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2008 SOUTHEASTERN NATURALIST 7(2):331–338
Status and Distribution of the Alligator Snapping Turtle
(Macrochelys temminckii) in Southeastern Missouri
Paul A. Shipman1 and J. Daren Riedle2,*
Abstract - Macrochelys temminckii Harlan (Alligator Snapping Turtle) is a large
aquatic turtle species that has been experiencing population declines throughout its
range. Unfortunately, little is known about the species’ basic biology or historic
status throughout the majority of its range. In order to better understand the status
and distribution of M. temminckii in southeastern Missouri, we visited 50 sites with
suitable habitat and trapped at 19 of them in Dunklin, Mississippi, New Madrid,
and Pemiscot counties, MO in 1994. We captured 37 M. temminckii at four sites in
Pemiscot and Dunklin counties. The Dunklin County site was resampled in 1997,
and radio transmitters were attached to 11 Alligator Snapping Turtles (6 males: 4
females: 1 unknown sex). Telemetered turtles were found at microhabitats consisting
of more cover, high-density canopy, and lower gradient banks than random locations.
We noted a significant difference in turtle size between sites that have and those that
have not experienced historical take of Alligator Snapping Turtles.
Macrochelys temminckii Harlan (Alligator Snapping Turtle), the largest
freshwater turtle in North America, is known to occur from the Florida panhandle
to eastern Texas and Oklahoma (Ernst et al. 1994) and as far north as
Kansas and Illinois (Clarke 1981, Galbreath 1961). In Missouri, the Alligator
Snapping Turtle is historically known to occur in the Mississippi River
and southern Ozarkian drainages (Anderson 1965, Johnson 2000). Pritchard
(1989) lists more specific Missouri localities along the White, Black, St.
Francis, and Mississippi rivers and records in Ozark and Taney counties,
particularly near Bull Shoals Lake. Little is known about their distribution
within the Missouri River, as only one specimen has been documented in
that stream, near St. Charles.
The majority of records of the Alligator Snapping Turtle in Missouri
occur along slow-moving rivers associated with the Mississippi Lowlands
of southeastern Missouri. The region was historically typified by Taxodium
distichum (L.) L.C. Rich. (bald cypress), Nyssa spp. (tupelo) swamps, and
bottomland hardwood forest. Lumbering and drainage programs have converted
most of the region to agriculture (Johnson 2000). The stream systems
originating on the Ozark Plateau are typically stream-fed, clear, and fairly
swift (Robison and Buchanan 1988), and Alligator Snapping Turtles occasionally
occur in these swift, upland streams (Phelps 2004).
1Department of Biological Sciences, Rochester Institute of Technology, 85 Lomb
Memorial Drive, Rochester, NY 14623. 2Department of Life, Earth and Environmental
Sciences, West Texas A&M University, Canyon, TX 79016. *Corresponding
author - email@example.com.
332 Southeastern Naturalist Vol.7, No. 2
The Alligator Snapping Turtle is thought to be declining throughout its
range, with overharvesting and habitat alteration listed as primary causes
(Reed et al. 2002). The United States Fish and Wildlife Service proposed
listing the Alligator Snapping Turtle as a threatened species in 1984, but listing
was precluded due to a lack of ecological information about the species
(United States Fish and Wildlife Service 1991). The Alligator Snapping Turtle
is currently listed as a species of conservation concern in Missouri (Johnson
2000). Our objectives were to survey the southeastern corner of Missouri,
augmenting work done previously by Santhuff (1993), and to determine current
distribution and habitat requirements for Alligator Snapping Turtles.
Materials and Methods
Oxbows, lakes, streams, and rivers were surveyed in Dunklin, New Madrid,
Mississippi, and Pemiscot counties, MO, from 6 June to 11 August 1994. The
St. Francis River in Dunklin County was re-sampled between April and August
1997. Turtles were trapped using commercial hoop nets that were 2.1 m
in length and constructed of 4 hoops (1.05 m in diameter) covered in 2.5-cm
square mesh. Nets were set upstream from submerged structures (i.e., logs and
log jams) or overhanging trees. Nets were baited with fresh fish suspended by
a piece of twine on the hoop furthest from the opening of the trap. We set nets in
the late afternoon or evening and checked them the following morning.
Sex and mass were recorded for all Alligator Snapping Turtles captured.
Turtles were marked by drilling a unique series of holes in the rear marginal
scute. Tarred nylon twine was tied through each hole to prevent the hole
from growing back during the course of the study. A numbered livestock tag
was also attached through one of the holes with nylon straps, to serve as an
additional means of identification.
Eleven Alligator Snapping Turtles (6 males: 4 females: 1 unknown sex)
were outfitted with radio transmitters between 29 April 1997 and 29 October
1997. Turtles were captured and tracked along a disjunct stretch of the St.
Francis River adjacent to Wilhelmina Conservation Area, Dunklin County.
This “old channel” is a remnant from earlier channelization efforts on the
St. Francis River. The 55-g radio transmitters (Wildlife Materials Inc.) were
attached by drilling holes in the rear marginal scutes of the carapace and
securing them with plastic cable ties. All turtle locations were marked with
a GPS unit, and TNTlite v5.8 (MicroImages, Inc.) was used to plot turtle
location and movement data. The average distance moved between location
fixes and the minimum linear home range (farthest location upstream to the
farthest location downstream for each turtle) was calculated.
Habitat data were recorded at all turtle locations and at sites representing
habitat available to the turtles in the St. Francis River. To represent available
habitat, transects were located evenly along the length of the channel
used by telemetered turtles. At each transect location, habitat variables were
recorded at six points evenly spaced across the width of the stream. A total
of 102 transects were surveyed along a 10.7-km stretch of stream.
2008 P.A. Shipman and J.D. Riedle 333
At each turtle location and all transect points, we measured water depth
(meters), and percent canopy cover using a concave forest densiometer
(Lemmon 1957). The number of tributaries present 25 m up and downstream
were also recorded. Amount of cover present was categorized as
follows: area cover ranked as none = 0, overhanging tree (not submerged) =
1, overhanging bank = 2, brush pile = 3, single log = 4, or log jam = 5; relative
number of fl oating or submerged logs 25 m upstream and downstream
ranked as none = 0, one to two = 1, three to five = 2, greater than five = 3; and
gradient of nearest bank ranked as 0 to 15 degrees = 0, 15 to 45 degrees = 1,
45 to 90 degrees = 2. Wilks’ lambda multivariate test for overall differences
and univariate F-tests to contrast independent variables were used to test for
differences between habitat use by Alligator Snapping Turtles and available
habitat. To control Type I error, the standard Bonferroni correction was used
to determine significance of P-values.
We visited 50 sites with potential Alligator Snapping Turtle habitat,
and trapped at 19 sites in Dunklin, Pemiscot, and Mississippi counties. The
remaining sites were either unsuitable for trapping (too shallow), or inaccessible
(private property). No sites in New Madrid County were suitable for
sampling. Our survey efforts consisted of 275 net nights at nineteen sites in
1994 and 121 additional net nights on the St. Francis River in 1997 (Fig. 1).
We captured 37 Alligator Snapping Turtles at four sites, within two general
Fig 1. Sites sampled for Alligator Snapping Turtles in Dunklin, Pemiscot, and Mississippi
counties, MO in 1994.
334 Southeastern Naturalist Vol.7, No. 2
localities: Wolf Bayou, Pemiscot County, and the St. Francis River, Dunklin
County. Eleven Alligator Snapping Turtles were captured in 1997, including
one recapture from the 1994 surveys.
We obtained 131 locations on ten individuals between 29 April 1997
and 29 October 1997. A field assistant released the 1 unknown sexed animal
before obtaining size measurements. Only two locations were obtained for
one individual due to either transmitter failure, or the turtle leaving the study
site. That individual was removed from subsequent analysis.
The mean linear home range for all turtles was 1793.5 m ± 857.1 m
(range = 549.7–3322.7 m). There was no significant difference in homerange
size between sexes (t = -1.734, df = 8, P = 0.126) nor did the distances
moved between core sites differ significantly (t = -1.931, df = 7, P = 0.094),
although females made longer movements in both cases (Table 1). Turtles
prefered specific microhabitats that contained submerged cover and differed
from the available habitat at transect sites (Wilks’ lambda F6, 182 = 15.5, P <
0.001) by having significantly more cover, lower gradient banks, and higher
percentage canopy cover (Table 2).
We noticed a marked size difference between individuals of Alligator
Snapping Turtles at Wolf Bayou and the St. Francis River. These data were
pooled with earlier survey data collected by Santhuff (1993) on the Black
River System in Missouri to test for size differences between populations
(Table 3). A one-way analysis of variance (ANOVA) was used to test for differences
in mass between populations. Pooling weights from all individuals
at all sites, there was no significant difference in mass between populations
(F2,51 = 0.801, P = 0.465). Several individuals that could not be sexed due to
their small size were dropped from the analysis (five from the Black River
drainage and three from the St. Francis River). Among adult turtles, there
was a significant difference in mass between populations (ANOVA: F2, 43
Table 2. Means (± 1 SD) and univariate F-test P-values for comparison of microhabitat variables
of core sites with available habitat in the old channel of the St. Francis River (P to reject
H0 = 0.006)
Variable Core sites mean (SD) Available habitat mean (SD) P-value
Cover 2.18 ± 2.02 0.94 ± 1.66 <0.0001
Canopy (%) 45.63 ± 38.89 26.38 ± 35.88 <0.0001
Bank rise 1.34 ± 0.94 2.03 ± 0.86 <0.0001
Area cover 1.57 ± 0.96 1.47 ± 0.61 0.8411
Depth (m) 2.52 ± 0.70 2.40 ± 1.05 0.3777
# of tributaries 0.06 ± 0.23 0.12 ± 0.32 0.1511
Table 1. Mean home-range size (± 1 SD) and mean distance moved between core sites (± 1 SD)
by male and female Alligator Snapping Turtles.
Sex n Mean home range (m) Mean distance moved between core sites (m)
Male 5 1309.5 ± 566.8 232.2 ± 108.4
Female 4 2207.4 ± 980.5 361.7 ± 87.5
2008 P.A. Shipman and J.D. Riedle 335
= 11.979, P < 0.001). The Wolf Bayou and Black River turtles were larger
than those in the St. Francis River. However, there was no difference in mass
between turtles in Wolf Bayou and the Black River.
The Alligator Snapping Turtle has been impacted heavily in southeastern
Missouri, largely due to habitat alteration. We were only able to sample 38%
of the 50 sites visited. Most sites had been manipulated for channelization
or drained and converted to agriculture fields. Riedle et al. (2005) noted a
drastic decline of Alligator Snapping Turtles in Oklahoma, due in part to
habitat degradation because of stream channelization and thermal alteration
by hypolimnetic releases from impoundments. Alteration of stream channels
turns a low energy meandering system with high habitat diversity into
a high-energy system with low habitat diversity (Moll and Moll 2000).
Straightening a stream channel decreases availability of cover sites and
potentially reduces foraging opportunities for Alligator Snapping Turtles.
Draining of backwater habitats along the Mississippi River fl oodplain has
probably had a major detrimental effect on not only Alligator Snapping Turtles,
but other turtle species as well. Conversion of these areas to agriculture
has the obvious effect of removing any available aquatic habitat. In addition
to habitat conversion, chemical runoff and erosion associated with agricultural
fields may have affected turtle populations. Heck (1998) and Riedle et
al. (2005) noted that these same factors may have contributed to the decline
of Alligator Snapping Turtles in eastern Oklahoma.
Results from radio-telemetry efforts were very similar to those conducted
on this species in Kansas (Shipman 1993), Oklahoma (Riedle et al. 2006),
and Louisiana (Harrel et al. 1996, Sloan and Taylor 1987), including the species’
relationship to submerged cover sites as resting and/or foraging sites.
Although there were no significant differences in distances moved, or homerange
size between sexes, females did make longer movements than males.
Riedle et al. (2006) noted that females also made longer movements and had
significantly larger home ranges during the course of their Oklahoma study.
We did lose one individual to either transmitter failure or movement out of
the study site. A long-distance movement is a likely scenario, and has been
reported in several other instances. Wickham (1922) reported on an individual
in Oklahoma that moved between 27–30 km in 3 years. Shipman et
Table 3. Mean mass, standard deviation, and range of adult and sub-adult Alligator Snapping
Turtles from three populations.
Population n Mean mass (kg) Range SD
Wolf Bayou 20 15.9 6.2–24.0 5.4
St. Francis River 14 7.4 3.3–11.7 2.7
Black River* 15 15.1 7.3–33.6 6.8
Pooled Statistics 49 13.2 3.3–33.6 6.4
*Data taken from Santhuff (1993).
336 Southeastern Naturalist Vol.7, No. 2
al. (1991) noted a 7-km movement in 5 years by an individual in Kansas. A
shorter-term movement of 16 km in a 2-month time period was documented
in Oklahoma (Riedle et al. 2006).
Commercial harvest of Alligator Snapping Turtles may have contributed
to local declines of the species in Missouri. There is evidence for historical
harvest of Alligator Snapping Turtles on the St. Francis River in both Missouri
and Arkansas. Until 1993, Arkansas allowed the commercial harvest
of Alligator Snapping Turtles (Santhuff 1993). The old channel of the St.
Francis River is 4.8 km from the Arkansas/Missouri border, where the main
channel becomes the political boundary separating the two states. Legally,
harvest could take place along the Arkansas side of the river pior to 1993.
Lacking data on the number of turtles harvested, and in the absence of preharvest
population data, there is no direct evidence that commercial harvest
of Alligator Snapping Turtles had a detrimental effect on their populations.
Several observations during the course of both Santhuff’s (1993) study and
ours have led us to the conclusion that harvest did impact Alligator Snapping
Turtle numbers on the St. Francis River. First, individuals of Alligator
Snapping Turtles captured on the St. Francis River were smaller than at other
sites, suggesting recent removal of larger adults. As we moved south along
the river, particularly where it bordered Arkansas, no Alligator Snapping
Turtles were captured despite the presence of seemingly suitable habitat.
Santhuff captured one small individual (160 mm midline carapace length
[MCL]) on the Ben Cash Wildlife Area (BCWA) during his 1993 survey.
We resampled this site in 1994, but captured no Alligator Snapping Turtles.
Large individuals have been reported on the St. Francis River; a 58-kg male
was captured near BCWA prior to the initiation of our 1994 survey (Tom
Johnson, Missouri Department of Conservation, Jefferson City, MO, pers.
comm.). Similar trends in size disparity between harvested and unharvested
sites have also been documented in Arkansas (Trauth et al. 1998), Georgia
(Jensen and Birkhead 2003), and Oklahoma (Riedle et al., in press).
Incidental mortality of Alligator Snapping Turtles due to trotlines and setlines
has been reported in Kansas by Shipman (1993). Moll and Moll (2004)
describe the use of baited setlines for commercial turtle harvest. During the
course of this study, we observed several hundred setlines and trotlines in
the old channel of the St. Francis River. On one occasion, we removed a live
Apalone spinifera LeSueur (Spiny Softshell Turtle) that was snagged on a
setline. Santhuff (1993) found one dead and one living Alligator Snapping
Turtle snagged on setlines during his survey. Unattended fishing gear is not
allowed in Wolf Bayou, possibly reducing direct take of Alligator Snapping
Turtles at that site.
Habitat loss has greatly reduced the number of sites where Alligator
Snapping Turtles might occur in southeast Missouri, but reducing the threat
of take will allow the species to recover at sites where suitable habitat still
occurs. There is still habitat available along stretches of the St. Francis River
in Dunklin County, although the only turtles captured during our surveys
2008 P.A. Shipman and J.D. Riedle 337
were in stream segments not shared with Arkansas. Congdon et al. (1993,
1994) demonstrated that any harvest of turtles is not viable. Riedle et al. (in
press) provided evidence that with the removal of harvest, Alligator Snapping
Turtles will recover over time. Continued protection of habitat and
possible reintroductions to former parts of the turtles range should secure
their future in unaltered segments of their range in southeastern Missouri.
We would like to thank the Natural History Division of the Missouri Department
of Conservation (MDC) for funding this project. The staff at the MDC Southeast
Regional Office in Cape Girardeau, the New Madrid Forestry Office, the Duck Creek
Conservation Area, and the Otter Slough Conservation Area provided logistical support.
We also want to thank K. Cole and A. Neeley for assistance in the field.
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