Mussel Relocation at Hannum’s Mill Dam
Buttons and Pollution: Mussels in Peril
Fresh water mussels are among the most threatened group of animals on earth. In North America, over 70% of the continent’s roughly 300 species are threatened, endangered, or extinct. Iowa alone has lost twelve of its fifty four native species, with nine more endangered and six threatened. Why?
The problem began in the late 1800s. Mussel shells became prized for making pearl buttons, driving the creation of a massive industry in Iowa. Muscatine (aka Pearl City) was the biggest producer of pearl buttons in the world, capable of churning out 1.5 billion buttons a year. By 1900, the demand for shells destroyed local mussel populations. Soon after, plastics would displace pearl buttons, and the industry, along with its demand for shells, dried up.
Despite the ultimate failure of the pearl button industry, mussel populations are still imperiled across the state. As relatively immobile filter feeders, they are completely dependent on good quality water to survive. Erosion, nutrient pollution, and low oxygen all negatively affect mussels. So when water quality is poor, as it is in most Iowa streams and rivers, mussels suffer.
Locally threatened species Creek Heelsplitter (left/top) and Cylindrical Papershell (right/bottom)
The Mission: Save Some Mussels
Hannum’s Mill Dam
Hannum’s Mill Dam
In preparation for an upcoming modification of Hannum’s Mill Dam on the South Skunk River just north of Ames, IA, Story County Conservation staff, DNR biologist Jennifer Kurth, and volunteers set out to find and relocate mussels downstream of the dam. While dam removals and modifications can ultimately benefit mussel populations, short term changes in water levels and disturbances to sediments can leave mussels exposed to the air or fatally buried in silt. By relocating them before construction begins, we can ensure minimum harm and greater future population success.
The crew set out on foot, searching for mussels visually and by scouring the gravel and sand by hand. Mussels typically bury themselves vertically in the substrate with their “mouths” – more accurately called intake siphons – poking up into the water to collect food from the water. In the video below, you can see Story County Conservation Tech Kallie Webber unearth a Plain Pocketbook mussel with its foot extended, a fleshly, muscular organ used to dig and hold on to the substrate.
By the end of the afternoon, the team managed to collect more than 450 mussels, including two locally threatened species, the Creek Heelsplitter and Cylindrical Papershell. Finding these species highlights the importance of this work. By relocating them prior to dam modification, we can give them a chance to contribute to the continuation of their species.
Volunteer and Prairie Rivers board member Rick Dietz helps sort mussels by species.
If you’re interested in this kind of work, consider volunteering for this year’s Mussel Blitz on August 17-19. Reach out Jennifer Kurth with the DNR Watershed Improvement Program: 515-639-8464 or Jennifer.Kurth@dnr.iowa.gov
A big thank you to Story County Conservation and the Iowa DNR for making this event possible.