The Tampico Pearlymussel (Cyrtonaias
tampicoensis) Shades of the Old West
by Robert G. Howells
Undeniably those vulnerable and fascinating mollusks we variously
call freshwater or pearly mussels, naiads, unios, or river clams
are becoming scarcer by the day due to agricultural, residential
and industrial pollution, habitat destruction, dams, poaching
and over-fishing. But those of you who just got interested or
thought freshwater musseling opportunities were going the way
of the typewriter and boy-calls-girl just haven't checked out
Texas. Bob Howells of the Texas Parks and Wildlife Department,
Heart of the Hills Research Station in Ingram, Texas, actually
approached us about interesting collectors in his unique mussels.
Shell collectors often venture
far and wide in pursuit of unique mollusks. Yet travelers to
the other side of the planet after that special shell may be
overlooking an especially unique species right at home. Long
before Lyndon Johnson carried his dog around by its ears, before
Davy Crockett ever fired Old Betsy at the Alamo, and before
the Yellow Rose of Texas first rolled in the hay with Santa
Ana, early Spanish explorers ventured into western Texas in
search of the Tampico pearlymussel (Cyrtonaias tampicoensis;
family Unionidae) and the gem-quality freshwater pearls it frequently
produces. Clemmens (1981) reported how Hernan Martin and Diego
del Castillo arrived in 1650 near what is now the city of San
Angelo on the Concho River (river of shells) in western Texas.
Pearls they obtained there were sent back to Sante Fe and caused
enough excitement that in 1654, Diego de Guadalajara was also
sent into the area to locate as many pearls as possible. Some
reports suggest excessive harvest of mussels and others mention
enlisting the local Indians in the pearl- harvest efforts. Most
agree the number of pearls obtained were apparently well below
At least in part because of the
Tampico pearlymussel and its pearls, Spanish attention was drawn
to this area. Missions were constructed and ultimately the present
city of San Angelo developed. Although Spanish colonial days
have long ended, San Angelo, the Concho River and Tampico pearlymussels
endure. A fishery for the mussels and the pearls they produce
Tampico pearlymussel occurs from
northeastern Mexico into the Colorado and Brazos Rivers of central
Texas. Although many, if not most, members of the family have
declined dramatically in recent years, Tampico pearlymussel
numbers have held up rather well. It evolved as a riverine mussel
(there were no natural lakes within its range in Texas); however,
it has adapted well to man-made impoundments. While riverine
populations have been subjected to dewatering during droughts
and severe scouring during floods, some reservoir populations
have flourished. Today, reservoirs from the Rio Grande to Abilene
and Waco still support significant populations of Tampico pearlymussels,
as do some rivers and streams.
This unique unionid reaches over
130mm in shell length and has a general shape reminiscent of
Mercenaria or Spisula. There is no significant external shell
sculpturing. Coloration varies from yellowish-brown with faint
green rays to dark brown and black. Internally, nacre is typically
purple, but may be lavender, pink, orange, salmon, white or
multicolored. Boldly-colored nacres are comparable to anything
grown on a tropical coral reef. Tampico pearlymussel pearls
are the same colors as the nacre (imagine a deep purple pearl).
Pearls occur freely in the soft tissues of about 3-4% of individuals,
with about that same percentage having pearls or other imperfections
attached to the shell. Although some individuals have taken
pearls over 10mm in diameter and valued at thousands of dollars,
true gem-quality pearls are very rare . . .perhaps one in 500
to 1,000. Realistically, if pearls were common, their value
would be far less.
Habitat of Tampico pearlymussel
ranges from relatively small streams to large reservoirs. Although
they sometimes occur at substantial depths, most usually inhabit
waters less than 20' deep. They seek out substrates of sand,
mud and fine- to moderate-sized gravel and avoid deep-shifting
sands, very soft silts, and hard cobble and bedrock. Many musselers
locate Tampico pearlymussels by wading shallow waters and feeling
for specimens with their feet. Still others snorkel or dive
with SCUBA or hookah pumps. It is important to remember most
reservoirs which harbor Tampico pearlymussels lack the clarity
of coral reefs of the South Pacific. Visibility is usually near
zero and collection is almost completely by touch (not a harvest
method for the claustrophobic).
Another similar unionid called
bleufer (Potamilus purpuratus), somewhat similar in appearance,
occurs in most of the same areas as Tampico pearlymussels. It
typically ranges throughout much of the Mississippi River Valley
west into western and southern Texas. Bleufer has purple nacre
which often appears slightly more rosy in western populations.
Sexually dimorphic, the males are more elongate and females
more posteriorly truncated and inflated. Much deeper bodied
posteriorly than the Tampico pearlymussel, some bleufers are
rather alate (winglike). Even some past experts have confused
these two species.
Current mussel-harvest regulations
in Texas allow collection of up to 25 pounds of whole mussels
per day with a standard fishing license. Harvest of greater
amounts requires a commercial mussel license. Additionally,
there is a 2.75-inch minimum shell height requirement; smaller
specimens must be released unharmed. Most musselers determine
legal size by passing the mussel through a ring of PVC pipe
with a 2.75" inside diameter. Harvest in Texas is also
restricted to hand collection; dredges, brails and other harvest
devices are prohibited. Lastly, there are 28 no-harvest mussel
sanctuaries around the state which hopefully provide protection
to brood stocks which will distribute offspring up- and down-stream
from the sanctuary sites to perpetuate the fishery.
Although some individuals have
expressed disdain over the continued harvest of Tampico pearlymussels
for pearls, this harvest may actually serve a purpose. Freshwater
mussels of the family Unionidae are among the most rapidly declining
faunas in North America. Roughly half are extinct, endangered,
threatened or in line to be listed. Continued harvest of the
Tampico helps draw attention to a largely unnoticed but seriously
troubled group of animals. Were it not for sport and commercial
harvest, freshwater mussels in Texas would likely still remain
largely unstudied and unprotected.
A number of reservoirs in Texas
support relatively easily collectible Tampico pearlymussel populations.
Falcon and Armistad Reservoirs on the Rio Grande are currently
at very low levels which have left many mussels stranded on
dry lake beds or in shallows. Lake Corpus Christi on the Nueces
River, Nasworthy Reservoir on the Concho River and Lake Buchanan
on the Colorado River can be noteworthy collection sites. Ease
of collection, however, often reflects recent hydrological conditions.
For example, Lake Buchanan experienced a decline in water level
for a period of years, but in 1992, it abruptly caught 30' of
water during a very wet spring. No living mussels could be found
at shallower depths, and it took nearly a year for them to crawl
slowly back into shorezone areas. If water levels rise suddenly,
collection may be difficult for an extended period of time.
Next time the lure of far-away,
expensive collection sites calls, without the time and funding
to satisfy the urge, consider overlooked species at home. Although
it is true that waters harboring the Tampico pearlymussels do
not have attractive island women is grass skirts dancing on
the shoreline, when was the last time anyone collected a Golden
Cowrie under the scrutiny of a herd of longhorns? While the
threat of man-eating sharks and poisonous sea snakes is also
lacking, the occasional giant alligator gar or ill-tempered
water moccasin can still prove interesting. Following tracks
of the early conquistadors in central and western Texas can
be an experience in itself.
Texas Parks and Wildlife Department,
Heart of the Hills Research Station, HC07, Box 62, Ingram, TX
78025 Fax: 210/866-3549 Email: firstname.lastname@example.org and indicate Attn.:
Many species of freshwater mussels fall under a variety of
federal and state regulations, and regulations can sometimes
change rather quickly. Species which can be legally harvested
in one state may be considered endangered in another. Always
check with local authorities before collecting any freshwater
mussel or transporting it into another state. Also remember,
collecting freshwater mussels can be extremely hazardous. Broken
glass and rusty cans can cause cuts; branches and trotlines
may cause entangling problems. Both scientific and commercial
divers have been lost while collecting mussels. Always use caution.
Latest information from Bob Howells indicates that his book,
Freshwater Mussels of Texas, written with Raymond Neck and Harold
Murray will be ready about the end of August or early September.
We hope to have a few order forms at the convention in July
at the COA table.
And a rather rewarding development
in the study of these remarkably sturdy mussels is the discovery
this spring of the host fish for their reproductive cycle: the
Longnose gar. Continued health of the Tampico pearlymussel species
depends on the continued presence of this fish.
Clemmens, G. 1981. The Concho Country. Mulberry Ave. Books,
Howells, R.G., R.W. Neck and H.D. Murray. In press. Freshwater
Mussels of Texas.
Texas Parks and Wildlife Department, Austin.
Kennedy, I. 1985a. Hill Country pearls. Texas Monthly (October):187-188.
______ 1985b. From the Colorado River bed: freshwater pearls.
Pinkard, T. 1979. Pearls of the Concho. Texas Highways (August):30-33.
Portwood, T. 1992. Pearl fever. Treasure (January):74-77.
Williams, R. 1990. Pearls of the Concho. Texas Highways (August):34-40.