Unios in Massachusetts

[Caitlin]

Unios in Massachusetts LINK

FRESHWATER MUSSEL


For inquiries contact Doug Smith, Lecturer, Biology Department, University of Massachusetts Amherst


A conspicuous organism in the benthos of the Connecticut River is the freshwater mussel.

All freshwater mussels belong to the mollusk order Unionoida, a solely freshwater group. These animals are large (up to 150 mm or 6 inches in length) bivalved creatures possessing a hinge which is most developed posterior of the beaks or umbos. The shells are typically covered by a thick skin or periostracum that is variously colored and sometimes rayed on the disk depending upon the species. Internally, the shell has a "pearly" appearance due to the nacreous lining of the inner shell surfaces. These features have made freshwater mussels popular among collectors since the early 19th century.
In the region of the shell hinge, articulating "teeth" are variously developed or absent. When present, these teeth radiate from the beaks. The anterior teeth, when present, are called pseudocardinals and are thick, short, and, when well developed, grooved, and serrated. The posterior teeth, when present, are called laterals and are always elongate and lamellate.

The gross anatomy of North American freshwater mussels is characterized by the presence of an anterior adductor muscle (AA), a posterior adductor muscle (PA), a labial palp (P) for transporting food to the mouth, and a large muscular foot (F) which is used for digging and anchorage. The gills (a and b) are composed of a series of folded plates; two plates (demibranchs) occur on either side of the foot. Surrounding the animal and lining the inner surfaces of the shell is a mantle which is open along the margins of the shell. Posteriorly, the mantle margins, in conjunction with the demibranchs, form the inhalent (IN) and exhalent (EX) openings through which water circulates in the animal.

Species of freshwater mussels, exclusively among bivalve mollusks, produce a larva called a glochidium that is parasitic on fish or amphibians. The larvae, prior to release, are brooded in the parent's demibranchs (inner and/or outer gills) for a varying period of time depending upon the species. Metamorphosis to the adult morphology occurs while attached to the host. The vast majority of freshwater mussels, including all Massachusetts species, are dioecious. Adult freshwater mussels are infaunal filter feeders. Typically, the only movements undertaken are vertical adjustments of the animal's position in the substrate in response to changing environmental conditions. Migrations occur, but are usually of short duration and distance and, for the most part, are undertaken to withdraw from unsuitable habitats. Dispersal is principally accomplished during the parasitic larval stage. See reproduction for more information.
Two families of unionoid mussels are present in Massachusetts. The Margaritiferidae is represented by a single species, Margaritifera margaritifera, which is widespread in New England and northwestern Europe and Scandinavia. In North America, scattered populations occur in New York and Pennsylvania as well. Margaritiferids are chiefly distinguished from other unionoid mussels by a unique non-septate gill structure and a simple diaphragm, which separates incoming water in the branchial chamber from outgoing water in the suprabranchial chamber.
The other family occurring in Massachusetts is the Unionidae. This is the largest family of unionoid mussels and contains species living in North and Central America, and throughout the Palearctic region. Eleven species live in Massachusetts. All belong to a zoogeographical assemblage called the Atlantic Slope fauna. The Unionidae are characterized by the possession of gill septa in the demibranchs and a complex diaphragm.
The freshwater mussels are among the most endangered organisms in North America. About 3% of the North American fauna is extinct and nearly 50% of the species are considered endangered. In Massachusetts, seven of the eleven known species are protected by law. In the Connecticut River, only one species remain common, Elliptio complanata.

REFERENCES: Pennak, R.W. 1978. Fresh-water invertebrates of the United States, 2nd edition. John Wiley and Sons, New York.

Smith, Douglas G. 1995. Keys to the Freshwater Macroinvertebrates of Massachusetts. Published by D. G. Smith, Amherst, MA. Note: this book can be ordered for the very reasonable price of $22.50, shipping included (Mass. residents should also add 5% sales tax). If interested contact Doug Smith at (413)-545-1956 for more information.
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[Mikeyy]

The freshwater mussels are among the most endangered organisms in North America. About 3% of the North American fauna is extinct and nearly 50% of the species are considered endangered.

I like the way they always put that in there. Does anyone know the last time shells were taken commercially from Massachusetts. Because I don't ever remember it. And I have done this work for almost 40 years. It is always assumed that when it is represented that many species are endangered that it is because of over fishing. The fact is these are not commercial shells. They were never harvested for commercial use. So why have they disappeared?

 

[Caitlin]

Hi Mikeyy
Have you read Kunz 1908?
I remember from that book that looking for mussel pearls was a huge pastime in the late 19th century. That was after centuries of Spaniards and other Europeans had traded trinkets for massive numbers of pearls from the American heartland.

He mentions that in the previous 2 decades 1888-1908) several pearl companies had formed and were still yielding over 1/2 million $ in pearls annually. He cites 8 pages of examples, recounting which rivers were cleared out first then a chronological record of the ongoing plunder. No one stopped until all the pearls were gone in any popular river and there were so few mussels, it was no longer fun for American families to picnic by rivers and looks for mussels with pearls.

Then someone would find another river or creek and every one would fish that one out. Many of those areas followed the same pattern of the South American and Panamanian pearls plunders. Also the Bay of Cortez pearls. 99% of the early sources for American pearls have still not recovered.

The Americas have yielded incredible numbers of pearls to the early explorers, but just about everything was gone by shortly after Kunz wrote his book-- a fantastic book about pearls written before the advent of cultured pearls.

 

[Slraep]

So why have they disappeared?

Being quite sessile and filter feeders, pollution and loss of habitat would do it. In other words, it is because of the unfortunate ways of man, who, on the contrary, is quite mobile and omnivorous.

Slraep

 

[MABE BRAZIL]

one important fact is the way these mussels reproduce. Since they need a specific host (fish), if the fish disappear they will desappear too. And the construction of dams to keep reservoir or to produce eletricity is one of the main reason to endangered the mussels.

Ricardo

 

[Mikeyy]

Just as an example of the difference between anecdotal stories and facts. The area around Muscatine Iowa has always been an important shell area. The stories about pearling in that area say it was basically fished out around the turn of the century. Then the button factories sprung up and there were hundreds of thousands of pounds of shells produced from the same area. This area continued to provide a steady quantity of shells until the early eighties. It was then that the big rush on Washboard and 3 ridge shell really kicked in to gear. This same area that had been harvested for over a century was producing over 100 containers of shells per year. Now they shut down harvest of washboard shell a few years back. They used the threat of the Zebra mussel to shut down shell harvest. But I can tell you for a fact that there is still hundreds of thousands of pounds of shell in the U.S. that can be harvested without damaging the shell reproduction. And this is just a section of river 16 miles long. There are thousands of miles of rivers that have never been opened for commercial harvest. There are only a few shells needed for the nuclei business. And none of them are endangered. You will read things like "Special Concern" or the like to discribe a particular shells situation. But that is code for we don't know. We haven't run a study. We think it could be bad but we don't know. I am all for protecting any species that is in danger of extinction or even over fishing. But I would love to see any study that has actual numbers that are varifiable. OK rant over

 

[Caitlin]

Hi Mickyy

Isn't Billie Button from Muscatine? LINK

I am not talking about commercial harvest, but the hunt for pearls, by families in the smaller rivers and creeks. I was primarily talking about the kinds of streams and rivers people could get mussels by wading. Kunz' account details the actual finds in various rivers (pp252-278). I am talking about the 19th century when many of the Small rivers and streams were entirely depleted of mussels.

I just scanned the first page I saw and saved it: There are 26 pages of details in that section.

 

[Mikeyy]

Hi Mickyy

Isn't Billie Button from Muscatine? LINK

I am not talking about commercial harvest, but the hunt for pearls, by families in the smaller rivers and creeks. I was primarily talking about the kinds of streams and rivers people could get mussels by wading. Kunz' account details the actual finds in various rivers (pp252-278). I am talking about the 19th century when many of the Small rivers and streams were entirely depleted of mussels.

I just scanned the first page I saw and saved it: There are 26 pages of details in that section.

Actually that area was capable of being waded across. This was pre lock and dam. Since the dams were not built until the 30's.
I don't mean to sound argumentative. I really don't. I just see that there is an assumption that has been promoted by some that Washboard and 3 ridge shells are endangered. They are not endangered species. I realize its not your fault. I have yet to read a government paper that doesn't include this threat. I am all for conservation. I am what you might call a liberal tree hugger. But I know what I know. The shells are there. And we could harvest many more shell if we could get the agencies involved to work at operating a proper shell harvest.

You shouldn't harvest the same areas year after year. There should be a limit to the amount of shells harvested. And a limited number of licenses or contracts for divers. Its not that hard to do. Its a matter of how much you want to make it work. Right now the Fish and wildlife agencies are not even willing to address it.