Freshwater mussels can be found living in most of our waterways. Their open shells are a common sight along the banks of rivers and ponds, they can be found alone or in small piles called middens. These middens are the work of hungry muskrats that consider the mussel a delicacy. In shallow water the mussels peculiar trails can be seen along sandy bottoms where they push themselves along with their powerful foot muscle. Until recently I like many others considered the freshwater mussel somewhat of a curiosity, I knew they were there but did not understand where or how they fit into the larger scheme of things. My introduction into the fascinating world of the freshwater mussel began a couple of years ago on the Satucket River in East Bridgewater.
My brother and I were checking below the Carver Cotton Gin Dam for alewives, at the time we did not know whether or not the alewives made it up to the dam. Not seeing any sign of them, we walked down stream to check below the old mill buildings. Here we found a muskrat midden. My brother plucked several shells from the midden and looked them over carefully. Holding up one of the shells he said, " The alewives have been up here " what do you mean I replied. He then introduced me to Anadonta Implicata, the freshwater mussel commonly known as the Alewife Floater and its fascinating life cycle.
Alewife floaters along with the rest of the fresh water mussel clan have a unique way of dispersing themselves throughout our rivers and ponds; their juveniles (glochidia) are hitchhikers. Female mussels release the glochidia into the water column where they attach themselves to fish. Depending on the species, they will continue as hitchhikers for days or months. When the hitchhiker stage is finished, they drop off their host fish to begin life on the bottom. Without their host fish the juvenile mussels (glochidia) can not survive.
Some mussel species are very host specific such as is the alewife floater, which must have alewives for a host. Therefore if you find alewife floaters in a waterway there must have been alewives there at some point in time. Some species have multiple fish hosts and therefore are more common. Other species like the Tide Water Mucket which we have found at Satucket and Robbins Pond are more host specific. It is thought that they require a sea run fish as a host. One of their primary host fishes may be the American Eel or Sea Lamprey, these are the only two fish species that would be able to access the upper Satucket due to the impassable Cotton Gin Dam.
In August 2001 the spill gates were opened at the Cotton Gin Dam on the Satucket River. As the impoundment drained, we walked along the drying mud of the former impoundment pitching stranded mussels back into the river channel. There appeared to be quite a few mussels in the former impoundment, some big some small, most looked about the same.
Later in the week we took a kayak trip down the upper part of the river above the influence of the former impoundment.
Heading down from Robbins Pond we came to the spot where the Poor Meadow Brook drains into the Satucket. The river becomes quite narrow here due to willow and alder thickets and requires a short portage from the Satucket to the Poor Meadow to get back into the Satucket. Here we found the river bed to be completely covered with mussels. Looking down into the water the river bed appeared to be gravel bottomed, but they were freshwater mussel beds! Along the shallow areas of the upper river you could drag your hand along the bottom and feel nothing but mussels.
This raised an interesting question? What were we seeing in the lower (formerly impounded) part of the river? Were we seeing a healthy thriving mussel population? Or were we seeing a remnant population struggling for survival in an altered man- made environment. This same question could be asked about many other species here and in other parts of our Great Rivers watershed.
So, what did we learn about freshwater mussels on the Satucket? The upper river that was least affected by the impoundment had the most diverse mussel population. Here we found the Eastern Elliptio, Eastern Lampmussel, Tidewater Mucket, Eastern Pond Mussel, Eastern Floater and the Triangle Floater. In the former impoundment we found only the more tolerant and adaptable species, Eastern Floater, Eastern Elliptio and Eastern Lamp Mussel.
It seemed that the upper river provided a diversity of habitat and therefore a more diverse mussel population. Here we found shallow fast flowing areas with sand and gravel bottoms, along with deeper slower moving areas with silty bottoms. This diversity of habitats seems to allow all the different species to find and populate the habitat that they naturally thrive in. In the former impoundment the habitat was limited by the sluggish flows and deep silt and therefore we found a less diverse and less numerous mussel populations.
From Biology in Focus
U.S. Geological Survey
Poised on the brink of mass extinction, freshwater mussels are the largest group of endangered animals in North America. About 70 percent of the 300 native species are considered endangered, threatened or of special concern. Biologists see the mussels' plight as a serious warning for our global ecology as a whole-when mussels begin to disappear, it is a sign that other species, and entire ecosystems, may be in peril as well.
Mussels not only oblige us as environmental barometers, but they also strengthen the health and stability of a stream. As mussels feed and breath, they filter water and make it cleaner. and because mussels are at the foundation of the aquatic food web, they contribute to the survival and vitality of other animals. A stream with abundant mussels can usually support more muskrats, otters, wading birds and game fish.
The number of imperiled mussels in the United States forecasts an extinction crisis that, unless prevented, may result in the complete loss of dozens of species and further impoverishment of aquatic ecosystems.
In our travels we have found no sign of freshwater mussels in the Salisbury Plain or Matfield Rivers?
Follow these links for more info on our good friends the Freshwater Mussels
Mussel beds below Robbins Pond at Satucket River