As I go down the river during trapping I often come across piles of freshwater mussel shells that very in size from about the size of a nickel to a fifty-cent piece. Sometimes hundreds in the area/ pile of about the size of a trash can lid. I assume it is muskrats. Has anyone also noticed this sign while out trapping, have you set these locations, are these areas frequently visited or is it a seasonal thing not associated with trapping season.

I have found that muskrats which dine on mussels regularly run larger than others. Mussels aren't everywhere, but when the rats find them they wear them out. They look like bodybuilders when you skin them out.

Muskrats or otter

Muskrats feed heavily on mussels where they occur. Often times the muskrats will dig them and put them on the bank. There are a lot of theories as to how they open them as Muskrats don't have very strong front feet with a lot of dexterity. Some believe the muskrats run their claws over the shell and it relaxes the mussels so they open up some and they can eat the meat. My personal theory as a mussel biologist is that the muskrats deposit them at a feeding station and then come back and eat the meat as the mussels start to gape after being out of water for a bit. Of course, the feed stations get raided by raccoons, otters, mink, dogs, etc. as well.

I work frequently on the Duck River in middle Tennessee which is generally regarded as the most diverse and abundant mussel assemblage in the world with as many as 72 mussel species known from the river and around 50 species still ocuring.. At a few long-term monitoring sites, I have collected thousands of shells of several species including a number of federally endangered species that have all been eaten by muskrats, otters, and raccoons. A few years ago I collected all of the mussels I found at a muskrat feeding station on an old pickup truck tire and counted them. I then looked up their values in a book published by the American Fisheries Society and the estimated value of the mussels that a few muskrats ate was about $58,000. Of course this doesn't count all of the costs associated with endangered species recovery as well so this value is probably on the low side. We had one species that we are restoring that have very high levels of predation from muskrats. Approximately 20% of the animals we released were likely eaten by muskrats in the first year after release.

We tend to think of predators largely as wolves, coyotes, fox, raccoons, etc. but even muskrats are extremely predatory in some waters. This is a prime example of another species that needs managed for the recovery of endangered species. I've know of several agencies and organizations that have utilized muskrat and raccoon trapping to reduce predatory pressure on mussels for recovery activities.