FreshwaterMussels

America’s Hidden

Treasure

®®
U.S. Department of the Interior

U.S. Fish & Wildlife Service

http://www.fws.gov

National Wildlife Federation

http://www.nwf.org

For the Record

No other country in the world equals 

the United States in freshwater mussel

variety. While all of Europe supports only

12 species, nearly 300 kinds live here,

mostly within the vast watershed of the

Mississippi River.

Unfortunately, these animals may be the

most troubled natural resources in this

country. It’s estimated that 70% (Williams,

et al, 1993) of our freshwater mussels are

extinct, endangered, or in need of special

protection. Many of their problems stem

from how they live and changes that 

have occurred to their habitat during 

the past 200 years.

Life Down Under

Most freshwater mussels live burrowed 

in sand and gravel at the bottom of rivers

and streams. Only a few are adapted to the

quiet water and muddy depths of lakes,

ponds, and reservoirs.

Unlike most animals, which must travel 

in search of food, their food drifts to them,

mainly tiny plants and animals called

plankton suspended in the water. By

drawing water inside their shells through

a siphon, their gills filter out food and 

take in oxygen.

Mussels usually don’t move much, but a

muscular “foot” helps them burrow and

allows limited travel if

disturbed by floods

or drought.

The foot also helps anchor them against

strong currents and may prevent a hungry

muskrat from tugging them out for its

dinner! A mussel’s shell, however, provides

its main protection from predators.

Their hard, calcium-based shells consist 

of two halves joined by a hinge. Unique

names like “monkeyface,” “threehorn

wartyback,” and “pink heelsplitter” refer

to the wide range of shell size, color, shape,

and texture found among mussel shells.

Something “Fishy”

Freshwater mussels need a lot of luck to

successfully reproduce. Their unusual life

cycle begins when eggs held inside the

female are fertilized by sperm drawn

inside her while siphoning water. For

some, if a male of her kind isn’t nearby

upstream, she can’t reproduce. For a few,

this is not a problem because they seem

able to fertilize themselves.

Once fertilized, the eggs develop into a

larval stage inside the female before they

are released into the water to begin a

parasitic stage. With little time to waste,

these youngsters, called glochidia, must

attach themselves to a host fish or perish.

For some mussels, the host is limited to

only a few fish species. This generally

harmless parasitic stage lasts a matter of

weeks before the larvae transform into

young mussels and are ready to drop off

the fish and begin a life in the

stream bottom.

Built-in Fish Lure

To increase the chances of their young

making contact with a fish host, some

females “go fishing.” By displaying

specially adapted tissues that look like 

fish prey, they try to lure fish to swim 

near them. Sensing a fish nearby, the

female releases her young into the water,

ready to clamp onto the fish.

Mussel Aches

Our native freshwater mussels face

greater problems today than they did just

a few years ago. Some problems aren’t

new. Although water quality has improved

in some areas, pollution, especially 

non-point source pollution, causes the

greatest threat to native mussels. Also

sedimentation continues to take a serious

toll. Habitat losses through channelization,

clearing of riparian and streambank

vegetation, dredging, and dam

construction still persist. Mussels are

impacted by loss of fish hosts from fish

kills or dams that prevent fish migration.

However, in some parts of the country, 

it’s a non-native mussel causing the 

most concern.

Zebra Mussel Invasion 

In 1988, the first zebra mussels were

spotted in Lake St. Claire near Lake Erie

in Ohio. Assumed to be stowaways in the

ballast water of a trans-Atlantic ship, 

this native of eastern Europe is now

widespread throughout waterways in 

the eastern half of the United States.

Besides other problems, zebra mussels

have nearly eliminated native mussels in

some locations.

Unlike native mussels, the much smaller

zebra mussel (less than 2′′ in length) does

not use a host animal in its life cycle, and

reproduces at a tremendous rate. They

can attach themselves to hard surfaces

with thread-like structures called byssal

threads. In zebra mussel-infested waters,

it is not unusual for native mussels to be

completely covered by zebra mussels.

Competition for food and oxygen weakens

and eventually starves native mussels.

They Lose, We Lose

Freshwater mussels have played a long

and varied role in people’s lives. Native

Americans used them for food, tools, 

and jewelry. From about 1890 until the

invention of plastics around 1950, mussel

shells supported this country’s button

industry. More recently, the world’s

cultured pearl industry relies on implant

beads made from the superior shells of

North American mussels. In states where

mussel collecting is legal, harvesting

provides jobs and income to residents

along rivers.

Mussels have other values more difficult 

to measure. In the rivers and lakes where

they live, their filtering ability makes 

them natural water purifiers. They play 

an important role in the aquatic food chain

as a food source for wildlife including

muskrats and otters.

Midden with Muskrat

They also can tell us something about the

health of the environment on which we

both depend. Mussels respond to changes

in water quality. Gradual mussel die-offs or

sudden mussel kills are reliable indicators

of water pollution problems and other

environmental health concerns. Stable,

diverse mussel populations generally

indicate clean water and a healthy aquatic

environment.

If we lose our freshwater mussels, we lose

more than a biological legacy unmatched

in the world. We lose a part of our cultural

heritage, we lose an economic resource,

and we lose an environmental health

maintenance and warning system.

Fortunately, there are efforts being 

made to avoid these losses and things

everyone can do to help save our

freshwater mussels.

Mussels in our Future

Biologists from the U.S. Fish and Wildlife

Service (Service) and the U.S. Geological

Survey along with other Federal, State,

and private agencies are working together

to find solutions to problems facing our

mussels. These partners have developed a

National Strategy for the Conservation of

Freshwater Mussels, which will serve as a

blueprint for native mussel restoration.

Mussels and their habitats are being

surveyed, monitored and restored. The

Service’s endangered species program is

working to conserve these species and

their habitat. Some mussels facing

extinction in the wild have been removed

and brought to the Service’s National 

Fish Hatcheries and State facilities for

safe-keeping. Hatcheries are developing

techniques for propagating rare mussels

for release. We are beginning to

reestablish mussel populations into

restored streams and rivers. The Service’s

Fishery Resources Offices help by

providing technical assistance on habitat

restoration and enhancement for mussels.

Aquarium and zoo personnel are also

assisting with conserving endangered

freshwater mussels through efforts such

as research and education programs. The

National Wildlife Federation has a long

history of working to enhance national

water quality and protect endangered

species through advocacy, education, and

on-the-ground programs. These efforts—

including the “Keep the Wild Alive”

campaign, which celebrates endangered

species protection efforts worldwide—

are helping to improve conditions for

imperiled freshwater mussels.But 

there’s more that needs to be done and 

you can help.

There are ways that you can help to

provide a secure future for mussels. 

For instance, avoid contributing to water

pollution. Follow application directions 

and don’t use fertilizers and pesticides

excessively. Leave stream sides vegetated

even if it means giving up part of the view.

Keep cattle and other livestock out of

streams. Report suspected pollution

problems to authorities. Get involved with

land use planning in your community. 

In the long run, freshwater mussels will

benefit from improvements in water

quality. And so will you!

U.S. Fish & Wildlife Service

America’s Hidden Treasure

DiscoverFreshwaterMussels

They make no

sound.They cannot

see. Some may live

for decades, but

seldom move from 

a secure spot. Yet,

freshwater mussels

are causing a stir,

becoming noticed

and making us

ponder their future

as we make plans

for our own.

Encrusted 

Native Mussel

Buttons from

Days Past

Surveying Mussels