Intruder Alert

As Spring creeps up, I look forward to enjoying the picturesque waters and shorelines throughout the Madison Valley, however a threat looms nearby. A couple of unruly mollusks, zebra, and quagga mussels, have made their way out west.

What are Invasive Mussels and Where Did They Come From?

Invasive mussels, specifically zebra and quagga mussels, are small freshwater mollusks that infest waters and quickly expand their population to sizable numbers. These mussels, which are native to the Black and Caspian Sea in Eurasia, are believed to have been introduced to the United States through ballast water of trans-oceanic ships. Zebra mussels were first discovered in North America in 1988 in the Great Lakes. The following year, quagga mussels were discovered in the same area. Since then, these mussels have spread rapidly throughout the Great Lakes region and rivers east of the Mississippi drainage. They have also been found in Texas, Colorado, Utah, Nevada, California, Idaho, and South Dakota. The detections in Idaho (Snake River) and South Dakota (Pactola Lake) are especially concerning, when you consider their close proximity to our waterways.

Figure 1: Quagga and Zebra mussel. PHOTO COURTESY DAVE BRENNER

Zebra and quagga mussels can vary in size, from microscopic to their adult size of about 2 inches long. Unlike our native mussels, Zebra and Quagga mussels can attach to hard surfaces because of their strong, thread-like appendages that can be released. If you see a mussel stuck to a hard surface, it is likely invasive!

What threat do mussels pose to the Madison Valley?

Invasive mussels can severely impact infrastructure, as well as other animals and large-scale food-web interactions.

When invasive mussels invade waterways, their clustered nature can clog irrigation intakes, valves, pipes, screens, sprinklers, and other parts. This clogging also usually results in decreased flow rates through irrigation components. The same phenomena impact utilities, by reducing water-pumping capabilities for power and water treatment plants. Regarding anglers and boaters, mussels can ruin equipment, clog cooling systems in motorboats, foul hulls, and jam the centerboard wells, reducing performance and efficiency.

Zebra and Quagga mussels are filter feeders, meaning they consume large amounts of plankton that form the base of the food web. This greatly reduces the food available for native fish and other animals. Removing the plankton also promotes vegetation growth by allowing more sunlight to reach deeper sections of water, decreasing overall water quality. In addition to limiting food and reducing water quality, mussels can also harm aquatic life, such as native shellfish, by attaching to their bodies and reducing movement or completely incapacitating them.

Figure 2: Invasive Mussels attached to a Boat Prop. PHOTO COURTESY FLATHEAD LAKERS

Once a mussel population is established it is extremely difficult to remove them from a waterway. Their small size and rapid reproduction rate – females produce anywhere from 100,000 to 1 million eggs per year – makes them difficult to detect and control. On the nearby Snake River, officials in Idaho attempted a $3 million approach to eradicating quagga mussels detected in September. The strategy involved treating a 16-mile section of the river with a copper-based chemical that is harmful to mussels and fish. The aggressive nature of this treatment also forced officials to create a plan to restock the area’s most affected fish populations, such as sturgeon. Officials will not know how effective this treatment was until waters warm up and sampling begins again in Spring.

If mussels establish in Montana, it is estimated to cost the state $234 million per year just to manage, not eliminate the population.

What can you do? 

Zebra and Quagga mussels are a costly nuisance, so what can we do to stop these aquatic hitchhikers? Prevention is best strategy!

• Clean all equipment that has come into contact with water. Remove all mud from waders, boats, trailers, etc. before leaving any body of water.
• Drain all water from every compartment of boats and equipment. Sponge or towel any remaining standing water.
• Dry your watercraft and equipment. The longer you keep your watercraft, trailer, waders, and other equipment outside in the hot sun, the better.
• Stop for watercraft inspections
• Report any suspect infestations at https://nas.er.usgs.gov/SightingReport.aspx