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of the
FLORIDA STATE MUSEUM
Biological Sciences
1988
Number 1
ASPECTS OF THE BIOLOGY OF THE
FLATTENED MUSK TURTLE,
STERNOTHERUS DEPRESSUS
IN NORTHERN ALABAMA
C. Kenneth Dodd, Jr., Kevin M. Enge,
and James N. Stuart
UNIVERSITY OF FLORIDA
Volume 34
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ASPECTS OF THE BIOLOGY OF THE
FLATTENED MUSK TURTLE,
STERNOTHERUS DEPRESSUS,
IN NORTHERN ALABAMA
C. Kenneth Dodd, Jr., Kevin M. Enge, and James N. Stuart*
ABSTRACT
The flattened musk turtle, Sternotherus depressus, is endemic to streams and rivers of the
Warrior River Basin in northern Alabama. Threats of habitat alteration and commercial
collecting led to its listing as a threatened species under U.S. federal law. The life history of the
species is poorly known. From April through September 1985 we surveyed 1 km sections of 10
streams to determine life history information, population structure, and habitat use. We further
evaluated the effects of habitat degradation on turtle populations as a result of coal mining. The
results suggest that mining siltation has a negative impact on the distribution and population
structure of the flattened musk turtle. Turtle populations in mine-impacted sites were small with
population structures skewed toward old individuals compared with sites not impacted by mining.
Only the population at Sipsey Fork, unaffected by mining, had a large population of S. depressus,
but numbers and total biomass were less than literature reports for other kinosternid turtles.
Another population unaffected by mining was small but showed good recruitment while two
additional unaffected populations showed population structures reflecting commercial collecting.
Except at Sipsey Fork (with approximately 600 flattened musk turtles), there were too few turtles
with which to make reliable population estimates despite intensive sampling. The overall sex ratio
was 1.5 males per female, but varied substantially between populations.
The environmental variables correlated with viable turtle populations were low
conductivity, a pH between 6.5 and 7.5, and. an oxygen value > 7.0 ppm. Turtles avoided deep
slow-moving pools, shallow sandy areas, and areas affording little cover. S. depressus remains in a
small area most of the time, with occasional long distance movements of unknown purpose.
Turtles moved from 0 m to 460 m overnight, with males moving more often and for longer
distances than females. Neither local nor occasional long distance movements were influenced by
weather variables. Individual turtles overlapped both in movement and cover site selection, and
there was no evidence of competition for cover sites.
We recorded 67 instances of basking. Basking platforms included branches, logs, rocks, a
rock face, and land. Turtles selected sites over deeper (> 450 mm) water. Turtles basked aerially
* The senior author is a Research Zoologist and the junior authors were Biological Technicians at the National Ecology
Research Center, US. Fish and Wildlife Service, 412 N.E 16th Avenue, Gainesville FL 32601. The senior author is also a Field
Associate at the Florida State Museum, University of Florida, Gainesville.
DODD, C.K, JR., K.M. ENGE, and J.N. STUART. 1988. Aspects of the Biology of the
Flattened Musk Turtle, Sternotherus depressus, in Northern Alabama. Bull. Florida State Mus.,
Biol. Sci. 34(1):1-64.
BULLETIN FLORIDA STATE MUSEUM VOL. 34(1)
in the direct sun and were alert, but many appeared sick. Cloacal temperatures were as high as
33.10C.
Power function exponents of regressions of weight on carapace length were near 3.0, as
expected. Regressions of weight on carapace width, plastron length, and plastron width were also
near 3.0 indicating similar growth relationships among these characters. Regressions of other
morphological comparisons were often significant but explained only a small amount of variance.
Past and present threats of habitat degradation from mining, agricultural and municipal
sources, and impoundments have combined to isolate the remaining populations of this species.
Habitat fragmentation may be the most serious threat to the long-term survival of the flattened
musk turtle.
RESUME
La tortuga almizclera aplanada, Sterotherus depressus, es end6mica en rios y corrientes de la
cuenca del Warrior River en el norte de Alabama. Se ha denominado especie amenazada seg6n
la ley federal de los E.UA. debido a alteraci6n de ambiente y recolecci6n commercial. Se conoce
poco de su historic natural. De abril a septiembre de 1985 hemos estudiado tramos de 1 km en
10 corrientes para determinar datos de historic natural, estructura poblacional y uso del
ambiente. Ademas, hemos evaluado los efectos de degradaci6n ambiental por minas de carb6n.
Los resultados sugieren que sedimentaci6n causada por las minas tiene un impact negative en la
distribuci6n y poblaci6n de la tortuga. Poblaciones en areas afectadas por mineria eran pequefias
y tenian mayor proporci6n de individuos viejos, comparadas con sitios no alterados por mineria.
Solamente Sipsey Fork, donde no hay mineria, tenia una gran poblaci6n de S. depressus, pero los
ntimeros y la biomasa eran menores comparados con datos publicados sobre otras tortugas
kinostrnidas. Otra poblaci6n no afectada por la mineria era pequefia pero mostraba buen
restablecimiento, mientras que dos otras areas sin mineria mostraban poblaciones afectadas por
la recolecci6n commercial. Con la excepci6n de Sipse Fork (con aprox. 600 tortugas por km),
habian muy pocas tortugas para hacer un cAlculo confiable de poblaciin, a pesar del muestreo
intensive. Habian 1.5 machos por hembra, pero la relaci6n variaba notablemente entire
poblaciones.
Los variables ambientales relacionados con poblaciones viables de tortugas eran:
conductividad baja, pH entire 6.5 y 7.5, y mas que 7.0 ppm de oxigeno. Las tortugas evitaban
charcos hondos y lentos, areas arenosas de poca profundidad, y areas sin vegetaci6n o esc6ndite.
S. depressus normalmente queda en una area reducida, haciendo de vez en cuando viajes mis
largos de motive desconocido.
Las tortugas viajaban de 0 m a 460 m durante la noche, con los machos mudAndose con
mayor frecuencia y a mayores distancias. Factores meteorol6gicos no influian ni en los
movimientos locales ni en los movimientos fortuitos de larga distancia. Tortugas individuals
coincidian en movimiento y en selecci6n de esc6ndite, y no habia evidencia de competici6n por
esc6ndites.
Registramos 67 casos de asoleamiento. Plataformas para asolear incluian ramas, troncos,
piedras y tierra. Las tortugas escogian sitios encima de agua relativamente honda (mas que 450
mm). Se asoleaban en el aire y sol director y eran vigilantes, pero muchas parecian enfermas.
Temperatures cloacales llegaban hasta 33.10C.
El resultado de regresiones de peso respect al largo de carapacho era aprox. 3.0, como se
esperaba. Regresiones de peso respect al ancho de carapacho, y largo y ancho del plastr6n
tambien daban aprox. 3.0, indicando relaciones similares de crecimiento entire estas
caracteristicas. Regresiones de otros aspects morfol6gicos eran significantes con frecuencia,
pero explican una pequefia parte de la variabilidad.
Las amenazas hist6ricas y actuales de degradaci6n ambiental por mineria, agriculture y
fuentes municipales, y represas han combinado para aislar las poblaciones restantes de esta
especie. La fragmentaci6n del ambiente pueda ser la amenaza mis seria para la sobrevivencia de
S. depressus.
DODD ET AL.: STERNOTHERUS DEPRESSUS IN NORTHERN ALABAMA 3
TABLE OF CONTENTS
Introduction............................................ ................................................................................... 3
A know ledgem ents........................................................................................ .................................. 4
Physiography and Water Quality of the Warrior Basin.................................. ........................ 4
The Biology of S. depressus.......................................................................................... ...................... 5
M ethods................................................................... ........................................ ....................... 6
Results................................. .. .......................... ......... ......... 14
Turtle Capture............................................................. 14
Habitat Characteristics ...................................................................... 16
Population Biology. ..... ......... ............................... ......... 18
Shell Erosion........... ................................................... 28
M movements and Habitat Use.................................... ................. ............... ............. 34
Basking.............................................. ............... ........... 41
M orphological Analysis.............................. ........ ................................ 42
M miscellaneous Notes..................................................... 47
D iscussion................................................................................................... 48
Literature Cited.................... ....... ................................... 61
INTRODUCTION
The flattened musk turtle, Sternotherus depressus, was described by Tinkle
and Webb (1955) from specimens collected in the Mulberry Fork of the Black
Warrior River. The turtle is endemic to the Warrior River Basin above the Fall
Line (Tinkle 1959; Mount 1975). Since its description, the biological
information that has appeared on it has centered on the turtle's distribution,
taxonomic status, and reproductive biology (Tinkle 1958; Estridge 1970; Mount
1975; Iverson 1977a, 1977b; Seidel and Lucchino 1981; Seidel et al. 1981; Close
1982).
Throughout the Warrior Basin, major habitat changes have occurred
within the last 20 years because of increased human population and associated
development, industrial expansion, and agriculture. Detrimental impacts from
pollution and siltation result from a variety of sources, including municipal
development, strip mines, clearcutting, and agricultural runoff (U.S. Fish and
Wildlife Service 1987). Although quantitative data are lacking, observations by
Alabama biologists during the late 1960s and early 1970s suggested that the
flattened musk turtle was decreasing in abundance because of these combined
impacts (R. Mount pers. comm.). In 1980 and 1983, the U.S. Fish and Wildlife
Service and the Alabama Coal Association, respectively, issued contracts to
assess the turtle's status (Mount 1981; Ernst et al. 1983). Mount's (1981) report
recommended Federal protection but Ernst et al. (1983) thought the turtle
merited a "special concern" status.
BULLETIN FLORIDA STATE MUSEUM VOL. 34(1)
In 1985, we received a contract to assess the effects of coal mining on the
flattened musk turtle and to make suggestions to reduce future mining
impacts. In addition to surveying turtle populations, we collected comparative
data on the life history, population structure, and habitat of Stemotherus
depressus. Since few studies have concentrated on stream-dwelling species,
these data could assist in understanding the ecology of freshwater turtles in
different habitat types and under adverse environmental conditions. This paper
reports results, in part, from our surveys. The turtle is now protected by
Alabama State Law, and has been listed as threatened under provisions of the
Endangered Species Act of 1973 (U.S. Fish and Wildlife Service 1987).
ACKNOWLEDGEMENTS
We thank the following for advice and assistance during this study: Robert Mount, Ken
Marion, Carl Ernst, Herbert Boschung, R. Bruce Bury, John Christian, Ricky Ingram, John
Pulliam, Jose Gallo, Dale Jackson, Justin Congdon, Randy Johnson, Sharon Henson, Bill Harris,
John Brewer, Larry Hedrick, Jim Hughes, and Dick Evans. We also thank the numerous residents
of the Warrior Basin who told us about themselves, the rivers, and the animals of the rivers, while
we were catching turtles.
We thank Herbert Boschung (University of Alabama), Peter Meylan (formerly of the Florida
State Museum), Robert Mount (Auburn University), and Robert Reynolds and George Zug
(U.S. National Museum) for allowing us to examine specimens in their respective collections.
Dona Bentzien, R. Bruce Bury, Carl H. Ernst, J. Whitfield Gibbons, and J. B. Iverson provided
constructive comments and criticism of various drafts of the manuscript. Luana Whitehead and
Anita Brand typed early drafts, and Anita Brand helped extensively with the administration of this
project; we could not have carried out the study without her almost daily assistance.
This study was conducted under contract No. 14-16-0009-84-1896 between the Office of
Surface Mining, Department of the Interior, and the U.S. Fish and Wildlife Service. Collecting
was authorized under Scientific Collecting Permit No. 172, as amended, from the Alabama
Department of Natural Resources.
PHYSIOGRAPHY AND WATER QUALITY OF THE WARRIOR BASIN
The Warrior Basin comprises approximately 16174.5 km2 in north central Alabama. The area
is part of the Cumberland Plateau Physiographic Provence and lies between the Tennessee Valley
to the north, the Appalachian Mountains to the east, and the Coastal Plain and Fall Line to the
south and west. The land is a peneplain dissected by rivers and streams producing many gorges.
Much of the rock is comprised of Pennsylvanian Age sandstone of the Pottsville Formation which
reaches a thickness of approximately 366 m in Winston County (Wahl et al. 1971). Much
streambed load consists of naturally eroded sand.
The major river in the drainage is the Warrior (or Black Warrior) River. The drainage area
within the range of S. depressus above Bankhead Dam is approximately 10308.3 km2 and includes
three major tributaries: Locust (3131 km-), Mulberry (1463 km ), and Sipsey Forks (2580 km).
Within the range of S. depressus, there are three major impoundments: Bankhead Lake,
completed over 60 years ago; the lake behind Holt Dam, created ii: 1968; and Lewis Smith Lake,
DODD ETAL.: STERNOTHERUSDEPRESSUS IN NORTHERN ALABAMA 5
created in 1961. The upper reaches of Bankhead and Lewis Smith are known to contain S.
depressus (Mount 1981; Ernst et al. 1983).
The Warrior Basin includes the most productive of Alabama's three coal mining regions, the
Warrior Coal Basin, and accounts for 89.9% of Alabama's coal production. The Basin underlies a
substantial portion of the flattened musk turtle's range, including parts of Blount, Cullman,
Jefferson, Walker, and Winston counties. The coal, in general, is high grade bituminous noted for
its low percentage of sulfur and ash.
As of 1983, there were 167 area and contour surface mines in the Warrior Basin accounting
for 55% of the coal production in Alabama (Tolson 1984). Blount, Cullman, Jefferson, Walker,
and Winston counties account for 67.9% of surface mining production. Tolson (1984) estimated
disturbed acreage from surface mining based on aerial surveys in 1978 within the range of the
flattened musk turtle as follows: Blount 7657, Cullman 4711, Jefferson 23190, Walker 36640, and
Winston 5077. The area (acres) permitted for surface mining in 1982-3 in the same counties were:
Blount 279, Cullman 3353, Jefferson 10466, Walker 13793, and Winston 2415. In 1983, these five
counties contained 103 active surface mines.
In 1949, the water quality within the basin was considered reasonably good, although Village
Creek, Valley Creek, and Five Mile Creek were "grossly polluted" (Anon. 1949). This paper
provided baseline data on water quality for many of the streams known to contain S. depressus.
Water pollution has adversely affected the fishery resources of the Warrior Basin (U.S. Fish and
Wildlife Service 1987, and references therein).
THE BIOLOGY OF s. DEPRESSUS
The flattened musk turtle is a relatively small turtle with the largest known
individual 119 mm in carapace length (CL) (Mount 1981). Estridge (1970)
reported carapace measurements for a hatchling of 25 mm long by 12 mm
wide. Hatching took about 12 h and the carapace flattened within 13 days.
Close (1982) reported males required 4-6 years to reach sexual maturity
whereas females required 6-8 years. Tinkle (1958) thought maturity occurred in
males at 75 mm CL and in females at 90-100 mm CL. Close (1982) noted that
males of 60-65 mm CL may have sperm in their epididymus and suspected
females mature at 70-75 mm CL. Longevity is unknown but individuals of other
species of Stemotherus have lived > 25 years in the wild (Ernst 1986).
The flattened musk turtle lays from 1 to 3 eggs per clutch, and two clutches
per season appear normal, as is common in kinosternids (Close 1982; Wilbur
and Morin 1988). Close (1982) reported an average reproductive potential of 4.2
eggs, and found evidence for a third clutch in at least one individual. The average
length of incubation was 92.4 days (N = 17) (Close 1982), but the egg hatched by
Estridge took 122 days to hatch. Neither author reported incubation
temperature. Ovulation by most turtles initially occurs in May, with a second
clutch in June (Close 1982). Ovulation stops and oviposition has been completed
by early July, and Close (1982) estimates the last clutch is deposited between
mid-June and early July.
Little is known concerning population structure. Of the type series, a large
percentage were juveniles (Tinkle and Webb 1955). Indeed, 55% of the S.
depressus collected prior to 1970 were juveniles. Of the turtles collected by
BULLETIN FLORIDA STATE MUSEUM VOL. 34(1)
Mount (1981) and Ernst et al. (1983), 14% and 16.7%, respectively, were under
70 mm CL. Tinkle (1958) gave a male:female sex ratio of 1:3, but stated that
the uneven sex ratio might be due to sampling bias rather than a bias toward
females in the population.
Mount (1981) reported S. depressus to be opportunistic feeding on mollusks
when present, and arthropods when mollusks were scarce or absent. Tinkle
(1958) noted a prevalence of hapliplid beetles in the feces of juveniles. In a
more extensive food analysis, K.R. Marion (pers. comm.) and his students
found snails comprise 75% by weight of the diet, with Corbicula (12%), insects
and larvae (8%), crayfish (3%), fish (1%), and plant material (1%) constituting
the remainder.
The flattened musk turtle is principally a stream-dwelling turtle, although
the upper reaches of reservoirs are inhabited. Ideal habitat includes submerged
rocks, crevices, and logs (Fig. 1). Juveniles often are found in shallow riffles
and weed beds. Mount (1981) reported optimal habitat conditions as follows:
(1) drainage area between 130 and 1295 km2; (2) a depth averaging 60 cm with
vegetated shallows alternating with deeper pools; (3) pools containing a
detectable current; (4) abundance of submerged rocks and crevices; (5) low
silt load and minimal silt deposits; (6) abundant molluscan fauna; (7)
relatively low nutrient content and bacterial count; (8) moderate temperature;
and (9) minimal pollution. Ernst et al. (1983) noted that S. depressus was
found in sandy habitats if adequate cover and food were nearby.
The earliest in the season S. depressus has been collected is April 18 and
the latest is October 20 (D. Close pers. comm. to R. Mount); this activity
period is similar to that reported for some other Sterotherus (e.g. Ernst
1986). Overwintering habits are unknown.
METHODS
Site Selection.- We plotted locality data from Mount (1981) and Ernst et al. (1983) on U.S.
Geological Survey (U.S.G.S.) 1:250000 topographical maps (Birmingham and Gadsden
quadrangles) along with statements by these investigators as to the suitability of the habitat and
the status of the S. depressus population. Sites then were located on both the Geological
Survey of Alabama drainage map for the Upper Black Warrior Basin (Scott 1978) and U.S.G.S.
7.5 minute series topographic maps. After on-site visits, we selected ten areas for intensive study
(Fig. 2).
The main criteria for site selection on streams not affected by mining were that they contain
a known population of flattened musk turtles, were free from obvious degradation due to mining,
were at least 8 km downstream from any known direct contamination or stream discharge from a
mining operation, and were as free as possible from other sources of sedimentation.
We selected mine-affected study sites either adjacent to or immediately downstream from
mining operations in streams containing known populations of flattened musk turtles. We selected
streams that were not affected, or affected as little as possible, by other sources of
sedimentation. We determined when mines were operated as well as when permits were issued for
active mines presently operating. Because no public records of mining activities exist prior to 1970
Figure 1. Optimum habitat of the flattened musk turtle. The water should be clean with abundant crevices for cover. Sipsey Fork.
BULLETIN FLORIDA STATE MUSEUM VOL. 34(1)
WARRIOR BASIN
S1 IP8EY FORK
2 BRU8HY CREEK
3 CLEAR CREEK
4 BLACKWATER CR.-CAMP O'REAR
5 BLACKBURN FORK
6 LOST CR.-POCAHONTAS
7 LOST CR.-TOWNLEY
8 BLACKWATER CR.-HARRIS BR.
9 TURKEY CREEK
10 GURLEY CREEK
Figure 2. Map of the Warrior Basin showing the location of study sites. The circles represent
sites unaffected by mining, and the triangles represent mine-affected sites.
DODD ET AL.: STERNOTHERUS DEPRESSUS IN NORTHERN ALABAMA 9
(R. Johnson, Alabama Surface Mining Commission, pers. comm.), dates of operation were
estimated through comparison of old and updated topographic maps, and through discussions with
local residents.
Site Description.- The sites unaffected by mining were as follows:
1) Sipsey Fork (T9S R8W S33 and 34). Sipsey Fork primarily consists of stretches
of sluggish water separated by short riffle zones. Water clarity is excellent and
tree cover averages 10%.
The stream banks, other than for some sandstone bluffs, are moderately
steep, sandy, and well-vegetated. The stream bottom is bedrock overlain by
patches of sand and slab-like boulders. Water depth ranges from a few
centimeters in riffle areas to a maximum of about 1 m. Sand-covered areas
primarily consist of extrusions below riffles. Log debris is present and generally
clustered near the shorelines. The stream rises in the Sipsey Wilderness and
flows through Bankhead National Forest.
2) Brushy Creek (T9S R7W S23). Habitats range from deep quiet water to shallow
rapids, and some areas are similar to Sipsey Fork. Cover on the stream bottom
is provided by boulders, although some log debris also is present. Tree cover
averages 25%. The stream banks are generally steep and vegetated, and water
clarity is good except in areas of deeper water and downstream from the
confluence of Capsey Creek. The stream flows through Bankhead National
Forest.
3) Blackwater Creek Camp O'Rear (T13S R7W S14, 15, 22, and 23) This site lies
17 km downstream of the Harris Bridge site and about 6.5 km downstream of
the Musgrove Country Club dam. The stream flow is moderate to fast with an
average depth of 0.5 m. The bottom consists of fissured and broken bedrock,
blackish in color, overlain by rock slabs and irregular boulders. Sand and gravel
occur in small patches. Banks are sandy, abrupt but fairly low, and well-
vegetated. Tree cover averages 10%. Water clarity tends to be fair to good,
although the water is "tea-colored," possibly due to tannin staining. The river
flows through wooded and pasture land.
4) Clear Creek (T11S R9W Sl). Clear Creek is comparable to Blackwater Creek
(Camp O'Rear) in its steady flow and bedrock bottom, but lacks an extensive
bottom cover and sand-free crevices. Long stretches of exposed, convoluted
bedrock predominate, interspersed with sand-filled depressions. Overall tree
cover averages 25%, and the stream banks are steep, sandy, and well-vegetated.
Water depth averages about 0.5 m, and the current is a continuous swift flow in
midstream and along most of the shoreline. This stream flows partly through
Bankhead National Forest, and there is some pasture land adjacent to it and in
its headwaters.
5) Blackburn Fork (T13S R1E S30). At this site, the stream is fairly slow, with
intermittent small riffles and several deep holes. The stream banks are abrupt
and moderately steep in most places, and there are some rocky bluffs. Most of
the adjacent terrain is wooded hillside except for one large pasture. Tree cover
averages 40%. Sharp-edged bedrock shelving, arranged perpendicular to and
angled into the current, is found in four widely separated stream sections. This
site is located below Inland Lake and the stream flows through a valley lined
with woods and pastures.
The mine-affected sites were as follows:
1) Lost Creek-Pocahontas (T13S R9W S28 and 29). This site differs from the
downstream site near Townley in its rockiness and lack of extensive
sedimentation. The stream banks are rather steep due to erosion 300 m
downstream from station 0. Below this station, the banks tend to be low to
moderate and well-vegetated. Tree cover averages 33%. Water clarity tends to
be fair to good except in deeper water. The confluence of Mill Creek occurs
BULLETIN FLORIDA STATE MUSEUM VOL. 34(1)
within the study area. Near the beginning of our study area, the site abuts a strip
mine worked prior to 1975.
2) Lost Creek-Townley (T14S R8W S7). Located about 14 km downstream from
the Pocahontas site, this portion of the stream lacks large rocks or exposed
bedrock bottom. A mixture of sand, gravel, and silt containing abundant
fragments of coal and coal fines covers much of the bottom. Log debris is
abundant. Tree cover averages 45% with a pronounced canopy overhang due to
bank erosion. The site is adjacent to an abandoned strip mine operated > 11-15
years ago, and late in 1985 mining operation resumed. An active mine is
operated across the stream. Drummond's large Cedrum mine is located about 3
km above this site.
3) Blackwater Creek-Harris Bridge (T13S R8W S13). This segment bears little
resemblance to the downstream site at Camp O'Rear. Boulders and cobbles are
either lacking or covered by sediment. The bottom is mostly sand or silt, with
little exposed bedrock.
Log debris is extensive and completely covers the bottom in some places. The
stream banks are steep, 1-2 m high, and heavily eroded giving the stream an
"entrenched" appearance. Tree cover averages 45% and is accentuated by
leaning bankside trees. Two small polluted seepages and a larger channel
carrying little water enter the stream. Water clarity is poor to fair, with
noticeable staining. Water depth averages 1.0-15 m. This site is approximately
17 km upstream from Camp O'Rear, and abuts an abandoned strip mine. It
appears this mine has not been worked since the late 1940s, but aerial
photographs show a small operation a few kilometers upstream, and there is a
large number of abandoned mines still farther upstream.
4) Turkey Creek (T15S R3W S2). At this site, there is a series of rapids separated
by stretches of calm water. Water depth ranges from shallow riffles to pools over
1.0 m. Tree cover averages 10%. Shorelines are characterized by fairly steep
banks, rock walls, or low cobble-covered flats. Water clarity is poor to
good. There are two active mines operated > 35 km upstream. Drummond
Coal Company's Morris mine is near this site, as are several reclaimed mines. In
addition, Interstate Highway 65 has cut through reclaimed mines directly to the
west.
5) Gurley Creek (T14S R2W S14, 23, and 24). Gurley Creek is variable at this
location, with very shallow riffles to deep, still pools. Tree cover averages 35%.
The streamside slope varies from steep to almost non-existent. Water clarity is
good to excellent in shallow areas, but becomes poor in deeper spots. This site is
adjacent to an abandoned mine and large strip pit operated approximately 20
years ago.
Detailed site descriptions and maps are provided in Dodd et al. (1986).
Study Design.- Each study site was measured in 100-m sections from a position in the
center of the stream for 1 km and marked. The station farthest upstream was designated Station
0.
Trapping was conducted at approximately 14-day intervals, depending on water conditions,
between 18 April and 16 September 1985 using 2.54 cm mesh wire basket traps (Iverson 1979)
baited with sardines. Cans were partially opened or punctured and placed in the bottom of the
trap. Two traps were set in the vicinity of 10 trap stations located approximately 100 m
apart. Traps were set in areas likely to have turtles, i.e. along logs and in the vicinity of rock
crevices, and were placed in such a manner that the trapped turtles could breathe. Traps were set
between 1700 and 1830 h each evening and retrieved between 0800 and 0930 h the next
morning. The amount of time the traps were in the water and the time spent wading were
recorded to the nearest 0.5 h.
Habitat Characterization.- Before setting traps, data on incident light, time of light
reading, air temperature, water temperature at the shore, in the center surface of the stream, and
DODD ET AL.: STERNOTHERUS DEPRESSUS IN NORTHERN ALABAMA 11
at a depth of 1 m, oxygen, pH, conductivity, water visibility, weather conditions, and water level,
were taken from approximately the same location. Sediment particle size was measured using
screens with U.S.G.S. mesh sizes 10, 18, 35, 60, 120, and 230.
We estimated the depth of the water and bottom conditions throughout the study site four
times: during the initial location of stations, the first trap set, in the middle of summer, and late
in the season. To determine the relative amounts of substrate types, we estimated the percentage
of bedrock, boulders, cobble, pebbles, sand, and silt at stations 2 and 8, and averaged them.
Water quality was measured for alkalinity (bicarbonate), calcium, chloride, total dissolved
solids, hardness, iron, magnesium, nitrate, phosphorus, and sulfide using a LeMotte Chemical kit
model AM-21. Samples were taken during the second and third weeks in July when 7-day low
flows might be expected (Hayes 1978).
Samples (N=17) reflecting different sediment conditions were collected and analyzed for
% organic matter, phosphorus, potassium, magnesium, calcium, pH, hydrogen, cation exchange
capacity, % base saturation of K, Mg, Ca, and H, and ppm iron. Analyses were performed by A &
L Agricultural Laboratories, Memphis, Tennessee. Samples were taken during the second and
third weeks in July. We collected samples from seven locations at the five sites unaffected by
mining activities, and from ten locations at mining-affected sites. These locations were chosen to
reflect a variety of bottom conditions. For instance, three locations were selected at Turkey
Creek, one from the center of the stream with a sandy bottom, one from the mouth of a tributary
draining a former strip mine now disturbed by road construction, and one from a slow-moving
section of stream where the bottom was covered by soft ooze. When the bottom characteristics of
the stream were largely uniform, only one sample was taken.
Maximum and minimum temperatures, and daily rainfall, were recorded at Haleyville,
Alabama, using a maximum-minimum thermometer and a rain gauge (Fig. 3).
Data Collection.- Carapace length (CL), plastron length (PL), carapace width (CW)
(measured between pleural 3-4), shell depth (SD) (measured between pleural 3-4), the length and
width of the second pleural (PL2L, PL2W), the length and width of the gular (GL, GW), and
interhumeral length (IL) were recorded to the nearest 0.1 mm. Sex was recorded; turtles > 70
mm CL were considered adults (Close 1982). Mass was recorded to the nearest 0.5 g. The same
measurements, except for mass, were taken for S. depressus in the following museum collections:
Auburn University, 32366, 32367, 32368, 32370, 32388, 32554, 32555, 32686, 32689; University of
Alabama-Tuscaloosa, 52-1065 (Paratype); University of Florida/Florida Museum of Natural
History, 57632, H3275, H3276, H3277; United States National Museum of Natural History,
221785, 230330, 230331, 247950-247975. For morphological analyses, these data were pooled with
data collected during field surveys.
Each turtle was assigned an individual identification number (ID) by notching marginal
scutes (Cagle 1939). Carapace erosion was noted and drawn on a diagram that included the
turtle's identification number, location, and capture date. Unusual scars, missing limbs, abnormal
scute arrangements, and excessive algae were noted on the diagram. Each turtle was
photographed for future reference.
Telemetry.- In Sipsey Fork, 13 adults were fitted with LF-1 transmitters with 803 lithium
batteries weighing approximately 3.7 g (Custom Electronics, Urbana, Illinois). Transmitters were
attached to the turtle's carapace with an industrial strength adhesive (Hardman Inc., Belleview,
N.J.) and coated with a silicon seal. The whip antenna was not sealed to the carapace and
remained free. Turtles were retained 24 h prior to release to ensure that transmitters were
properly affixed.
Activity was monitored daily from 1 July to 31 July and from 14 August to 6 September
using a CE-12 dual band receiver (Custom Electronics, Urbana, Illinois) and a hand-held yagi
antenna. Tracking took place during morning hours; water conditions, water temperature, and
weather conditions were recorded daily. When a turtle was located, its position was plotted and
the type of cover site, distance from previous location, and whether the turtle was sighted were
recorded. Turtles were periodically examined to determine the condition of the transmitter,
antenna, and tightness of the seal.
We chose Sipsey Fork as the study site for radio-telemetry because of its large S. depressus
population, the clarity and shallowness of the water, and its proximity to our field camp.
I I I
L
APRIL
--\ MAX
'I
i -i
SEPTEMBER
MAY JUNE JULY AUGUST
Figure 3. Rainfall and temperature data recorded at Haleyville, Alabama.
DODD ET AL.: STERNOTHERUS DEPRESSUS IN NORTHERN ALABAMA 13
Basking.- Early in the season, we saw few instances of basking. However, during the course
of daily radio-tracking on Sipsey Fork, basking S. depressus were frequently sighted. We therefore
made observations on basking incidental to the tracking study. If a turtle was observed basking,
we attempted to catch it before it escaped. The cloacal temperature was taken using a quick-
reading cloacal thermometer (Miller & Weber, Ridgewood, New York). We noted whether the
turtle was in the sun or shade, whether it was alert, and if the turtle had any signs of disease
(Dodd 1988b). The type of basking platform (rock, branch, log, or land) was noted, as was its
width, height above water, and the depth of the water directly beneath the basking platform.
Basking locations were plotted on a map of the study site.
Statistical Analysis.- For statistical analyses, we applied parametric procedures whenever
possible. Levene's Test of Equality of Variances (BMDP 1979) was used to determine if variances
were equal. In cases where variances were equal, we applied parametric procedures, e.g. an
analysis of variance for a repeated measures design with one grouping factor (example: mesh
data), or a multivariate analysis of variance (MANOVA) where we had different dependent
variables or measurements (example: pH, conductivity, oxygen data).
To determine which environmental factors (various temperature readings, 0 conductivity,
pH, etc.) affected trapping success, we ran a stepwise regression to determine which factors to
use as covariates. Once these factors were determined, we used a multivariate analysis of variance
to compare affected and unaffected sites, and a general linear models procedure to compare
individual variables.
We examined trapping success to determine differences between stations (treatments) and
sampling days (blocks) at a location using a randomized block design to control variability from
day to day. Because planned comparisons were involved, we used the Waller-Duncan procedure
(Milliken and Johnson 1984) to determine where differences were occurring.
In cases where the variances were unequal, we used the following nonparametric
procedures: MRANK procedure in SAS (SAS Institute, Inc. 1985); Friedman's test; Mann-
Whitney U test; X test of independence. Because three chi-squares were obtained and the
experiment-wise error rate was not controlled for in the overall analysis, the level of significance
was set at 0.05/4 or a = 0.0125. In all other analyses, the level of significance was set at a0= 0.05.
To determine if the overall sex ratio varied from 1:1, we first used a Mann-Whitney U test to
determine if a difference existed between affected and unaffected sites. Because it did not, we
carried out a test to determine if a significant difference existed among the ratios based on a chi-
square where:
X2 1
i=1
p = n.1 ni. = total in sample i
n.. n.. = total sample size
n.1 = total having one of the characters, e.g. males
pi = nil nil = total with character 1
ni. in sample i
Morphological data were analyzed by sex using Pearson Correlation Coefficients. The data
were plotted, and a linear regression line (y = a + bx) was fitted to the plotted points. When the
plots indicated that a curvilinear relationship might be more appropriate, data were fitted to the
general allometric equation y = ax in the form log y=log a + b(log x), by the method of least
squares regression analysis.
Ratios of CW/CL, PW/PL, PL2W/PL2L, and GW/GL were generated. Standard deviations
accompanying means are intended as a relative measure of character variability, without
implication of statistical significance, because character ratio values may not be normally
distributed (Atchley et al. 1976; Atchley and Anderson 1978).
BULLETIN FLORIDA STATE MUSEUM VOL. 34(1)
RESULTS
Turtle Capture
During the course of this study, 712 S. depressus were captured, the
majority (549 captures and recaptures) at Sipsey Fork. Of the total, 663 were
caught at sites unaffected by mining while 49 were captured at sites where
mining influenced stream quality. Trapping accounted for 461 S. depressus, or
one turtle every 59.7 trap hours (Table 1). A total of 27,503 trap hours and
approximately 653 man-hours wading were spent at all sites.
Of the mine-unaffected sites, S. depressus was trapped at all except Clear
Creek. Of the affected sites, we also obtained S. depressus from four of five
sites, but we trapped only one turtle from another site, Lost Creek-
Townley. The smallest S. depressus trapped was 51.7 mm at Blackwater Creek-
Camp O'Rear.
There was a significant difference in trapping success between mine-
affected and unaffected sites although our trap effort was equal between site
type (F = 0.98; p > 0.35). At unaffected sites, the trap success was 1:33.1, while
at affected sites, the success was 1:287.9 (Table 1). These figures include
results from Clear Creek and Blackwater Creek-Harris Bridge, neither of
which yielded S. depressus. We further determined trapping success of previous
studies at the same or a nearby site (Table 1). Ernst et al. (1983) had better
trap success at each location except Gurley Creek and Blackwater Creek-
Harris Bridge.
Turtles were evenly distributed in Blackwater Creek at Camp O'Rear and
at Brushy Creek where the habitat was largely uniform (Table 2). At other
sites, the turtles avoided pools with deep sediment layers (Station 7 at Turkey
Creek and Stations 2-3 at Gurley Creek), or very shallow areas with little cover
(Stations 6-7 at Blackburn Fork; Station 7 at Blackwater Creek-Camp O'Rear;
Stations 4-5 at Gurley Creek). At a few sites, such as at Lost Creek-
Pocahontas, S. depressus was found to be spatially limited, although suitable
habitat appeared to be available elsewhere within these sites. Turtles in Sipsey
Fork were found less often in riffle areas (Station 9), areas of shallow water
and extensive sand deposits (Station 10), and areas of bedrock with few cover
sites (Station 6).
The environmental factors most correlated with turtle capture were low
conductivity (F = 3.75, p < 0.05), a pH between 6.5 7.5 (F = 9.50, p < 0.01),
and oxygen values > 7.0 (F = 5.43, p < 0.05). There were no differences
between mine affected and unaffected sites (F = 1.53, p > 0.05) in overall trap
success x environmental factors. However, conductivity values were
significantly higher at affected sites, and were inversely correlated with trap
success (F = 6.05,p < 0.05).
DODD ET AL.: STERNOTHERUS DEPRESSUS IN NORTHERN ALABAMA
Table 1. Comparison of trapping success ratios in three studies of S. depressus in northern
Alabama.
Turtles/
Location Trap hours No. turtles hour
Unaffected Sites
Sipsey Fork 2640 320 1:8.3
707 198 1:3.6#
Brushy Creek 2727 42 1:64.9
806 29 1:27.8#
Clear Creek 2755 0 0
671 2 1:335.5#
Blackburn Fork 2813 30 1:93.8
871 33 1:26.4#
Blackwater Creek 2750 21 1:131.0
(Camp O'Rear) 1079 33 1:32.7#
Total 13685 413 1:33.1
Affected Sites
Turkey Creek 2701 29 1:93.1
931 26 1:35.8#
Gurley Creek 2772 7 1:396.0
907 0 0#
Lost Creek 2755 11 1:250.5
(Pocahontas) 490 11 1:44.5#
Lost Creek (Townley) 2775 1 1:2775.0
Blackwater Creek 2815 0 0
(Harris Br.) 214 0 0#
Total 13818 48 1:287.29
Overall Total 27403 461 1:59.7
Mount (1981) 3808* 110 1:34.6
Ernst et al. (1983) 20170 509 1:39.6
# Data from Ernst et al. (1983) at the same or a nearby site.
* Estimate provided by R. Mount (pers. comm.) based on 272 trap nights and 14 hours per trap night.
BULLETIN FLORIDA STATE MUSEUM VOL. 34(1)
Table 2. Results of trapping and wading for S. depressus by station at sites in northern Alabama,
1985. These results only include data from the sampling period and not turtles collected incidental to
radio-telemetry observations on Sipsey Fork. F values represent comparisons of differences within
sites.
Location 0 1 2 3 4 5 6 7 8 9 10 F
Sipsey Fork 34 53 51 45 63 40 32 44 36 23 20 3.32*
Brushy Creek 4 5 9 5 1 6 8 6 4 2 2 1.12
Blackwater Creek 2 5 3 3 1 0 3 0 4 2 0 1.19
(Camp O'Rear)
Blackburn Fork 7 3 4 2 8 3 0 0 1 7 4 2.10*
Turkey Creek 1 10 3 4 0 0 5 0 1 1 4 2.11*
Gurley Creek 0 1 0 0 0 0 1 3 0 0 2 2.07*
Lost Creek 0 0 1 2 7 0 1 0 1 0 0 2.07*
(Pocahontas)
Lost Creek 0 0 1 0 0 0 0 0 0 0 0 1.00
(Townley)
*p < 0.05
Habitat Characteristics
Water Quality.- Conductivity, pH, and oxygen content varied considerably
during the course of the summer (Table 3). We found no significant effects of
oxygen and pH between mine-affected and -unaffected sites (F = 1.49; p
> 0.30). The average pH of mine-unaffected sites was 7.0 compared with 7.3 for
affected sites. Oxygen averages were nearly equal, although with considerable
variation both within and among sites. Conductivity values were significantly
different, with an average of 83 p/mhos for unaffected sites versus 325 pmhos
for affected sites (F = 5.92; p < 0.05). The highest conductivities were found at
Lost Creek-Townley (1000 and 1100 p mhos) and at a tributary to Turkey
Creek (1000 p mhos). Similar chloride, iron, nitrate, phosphorus, and sulfide
values were found among mine-unaffected and -affected sites. Values for
alkalinity, calcium, total dissolved solids, hardness, and magnesium were all
higher at mine affected sites than unaffected sites. However, Blackburn Fork
often had values closer to the average of mine-affected sites, whereas
Blackwater Creek-Harris Bridge had values closer to the mine-unaffected sites
(see Dodd et al. 1986, for values).
Sediments.- There was considerable variation in the results of sediment
analyses among sites. Mine-unaffected sites had lower percentages of larger
DODD ET AL.: STERNOTHERUS DEPRESSUS IN NORTHERN ALABAMA 17
Table 3. Comparison of pH, conductivity, and oxygen values for mine-affected and unaffected
sites inhabited by S. depressus in northern Alabama, 1985. Conductivity inmunhos, oxygen in ppm.
pH Conductivity Oxygen
average range average range average range
Unaffected Sites
Sipsey Fork 7.3 6.4-7.9 58.4 44-71 8.2 6.6-9.8
Brushy Creek 6.5 5.8-7.4 32.4 25-38 7.4 6.5-8.6
Clear Creek 6.3 5.4-7.2 32.4 25-38 7.4 6.5-8.6
Blackburn Creek 7.3 6.8-8.2 77.2 50-111 7.0 5.9-9.1
(Camp O'Rear)
Total 7.0 82.8 7.6
Affected Sites
Turkey Creek 7.6 6.7-8.0 295.5 220-330 8.9 7.3-11.6
Gurley Creek 7.6 7.1-8.1 192 30-250 7.4 5.8-11.0
Lost Creek 7.4 6.9-7.9 520 230-730 7.8 6.9-10.5
(Pocahontas)
Lost Creek 7.4 6.8-8.4 551 220-1100 7.6 6.5-9.9
(Townley)
Blackwater Creek 6.6 6.1-7.1 66.5 55-88 7.2 6.0-8.6
(Harris Br.)
Total 7.3 325 7.8
For all observations at Brushy Creek, N =9. At other sites, N= 10 for pH and conductivity and N =9 for oxygen. Observations
began 22 April and ended 13 September.
particles (meshes 10 and 18) and silt (meshes 120 and 230), and higher
percentages of sand (meshes 35 and 60) than mine-affected sites. However,
there were no statistical differences between affected and unaffected sites (F=
0.94; p > 0.35), particle size distribution within sites (F = 1.45; p > 0.2), or
particle size x site interaction (F = 1.17; p > 0.3). These values reflect the
average percentages of bottom sediments at particular points in time at a
particular spot in the stream, and small sample sizes make the interpretation of
these results difficult.
While there was variation in individual sediment chemical measurements,
there were no clear-cut differences between sites unaffected and affected by
mining. For instance, high levels of magnesium were found at Brushy Creek,
Lost Creek, Gurley Creek, and Turkey Creek, the last three affected by mining.
Even within a stream, there was considerable variation; for example, calcium
levels ranged between 70 and 830 ppm in Turkey Creek. Extremely high iron
BULLETIN FLORIDA STATE MUSEUM VOL. 34(1)
concentrations were recorded at Turkey Creek (Station 0), at Lost Creek-
Pocahontas above the highway bridge, and in Brushy Creek. These probably
result from natural iron seeps rather than acid mine pollution. Values from all
analyses are provided by Dodd et al. (1986).
Population Biology
Sex Ratio.- The overall sex ratio of S. depressus was 1.5 males per female
(230 males, 148 females) (Table 4) and is significantly different from 1:1 (X2 =
12.76; p < 0.05). At unaffected sites, the ratio was 1.6:1 whereas at affected
sites the ratio was 1.4:1. There were no significant differences in the sex ratios
between affected and unaffected sites (U = 0.3725; p > 0.05). There were
more males at all sites except Brushy Creek and Lost Creek-Pocahontas, and
Table 4. Sex ratio and recapture information on Sterotherus depressus at sites in northern
Alabama, 1985.
Location Number Recap M F J Sex ratio
Unaffected Sites
Sipsey Fork 549 198 165 98 83 1.7:1
Brushy Creek 53 12 11 10 10 1:1.8
Clear Creek 0 0 0 0 0
Blackburn Fork 39 3 22 11 3 2:1
Blackwater Creek 22 2 8 2 10 4:1
(Camp O'Rear)
Total 663 215 206 131 110 1.6:1
Affected Sites
Turkey Creek 29 4 15 10 0 1.5:1
Gurley Creek 7 2 4 1 0 4:1
Lost Creek 12 0 5 6 1 1:1.2
(Pocahontas)
Lost Creek 1 0 1 0 0
(Townley)
Blackwater Creek 0 0 0 0 0
(Harris Br.)
Total 49 7 24 17 2 1.4:1
Overall Total 712 222 230 148 112 1.5:1
Total includes one adult for which sex was not determined.
DODD ET AL.: STERNOTHERUS DEPRESSUS IN NORTHERN ALABAMA 19
male bias was greatly in evidence at Blackwater Creek-Camp O'Rear and at
Gurley Creek.
Population Estimate.- Many turtle studies have used the Lincoln Index,
Schnabel, or Schumacher-Eschmeyer tests to estimate population size. Since
we were working with open populations with repeated sampling, it is
impossible to satisfy the conditions of these tests (Caughley 1977). The limited
amount of movement of S. depressus within Sipsey Fork (see below) might
have allowed using the Schumacher-Eschmeyer test and treating the
population as closed assuming no immigration or emigration. However, we had
known mortality from disease (Dodd 1988b), and hatchlings were common
during the latter part of the summer indicating recruitment. In order to
estimate the population size at Sipsey Fork, we therefore used the Jolley-Seber
method (Caughley 1977). As the season progressed, the estimate increased
from 278 (95% confidence limits = 200-356) to 644 (95% C.L. = 442-824)
during the sixth sample in early July (Fig. 4). However, from early July onward,
the estimates declined dramatically; the mid-July estimate was only 310 (95%
C.L. = 195-411). Because the mid-July estimate was only two weeks later than
the highest estimate in early July, and because the Jolly-Seber method is
cumulative, a population decline was indicated.
Even though the conditions of the Schumacher-Eschmeyer test may not be
rigorously satisfied, we nevertheless computed an estimate of 600 (95% C.L. =
498-762) for Sipsey Fork, and 88 (95% C.L. = 68-127) for Brushy Creek. There
were not enough turtles captured at other locations to allow even crude
estimates of population size.
Size Class Structure.-For combined data, the population structure
showed a preponderance of adults and a substantial proportion of juveniles and
younger adults (Fig 5). A different picture emerged when size classes were
compared between unaffected and affected sites (Fig. 6). Indeed, the majority
of turtles in the smaller size classes in Fig. 5 can be attributed to Sipsey Fork
alone (Fig. 7A). The population at Brushy Creek, although small, was rather
healthy in terms of its composition, whereas Blackwater Creek-Camp O'Rear
contained a preponderance of younger individuals. At Blackburn Fork (Figs.
7B, C), there were few small individuals and the population was skewed toward
large and old adults.
Populations at mine-affected sites were even more weighted toward very
large adults (Fig. 6). Almost no recruitment is indicated, and except at Turkey
Creek, there were few small adults (Figs. 7C, D).
Biomass.- Those sites unaffected by mining activities supported an average
of 3.75 kg of S. depressus/ha versus 0.80 kg/ha in mine affected sites (Table 5).
The highest values were at Sipsey Fork (10.72 kg/ha). The high percentage of
BULLETIN FLORIDA STATE MUSEUM VOL. 34(1)
SIPSEY FORK
900
800
700
w 600
I-
.-D
w 500
z
0
Z
I-
0 400
30
a.
300
200
100
2 3 4 5 6 7 8 9
SAMPLING PERIOD
Figure 4. Population estimates of S. depressus in Sipsey Fork, with 95% confidence intervals,
using the Jolley-Seber method.
ALL SITES
N-485
440.0 40.0-49.9 50.0-508. 80.0-69.9 70.0-79.9 80.0-89.9 90.0-90.9 Z100.0
CARAPACE LENGTH (MM)
Figure 5. Histogram showing the combined size class frequencies of S. depressus caught during the summer
Juveniles = diagonal bars; males = open bars; females = solid bars.
of 1985 in northern Alabama.
BULLETIN FLORIDA STATE MUSEUM VOL. 34(1)
AFFECTED SITES
7 nF f
lo- N-42
A-u
UNAFFECTED SITES
N-443
CARAPACE LENGTH (MM)
Figure 6. Histograms comparing size class frequencies of S. depressus between mine-affected
and -unaffected sites in northern Alabama during the summer of 1985. Juveniles = diagonal
bars; males = open bars; females = solid bars.
_
BLACKWATER CREEK (CAMP O'REAR)
N-345
.40 40.444.* so.o-o4 e s o.o-40 0 744.e 7 o.o-e.s 04 .o-e440 41n4
CARAPACE LENGTH (MM)
B BRUSHY CREEK
N-41
0
i-1
o NBLACKBURN FORK
3 o
.o o4. .....o... o.o-e..CARAPACE LENGTH .. -. oo
CARAPACE LENGTH (MM)
i L%
N-25
TURKEY CREEK
n r l6
CARAPACE LENGTH (MM)
D GURLEY CREEK
N-5
]___________r
LOST CREEK (POCAHONTAS)
N-12
(TOWNLEY)
CAo.o Ao -s o >se a o.oe LENGTH (MM)eo.o-e so.o-*. coo a
CARAPACE LENGTH (MM)
Figure 7A-D. Histograms showing the size class frequencies of S. depressus caught at eight study sites during the summer of 1985. Juveniles =
diagonal bars; males = open bars; females = solid bars.
SIPSEY FORK
BULLETIN FLORIDA STATE MUSEUM VOL. 34(1)
Table 5. Biomass of Sternotherus depressus at sites in northern Alabama. Weights are in kg;
Parentheses indicate the number of observations; and area is in hectares.
Location Males Females Juveniles Total Area kg/ha
Unaffected Sites
Sipsey Fork 13.68(166) 8.58(98) 1.75(87) 24.01 2.24 10.72
Brushy Creek 0.93(11) 2.11(20) 0.22(10) 3.26 1.99 1.64
Blackburn Fork 2.51(22) 1.42(11) 0.02(3) 3.95 1.98 2.00
Blackwater Creek 0.56(8) 0.13(2) 0.25(10) 0.94 2.37 0.40
(Camp O'Rear)
Total 17.67 12.24 2.24 32.16 8.58 3.75
Affected Sites
Turkey Creek 1.59(15) 1.28(10) --- 2.87 1.98 1.45
Gurley Creek 0.54(4) 0.18(1) --- 0.72 1.17 0.62
Lost Creek 0.53(5) 0.89(6) 0.004(1) 1.43 1.65 0.90
(Pocahontas)
Lost Creek --- 0.05(1) 0.05 6.52 0.80
(Townley)
Total 2.66 2.35 0.054 5.07 6.52 0.80
juvenile turtles at Blackwater Creek-Camp O'Rear was reflected by the low
biomass of 0.40 kg/ha. A few large S. depressus at Turkey Creek elevated its
biomass closer to that of the unaffected sites.
There was a significant difference between unaffected and affected sites
(X2 = 9.07; p < 0.05) in terms of total turtle biomass (S. depressus and all
other species), with approximately 70 kg for the unaffected and 43 kg for the
affected sites (Table 6). Of this, S. depressus constituted 52% of the biomass
from unaffected sites and only 12% from the affected sites. There was
considerable variation between sites (Table 5).
Growth.- Data on turtles captured during this study previously marked by
Ernst et al. (1983) were available for preliminary analysis (K.R. Marion
pers. comm.). We considered changes in carapace length (X = +2.3 mm; 1.15
mm/yr), plastron length (X = +0.65 mm) and weight (X = +4.8 g) most
reliable for comparison between studies since we took measurements of
plastron width, carapace width, and shell depth slightly different.
Turtles increased in carapace length from 0.0 to nearly 0.30 mm/yr with
males growing slightly faster than females (Fig. 8). The maximum growth of
any turtle was 6.7 mm (3.35 mm/yr) CL. There appeared to be only a slight
DODD ET AL.: STERNOTHERUS DEPRESSUS IN NORTHERN ALABAMA 25
tendency for animals > 92 mm to decrease growth. Plastron lengths increased
very little except for one 77 mm male from Sipsey Fork (Fig. 8B); the large
increase is probably due to a measurement error.
Weight Change.- Nearly all data on within-season weight changes were
based on turtles from unaffected sites; hence, we could not compare data
between unaffected and affected sites. Males showed a slight tendency to gain
weight early, then either maintain or lose weight as the season progressed (Fig.
9A). In some instances, substantial weight loss occurred in a rather short period
of time. One male lost 16 g in 27 days, while one lost 13 g in 14 days. Weight
gains were less dramatic, although one male gained 13 g between 1 June and 27
August. Of 112 weight change observations on males in Sipsey Fork, 46
increased, 66 decreased, and 10 had no change.
The change in female weight within a season is complicated by egg
deposition. Although we had fewer observations for females than males, a
Table 6. Comparison of total turtle biomass and S. depressus at sites in northern Alabama,
summer 1985. Biomass is in kg.
Total Turtle S. depressus Percent
Location Biomass Biomass S. depressus
Unaffected Sites
Sipsey Fork 27.63 24.01 86.9
Brushy Creek 7.60 3.26 42.9
Clear Creek 6.24 0.0 0.0
Blackburn Fork 13.68 3.95 28.9
Blackwater Creek 6.84 0.94 13.7
(Camp O'Rear)
Total 61.99 32.16 51.9
Affected Sites
Turkey Creek 5.57 2.87 51.5
Gurley Creek 15.62 0.72 4.6
Lost Creek 1.61 1.43 88.9
(Pocahontas)
Lost Creek 14.77 0.05 0.3
(Townley)
Blackwater Creek 5.09 0.0 0.0
(Harris Br.)
Total 42.66 5.07 11.9
A
N-48
BULLETIN FLORIDA STATE MUSEUM VOL. 34(1)
* EIPSEY FORK MALE
o 81P8EY FORK FEMALE
S81P8REY FORK UNKNOWN
* BRUSHY CREEK MALE
O BRUSHY CREEK FEMALE
TURKEY CREEK MALE
* BLACKWATER CREEK MALE
26
0.30-
I-
z
0
0.20-
0
UJ
0
I< 0.10-
0
o
0.30-
I
M 0.10,
I
I
0
0
-Jolo
0.
0 *
60 65 70 75 80 85 90 95 100
CARAPACE LENGTH (MM) UPON RECAPTURE
B
N-41
o
0 *
0 0 0
o. o 0
. . . . Io o o
60 65 70 75 80 85 90 95 100
CARAPACE LENGTH (MM) UPON RECAPTURE
Figure 8. Carapace (A) and plastron (B) growth rates (mm/month) as a function of recapture
carapace length for S. depressus initially captured in 1983 and recaptured in 1985.
* .
. 0
0
o
0
0 0
DODD ET AL.: STERNOTHERUS DEPRESSUS IN NORTHERN ALABAMA
MAY JUNE
JULY
AUGUST
Figure 9. Patterns of seasonal weight changes for male (upper) and female (lower) S.
depressus recaptured at study sites during the summer of 1985 in northern Alabama.
SEPT
BULLETIN FLORIDA STATE MUSEUM VOL. 34(1)
cumulative diagram (Fig. 9B) showed females tended to lose weight in the
middle of the season followed by a gradual gain throughout the remainder.
This is illustrated by weight change data for 22 females from all locations (Fig.
10). The greatest weight loss in females (at Sipsey Fork) was 21 g between 25
July and 4 September; the largest gain, 10.5 g (at Brushy Creek), occurred
between 22 June and 11 September. Only two females showed no differences
in weight.
At all locations, juvenile turtles showed a tendency to lose weight (Fig. 11);
we recorded 21 weight losses (0.1 6.5 g), 3 no change in weights, and only 4
weight increases (0.5 4.0 g) among 23 turtles.
For inter-seasonal weight changes, data were available from 41 S. depressus
marked by Ernst et al. (1983). These data showed an average increase of 4.8 g
between 1983 and 1985, with a maximum gain of 15.7 g in an 86.9 mm female.
Several females showed substantial weight gains, but these increases may be
associated with egg development prior to oviposition. In general, turtles
increased most in the range of 0.10-0.30 g/month regardless of carapace length
(Fig. 12).
Nests and Hatchlings.- Prior to this study, natural nests of this species
were unknown. On 31 July, CKD found a natural nest on the north shore of
Sipsey Fork on a high, sandy bank. This bank had been checked daily since 1
July; attention was drawn to the nest by a fresh crawl. The nest was located 6.5
m from water in such a position that it would receive the afternoon sun. It was
shallow and located under slight vegetative cover similar to the nests of S.
minor (Carr 1952). Hatchlings would have only to go directly downhill to reach
the water. Two freshly deposited eggs were uncovered. Dimensions (length,
width, mass) were as follows: 33.1 mm, 16.1 mm, 6.0 g; 31.1 mm, 15.7 mm, 5.5
g. These figures are similar to those reported by Estridge (1970) for shell
measurements of one hatchling and the average mass of 5.23 g (N = 15) for
hatchlings given by Close (1982).
The eggs were incubated at 250C. Hatching began 14 September (45 days)
for one egg and 16 September (47 days) for the other; incubation duration thus
was much shorter than reported for other kinosternids (Ewert 1985; Ernst
1986). Both took about two days to complete hatching, and hatching occurred
in a sequence similar to that reported by Estridge (1970). There was barely a
trace of a yolk scar on both turtles upon release on 18 September.
Shell Erosion
Erosion affecting the carapace has been noted by a number of biologists
and commercial collectors working with S. depressus. Of 437 S. depressus from
0
160
140
120
100-
80
N-17
I I II I 'I
APRIL MAY JUNE JULY AUGUST SEPT
Figure 10. Intraseasonal weight changes of female S. depressus recaptured at study sites in northern Alabama during the summer of 1985.
10
z
0 5
2
0
32 2
4 2432
5 O
o
10-
15J
MAY JUNE JULY AUGUST SEPT O
Figure 11. Patterns of seasonal weight changes for juvenile S. depressus recaptured at study sites in northern Alabama during the summer of
1985.
0.70 -N-48
0.60
0.50-
I-
2 0.40-
O
0
0.30
2
I 0.20-
- 0.20-
I-
0 0.10-
w
0.00
-0.10
-0.20
* 81P8EY FORK MALE
o 81P8EY FORK FEMALE
O 81P8EY FORK UNKNOWN
* BRUSHY CREEK MALE
O BRUSHY CREEK FEMALE
* TURKEY CREEK MALE
* BLACKWATER CREEK MALE
* 0
0
0
0
0
0* *
*
*
95 100
Figure 12. Rates of weight change (g/month) as a function of recapture carapace length for S. depressus caught in 1983 and recaptured in 1985.
60 65 70 75 80 85 90
CARAPACE LENGTH (MM) UPON RECAPTURE
BULLETIN FLORIDA STATE MUSEUM VOL. 34(1)
unaffected sites, 150 (34.3%) were eroded; 58.1% of the mine-affected site
turtles (25 of 43) were eroded. These differences were statistically different (X2
= 11.59; p < 0.001). There was considerable variation between populations as
to the percentage of eroded turtles, from 0% at Lost Creek-Pocahontas to
91.7% at Blackburn Fork (Table 7). The patterns of erosion, however, seem to
vary little between populations, except at Sipsey Fork and Brushy Creek
(Fig. 13). Marginals were equally liable to be eroded regardless of location on
shell or study site. At Brushy Creek, erosion was concentrated on the front and
sides of the carapace; no erosion was found on marginals 10 and 11. At Sipsey
Fork, the nuchal and first marginals were most likely (> 65% of the time on
eroded turtles) to be eroded.
Table 7. Prevalence of eroded shells in populations of S. depressus.
Location N N eroded % eroded
Unaffected Sites
Sipsey Fork 345 112 32.5
Brushy Creek 36 5 13.9
Blackburn Fork 36 33 91.7
Blackwater Creek 20 0 0.0
(Camp O'Rear)
Total 437 150 34.3
Affected Sites
Turkey Creek 25 20 80.0
Gurley Creek 5 5 100.0
Lost Creek 12 0 0.0
(Pocahontas)
Lost Creek 1 0 0.0
(Townley)
Total 43 25 58.1
Overall Total 480 175 36.1
DODD ET AL.: STERNOTHERUS DEPRESSUS IN NORTHERN ALABAMA
17 -16 (4)3- 3(4)
N-20
1 17 17 4) (GURLEY CREEK) (4)
17 16 (4)3k3 3(4)
15 17 (5)2' 2(5)
12 13 0 0
14 13 (3) 0 0 (5)
(3) (3)
Figure 13. Carapacial erosion patterns of the marginal scutes of S. depressus. Numerals
outside carapace indicate the number of individuals affected at that site.
BULLETIN FLORIDA STATE MUSEUM VOL. 34(1)
Movements and Habitat Use
We followed 13 adult S. depressus from 4 to 40 days (Table 8). Males
moved 69% of the days and females moved 50%. Movements ranged from 0.5
to 460 m overnight, although movements > 30 m were unusual. Males moved
greater distances than females (X = 31.2 m, N = 81; X = 19.2 m, N = 25),
although there were exceptions. Individuals overlapped specially in terms of
movement and cover site selection.
Examination of individual movement patterns (Figs. 14A-G) demonstrated
that flattened musk turtles tend to stay in a particular area, and return
continuously to the same cover sites. An example of this pattern was shown by
turtle No. 4600 (Fig. 15) which ventured more than 20 m on five occasions, two
of which were to baited traps upstream. Turtle No. 6774 at one point remained
under the same ledge for eight days before making an overnight move 43 m
upstream; after one night, it returned to its ledge (Fig. 14F).
Table 8. Movement of S. depressus based on radio-telemetry data.
Turtle Sex Length Days/0 Days/ Range
No. (mm) Movement Movement (m)
4330 M 90.5 1 3 1-25
4600 M 97.9 8 32 0.5-24
4612 M 84.4 4 15 0.5-35
4618 M 85.6 2 2 10-135
4335 M 85.6 3 15 0.5460
6774 M 88.7 8 6 7-103
4280 M 88.6 11 8 6-64
Total Males 37 81
(31.4%) (68.6%)
4614 F 86.5 1 3 3.5-160
4616 F 85.5 3 2 2-150
4619 F 83.9 1 3 6-50
4665 F 78.2 10 11 0.5-16
4716 F 93.9 4 4 2-3
4717 F 94.1 6 2 2-4
Total Females 25 25
(50.0%) (50.0%)
Total (N= 13) 7:6 62 106 05-460
(36.9%) (63.1%)
DODD ET AL.: STERNOTHERUS DEPRESSUS IN NORTHERN ALABAMA 35
Table 9. Cover sites used by S. depressus in Sipsey Fork based on radio-telemetry data.
Root-
Turtle N Rock Crevice Mud Debris Log
Males
4330 4 2 2
4600 41 6 6 14 15
4612 16 1 1 10 4
4618 4 4
4335 16 3 10 3 10
6774 14 3 10 1
4280 15 14 1
Total 110 31 11 18 24 26
Females
4614 4 2 2
4616 5 5
4619 4 1 3
4665 8 1 7
4716 19 18 1
4717 8 8
Total 48 32 2 1 1 12
Overall Total 158 63 13 20 26 38
S. depressus occasionally makes long distance movements for relatively
short periods of time. This was shown by turtle No. 4335 which generally
remained under a stump and brush pile but made two long movements
overnight, the farthest 460 m upstream to a log jam where it remained two
nights (Fig. 14G). Long distance movements were always upstream and for
short duration, i.e. one to two days. We were unable to correlate these
movements either with particular weather or stream conditions, as turtles
made such movements independent of one another. Both sexes made long
distance movements.
Individual turtles used similar cover sites, i.e. some turtles favored mud,
some root debris, and others rocks and crevices (Table 9). Overall summaries
give the impression that turtles had no preferences, whereas individual
summaries clearly show site preferences. Females tended to prefer rock cover
(X2 = 27.72;p < 0.001).
WATER PLANTS
LOGS
STREAM
ROCK
1|',STUMP
UNDERWATER LOSS
TREE OVER WATER
,ROCK
RIFFLES
1 '
WATER PLANTS LOGS
so "
TREE OVER WATER 1
I
ROCK TREA
EXPOSED STUMP
ROCI
IS
UNDERWATER S RIFFLEO
TREE OVER UTERE
o 05 10SHALLOW AND ROCK
TREE BRANCHES ROCK
RIFFLES -
RFLSo ;\
Figure 14 A-G. Locations and movements of radio-telemetered S. depressus in Sipsey Fork. A star indicates the initial release point; a large
circle indicates that there were many fixes in the same location. The striped line indicates a particularly long overnight movement.
* 4610 N R 7
o 461B N B
ROCK
ROCK
TREE BRANCH
100 M
ROCK
WATER PLANTSa
EXPOSED STUMP
UNDERWATER LOGS
SA0
oREE OVER
TREE OVER WATEI
* 4380 N 1 S
04000 N 48
100 I I
RIFFLEI
Figure 14 -- Continued.
WATER PLANT
TREE OVER WATER
ROCK/
LOSE
STREAM
ROCK
8TUMP
* \/ OK
ROCK
I Looa
STREAM
SROCK
\ STUMP
TREE OVER WATI
4 16 N- 2
0
0
tR
o
Ro
ROCK
ROCK
,ROCK
TREE BRANCH
100 M
ROCK
6 6
WATER PLANTS LOGS WATER PLANTS LOS
50o 0 S5/ 0
TREE OVER WATER TREE OVER WATER
ROCK ROCK
STREAM STREAM
1 r1
EXPOSED STUMP EXPOSED OTUMP
UNDERWATE LOG DERWATER LOGS R
N STUMP I STUMP
o 0o
TREE OVER WATEROC K TREE OVER WATERROCK
N 4S1A S 2SM 1-7 I 6
SHALLOW SAND ROCK o 4717 N SHALLOW SAND ROCK
RIFFLES RIFFLES
TREE BRANCH ROCK TREE BRANCHES ROCK
100 M 100 M
RIFFLES -- 1 RIFFLE8; -
'C
Figure 14 -- Continued.
WATER PLANTS
r LOGe
STREAM
ROCK
STUMP
EXPOSED STUMP
TREE OVER
e4.8S N IE
TREE BRANCH
1-------0
100 M
200 M UPiTREAM
Figure 14 -- Continued.
t
0
z
ROCK
oo
2O0
2M
V135
al ABOVE WATER LOG
UI UNDERWATER LOG
r FLAT ROCK
p PLANTS
rSROCK SHELF
rd ROOT DEBRIS
mb MUD BANK
Figure 15. Locations and movements of radio-telemetered turtle 4600. The boxes indicate an overnight movement outside the area normally
occupied by the turtle, and the distance traveled. The star is the initial release point; R is the final recapture location. The light numbers indicate
water depth in mm, and the shoreline is represented by the thick black line.
DODD ET AL.: STERNOTHERUS DEPRESSUS IN NORTHERN ALABAMA 41
Table 10. Cloacal temperatures of individual basking S. depressus in Sipsey Fork, 1985.
Parentheses indicate the time when the reading was made.
Water
Air Temp. Cloacal Alert-
Turtle Date Weather Temp (Time) Temp. Light ness Notes
4684 08/22 clear, cool 22.0 32.6 Sun No on log
(0850)
4757 08/22 clear, cool 22.0 30.2 Sun Yes
(0850)
6500 08/23 overcast, 23.0 22.2* 22.2 Overcast ? turtle
cool (0900) wet
4684 08/26 clear, cool 20.0 22.0 24.0 Sun No on land,
(0930) died
08/27)
4628 08/28 clear 23.4 22.0 25.8 Shade Yes on rock
(1000)
4782 08/28 clear 23.4 22.0 26.6 Sun Yes
(1000)
4641 09/01 clear, warm 24.0 33.1 Sun No on log
(1040)
4628 09/03 partly cloudy 23.0 22.0* 24.0 Shade No
The maximum water temperature at Sipsey Fork on 08/23 was 25"C; on 09/03 it was 27"C.
For turtle No. 4600, an adult male, 39 data points were available for
determining a core area of habitat use (Kaufmann 1962). We excluded several
points inasmuch as they were > 20 m from the main center of activity and
represented either exploratory movements or movements toward a baited trap.
We used a variety of home range estimators, including minimum convex
polygon, harmonic mean transformation (Dixon and Chapman 1980), 95%
ellipse, and fourier transformation (Anderson 1982) to compute the area of
concentrated use. These methods provided varied results, from 77 m2
(minimum convex polygon), to 88 m2 (50% value, fourier transformation,
Dixon and Chapman 1980) to 123 m2 (95% ellipse).
Basking
We recorded 67 instances of basking at three locations: 1 at Blackwater
Creek-Camp O'Rear, 1 at Blackburn Fork, and the remainder at Sipsey Fork.
BULLETIN FLORIDA STATE MUSEUM VOL. 34(1)
The earliest turtles were observed basking was May 16 at Blackwater Creek-
Camp O'Rear and the latest was 14 September at Blackburn Fork. The
majority of observations occurred between 14 August and 4 September at Sipsey
Fork. Turtles were most frequently observed during early to mid-morning
hours, but this may be a reflection of observer presence rather than a time
preference per se. Turtles as small as 33.1 mm CL were observed basking.
The cloacal temperatures of basking turtles (N = 8) were as high as 33.10C,
9.10C above the water temperature on that occasion (Table 10). The lowest
temperature, 22C, was recorded in a turtle that was wet, indicating it had just
emerged from the water, also 22*C. Even on cloudy days, turtles out of water
had body temperatures above that of the water. Turtles with low body
temperatures may not have been out of water for a long period.
Most basking turtles were in the direct sun (78.6%), were alert (66.7%),
and appeared to be sick (60.6%). Sick turtles (see Dodd 1988b) were less alert
than healthy turtles and were more likely to be out of water in shade than their
healthy counterparts (Table 11). Also, turtles in the sun appeared more alert
than those in shade.
Of the 47 basking platforms used by S. depressus, some were used more
than once, particularly a rock in the middle of Sipsey Fork that was used by at
least six different turtles on different occasions. Branches were the most
commonly used platform, followed closely by logs (Table 12). Branches were
higher above the water, narrower, and over deeper water than other perch
sites. We recorded two instances of the same turtle "basking" on land, although
this turtle was very sick and was recovered dead in shallow water the day after
the second observation. Basking sites were generally positioned such that they
received maximum morning or early afternoon sun (Fig. 16).
S. depressus is an adept climber. The highest we recorded a turtle was 910
mm over water on a 30 mm wide branch. To reach this position, the turtle had to
crawl around several branches and move upward at a steep angle. We noted
three instances of S. depressus perched vertically, once on a branch, once on a
rock in the middle of the stream, and once on a vertical cliff face.
Individuals apparently will also move over land to reach a desired basking
position; we observed turtles on branches over water that could only have been
reached by first crawling on land. Three turtles were perched on branches over
land but at the water's edge; when the turtles jumped, they fell on land and were
captured.
Morphological Analysis
All power function exponents of body mass regressions on the independent
variables of carapace length, carapace width, plastron length, and plastron width
DODD ET AL.: STERNOTHERUS DEPRESSUS IN NORTHERN ALABAMA 43
Table 11. Relationship of basking to position in direct sun, whether a turtle was sick, and
alertness in the flattened musk turtle, S. depressus, in northern Alabama. Number of
observations: sun = 42, sick = 33, alert = 57.
SunY SickY AlertY SunN SickN AlertN
SunY 33
SickY 8 20
AlertY 26 7 38
SunN 42 5 6 9
SickN 9 33 11 2 13
AlertN 7 12 57 3 2 19
SunY SickY 4 4
SunY SickN 8 1
SunN SickY 3 2
SunN SickN 1 1
Table 12. Basking platforms used by S. depressus in northern Alabama. Sipsey Fork, N=45;
Blackburn Fork, N=1; Blackwater Creek (Camp O'Rear), N= 1. Measurements in mm.
Height above water Width Depth of water
Type N X (range) X (range) X (range)
Branch 20 440 (60-910) 90 (30-180) 541.9 (155-840
N=16*
Log 16 156.6 (70-320) 230.9 (45-400) 405 (210-670)
Rock 8 236.3 (30-570) 315 (75-730) 462.5 (30-870)
Rock Face 1 Carapace touching -- 185
water
Land 2 1 turtle with nose in water,
the same turtle later observed
500 mm from water
Total 47 301.7 (30-910) 182.2 (30-730) 464.3 (30-870)
* An additional 3 turtles were basking over land; data not recorded for 1 turtle.
BULLETIN FLORIDA STATE MUSEUM VOL. 34(1)
ROCK CLIFF
MANY BRANCHES
--... RIFFLES
SAND BARS
O LARGE ROCKS
STATION
S STREAM
BASKING SITE
100 M
BRIDGE
Figure 16. Basking locations used by S. depressus at Sipsey Fork.
ROCK
WATER
DODD ET AL.: STERNOTHERUS DEPRESSUS IN NORTHERN ALABAMA 45
were highly significant and were near 3.0 (Table 13). According to Iverson
(1984), such values are to be expected for regressions of mass on carapace
length. There were small differences between the sexes, except for mass x
plastron width in juveniles and females; both had power function exponents
around 4.0. In addition, the power function of the regression of mass x plastron
length was lower for juveniles than the others, being only 2.4.
For other regressions involving morphological comparisons, all power
functions again were highly significant, and values for slopes were similar
Table 13. Relationship between body mass (Y) and carapace length (CL), carapace width (CW),
plastron length (PL), and plastron width (PW) (X variables) in Sternotherus depressus, based on
the equation Y = aXb. Units in gm and mm. The statistical significance of correlation
coefficients is indicated (**, p < 0.01).
Independent
Variable N b a r
Males
CL 225 3.2797 0.00004 0.952**
CW 224 3.4968 0.00005 0.797**
PL 225 3.0031 0.00047 0.938"
PW 224 3.1529 0.00134 0.900**
Females
CL 143 3.2622 0.00004 0.960*
CW 143 4.0544 0.000005 0.862**
PL 143 2.9670 0.00043 0.932*
PW 143 3.2468 0.00090 0.917**
Juveniles
CL 109 2.9237 0.00017 0.992**
CW 109 4.0198 0.000005 0.979**
PL 109 2.4739 0.00303 0.991**
PW 109 2.8087 0.00365 0.985**
BULLETIN FLORIDA STATE MUSEUM VOL. 34(1)
regardless of sex (Table 14). However, while statistically significant, the r2 values
for certain comparisons explained only a small part of the variance: gular length
x gular width-females (29.7%), males (42.3%), overall (46.3%); shell depth x
carapace width-females (40.9%); interhumeral length x plastron length-females
(11.7%), males (32.6%), overall (56.2%); shell depth x carapace length- females
(49.9%). Thus, predictions for one of these dependent variables based on the
size of the correlated independent variable would not be reliable, although a
trend might be indicated.
Character proportions of CW/CL, PW/PL, PL2W, PL2L, and GW/GL are
provided in Table 15.
Table 14. Relationship of various dependent variables (Y) to independent variables (X) of shell
measurements of Sternotherus depressus, based on the equation Y = a + bX. Units in mm.
Statistical significance of correlation coefficients is indicated (**, p < 0.01). C = combined
totals.
Sex Y X N b a r
M CL CW 251 1.2607 2.1x104 0.888**
F CL CW 159 1.6314 3.0x10 0.869**
J CL CW 116 1.6185 1.6x108 0.977**
C CL CW 539 1.6654 2.0x10"7 0.959**
M PL PW 251 1.4925 8.6x102 0.916**
F PL PW 159 1.8679 0.07183 0.938**
J PL PW 116 1.7736 0.05355 0.982**
C PL PW 539 1.8100 0.06399 0.977**
M GL GW 225 0.5046 2.82215 0.654**
F GL GW 143 0.5370 4.98832 0.545*
J GL GW 110 0.8790 1.23825 0.781**
C GL GW 479 0.5494 2.99906 0.681**
M SD CL 251 0.2687 5.08452 0.872**
F SD CL 159 0.2368 3.1x10 0.707**
J SD CL 116 0.2435 49.40245 0.954**
C SD CL 539 0.2589 19.73710 0.950**
M SD CW 251 0.3920 3.15598 0.898**
F SD CW 159 0.4023 5.38814 0.637**
J SD CW 116 0.3941 0.6259 0.932**
C SD CW 539 0.4527 0.10215 0.948**
M IL PL 251 0.0881 2.31822 0.571**
F IL PL 159 0.0566 19.20941 0.342**
J IL PL 116 0.1021 1.92803 0.831**
C IL PL 539 0.0827 3.40928 0.809**
M PL2L PL2W 251 0.6465 0.46580 0.938**
F PL2L PL2W 159 0.7663 0.02720 0.879**
J PL2L PL2W 116 0.5574 3.27363 0.909**
C PL2L PL2W 539 0.6553 0.53504 0.967**
CL = carapace length, CW = carapae width, PL = plastron length, PW = plastron width, GL gular length, GW = gular
width, SD = shell depth, IL = interhumeral length, PL2L = length of 2nd pleural, PL2W = width of 2nd pleural.
DODD ET AL.: STERNOTHERUS DEPRESSUS IN NORTHERN ALABAMA
Table 15. Character proportions of Sternotherus depressus. Mean ratios as percentages are
followed by one standard deviation. Character range appears below mean.
Sex N CW/CL PW/PL PL2W/PL2L GW/GL
Males 248 70.1 5.7 60.0 4.5 162.0 10.7* 144.3 48.5
(0.0-79.7) (0.0-68.9) (123.6-218.8) (73.5436.4)
Females 159 70.3 3.7 55.6 2.1 154.2 10.8 116.9 30.7**
(59.9-79.5) (49.5-61.4) (121.7-189.5) (41.2-228.6)
Juveniles 116 84.8 7.7 62.1 4.2 160.2 14.6 108.3 24.7***
(70.8-101.5) (47.6-74.1) (86.6-185.4) (51.7-190.9)
Overall 524 73.4 8.3 58.7 4.5 159.3 12.1# 127.6 42.0##
(0.0-101.5) (0.0-74.1) (86.6-218.8) (41.2-436.4)
*N=247; ** N=143; *** N=109; # N=523; ## N=471.
Miscellaneous Notes
The following observations were made on individual S. depressus during the
course of this survey. Physical deformities: deformed vertebrals- 1 (Sipsey
Fork); deformed marginals- 5 (Lost Cr., Blackburn Fork); flared carapace- 3
(Sipsey Fork, Turkey Cr., Blackburn Fork); pushed-in snout- 1 (Sipsey Fork);
extremely pitted carapace- 6 (Blackburn Fork); extra marginals- 1 (Blackburn
Fork); extreme facial algae- 2 (Blackburn Fork); abnormal growth or tumor- 1
(Sipsey Fork); lack of gular scute- 7 (Sipsey Fork, Blackburn Fork). Physical
signs of trauma: missing front foot- 1 (Sipsey Fork); missing rear foot- 5
(Sipsey Fork, Brushy Cr.); missing toes- 1 (Sipsey Fork); bite marks- 3 (Sipsey
Fork, Brushy Cr., Turkey Cr.); cracked & healed carapace- 2 (Sipsey Fork,
Lost Cr.); missing tail- 1 (Sipsey Fork); blind in one eye- 4 (Sipsey Fork,
Blackburn Fork). Many similar injuries have been reported for S. odoratus
(Ernst 1986).
BULLETIN FLORIDA STATE MUSEUM VOL. 34(1)
DISCUSSION
Turtle Capture.- While we were able to correlate certain environmental
variables with turtle captures, the subtle interaction of these variables and how
they might influence turtle behavior is unknown. We measured variables only
at 10 sites, and we do not know whether turtle capture and values for pH,
conductivity, and 02 would be similarly correllated at other locations. Turtles
tolerate values outside the range we report as optimum, and we urge caution in
extrapolating our results to the interpretation of habitat suitability elsewhere in
the Basin.
Trapping likely does not adequately sample a turtle population, especially
the smaller size classes. Ream and Ream (1966) noted that estimates of
population structure varied according to the type of trap used in their study of
Chrysemys picta in Wisconsin. We agree with Ernst et al. (1983) that juvenile
turtles (< 50 mm) are unlikely to be captured by traps and are potentially
underrepresented in some samples. However, if large numbers of turtles in the
50-70 mm size class are trapped, juveniles smaller than this should be in the
population. This appears to be the case at Blackwater Creek-Camp O'Rear.
When water conditions are favorable, such as at Blackburn Fork, Sipsey Fork,
Lost Creek-Pocahontas, and Brushy Creek, wading can supplement trapping to
estimate population structure and status.
Two problems with trapping have not been adequately addressed by previous
studies on S. depressus, i.e. how effective are the traps in drawing turtles to them
and how effective are they in retaining turtles once inside? Our results indicated
that radio-transmittered turtles could move > 30 m overnight to a baited
trap. However, on several occasions we attempted to catch a radio-transmittered
turtle under a large rock. Traps were baited less than two meters from the turtle
for several consecutive nights, yet the turtle was never trapped. On one occasion,
the turtle moved three meters directly past the trap. Thus, individual turtles vary
in trapability (also see Ream and Ream 1966).
Most researchers assume that once trapped, a turtle remains in the trap.
This may not be the case. One evening, we checked our traps in Sipsey Fork
after they had been in place 45 minutes. In one trap, we found two marked
turtles. After recording the numbers we left the turtles in the trap overnight.
The next morning, both were gone, and a different S. depressus was in the trap.
The probability of initially trapping an individual S. depressus, and the
probability of escape, are unknown. Repeated trapping may partially overcome
this problem.
Differences in trapping success from previous studies (Table 1) are
probably due to declines in the resident population of flattened musk turtles.
At Blackburn Fork and Blackwater Creek-Camp O'Rear, this most likely
resulted from commercial collecting since collectors have worked both streams
DODD ET AL.: STERNOTHERUS DEPRESSUS IN NORTHERN ALABAMA 49
at least since 1980. We interpret the lack of adults as reflecting collecting
pressure on larger animals. Capture variation at Sipsey Fork, Brushy Creek,
and Turkey Creek are more difficult to explain, but disease may be partly
responsible, especially at Sipsey Fork (Dodd 1988b). Collectors also have been
active in these streams (Guthrie 1986).
Differences in trap success between 1983 and 1985 at Lost Creek are easier
to explain. Lost Creek at Cedrum (Ernst et al. 1983) is excellent habitat with
good cover and food resources. At the Pocahontas site, the stream is much
smaller with fewer cover sites and a smaller mollusc population. Cedrum
probably has a larger population of S. depressus than Pocahontas because of
better habitat conditions.
We hypothesize that recruitment to the adult population was not taking
place if large juveniles were not captured during trapping. The lack of juveniles
in the 50-70 mm size class at Turkey Creek, for instance, probably reflects lack
of successful recruitment rather than the failure of trapping to reflect
population structure. We found a hatchling at Lost Creek-Pocahontas, but the
lack of large juveniles suggests that reproduction may be occurring without
recruitment to the adult population.
We caught no turtles in Clear Creek. Clear Creek is marginal S. depressus
habitat because of its fast current, lack of cover sites, and heavy sand load that
clogs available crevices. If there ever was a population of flattened musk
turtles, it is likely extirpated. Animals caught by Ernst et al. (1983) were
probably vagrants from downstream where habitat conditions are more
favorable.
Habitat Use, Activity, and Movements.- The flattened musk turtle
frequently used the same cover site or group of cover sites within a home range
(sensu Brown and Orians 1970) that overlapped those of conspecifics. Both
males and females made occasional long-distance movements of several days
duration prior to returning to a frequently used cover site. Plummer and Shirer
(1975) also found that male and female Apalone mutica occasionally made long
distance movements of unknown purpose both up- and downstream and noted
that females traveled long distances to nesting sites. We have no data for
nesting female S. depressus because our telemetry study began after the peak
of the nesting season.
We made no attempt to calculate home ranges of turtles, except for turtle
No. 4600, because of lack of sufficient data points. Mahmoud (1969) calculated
home ranges based on as few as five observations, but noted that home range
estimates seemed to decrease with more observations. By connecting the
points of most distant movement, he may have confused the periodic
movements of turtles with home range, and thus greatly overestimated the
extent of the home range. Our impression was that linear home ranges are not
greatly different for males and females, but more data are needed to confirm
BULLETIN FLORIDA STATE MUSEUM VOL. 34(1)
this. The area of concentrated cover site use by No. 4600 was probably less
than the estimates provided, although its area of activity was probably much
greater, because of procedural difficulties in applying and interpreting the
various home range techniques (see Samuel et al. 1985, and references within).
Plummer and Shirer (1975) found that A. mutica may shift home ranges
within a season. We were not able to determine if flattened musk turtles do
likewise, although several turtles did move from an often used area to a section
of stream 20-30 m distant. We do not know whether this represented a
temporary shift of home range or was simply a shift to a distant part of the
home range.
Another problem in the determination of home range is that we have few
data on movements within a 24-h cycle. Turtles likely foraged at night and
returned to the same or a nearby cover site each morning. More than 50% of
the turtles were known to shift cover sites from day to day. At least two turtles
moved > 30 m upstream from a favored cover site to a baited trap, but we do
not know if they normally foraged to this extent or were merely drawn to the
bait.
There is some disagreement as to the activity period of S. depressus (Tinkle
1958; Estridge 1970; Mount 1981; Ernst et al. 1983). Early in the season when
water temperatures were rather cool, S. depressus normally was diurnal, at
least in Sipsey Fork. However, some turtles were active either nocturnally or
crepuscularly, and were caught in traps. As the season progressed and the
water became warmer, diurnal activity became less obvious and capture
success decreased while wading. At the same time, nocturnal trapping success
increased. S. depressus is not strictly nocturnal, even during mid-summer. On
17 July, Dodd watched a flattened musk turtle for 15 min at 1000 h from a
large rock along the shore of Sipsey Fork as the turtle moved upstream from
rock to rock along the bottom as if looking for food items.
Juvenile S. depressus (< 40 mm CL), which frequent shallow riffles and
weed beds, were diurnal as they crawled along the bottom. We cannot rule out
nocturnal activity, because we only waded once at night at Sipsey Fork; during
3 man-hours of wading, we captured three adults. Diurnal activity in
inaccessible areas might protect juveniles from large, aquatic, night-foraging
piscine or chelonian predators.
Diurnal activity included basking, the primary function of which is assumed
to be to raise body temperature to assist digestion, with secondary benefits to
the skin and shell (Boyer 1965; Moll and Legler 1971; Hutchinson 1979).
Kluger (1979) noted that elevated body temperatures assist in suppressing
certain bacteria, and this may account for the basking seen in Sipsey Fork
S. depressus, many of which were diseased (Dodd 1988b). Both S. minor and S.
carinatus are adept climbers and baskers (Cagle and Chaney 1950; Carr 1952;
Cox and Marion 1978). The other member of the genus, S. odoratus, also has
been reported to bask aerially in the wild, albeit uncommonly (Risley 1933;
DODD ET AL.: STERNOTHERUS DEPRESSUS IN NORTHERN ALABAMA 51
Cahn 1937). It is not surprising, therefore, that S. depressus, a member of the
Carinatus group, also basks on occasion.
S. depressus selected basking positions over deeper water, often on
precarious perches. Such locations allow the turtle to drop into the water to
crevices under the perches, and thus readily escape. The narrowness of many
of these perches made them sensitive to the slightest disturbance which would
alert the turtle to the approach of a predator. Location of basking positions to
facilitate escape is not uncommon in turtles (Bury 1972; Waters 1974). Of
more interest were the perches located over land or in close proximity to the
shore. Turtles selecting such locations would be at a distinct disadvantage
should quick escape become necessary, and we easily captured two turtles after
they fell off a branch over land. Diseased basking turtles seemed less alert than
non-diseased baskers, and these turtles would be particularly vulnerable to
predation.
Population Estimates, Biomass, and Sex Ratio.- There has been little
work on population estimation of stream and river dwelling turtles. Mahmoud
(1969) gave estimates of 149.9 S. odoratus/ha in an Oklahoma creek, 228.7 S.
carinatus/ha in a river, and 159.3 and 258.4 K subntbrum/ha in two creek
populations. Cox and Marion (1979a) estimated 288 S. minor/ha in a north
Florida spring pool. Bury (1972 in Bury 1979) reported 419.9 Clemmys
marmorata/ha in a California stream. Plummer (1977) estimated 1900 A.
nmutica per 1.5 km of river but cautioned that estimates could be biased by
temporary emigration and immigration. E. Moll (1980) used a known number
of nesting females combined with a sex ratio from trapping to construct a
crude estimate of 1200-3600 Batagur baska in the Perak population, Malaysia.
Other workers (in Bury 1979; Congdon et al. 1986; Ernst 1986) have provided
estimates for pond and lake species.
The population estimate for Sipsey Fork during mid-summer (prior to
decline) translated to 28.75 S. depressus per hectare (range 19.7-36.8) assuming
even distribution and habitat suitability. There were probably more S.
depressus per hectare where appropriate cover sites were available. At Brushy
Creek, we estimated only 4.4 S. depressus per hectare (range 3.4-6.4). These
figures are considerably less than those reported for other river-dwelling
turtles (see references above), but similar to S. odoratus in a Pennsylvania
lake (Ernst 1986). We consider both populations stable and representative of
good populations for this species in similar-sized streams in the mid-1980s.
Beginning in mid-July, a decline in the size of the population of S. depressus
occurred in Sipsey Fork that was not seen in sympatric turtle species or in
other flattened musk turtle populations. One explanation is that females
congregated in this area to nest on an extensive sand bank and then dispersed
after the nesting season. Gibbons (1986) noted that excursions by females to
suitable nesting sites was one of the four categories of long-range movement of
BULLETIN FLOIPDA STATE MUSEUM VOL. 34(1)
turtles. However, this explanation is not supported by trapping results, and sex
ratios did not change appreciably among trapping periods. In addition, there
are sand banks all along Sipsey Fork, so it seems unlikely that nesting areas
represent a limiting resource.
Environmental factors may cause some species of turtles to move less often,
aestivate, or leave streams (Gibbons 1970b; Ernst 1986; R. Bury pers. comm.).
However, the radio-telemetry data in the latter half of the season showed that
flattened musk turtles moved > 50% of the time. We think it unlikely that
flattened musk turtles left our study site for any of these reasons.
A third hypothesis is that a population decline occurred. In this regard, we
started picking up dead and sick turtles with necrotic shells (discussed by Dodd
1988b). While disease may have contributed to the decline of the Sipsey fork S.
depressus population, it may be only partially responsible. Guthrie (1987)
reported that 200 S. depressus were removed from Sipsey Fork by commercial
collectors about the time we noticed the decline. Although this report cannot
be verified, collecting could partially account for the decrease in population
size.
Literature reports of unbalanced sex ratios may result from biased
technique or inadequate sampling (Ream and Ream 1966; Gibbons 1970a;
Bury 1979). Tinkle (1958) reported a ratio of one male to three females for S.
depressus, but the sample was small. Our results for localities other than Sipsey
Fork also may be biased by small sample size, but most of these populations
have few turtles. The data from Sipsey Fork constitute a larger sample size and
we did not rely as heavily on trapping as we did elsewhere.
While we recognize that the sex ratio of freshwater turtle populations may
vary seasonally (Morreale et al. 1984; Dodd 1988a; Mitchell 1988; K. Marion
pers. comm.), we believe our results mirror population size and structure and
note that male-biased sex ratios have been reported in other studies on
Sternotherus (Bancroft et al. 1983). We have no indication that trapping tends
to catch one sex more often than the other. However, males tend to move
more often than females, and we realize this may influence results especially
during certain times of the year (Morreale et al. 1984; Parker 1984; Gibbons
1986; Ernst 1986).
The literature on turtle biomass shows ranges from 1.83 to 3341 kg/ha for
kinosternid populations (Iverson 1982; Congdon et al. 1986). Values for S. minor
were 45.7 kg/ha (Cox and Marion 1979a); S. carinatus 14.35 kg/ha (Mahmoud
1969); and S. odoratus from 7.5-41.7 (Mahmoud 1969; Wade and Gifford 1965;
Iverson 1982; Congdon et al. 1986; Mitchell 1988). Our streams were less
productive with only 10.72 kg/ha in Sipsey Fork, the densest population, where
S. depressus comprised 87% of the total turtle biomass.
The maximum total turtle biomass of 27.63 kg in one 100-m study area of
Sipsey Fork was considerably less than the value for most species in Iverson's
(1982) review. Biomass estimates should increase with precise data on
DODD ET AL.: STERNOTHERUS DEPRESSUS IN NORTHERN ALABAMA 53
population size, but we suspect that the high values reported in the literature
on aquatic turtles reflects inadequate data on population size and structure.
Even when precise information is available (Congdon et al. 1986), biomass
tends to be higher than we observed in northern Alabama streams.
We suggest that some studies may have biased results by their choice of
study sites. If sites are chosen because large amounts of data can be gathered
within a reasonable time period, population and biomass estimates might
reflect the biology of turtles in unusual habitats rather than general estimates
for the species. Low-density populations, although more difficult to study, may
provide a different picture of population dynamics of aquatic turtles.
Comparative studies are necessary to ascertain the significance, if any, of the
low biomass estimates that we observed.
Growth and Weight Changes.- Except for sea turtles and certain tortoise
populations, there are few data on chelonian growth rates based on
measurements between or within seasons rather than estimates based on
annuli counts (see reviews by Gibbons 1976; Andrews 1982; Galbraith and
Brooks 1987). Growth might be expected to slow with maturity, or even to stop
(Gibbons 1967; Wilbur 1975; Moll 1976; Andrews 1982; Bancroft et al. 1983),
and may vary considerably between individuals (Cox and Marion 1979b) and
populations (Iverson 1985). Plummer (1977) and Vogt (1980) reported rates
from zero to very small values (unspecified) per year. Cox and Marion (1979b)
noted that S. minor in Florida had a slow absolute growth rate and hence
considered only data collected > 9 months apart to determine growth rates in
this species.
We collected 50 S. depressus marked by Ernst et al. (1983). Growth and
weight change analysis showed that, on the average, turtles grew < 1.15 mm/yr
during the two years between capture; weight changes also were minor. These
data are in accordance with studies on sexually mature turtles (Andrews
1982). The data further showed that growth does not slow uniformly with
sexual maturity, and that individual variation in growth rate is not correlated
with carapace length. Some large turtles grew at the same rate as turtles barely
sexually mature. These results are different than expected (Wilbur 1975;
Andrews 1982), although S. odoratus also continues to grow at larger sizes
(Ernst 1986).
There are two difficulties with interpreting these data. The first is that the
sample only includes turtles sexually mature or nearly so. Our smallest turtle
had the fastest growth rate, and we suspect that small S. depressus grow
considerably faster than 1-2 mm per year. The second is that different groups
of observers took the measurements, thus allowing for error due to
measurement technique. We have no way to assess the magnitude of these
factors, and we urge caution in the interpretation of these growth data.
BULLETIN FLORIDA STATE MUSEUM VOL. 34(1)
Few studies have measured biomass changes within a season. Iverson
(1982) recorded only two estimates of annual biomass production in turtles,
1.4-14.9 kg/ha/yr for Geochelone elephantina (Coe et al. 1979) and 6 kg/ha/yr
for Chrysemys picta. While we have not estimated annual production, our
measurements suggested reductions in biomass during the course of the year.
For females, this was not surprising since they lose a significant portion of their
biomass during oviposition. We observed weight increases during the latter
part of the summer which would indicate that females were regaining weight
lost during reproduction.
Males and juveniles also lost weight as the season progressed, but the data
could be biased by significant biomass decreases in a few individuals. Slight
differences in biomass could be accounted for by recent ingestion or defecation
of a large quantity of food before capture. D. Jackson (pers. comm.) has
suggested that males stop feeding late in the season and rely on lipid reserves
while courting females. However, Close (1982) found lipid levels increased
until October, which suggests that stored lipid is not used during autumn
courtship. Close (1982) concluded that lipid levels were not important to males
for reproduction in this species. We have no explanation for the weight changes
in males and juveniles unless these animals were diseased (Dodd 1988b).
Carapace Erosion.- There have been a few casual observations of
carapace erosion in turtles of the genus Stemotherus (Carr 1952; Tinkle 1958;
Jackson 1964). Carapace erosion primarily affected the posterior margin of the
shell. Jackson (1964) observed erosion more often on old animals and
suspected that individual and social behavior, and possibly algae, were causal
factors. We also observed extensive erosion on the edges of the marginals in S.
depressus, but unlike earlier observations, erosion occurred in equal probability
around the margins. We assume this reflects the tendency of S. depressus to
wedge into crevices at different angles, thus causing abrasion.
Pitting on the carapace of some turtles, particularly at Blackburn Fork, was
occasionally observed. One individual at Gurley Creek was so pitted that the
carapace was worn completely through leaving a depression with only a light
membrane between the outside of the body and the internal body cavity.
Pitting in terrestrial species is associated with tick infestation (Ernst and Ernst
1977), but we have no reason to believe ectoparasites were responsible for
pitting these aquatic turtles.
We observed three individuals at Blackburn Fork with what might be
described as scalloped shells. Instead of being smooth, the carapaces were
furrowed like those of captive turtles raised on a calcium deficient diet. We
suspect this could be a developmental abnormality, whereas the pitting is likely
due to unknown environmental conditions or disease (Dodd 1988b).
DODD ETAL.: STERNOTHERUS DEPRESSUS IN NORTHERN ALABAMA 55
Morphology.- The body mass versus carapace length regression of S.
depressus was similar to that of other species of turtles (Gibbons 1983;
reviewed by Iverson 1984; Dodd 1988a; Wilbur and Morin 1988). Turtles have
lower power function exponents than other vertebrates although direct
comparisons are difficult because the head is not included in the overall length
(Iverson 1984). He speculated that an exponent less than three indicated that
body length increased more with size than in groups with cubic exponents, or
that body mass decreases more with size than in other groups.
The length of the gular and interhumeral scutes were poor predictors of
gular width and plastron length, respectively, because of the great degree of
variation in shape and size of these scutes. This variation was more
pronounced in older individuals, indicating that growth was not uniform
relative to surrounding scutes. The size and shape of these scutes, or even the
absence of the gular, would not be useful systematic characters.
Carapace length and width were poor predictors of shell depth for female
S. depressus. This is due perhaps to reproductive constraints on the volume of
the female's body cavity for egg production (Iverson 1985). Values were similar
between males and juveniles.
Habitat.- We concur with Mount's (1981) assessment of optimum habitat of
the flattened musk turtle although we note that S. depressus can survive in
streams of less than a 130 km2 drainage area, such as Gurley Creek. We
observed S. depressus in streams with a sand bottom and concur that flattened
musk turtles can live in such habitats as long as food and cover are nearby. Too
much sand, even of natural origin as at Clear Creek, can be detrimental to S.
depressus and limit its distribution and abundance by clogging crevices and
covering potential cover sites along the stream margin. The telemetry data show
that while turtles may move across sandy areas, they do not choose locations in
sand for cover sites.
Trapping also showed that flattened musk turtles can live in heavily silted
streams, such as Turkey Creek, if suitable microhabitat and food are available.
In such cases, a strong current and good stream gradient are necessary to
provide available habitat. Lacking these, S. depressus disappears, such as at
Lost Creek-Townley and in sluggish portions of Gurley and Turkey Creeks.
In the late 1940s, a survey of water quality within the Warrior Drainage
provided a measure to assess changes that have occurred during the last 30+
years (Anon. 1949). Oxygen, pH, total dissolved solids, hardness, and alkalinity
are essentially identical to current values in Sipsey Fork, Clear Creek, Lost
Creek, and Blackwater Creek, with the exception of alkalinity in Lost
Creek. There has been a three- to four-fold increase in alkalinity in Lost
Creek. Our values also were similar to those obtained by Ernst et al. (1983)
and Anon. (undated).
BULLETIN FLORIDA STATE MUSEUM VOL. 34(1)
We found no indication that adverse modification of streams has affected
the parameters we measured, but we caution that we did not measure many
other variables in either the water or sediments that might affect either the
flattened musk turtle or its prey. Such variables include heavy metals,
particularly mercury and manganese, polychlorinated biphenyls, pesticides, and
sewage effluents. We observed high conductivity values in certain mine-
affected sites and at Blackburn Fork, but it is unknown what this means to
turtles. It is difficult to assess the effects of many chemicals that might be in the
habitat of S. depressus because very little is known concerning toxic side effects
of stream pollution on turtle populations.
Status.- In one of the few studies on the effects of habitat degradation on
river dwelling turtles, D. Moll (1980) demonstrated that three species,
Kinostemon flavescens, Apalone mutica, and Emydoidea blandingi, had
declined or disappeared from the Illinois River as a result of heavy pollution.
He attributed municipal and agricultural pollution, especially from siltation,
and direct habitat degradation as responsible for these declines. Additional
species that once were widespread, such as Graptemys, were confined only to
areas with their specialized prey.
D. Moll (1980) was fortunate in having baseline data on turtle populations
to compare with current information. Even then, he had difficulty in ascribing
individual sources of environmental degradation to their effects on turtles.
Because we have no baseline data on S. depressus populations, heavy metal and
other sources of pollution, and silt loads, it is difficult to assess individual
threats. However, it is possible to make a biologically reasonable hypothesis
that populations of this species are not as viable now as they were prior to the
influx of heavy siltation and that the species has disappeared in formerly
occupied habitat.
Previous studies of the distribution of the flattened musk turtle (Mount
1981; Ernst et al. 1983) drew conclusions about its status based on spot
sampling and examination of certain physical and chemical variables. Both
were valuable in providing a foundation on which to build future research and
management. However, the status of a species should be based on repeated
samples throughout at least one activity season and at a variety of locations.
Otherwise, estimates of population size and abundance may be in error.
Assessments based on spot sampling should be used with caution unless there
are clear and immediate threats to the species.
It is difficult to determine habitat characteristics and their effects on a
species through sampling physical parameters once during the course of a
single season or even at weekly intervals. Critical low values of oxygen, for
instance, may affect the flattened musk turtle or its food sources during
hibernation rather than during summer activity, and while average values of
DODD ETAL.: STERNOTHERUS DEPRESSUS IN NORTHERN ALABAMA 57
certain parameters may seem normal for a stream during spot sampling,
fluctuations of critical importance may be undetected.
Siltation has impacted the flattened musk turtle. This is evident at sites such
as Blackwater Creek-Harris Bridge and Lost Creek-Townley. While we cannot
attribute mining as the sole source of siltation even at these severely degraded
sites, mining, agriculture, and improper stream bank management have
contributed to the silt load.
There is little direct impact from mining at Blackwater Creek-Harris
Bridge, although it probably was severe when the numerous unregulated mines
in the vicinity were operating 20 or more years ago. Erosion continues at this
site where the bank is undercut resulting in numerous tree falls. There seems
little likelihood that S. depressus could exist in this section of stream nor in any
section above the Musgrove Country Club Dam. Ernst et al. (1983) also failed
to find S. depressus above the dam and noted the unsuitability of the habitat.
Blackwater Creek-Camp O'Rear, located 18 km downstream from Harris
Bridge, is suitable habitat for the turtle. Both Mount (pers. comm.) and Ernst
et al. (1983) considered this site optimal with a good S. depressus
population. The site is free of siltation because a dam is located 6.5 km
upstream. The Musgrove Country Club Dam creates a sluggish backwater to
Harris Bridge and beyond, but allows silt and debris to settle out in its
backwater. Anon. (undated) stated that mining was compatible with healthy S.
depressus populations because good populations were found in Blackwater
Creek only 1.6 km downstream from a strip-mine discharge stream. However,
this report did not mention the intervening dam. Whereas properly regulated
mining may have reduced impacts, the presence of S. depressus downstream in
Blackwater Creek is probably more the result of the Musgrove Dam than
reclamation laws.
There is reason for concern about the status of the population below the
dam since adults are known to have been removed by commercial collectors
(R. Guthrie pers. comm. to Peter Meylan; specimens in Florida State
Museum). S. depressus from Blackwater Creek are attractive with non-eroded
shells and a striking carapace pattern, and the site is easily accessible. We
collected fewer turtles than Mount (1981) and Ernst et al. (1983) although our
size classes indicated successful recruitment.
At Lost Creek, active mining is occurring immediately adjacent to the
creek. Mining occurred in the past as well, but not in the immediate
headwaters. The Pocahontas site contains a small population of flattened musk
turtles consisting mostly of old adults. Successful reproduction is occurring, but
we have no idea of recruitment to the adult population. We found no adult
turtles in Lost Creek-Pocahontas below Mill Creek, although suitable habitat is
present. Lost Creek-Pocahontas has a small but stable population that is
probably isolated from populations downstream.
BULLETIN FLORIDA STATE MUSEUM VOL. 34(1)
At Townley, 14 km downstream from the Pocahontas site and only about
2.5 km downstream from Cedrum, Lost Creek was extremely impacted by
mining and contained deep silt deposits. In some places, whole sandbars were
composed of coal fragments (Fig. 17), and the streambank was severely eroded
and contained many downed trees. We found one small adult male on one
occasion. This turtle likely moved downstream from Cedrum where suitable
habitat extends several hundred meters downstream from the base of the dam
of the old mill at Cedrum. A short distance thereafter, there are extensive
abandoned mines on the south bank that have not been reclaimed and from
which silt enters the creek. By the time Townley is reached, Lost Creek is
clogged by silt. Thus, S. depressus in Lost Creek does not constitute a continuous
population. Instead, the site has two remnant populations, a small one near the
headwaters where mining has not encroached, and another protected below
the dam at Cedrum.
Gurley Creek was, as previous studies have commented (Mount 1981; Ernst
et al. 1983), an enigma. While the water was not deep and the creek was small
in the section studied, mollusks were extremely abundant, cover sites were
available, and no adverse environmental variables were measured. We consider
this population a remnant and likely to disappear in the near future.
Factors causing the skewed older population at Gurley Creek could be
related to the unregulated mining nearly 20 years ago. Siltation is substantial in
certain sections where it settles out in pools. We were told by local residents
that catfish (Ictalurus sp.) had declined dramatically and that "stinking jims," a
local name for both S. odoratus and S. depressus, had become scarce. Blue
water was noted in an adjacent strip pit which receives water from the creek,
but we do not know what causes the coloration. We found dead and dying
muskrats (Ondatra zibethica) at Gurley Creek on several occasions.
It is difficult to assess the impacts resulting solely from mining at Turkey
Creek. Unlike other impacted sites, this location appears to have a good turtle
population, although weighted toward older adults. The stream not only has
been affected by mining but also by municipal sewage from the town of Morris
and by siltation from the construction of Interstate Highway 65 which cut
through an abandoned mine immediately west of the creek. Runoff from this
construction had high conductivity indicating mine contamination.
Selective habitat use by S. depressus at Turkey Creek was striking. The
turtle was found only in areas with good current and rock slabs. When weed
beds restricted the water to chutes or when the water pooled with a bottom
composed of deep muck, S. depressus was absent. Mining activities have
impacted the flattened musk turtle at this site, but they are certainly not the
only impacts. Recruitment does not appear to be occurring.
For mine-unaffected sites, the Brushy Creek population is relatively small
but stable, with good size-class distribution and reproduction although Ernst et
al. (1983) characterized the population as "dense." Ernst et al. (1983) stated
Figure 17. Excessive erosion of an adjacent coal strip mine may result in sedimentation which clogs streams and eliminates S. depresses. Lost
Creek near the former town of Holly Grove.
BULLETIN FLORIDA STATE MUSEUM VOL. 34(1)
that this location was atypical of S. depressus localities, but we do not think this
is the case.
Sipsey Fork may contain the only large viable population of S. depressus
throughout its range. The population was dense with good size-class
representation and vigorous reproduction. The headwaters of this river rise in
the Sipsey Wilderness and exhibit virtually no human-related adverse impacts.
At least from the Sipsey Recreation Area to the headwaters of Smith Lake,
population structure likely mirrors that in our study area.
We were surprised to find so few turtles at Blackburn Fork. Both Mount
(1981) and Ernst et al. (1983) considered this location as the best habitat for S.
depressus in the eastern part of its range. We concur that the habitat appears
excellent in terms of both cover and potential food items. Blackburn Fork is a
site for commercial collecting of S. depressus (Mount pers. comm.; J. Pulliam,
U.S. Fish and Wildlife Service, pers. comm.). Commercial collectors have been
known to return between 10% and 20% of the S. depressus collected here
because of the degree of erosion of the shells (J. Pulliam pers. comm.).
A student at the University of Alabama-Birmingham, A. R. Johnson, studied
food habits of S. depressus using animals from this population in 1983 and 1984.
She noted a decline between these years (K. Marion pers. comm.), a decline that
continued during our study. The size-class data indicated that no recruitment
had taken place for several years, which would affect animals that should be in
subadult stage.
Clear Creek also presents something of an enigma. Mount (1981) found
what he considered a good population of S. depressus at Camp McDowell
downstream from our sampling locality. Ernst et al. (1983) collected S.
depressus at several other locations on Clear Creek including the site we chose
for study. Clear Creek is a biologically depauperate creek with few species or
individuals of turtles, crayfish, fish, clams, snails, and insects. There is no
mining activity in the area, nor does the stream appear to receive much human
use. The reasons for a depauperate fauna remain unknown.
Habitat Fragmentation.- The importance of habitat fragmentation has
been recognized in terms of local extinction (see review by Wilcox and Murphy
1985). Wilcox and Murphy (1985) point out that fragmentation has three main
effects: populations (demographic units) may be destroyed; future sources of
immigration are lost; and immigration from remaining populations is impeded
by intervening unfavorable habitat. Each of these factors may be operating on
remaining flattened musk turtle populations and affect future conservation
efforts for this species.
It seems reasonable to assume that this turtle inhabited all major streams
and rivers of the Warrior Basin. Today, however, the rivers and streams of
northern Alabama are vastly different from what they were several hundred
years ago. Mount (pers. comm.) estimated that the flattened musk turtle had
DODD ET AL.: STERNOTHERUS DEPRESSUS IN NORTHERN ALABAMA 61
been extirpated from 350 km of favorable habitat; that it inhabited 163 km of
severely impacted streams, presumably at reduced population sizes; and that it
inhabited 540 km of seriously impacted streams. Only 229 stream km were
considered reasonably healthy, and he included both Blackburn Fork and
Blackwater Creek downstream from the Musgrove Country Club Dam, both
areas disturbed by commercial collecting, within this latter category. If these
estimates are even reasonably close, this species has already undergone
extensive habitat fragmentation.
The implications of habitat fragmentation, especially on small populations
or those depleted by collecting, should be obvious. Assuming that such
populations can recover naturally, protection from additional perturbation
becomes critical to their future survival. At the same time, the inability of S.
depressus to colonize seemingly favorable habitats, such as Gurley Creek,
indicates that immigration from viable source populations is a slow process, or
that some populations are already so isolated that such cannot occur. The low
reproductive potential of S. depressus (Close 1982) also indicates that recovery
will be a slow process. We agree with Wilcox and Murphy (1985) that "habitat
fragmentation is the most serious threat to biological diversity and is the
primary cause of the present extinction crisis." The degradation of the aquatic
biota of the Warrior Basin, from whatever sources, is a reminder of man's slow
and painful progress of recognizing the obvious.
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