa Stream (Final Report - Oct. 2000)
Age and Growth Rates of Freshwater Mussels
Assessing Iowa's Inland Stream Mussel Populations
More About the Project
Mussel Trivia
Iowa Species List and Conservation Status
Data Collection Procedures
Appendix A
References
Project Volunteers
More Detailed Mussel Information and Related Sites

Age and Growth Rates of Freshwater Mussels
By: James L. Anthony

Although freshwater mussels are quite diverse in North America, they are declining at an alarming rate. To develop the management and recovery plans necessary for the conservation of these animals, we need to understand their population dynamics. This depends largely upon a knowledge of their age and growth rates. My research involves the examination of the validity of current aging methods for freshwater mussels in Iowa. These methods which rely on various shell markings or banding patterns, may substantially underestimate age and overestimate growth rates. I am studying the validity of these techniques through a one year mark- recovery project in streams throughout the state of Iowa. Additionally, I am investigating various radiometric and chemical dating methods for use with living freshwater mussels. These methods may provide additional insight into the true age and growth dynamics of these mysterious creatures.

Assessing Iowa's Inland Stream Mussel Populations
By: Kelly Arbuckle

The importance of freshwater mussels has been recognized for decades. Historically, mussels were prized for their commercial value in the production of pearl buttons. More recently, their economic value is attributed to the Japanese culture-pearl industry. They are also important ecologically as a food source for terrestrial and aquatic animals and as water quality indicators. Once common in Midwestern rivers and streams, mussels are now reported as more at risk than any other group of animals. There are numerous biological, chemical, and physical factors adversely influencing freshwater mussel communities. These include commercial exploitation, lack of host fishes, exotic species (e.g. zebra mussels), and habitat degradation and destruction. Understanding the relationship between these factors and mussel populations is important to the management of these animals. Funded by the Iowa Department of Natural Resources, this project focuses on assessing inland stream mussel populations and identifying environmental variables influencing their distribution. The study includes a field survey to quantitatively assess current populations and GIS analysis to describe physical factors impacting Iowa mussels.

More About the Project

Statement of Purpose

Frest (1987) described mussel populations in most major Iowa streams as declining. He suggested at least half of Iowa’s interior stream mussel faunae should be considered in danger of extirpation. Frest recommended future studies including an examination of additional streams and more extensive surveys of several surveyed streams. Frest's report is the most current assessment of Iowa’s mussel faunae, but evaluated only a fraction of the streams having the potential to support mussel populations. A thorough assessment, including re-surveying sites of previous studies, evaluating new streams, quantification of abundance and impacts on mussel faunae in Iowa, is needed. The purpose of this study is to provide the Iowa Department of Natural Resources with a current assessment of Iowa’s lotic mussel populations. The study will include a field survey to assess current populations and GIS (Geographic Information Systems) analysis to identify factors impacting mussel populations.

Description of Work and Services

Field Survey

GIS/Predictive Study

Iowa Species List and Conservation Status

Before collecting the data, record your name, the date, and stream name on the data sheet. Recording the exact location at which you are collecting data is essential. Provide a description of the access area (e.g. Hwy. 30 bridge south of Ames, IA.) on the data sheet. Document the site location by marking it on the map.

If possible, take stream measurements from a data collection point at least 100 meters (about a football field length) from the access point to minimize its effect on stream characteristics (EPA 1997). Indicate on the data sheet if the data is collected upstream or downstream from the access point as well as the distance.

While proceeding to the data collection point (100 meters upstream or downstream from the access), complete a visual survey of stream banks and shallow water for mussel shell material and other aquatic animals (fish, crayfish and snails) and plants (algae, duckweed, and pondweed). Complete the aquatic plant and aquatic animal sections on the data sheet.

At the data collection point make the following measurements:

1. Stream width: Measure stream channel width in meters.

2. Water depth: Measure the depth (in cm) mid-channel of the stream.

3. Stream Flow: Research indicates 0.3 m/sec is a suitable stream velocity value for distinguishing between fast and slow conditions (Plafkin et al. 1989). Calculate the average velocity of the stream and indicate on the data sheet whether the stream flow is fast or slow. Instructions for measuring stream velocity are in Appendix A.

4. Water Clarity: In shallow streams, water clarity can be measured visually. If the streambottom is visible, water clarity is high. In deeper streams, clarity can be measured using a secchi disk, a round 20-cm diameter disk that is painted in black and white quadrants. Water clarity is high when secchi depth is greater than 60% of the water depth, moderate when between 30-60% of the water depth and low when less than 30% of the measured water depth. Instructions for using a secchi disk are located in Appendix A.

5. Substrate type: Evaluate substrate type (grab a handful!) at 5 random places at the data collection point. Indicate on the data sheet the dominant substrate type based on the following categories:

Boulder (< 256 mm or 7")
Cobble (64-256 mm or 2"-7")
Gravel (2-64 mm or 0.05"-2")
Sand (0.06-2 mm - gritty)
Silt (0.004-0.06 mm)
Clay(<0.0004mm)

6. Bank vegetation: The absence or presence of bank vegetation indicates the relative stability of a stream bank. Streams banks with little or no vegetation are usually more susceptible to bank erosion which adversely influences water quality. Assess the bank vegetation present on the right and left banks as absent or present.

7. Riparian zone: Land-use adjacent to the stream influences stream habitat and water quality. Assess the land-use and/or vegetation in the areas above the right and left banks. Indicate the most dominant feature observed.

8. Additional Notes: Record miscellaneous observations important to the assessing the habitat conditions of the stream reach.

Appendix A

Measuring Stream Velocity

Measuring stream velocity is important because it affects a variety of chemical, physical and biological characteristics of a stream. The objective is to calculate stream velocity by recording the amount of time (in seconds) it takes a floating object to travel a known distance. A simple way to do this is to attach a known length of line (2 meters is sufficient) to a cork (see diagram below) and record the time it takes the cork to float the distance of the full length of the line in the stream current.

Field instructions:
1. Hold the cork and attached line at the surface of the water. Position yourself so that you do not interfere with stream flow.
2. Release the cork (hold on to the other end of the line!) and start timing the float.
3. Stop timing when the cork has traveled the full distance of the attached line.
4. Record the time it takes the line to fully extend in the stream current.
5. Because velocity varies across the channel, repeat this process 5 times, sending the float down different paths at different location within the stream.
6. Calculate the average float time by dividing the sum of the timed values by the number of float trials.
7. The average surface velocity (m/sec) of the stream is simply the distance traveled (the length of the line) divided by the average float time of the 5 float trials.
8. Because stream velocity varies from surface to bottom, adjust this value to reflect the overall average velocity of the stream, by multiplying the average velocity by the correction factor 0.8 (Dunne and Leopold 1978).

Measuring Water Clarity

References

Dunn, T.B. and L.B. Leopold. 1978. Water in environmental planning. W.H. Freeman, San Francisco, CA.

EPA. 1997. Revision to rapid bioassessment protocols for use in streams and rivers: periphyton, benthic macroinvertebrates and fish. EPA/841-D-97-002. U.S. EPA, Washington, D.C.

Frest, T.J. 1987. Mussel survey of selected interior Iowa streams. University of Northern Iowa. Final Report to Iowa Department of Natural Resources and U.S. Fish & Wildlife Service. 354 pp.

Plafkin, J.L. M.T. Barbour, K.D. Porter, S.K. Gross and R.M. Hughes. 1989. Rapid bioassessment protocols for use in streams and rivers: benthic macroinvertebrates and fish. EPA/444/4-89-001. U.S. EPA, Assess. and Watershed Protection Div., Washington, D.C.

Project Volunteers

The "Skunk River Navy"
This group of Iowa State University students evaluated habitat conditions in the Skunk River, Story County. Lead by Jim Colbert, participants attended a monitoring workshop before heading to the field last Fall. In addition to collecting valuable habitat information, they collected an unbelievable amount of trash including a bath tub, hide-a-bed, and many, many automobile tires!