Variation in carapace damage within and among Loggerhead Musk Turtle (Sternotherus minor) populations in Florida spring-fed ecosystems

Abstract

Damage to a turtle’s shell can provide evidence of past events such as vehicle collisions, disease, predator encounters,
or even a behavioural interaction between members of the same species. Documenting shell damage as part of long-term mark
and recapture studies enables researchers to determine population trends, intraspecific interactions and identify potential issues
within turtle populations. This paper analyses shell damage in populations of the Loggerhead Musk Turtle (Sternotherus minor)
(Agassiz, 1857). We examined carapace shell damage frequency and severity in 2701 individual S. minor (1468 males and 1233
females) captured in spring-fed habitats in one state preserve and five state parks in central and northern Florida. We quantified
frequency as percent of individuals with at least some damage, and we created a carapace mutilation index (CMI) to quantify
the severity of damage. The frequency and severity of carapace damage varied among sites. Males were more frequently
damaged than females at all study sites, and had more severe damage, but only significantly at three sites. There was a positive
relationship between CMI and body size (plastron length) for males and for females, suggesting that adults accumulate damage
as they age. Damage may vary among sites due to habitat size, quality, or abundance of large adult male turtles. Future research
should look at movement patterns, site fidelity, social interactions, and how these are impacted by habitat size, quality, and
density, to determine what, if any, these factors have on population stability and fecundity.

Full text

Introduction
Damage to a turtle’s shell may preserve a record of
events that occur during its life. Scars or damage to
the
shell can serve as evidence of attempted predation
(Aresco
and Dobie, 2000; Heithaus et al., 2002; Parren,
2013; de Valais et al., 2020), a collision with a boat,
automobile, or agricultural machinery (Ashley and
Robinson, 1996; Saumure et al., 2007; Heinrich et al.,
2012; Hollender et al., 2018). Shells can also display
pitting, lesions, or discolouration due to infection or
disease (Hernandez-Divers et al., 2009; Woodburn et al.,
2019), and can document agonistic human interactions
(Moll and Moll, 2004). The ability of the turtle shell
to preserve evidence of physical trauma has long been
known to researchers who file or drill holes into the
marginal scutes and peripheral bones of the carapace
to individually identify turtles as part of capture-mark-
recapture studies (Cagle, 1939; Plummer, 1979). Damage
can also chronicle intraspecific aggression (Jackson,
1969) or coercive mating strategies (Moldowan et al.,
2020).
The Loggerhead Musk Turtle (Sternotherus minor) is
a small freshwater turtle endemic to the south-eastern
United States where it inhabits rivers, spring runs,
ponds, and lake margins (Ernst and Lovich, 2009; Scott
et al., 2018). The range of the turtle is from the Altamaha
Herpetology Notes, volume 16: 115-125 (2023) (published online on 19 February 2023)
Variation in carapace damage within and among Loggerhead
Musk Turtle (Sternotherus minor) populations in Florida
spring-fed ecosystems
Joseph J. Pignatelli III1,2,*, Katrina Campbell1, Brian P. Butterfield3, Gerald R. Johnston4, Joseph C. Mitchell5,
Grover J. Brown III6, J. Brian Hauge1,7, Andrew D. Walde1, and Eric C. Munscher1,8
1 Turtle Survival Alliance, 1030 Jenkins Rd. Ste. D, Charleston,
South Carolina 29407, USA.
2 Puget Sound Energy, 6500 Ursula Place S., Seattle,
Washington 98108, USA.
3 Freed-Hardeman University, 158 E. Main Street, Henderson,
Tennessee 38340, USA.
4 Department of Natural Sciences, Santa Fe College,
Gainesville, Florida 32606, USA.
5 Florida Museum of Natural History, University of Florida,
Gainesville, Florida 32611, USA. (deceased).
6 Department of Biology, Jacksonville State University, 700
Pelham Rd. N, Jacksonville, Alabama 36265, USA.
7 Department of Biology, Peninsula College, 1502 E. Lauridsen
Blvd., Port Angeles, Washington 98362, USA.
8 SWCA Environmental Consultants, 10245 West Little York
Road, Suite 600 Houston, Texas 77040, USA.
* Corresponding author. E-mail: Jpignatelli3@gmail.com
© 2023 by Herpetology Notes. Open Access by CC BY-NC-ND 4.0.
Abstract. Damage to a turtle’s shell can provide evidence of past events such as vehicle collisions, disease, predator encounters,
or even a behavioural interaction between members of the same species. Documenting shell damage as part of long-term mark
and recapture studies enables researchers to determine population trends, intraspecific interactions and identify potential issues
within turtle populations. This paper analyses shell damage in populations of the Loggerhead Musk Turtle (Sternotherus minor)
(Agassiz, 1857). We examined carapace shell damage frequency and severity in 2701 individual S. minor (1468 males and 1233
females) captured in spring-fed habitats in one state preserve and five state parks in central and northern Florida. We quantified
frequency as percent of individuals with at least some damage, and we created a carapace mutilation index (CMI) to quantify
the severity of damage. The frequency and severity of carapace damage varied among sites. Males were more frequently
damaged than females at all study sites, and had more severe damage, but only significantly at three sites. There was a positive
relationship between CMI and body size (plastron length) for males and for females, suggesting that adults accumulate damage
as they age. Damage may vary among sites due to habitat size, quality, or abundance of large adult male turtles. Future research
should look at movement patterns, site fidelity, social interactions, and how these are impacted by habitat size, quality, and
density, to determine what, if any, these factors have on population stability and fecundity.
Keywords. Sternotherus minor, intraspecies aggression, shell damage, carapace mutilation index, Florida, springs, long term
population study

Joseph J. Pignatelli III et al.
116
drainage of south-eastern Georgia to the Apalachicola
drainage down to central Florida across the aquifer
systems (Zappalorti and Iverson, 2006; Ernst and
Lovich, 2009; Krysko et al., 2011; Scott et al., 2018).
This turtle has well-developed, strong jaw musculature
for crushing mollusc and arthropod prey (Zappalorti
and Iverson, 2006; Ernst and Lovich, 2009).
Shell damage has been documented in S. minor
for more than half a century with the first report of
carapace damage in the species mentioned as “old,
eroded individuals” in Carr and Goin’s (1955) species
description. A decade later, Jackson (1965) reported
carapace erosion or damage in 40.4 % of juveniles,
61.4% of smaller adults, and 100% of large adults from
a pooled sample of 108 individuals. Jackson (1965)
hypothesised that intraspecific behavioural interactions
caused this damage. Jackson (1969) subsequently
provided evidence that intrasexual aggression between
males including biting the marginal scutes caused some
of the damage he observed. Later observations by Bels
and Caram (1994) document males biting females
during courtship, an action that may cause the observed
shell damage.
The Turtle Survival Alliance’s North American
Freshwater Turtle Research Group has been surveying
the turtles of various Florida spring-fed habits since
1999 and the Santa Fe River Turtle Project has similarly
been sampling freshwater springs in the Santa Fe River
basin since 2006. Both groups have been conducting
long-term ecological studies of the turtle assemblages
in these ecosystems (e.g., Adler et al., 2018; Johnston
et al., 2016, 2020; Munscher et al., 2013, 2015a, 2020).
Previous reports of shell damage in S. minor have been
anecdotal and have not included robust data sets or data
from multiple sites, which may inform causation, as
well as document the extent of the damage.
In this paper, we present data that expands on Jackson’s
(1965; 1969) observations. Specifically, we examine
how the occurrence and severity of carapace damage
vary among six S. minor populations from spring-
fed habitats in central and northern Florida. Within
each population, we evaluate the relationship between
carapace damage and body size (plastron length) in each
sex.
Materials and Methods
Field-Site Description.—The six Florida study sites
for this analysis include: Wekiwa Springs State Park
(WS), Orange County (2.67 ha); Volusia Blue Springs
State Park (VBS), Volusia County (1.9 ha); Manatee
Springs State Park (MS), Levy County (1.53 ha);
Fanning Springs State Park (FS), Levy County (0.7
ha); Rock Springs Run State Preserve (RSR), Seminole
County (1.41 ha); and Ichetucknee Spring State Park
(IS), Columbia and Suwannee Counties (10.99 ha; Fig.
1). These study sites are described more thoroughly by
Johnston et al. (2020), Munscher et al. (2015a, b, 2017,
2020), Riedle et al. (2016) and Walde et al. (2016). All
study sites are entirely fed by first or second magnitude
freshwater springs with clear flowing water.
Data Collection.—Researchers conducted multi-day
annual or semi-annual snorkel surveys between 2000
and 2019. For each sampling period, a variable number
of snorkelers hand-captured turtles from ca. 0800 –
1600/1900 h, depending on the time of year and weather
conditions. We placed turtles in labelled bins within
canoes that indicate the capture area and then brought
them to a central location for data processing.
We recorded maximum straight-line measurements
of carapace length (CL), plastron length (PL), carapace
width (CW), and shell height (SH) to the nearest
millimetre. We sexed turtles based on secondary sexual
Figure 1. Map depicting the six turtle study sites in Florida,
USA.

Variation in carapace damage within and among Loggerhead Musk Turtles in Florida 117
Figure 2. Carapace damage on Sternotherus minor observed at the various study sites in Florida, USA. (A) depicts a turtle with
a score of 1. (B) depicts a turtle with a score of 4. (C) depicts a turtle with a score of 6. (D) depicts a turtle with a score of 3.
Photographs by Jessica Weber.

characteristics, notably by visual inspection of tail length
and girth as described in Ernst and Lovich (2009) (Fig.
2). Females are sexually mature and distinguishable at 80
mm (Iverson, 1978), while males have been documented
at maturing at 60 mm (Etchberger and Stovall, 1990),
however this is likely ecosystem specific. We noted
all unique physical features such as damage, scars, or
coloration of each turtle to aid in confirming individual
identity. We weighed turtles to the nearest gram (g)
using Ohaus top loading digital scales (Ohaus Corp.,
New Jersey, USA). We individually marked turtles by
notching the marginal scutes and peripheral bones of
the carapace (Cagle, 1939) and we also notched the
plastron when necessary. The notches (created by a
saw or Dremel) do not resemble the damage created
naturally by the turtles biting each other. Beginning in
2009, we used passive integrated transponder (PIT) tags
as a secondary identification method for turtles with
CL greater than 70 mm. We injected PIT tags under
the turtle’s right bridge (Buhlmann and Tuberville,
1998; Runyan and Meylan, 2005). Once we completed
processing the turtles, we released them back into the
spring run at their approximate capture locations.
When we examined turtles for physical anomalies, we
noticed most of the shell damage was located along the
posterior marginal scutes, L9, 10, 11 and R9, 10 and
11, the same location where Carr (1952) had observed
erosion and Jackson found most of the damage he
reported in 1964, presumably because damage occurs
when males are in active pursuit of each other. We
assigned carapace mutilation index (CMI) scores
to each turtle based on a direct count of the number
of these scutes that had damage (Fig. 2 and Fig. 3).
Damage was categorised by chipped, broken, missing,
or eroded scutes. We did not include irregular scutation
as potential damage. We assigned a score of 0 if none of
these six scutes were damaged, and a score of 6 indicated
that all six of these scutes were damaged (Fig. 3). Other
researchers use similar scoring systems or “carapace
mutilation indexes” (Saumure et al., 2007), but due
to the nature of our damage predominantly occurring
within the aforementioned rear marginals, we modified
this system to better quantify the damage observed.
Statistical analysis.—We used nonparametric tests
for PL and CMI scores because these datasets were
not normally distributed. An alpha of 0.05 was set for
all comparisons. Within sites we used Wilcoxon Rank
Sum tests to evaluate CMI scores between sexes. Within
sites we compared numbers of turtles with and without
damage between sexes using a one-tailed Fisher’s
Exact Test to test the hypothesis that more males were
damaged than females. Among study sites we compared
the number of damaged and undamaged turtles by sex
with a Pearson’s Chi-square test. We then searched for
differences between sites with Pearson’s Chi-square
tests and adjusted the alphas with a Benjamini-Hochberg
correction. We also compared CMI scores by sex
across sites with a Kruskal-Wallis tests and used Steel-
Dwass post hoc tests to determine pairwise significant
differences. Finally, we used Pearson’s Correlation
Coefficients (r) to evaluate the relationship CMI and
PL for each sex at each site and used binary logistic
regression analyses to test for the influence of plastron
length (continuous predictor) on the presence or absence
of damage (dichotomous dependent variable).
Results
We evaluated 1468 male and 1233 female S. minor
across six study sites (Table 1). The number of damaged
Figure 3. Depiction of Carapace Mutilation Index for
Sternotherus species with overlapping vertebral scutes.
Joseph J. Pignatelli III et al.
118

versus undamaged individuals varied among sites for
both males (χ2 = 150.95, df = 5, P < 0.0001) and females
(χ2 = 48.71, df = 5, P < 0.0001). We found significant
differences in damage frequencies for males between:
IS and each of the other sites, VBS and FS, VBS and
RSR, VBS and WS, FS and MS, MS and RSR, and MS
and WS. For females, we found significant differences
in damage frequencies between: VBS and FS, VBS and
IS, VBS and RSR, VBS and WS, IS and MS, IS and
WS, MS and RSR, and MS and WS (Table 2). CMI
scores also differed among sites for males (χ2 = 148.94,
df = 5, P < 0.0001) and females (χ2 = 49.05, df = 5,
P < 0.0001). We found significant differences in males
between: IS and each of the other sites, MS and FS,
and MS and RSR. We found significant differences for
females between: IS and VBS, IS and MS, IS and WS,
VBS and RSR, VBS and WS, MS and RSR, and MS
and WS (Table 3). Damage occurred more frequently
in males than females at all six sites. CMI was higher in
males than in females at all sites, but only significantly
at three sites (Table 4).
Among males, damaged individuals were significantly
larger (PL) than undamaged individuals at five of the
six sites (Table 5). We found significant relationships
between CMI and PL for males at VBS (r = 0.17, df =
182, P = 0.021), FS (r = 0.422, df = 49, P = 0.002), IS (r
= 0.175, df = 318, P = 0.002), MS (r = 0.31, df = 206, P
< 0.0001), and WS (r = 0.254, df = 619, P < 0.0001). We
found no significant relationship between CMI and PL
for males at RSR (r = 0.105, df = 82, P = 0.341). Among
females, damaged individuals were significantly larger
(PL) than undamaged individuals at two sites (Table 6).
Damaged and undamaged females were similar in size
at four sites. We found significant relationships between
Table 1.
Table 2.
Site VBS FS IS MS RSR WS
Volusia Blue Spring (VBS) - * * ns * *
Fanning Springs (FS) * - * * ns ns
Ichetucknee (IS) * ns - * * *
Manatee Springs (MS) ns ns * - * *
Rock Springs (RSR) * ns ns * - ns
Wekiwa Springs (WS) * ns * * ns -
Table 3.
Site VBS FS IS MS RSR WS
Volusia Blue Spring (VBS) - ns * ns ns ns
Fanning Springs (FS) ns - * * ns ns
Ichetucknee (IS) * ns - * * *
Manatee Springs (MS) ns ns * - * ns
Rock Springs (RSR) * ns ns * - ns
Wekiwa Springs (WS) * ns * * ns -
Carapace Mutilation Index Score
Site Sex N 0 1 2 3 4 5 6
Volusia Blue Spring F 126 78 (62%) 21 (17%) 17 (13%) 5 (4%) 4 (3%) 0 1 (1%)
M 184 76 (41%) 31 (17%) 51 (28%) 21 (11%) 4 (2%) 1 (1%) 0
Fanning Springs F 38 31 (82%) 3 (8%) 3 (8%) 1 (3%) 0 0 0
M 51 32 (63%) 2 (4%) 10 (20%) 4 (8%) 3 (6%) 0 0
Ichetucknee Springs F 167 149 (89%) 5 (3%) 9 (5%) 3 (2%) 1 (1%) 0 0
M 320 266 (83%) 16 (5%) 21 (7%) 12 (4%) 2 (1%) 1 (0%) 2 (1%)
Manatee Springs F 156 99 (63%) 25 (16%) 25 (16%) 2 (1%) 4 (3%) 0 1 (1%)
M 208 74 (36%) 30 (14%) 57 (27%) 22 (11%) 18 (9%) 5 (2%) 2 (1%)
Rock Springs F 71 58 (82%) 8 (11%) 5 (7%) 0 0 0 0
M 84 56 (67%) 9 (11%) 15 (18%) 1 (1%) 3 (4%) 0 0
Wekiwa Springs F 675 532 (79%) 72 (11%) 56 (8%) 9 (1%) 3 (0%) 3 (0%) 0
M 621 371 (60%) 76 (12%) 115 (19%) 36 (6%) 17 (3%) 4 (1%) 2 (0%)
Table 1. Number of individual Sternotherus minor by Carapace Mutilation Index score (% of occurrence) from Florida springs
study sites in the USA.
Table 1.
Table 2.
Site VBS FS IS MS RSR WS
Volusia Blue Spring (VBS) - * * ns * *
Fanning Springs (FS) * - * * ns ns
Ichetucknee (IS) * ns - * * *
Manatee Springs (MS) ns ns * - * *
Rock Springs (RSR) * ns ns * - ns
Wekiwa Springs (WS) * ns * * ns -
Table 3.
Site VBS FS IS MS RSR WS
Volusia Blue Spring (VBS) - ns * ns ns ns
Fanning Springs (FS) ns - * * ns ns
Ichetucknee (IS) * ns - * * *
Manatee Springs (MS) ns ns * - * ns
Rock Springs (RSR) * ns ns * - ns
Wekiwa Springs (WS) * ns * * ns -
Carapace Mutilation Index Score
Site Sex N 0 1 2 3 4 5 6
Volusia Blue Spring F 126 78 (62%) 21 (17%) 17 (13%) 5 (4%) 4 (3%) 0 1 (1%)
M 184 76 (41%) 31 (17%) 51 (28%) 21 (11%) 4 (2%) 1 (1%) 0
Fanning Springs F 38 31 (82%) 3 (8%) 3 (8%) 1 (3%) 0 0 0
M 51 32 (63%) 2 (4%) 10 (20%) 4 (8%) 3 (6%) 0 0
Ichetucknee Springs F 167 149 (89%) 5 (3%) 9 (5%) 3 (2%) 1 (1%) 0 0
M 320 266 (83%) 16 (5%) 21 (7%) 12 (4%) 2 (1%) 1 (0%) 2 (1%)
Manatee Springs F 156 99 (63%) 25 (16%) 25 (16%) 2 (1%) 4 (3%) 0 1 (1%)
M 208 74 (36%) 30 (14%) 57 (27%) 22 (11%) 18 (9%) 5 (2%) 2 (1%)
Rock Springs F 71 58 (82%) 8 (11%) 5 (7%) 0 0 0 0
M 84 56 (67%) 9 (11%) 15 (18%) 1 (1%) 3 (4%) 0 0
Wekiwa Springs F 675 532 (79%) 72 (11%) 56 (8%) 9 (1%) 3 (0%) 3 (0%) 0
M 621 371 (60%) 76 (12%) 115 (19%) 36 (6%) 17 (3%) 4 (1%) 2 (0%)
Table 2. Among site comparisons of the number of Sternotherus minor with damage and without damage from Florida Springs
study sites in the USA. Male comparisons are above the diagonal and female comparisons are below the diagonal. * indicates
statistical significance (P < 0.05). ns indicates no statistical significance. Top axis acronyms only.
Variation in carapace damage within and among Loggerhead Musk Turtles in Florida 119

CMI and PL for females at VBS (r = 0.244, df = 124,
P = 0.006), MS (r = 0.236, df = 154, P = 0.003), and WS
(r = 0.078, df = 673, P = 0.042). We found no significant
relationships between CMI and PL for females at FS (r
= -0.155, df = 36, P = 0.352), IS (r = -0.004, df = 165, P
= 0.959), and RSR (r = -0.027, df = 69, P = 0.824).
The binary logistic regression analysis showed that
shell damage was significantly related to plastron
length in females from three sites and males from four
sites (Table 7). Shell damage was nearly significantly
related to plastron length (P = 0.0515) in males from
Ichetucknee Springs.
Discussion
Damage to the posterior marginal scutes was
ubiquitous across all sites. At most sites, the severity
and percentage of turtles with damage differed between
the sexes, with males being more frequently damaged
and having more severe damage based on the CMI. The
Wilcoxon Rank Sum tests found that males showed a
significantly higher percentages of shell injury than
females, and larger males exhibited significantly more
damage at five of the six sites and the binary logistic
regression analysis showed shell damage in males
was significant at four sites and nearly significant at
Ichetucknee Springs, while being significant in three
sites in female tests. This suggests that damage is non-
Table 3. Among site comparisons of Sternotherus minor CMI scores from Florida Springs study sites in the USA. Male comparisons
are above the diagonal and female comparisons are below the diagonal. * indicates statistical significance (P < 0.05). ns indicates
no statistical significance. Top axis acronyms only.
Table 1.
Table 2.
Site VBS FS IS MS RSR WS
Volusia Blue Spring (VBS) - * * ns * *
Fanning Springs (FS) * - * * ns ns
Ichetucknee (IS) * ns - * * *
Manatee Springs (MS) ns ns * - * *
Rock Springs (RSR) * ns ns * - ns
Wekiwa Springs (WS) * ns * * ns -
Table 3.
Site VBS FS IS MS RSR WS
Volusia Blue Spring (VBS) - ns * ns ns ns
Fanning Springs (FS) ns - * * ns ns
Ichetucknee (IS) * ns - * * *
Manatee Springs (MS) ns ns * - * ns
Rock Springs (RSR) * ns ns * - ns
Wekiwa Springs (WS) * ns * * ns -
Carapace Mutilation Index Score
Site Sex N 0 1 2 3 4 5 6
Volusia Blue Spring F 126 78 (62%) 21 (17%) 17 (13%) 5 (4%) 4 (3%) 0 1 (1%)
M 184 76 (41%) 31 (17%) 51 (28%) 21 (11%) 4 (2%) 1 (1%) 0
Fanning Springs F 38 31 (82%) 3 (8%) 3 (8%) 1 (3%) 0 0 0
M 51 32 (63%) 2 (4%) 10 (20%) 4 (8%) 3 (6%) 0 0
Ichetucknee Springs F 167 149 (89%) 5 (3%) 9 (5%) 3 (2%) 1 (1%) 0 0
M 320 266 (83%) 16 (5%) 21 (7%) 12 (4%) 2 (1%) 1 (0%) 2 (1%)
Manatee Springs F 156 99 (63%) 25 (16%) 25 (16%) 2 (1%) 4 (3%) 0 1 (1%)
M 208 74 (36%) 30 (14%) 57 (27%) 22 (11%) 18 (9%) 5 (2%) 2 (1%)
Rock Springs F 71 58 (82%) 8 (11%) 5 (7%) 0 0 0 0
M 84 56 (67%) 9 (11%) 15 (18%) 1 (1%) 3 (4%) 0 0
Wekiwa Springs F 675 532 (79%) 72 (11%) 56 (8%) 9 (1%) 3 (0%) 3 (0%) 0
M 621 371 (60%) 76 (12%) 115 (19%) 36 (6%) 17 (3%) 4 (1%) 2 (0%)
Table 4.
Table 5.
Male vs Female
damage frequency
Male vs Female
damage severity
Site Sex N % Damage P Damage score
mean (± SD)
P
Volusia Blue Spring F 126 38.1 0.0003* 0.7 ± 1.2 0.0021*
(VBS) M 184 58.7 1.2 ± 1.2
Fanning Springs F 38 18.4 0.0434* 0.3 ± 0.7 0.134
(FS) M 51 37.3 0.9 ± 1.3
Ichetucknee Springs F 167 10.8 0.0459* 0.2 ± 0.7 0.5862
(IS) M 320 16.9 0.3 ± 1.0
Manatee Springs F 156 36.5 <0.0001* 0.7 ± 1.1 <0.0001*
(MS) M 208 64.4 1.5 ± 1.5
Rock Springs F 71 18.3 0.026* 0.3 ± 0.6 0.0894
(RSR) M 84 33.3 0.6 ± 1.0
Wekiwa Springs F 675 21.2 <0.0001* 0.4 ± 0.8 <0.0001*
(WS) M 621 40.3 0.8 ± 1.2
Site N Damage PL (mm) P
Volusia Blue Springs 76 N 62.0 ± 14.4 0.0177*
(VBS) 108 Y 67.3 ± 10.6
Fanning Springs 32 N 54.9 ± 11.3 0.0055*
(FS) 19 Y 66.3 ± 14.6
Ichetucknee Springs 266 N 59.6 ± 13.1 0.0382*
(IS) 54 Y 63.4 ± 13.0
Manatee Springs 74 N 61.6 ± 15.6 <0.0001*
(MS) 134 Y 69.8 ± 13.7
Rock Springs 56 N 54.5 ± 12.1 0.3567
(RSR) 28 Y 56.2 ± 10.9
Wekiwa Springs 371 N 56.9 ± 11.7 <0.0001*
(WS) 250 Y 62.4 ± 11.3
Table 4. Within site comparisons between sexes of Sternotherus minor in Florida Springs study sites in the USA. % Damage =
Percent of turtles with any damage; Male vs Female damage = probability that males are more likely to have any damage; Damage
Score = probability that damage scores differ between sexes. * indicates statistical significance (P < 0.05).
Joseph J. Pignatelli III et al.
120

random, accumulated over time, and is related to male
behaviour.
Males show a higher CMI as turtle size increases
while damaged females at two or three sites were larger
than undamaged females and similar in size at the
other sites. This suggests that male turtles accumulated
damage over their lifetime, and not as the result of a
singular event. The fact that most of the sites did not
show increased female CMI as size increased suggests
that larger females may not accumulate damage at
the same rate as smaller ones and may stop accruing
damage when they rival or exceed the size of the males.
This may be because female damage is accumulated
during mating events. Males of this species use
combative mating tactics (Bels and Crama, 1994) and
may therefore prefer smaller adult females that are
easier to coerce. We have observed this accumulation
of damage over time first hand. Over the near 20-year
study many of the hard marks that have been used to
identify individuals have been damaged and or broken
off entirely, making identification of the individual
problematic if not for the use of PIT tags as a secondary
marking method. PIT tagging our individual turtles has
proven to be a necessary while studying this species, and
we recommend anyone conducting long term research
on turtle species that may engage in potentially shell
Table 4.
Table 5.
Male vs Female
damage frequency
Male vs Female
damage severity
Site Sex N % Damage P Damage score
mean (± SD)
P
Volusia Blue Spring F 126 38.1 0.0003* 0.7 ± 1.2 0.0021*
(VBS) M 184 58.7 1.2 ± 1.2
Fanning Springs F 38 18.4 0.0434* 0.3 ± 0.7 0.134
(FS) M 51 37.3 0.9 ± 1.3
Ichetucknee Springs F 167 10.8 0.0459* 0.2 ± 0.7 0.5862
(IS) M 320 16.9 0.3 ± 1.0
Manatee Springs F 156 36.5 <0.0001* 0.7 ± 1.1 <0.0001*
(MS) M 208 64.4 1.5 ± 1.5
Rock Springs F 71 18.3 0.026* 0.3 ± 0.6 0.0894
(RSR) M 84 33.3 0.6 ± 1.0
Wekiwa Springs F 675 21.2 <0.0001* 0.4 ± 0.8 <0.0001*
(WS) M 621 40.3 0.8 ± 1.2
Site N Damage PL (mm) P
Volusia Blue Springs 76 N 62.0 ± 14.4 0.0177*
(VBS) 108 Y 67.3 ± 10.6
Fanning Springs 32 N 54.9 ± 11.3 0.0055*
(FS) 19 Y 66.3 ± 14.6
Ichetucknee Springs 266 N 59.6 ± 13.1 0.0382*
(IS) 54 Y 63.4 ± 13.0
Manatee Springs 74 N 61.6 ± 15.6 <0.0001*
(MS) 134 Y 69.8 ± 13.7
Rock Springs 56 N 54.5 ± 12.1 0.3567
(RSR) 28 Y 56.2 ± 10.9
Wekiwa Springs 371 N 56.9 ± 11.7 <0.0001*
(WS) 250 Y 62.4 ± 11.3
Table 5. Within site comparisons of mean (± SD) plastron lengths (PL) between damaged (Y) and undamaged (N) male
Sternotherus minor in Florida springs Study Sites in the USA. * indicates statistical significance (P < 0.05).
Table 6.
Site N Damage PL (mm) P
Volusia Blue Springs 78 N 66.2 ± 14.7 0.0506
(VBS) 48 Y 71.5 ± 10.2
Fanning Springs 31 N 59.9 ± 17.0 0.3557
(FS) 7 Y 52.4 ± 18.6
Ichetucknee Springs 149 N 74.0 ± 10.7 0.5287
(IS) 18 Y 71.7 ± 12.4
Manatee Springs 99 N 68.1 ± 17.3 0.0022*
(MS) 57 Y 76.2 ± 12.7
Rock Springs 58 N 58.2 ± 15.5 0.5718
(RSR) 13 Y 56.5 ± 19.2
Wekiwa Springs 532 N 60.2 ± 13.1 0.0376*
(WS) 143 Y 62.7 ± 11.9
Table 6. Within site comparisons of mean (± SD) plastron lengths (PL) between damaged (Y) and undamaged (N) female
Sternotherus minor in Florida springs study sites in the USA.*indicates statistical significance (P <0.05).
Variation in carapace damage within and among Loggerhead Musk Turtles in Florida 121

damaging activities, employee a secondary marking
technique in order to assure individual recognition.
The difference in the frequency of damage between
males and females suggests that male damage is non-
random and likely due to competition. Female turtles
do not have as strong a correlation between size and
damage accumulation. Female turtles may be less
aggressive and more likely to flee or hide than males if
found in potentially agnostic confrontations. Therefore,
the driving factor in female damage accumulation could
be sexual activity and not resource based competition.
Furthermore, the cohesive mating strategies of this
species are not completely understood, as not all
reproduction is combative. It is possible that the damage
accumulated by female turtles is a result of aggressive
mating strategies with males invading new territory, and
not caused by the resident males.
The frequency and severity of damage differed among
our study sites. This could be due to habitat variability
among sites, as these variables are known to impact turtle
populations (Sirois et al., 2014). Constructed swimming
areas, boat launches, and the removal of debris and fallen
limbs at all the sites has been documented as potentially
impacting the S. minor populations (Riedle et al., 2016;
Johnston et al., 2020; Munscher et al., 2020). It is
possible that these augmentations eliminate or lessen
microhabitats used for refuge, and therefore result in
increased interactions and competition. Additionally,
there are large differences in the size of these spring
systems and the available floodplain habitat. Looking
across all these factors; size of spring, anthropogenic
impacts, and density, none of them clearly explain the
differences in amount of damage we observed at each of
the springs but could all result in increased adversarial
interactions. Human actions and interactions can have
direct negative effects on turtle populations like the
alteration and destruction of habitat, including nesting
areas (Garber and Burger, 1995; Moore and Seigel,
2006; Selman et al., 2013) and the increase of hazards
including chemical pollutants, litter, fishing gear;
Table 7. Summary of logistic regression analyses of the influence of plastron length on the presence of damage in Sternotherus
minor from Florida Springs Study sites in the USA. * indicates statistical significance (P < 0.05).
Table 7.
Site Sex Coefficient SE Wald’s X
2
P Odds ratio 95% CI
Volusia Blue Spring F 0.031 0.015 4.46 0.0346* 1.03 1.00 – 1.06
(VBS) M 0.035 0.012 7.83 0.0051* 1.04 1.01 – 1.06
Fanning Springs F -0.027 0.026 1.06 0.3030 0.97 0.92 -1.02
(FS) M 0.069 0.025 7.34 0.0067* 1.07 1.01 – 1.13
Ichetucknee Springs F -0.020 0.023 0.75 0.3879 0.98 0.94 – 1.03
(IS) M 0.022 0.011 3.79 0.0516 1.02 1.00 – 1.04
Manatee Springs F 0.034 0.012 8.60 0.0034* 1.03 1.01 – 1.06
(MS) M 0.040 0.011 13.83 0.0002* 1.04 1.02 – 1.06
Rock Springs F -0.006 0.019 0.11 0.7419 0.99 0.96 – 1.03
(RSR) M 0.013 0.020 0.40 0.5254 1.01 0.97 – 1.05
Wekiwa Springs F 0.015 0.007 4.16 0.0413* 1.02 1.00 – 1.03
(WS) M 0.041 0.007 31.44 <0.0001* 1.04 1.03 – 1.06
Table 8.
Site Study Site Size (ha) Density (Turtle/ha)
Volusia Blue Spring (VBS) 1.9 132/ha
Fanning Springs (FS) 0.7 848/ha
Ichetucknee Springs (IS) 10.99 199/ha
Manatee Springs (MS) 1.53 807/ha
Rock Springs (RSR) 1.41 N/A
Wekiwa Springs (WS) 2.67 1279/ha (Munscher et al., 2020)
Table 8. Sternotherus minor Population Density from Florida Springs study sites in the USA.
Joseph J. Pignatelli III et al.
122

disturbance, collection, and predator attraction (Burger
and Garber, 1995). Human interactions can result in
unforeseen impacts like the alteration of food sources
(Morrison et al., 2019), increased predation (Munscher
et al., 2012), or population crashes from low impact
passive recreation and indiscriminate collection (Garber
and Burger, 1995; Godwin et al., 2021).
The variation of habitat types and uses makes it
impossible to definitively identify the causation in the
inconsistent damage. At IS, larger males have a higher
percentage of damage. Interestingly, this is the largest
site surveyed (199/ha) and damaged turtles were found
in the lowest overall percentages despite this site having
the third highest population density (Table 8) (Johnston
et al., 2020). VBS has the second highest percentage of
damaged turtles, and unlike the other sites, is home to
a large manatee population which defoliates the spring
regularly – potentially decreasing suitable refugia and
food resources, while increasing turtle visibility, leading
to a heightened potential for intraspecific sightings
and aggression (Riedle et al., 2016). The site with
the highest percent damage observed, MS, is one of
the least impacted anthropogenically, suggesting that
habitat augmentation is not the only variable impacting
turtle shell damage. The individuals from this site are
the largest S. minor sampled across all six sites, further
supporting our hypothesis that size of the individual
is an underlying link to the level of damage observed.
This data prompts further investigation into whether
aggression is driven by population density resulting in
competition for resources, space, and mates within their
environments, all factors that favour larger individuals
(Berry and Shine, 1980).
The S. minor within our study sites are engaging in
intraspecies, intrasexual aggression. This species is
known to attain very high densities in spring systems,
and their potential competitive interactions have long
interested turtle biologists. In Carr’s Handbook of
Turtles (1952), he references Marchland (1942) who
commented on a robust population of S. minor from IS
Springs, where 500 or more S. minor could be seen on
a given day, and both authors question how these large
populations find sustenance. Akin to male-male combat
in large mammals, we speculate that the aggression
between males is likely tied to competition for resources
and specifically females. We observed this aggressive
behaviour in both human altered and unaltered spring
habitats alike, and our results suggest that both individual
and habitat size are the drivers of this aggression. Our
observations support Jackson’s earlier hypothesis that the
damage identified in S. minor is the result of intraspecies
aggression. Additional research should focus on habitat
variables, such as subaquatic vegetation density, as we
suggest habitat alterations or denudation of vegetation
increases aggressive interactions in this species, which
may warrant management of these springhead habitats
in Florida. If these alterations have not historically
influenced aggressive interactions, as they have been
cited since the mention of “old, eroded individuals” in
Carr and Goin’s (1955), then this study is the first to
quantitatively document these intrasexual intraspecific
competitive interactions in Sternotherus minor. Future
research should look at movement patterns, site fidelity,
social interactions, and how these are impacted by
habitat size, quality, and density, to determine what,
if any, these factors have on population stability and
fecundity.
Acknowledgments. We thank the following for supporting this
research: past and current staff of Ichetucknee Springs, Fanning
Springs, Manatee Springs, Volusia Blue Springs, and Wekiwa
Springs State Parks as well as Rock Springs Run State Preserve,
the Florida Department of Environmental Protection, the Florida
Fish and Wildlife Conservation Commission, Pennsylvania
State University, Freed-Hardeman University, University
of North Florida, Peninsula College, Santa Fe College, and
Western Washington University. We also thank P. Butt, C. Cox,
I. Gaz, E.A. Havens, G. Hrycyshyn, M. Johnson, J. Kuhns, J.
McDonald, L. McEwuen, J. Munscher, D. Rogers, N. Salvatico,
G. Shemitz, B. Taylor, E. Walton, and the many other students
and biologists who make up the Turtle Survival Alliance-North
American Freshwater Turtle Research Group and Santa Fe River
Turtle Project. A special thank you to Deborah Shelly, Virginia
Oros, and Barbara Howell from the FDEP Aquatics Preserve
for their years of constant support in and out of the field. Their
contributions were truly impactful to this long-term study. We
thank the Friends of the Wekiva River Foundation, Wekiva Wild
and Scenic Committee, Guy Marwick, The Felburn Foundation,
and Keep Seminole Beautiful for providing much-needed grant
money over the many years of this study. Additional thanks go
to SWCA Environmental Consultants for their constant support,
to Alice Bard of the Florida Department of Environmental
Protection for issuing research permits for the past 20 years,
and EcolSciences Inc. The study was conducted under permits
06240913, 06040412, and 06241610A from the Florida
Department of Environmental Protection and permits LSSC-
09-0411 and LSSC-10-00039 (originally WX04230) from the
Florida Fish and Wildlife Conservation Commission.
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