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The freshwater mussels that inhabit the streams of Illinois spend most of their lives buried in the substrate, exposing only the parts they use to take in and expel a steady flow of water, from which they filter their food. This mode of living poses certain challenges for the scientists whose work it is to monitor mussel populations.
As Illinois Natural History Survey (INHS) field biologist Alison Price explained to me, it is sometimes possible to sample for mussels visually, but only in waters that are shallow and clear enough to afford a good view of the streambed—a rare case in the Prairie State. More often, she and her colleagues sample for mussels by “grubbing.” “It is what it sounds like,” she quipped. “You reach down and rake your fingers through the sand and gravel until you feel a shell.” [Photo: Price grubbing for mussels in the Mackinaw.]Recently, I spent some time in the field with Price and her colleagues, to learn about their work and even do a little grubbing myself.
Our day began at a site on the Mackinaw River northeast of Bloomington, with a “maximum effort survey,” which was performed in part to collect data for a UI graduate student who is studying the efficiency of current sampling methods. In conducting this survey, members of a crew that included biologists and technicians from both the Natural History Survey and the Illinois Department of Natural Resources collected all of the mussels they could find from a predetermined stretch of river in a set amount of time. Then, without returning any of the mussels previously collected, they covered the same territory again three more times.
What they turned up was amazing to me, although about what they expected. One-hundred-fifty-one live mussels were collected, with representatives from 10 different species, most numerous among them fatmuckets, plain pocketbooks and round pigtoes (and which, I admit, I list here just because I find the colorful common names of mussels enjoyable). After these were all sorted and measured they were returned to the river, where, presumably, they hunkered right back into the substrate and resumed filtering the water for food.
By analyzing data collected through this and other “maximum effort” surveys, the UI student is seeking to answer the question of whether current sampling protocols provide information that is reliable enough to accurately assess populations of rare mussel species. The question arises since rare species are more likely to be missed altogether or underrepresented using current techniques.[Photo: UI graduate student Jain Huang and INHS field biologist Diane Shasteen sorting mussels collected from the Mackinaw.]More importantly, data from the Mackinaw River survey I observed will be combined with data gathered by Price and others at approximately 800 sites around the state as part of a three-year project. This project will ultimately provide state agencies with the information needed to manage and protect populations of mussels, which are among the most endangered groups of animals that occur in Illinois.
My day in the field with Price and her crew also included a second stop, to rescue mussels from a drainage ditch beneath a county road bridge that is slated for demolition. This effort was mandated by the known presence there of slippershell mussels, which are listed as threatened in the state. Our inelegant, yet highly effective method of finding mussels for removal there was to form a shoulder-to-shoulder line across the stream and crawl through the target area, grubbing as we went.
From this small stretch of unpromising looking stream, we retrieved 359 live mussels, including 11 slippershells. All of these were moved to reaches of the stream that would not be affected by the bridge work.Illinois has already lost 20 of the 80 species of mussels that once occurred here, and our streams have become poorer as a result. Wouldn’t it be a great accomplishment if we could use the knowledge generated by today’s scientists to prevent further declines?
To learn more about mussels on the Web, you might want to start with the following:
Freshwater Mollusk Conservation Society
http://molluskconservation.org/
Illinois Natural History Survey Mussels:
http://www.inhs.uiuc.edu/animals_plants/mollusk/
