A Diverse Aquatic Turtle Assemblage in an Urban Mississippi Oasis
Gracie Bellnap1 and Will Selman1*
1Department of Biology, Millsaps College, 1701 North State Street, Jackson, MS 39210 USA *Corresponding Author.
Urban Naturalist, No. 52 (2022)
Abstract
The loss of natural habitats associated with urbanization is increasing, and natural areas may serve as refuges for wildlife in urban areas. In central Mississippi, one such area is LeFleur’s Bluff State Park (LBSP, ~120 ha), located primarily in the floodplain of the Pearl River but also surrounded by highly developed areas of Jackson, Mississippi. We investigated a diverse aquatic turtle assemblage in 3 LBSP cypress ponds during the summers of 2017 and 2018 using 3 different capture methods. Trachemys scripta (Slider Turtle), a cosmopolitan generalist, was the most commonly encountered species, but aquatic turtle richness was high and richness/diversity varied across study ponds; the assemblage included Macrochelys temminckii (Alligator Snapping Turtle), a species currently proposed for listing under the US Endangered Species Act. Collectively, we captured 9 turtle species typically associated with both pond and riverine habitats, and this finding is suggestive of connectivity between our study ponds and the nearby Pearl River. Fyke nets caught the highest number of species and had the highest trapping efficiency of all methods tested. Our data serve as baseline information on this diverse urban turtle assemblage, and we also provide methodological recommendations for researchers working in similar aquatic environments.
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Volume 9, 2022 Urban Naturalist No. 52
A Diverse Aquatic Turtle
Assemblage in an Urban
Mississippi Oasis
Gracie Bellnap and Will Selman
Urban Naturalist
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Cover Photograph: Juvenile Alligator Snapping Turtle (Macrochelys temminckii) captured in Daisy
Pond, Lefleur’s Bluff State Park. Photograph © Gracie Bellnap.
Urban Naturalist
G. Bellnap and W. Selman
Vol. 9, 2022 No. 52
1
Vol. 9, 2022 URBAN NATURALIST 52:1–12
A Diverse Aquatic Turtle Assemblage
in an Urban Mississippi Oasis
Gracie Bellnap1 and Will Selman1*
Abstract - The loss of natural habitats associated with urbanization is increasing, and natural areas
may serve as refuges for wildlife in urban areas. In central Mississippi, one such area is LeFleur’s
Bluff State Park (LBSP, ~120 ha), located primarily in the floodplain of the Pearl River but also surrounded
by highly developed areas of Jackson, Mississippi. We investigated a diverse aquatic turtle
assemblage in 3 LBSP cypress ponds during the summers of 2017 and 2018 using 3 different capture
methods. Trachemys scripta (Slider Turtle), a cosmopolitan generalist, was the most commonlyencountered
species, but aquatic turtle richness was high and richness/diversity varied across study
ponds; the assemblage included Macrochelys temminckii (Alligator Snapping Turtle), a species currently
proposed for listing under the US Endangered Species Act. Collectively, we captured 9 turtle
species typically associated with both pond and riverine habitats, and this finding is suggestive of
connectivity between our study ponds and the nearby Pearl River. Fyke nets caught the highest number
of species and had the highest trapping efficiency of all methods tested. Our data serve as baseline
information on this diverse urban turtle assemblage, and we also provide methodological recommendations
for researchers working in similar aquatic environments.
Introduction
Urbanization is often cited as the primary cause of species loss, as natural habitats are
destroyed or degraded by human infrastructure (Alford and Richards 1999, Czech et al.
2000, Edmondson 1991, Gibbons et al. 2000, McKinney 2008). Some regions of the United
States (US) retain less than 20% of the wild acreage they once had (Gibbons et al. 2000),
and existing natural areas (e.g., parks, refuges, and wildlife management areas) may be
inadequate to preserve biodiversity. Nonetheless, within urban centers, the establishment
of natural areas may mitigate local wildlife losses (Savard et al. 2000). Without natural
areas embedded in urbanized landscapes, some species may become extirpated (Nielsen
et al. 2014). Therefore, studies of biodiversity in urban settings are of increasing interest,
particularly those quantifying natural area biodiversity and how biodiversity may persist in
human-modified settings.
The southeastern US is one of the most diverse aquatic regions in the world, and it was
recently designated a global biodiversity hotspot (Noss et al. 2015). The Gulf Coastal Plain
in the southeastern US is considered a chelonian biodiversity hotspot (Buhlmann et al. 2009,
Mittermeier et al. 2015), but some of its turtles are species of conservation concern. Turtles
face numerous threats in the region, including habitat destruction and fragmentation, fisheries
by-catch, and collection for the international pet, food, and traditional medicine trades
(Rhodin et al. 2018). These factors have collectively contributed to declines in freshwater
turtle populations. Because turtles make up most of the vertebrate biomass in wetland
communities, reduced numbers of turtles may significantly change the ecological function
and integrity of aquatic ecosystems (Lovich et al. 2018). For example, turtles act as both
consumers of plants and animals and as prey to larger animals, with the latter typically as-
1Department of Biology, Millsaps College, 1701 North State Street, Jackson, MS 39210 USA
*Corresponding Author: will.selman@millsaps.edu.
Associate Editor: Travis Ryan, Butler University.
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Vol. 9, 2022 No. 52
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sociated with the egg and juvenile stages (Glorioso et al. 2010). Thus, the natural balance
of ecosystems can be disturbed by the decline of turtle populations. Urban parks may serve
as important refuges for local turtle populations because they usually include natural and/or
semi-natural aquatic and terrestrial habitats. If the parks are large enough and offer the requisite
resources for turtles, these parks may support turtle populations that might otherwise
not exist in urban and suburban environments (Dupuis-Désormeaux et al. 2019).
We studied the turtle assemblage of 3 small (all ≤1.1 ha) cypress ponds at LeFleur’s Bluff
State Park (LBSP; ~123 ha), a small urban park in Jackson, Mississippi. At the time of this
study, the population of Jackson and surrounding suburban areas (tri-county area: Hinds,
Madison, Rankin counties) was 493,918 (US Census Bureau 2021). Our goal was to document
the aquatic turtle assemblage at these locations in the Pearl River floodplain. While investigating
the turtle assemblage, we also tested the efficacy of a variety of trapping methodologies
for floodplain turtle assemblages, and we provide a cost–benefit analysis for each method.
Materials and Methods
Study Sites
LeFleur’s Bluff State Park is located in Jackson, Mississippi (Hinds County). Most of the
park occurs within the floodplain of the Pearl River. We studied the turtle assemblage in 3
cypress ponds (Hammock, Armadillo, and Daisy) in the southern portion of LBSP (Fig. 1).
Figure 1. Sampled ponds in
the Pearl River floodplain of
Lefleur’s Bluff State Park, Jackson,
MS, USA (Hammock—1,
Armadillo—2, Daisy— 3). The
Mississippi Museum of Natural
Science is located at the
white triangle, and the Pearl
River extends along the southern
border of Lefleur’s Bluff
State Park. Eubanks Creek is
outlined in white. The red star
on the inset map indicates the
location of Jackson, Mississippi.
Aerial photograph was taken in
2017 (Esri, used with permission
under Millsaps College site
license).
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Vol. 9, 2022 No. 52
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These ponds were characterized by a wide diversity of plant and animal life, muddy and
organic substrates, and water levels that seasonally fluctuated with rainfall and river levels.
Dominant tree species in the floodplain included Taxodium distichum (L.) Rich. (Baldcypress),
Nyssa aquatica L. (Swamp Tupelo), oak trees (Quercus lyrata Walter [Overcup
Oak], Quercus michauxii Nutt. [Swamp Chesnut Oak], Quercus nigra L. [Water Oak]), and
the invasive Triadica sebifera (L.) (Chinese Tallowtree).
Hammock Pond was ~1.10 ha in size (32.32677°N, -90.15546°W). Maximum water
depths ranged from ~1 to 1.5 m; depths were sometimes slightly deeper than this near the
center of the pond depending upon the season. The northern and southern ends of the pond
were shallower (<0.5 m deep) and had a thick, organic substrate. Swamp Tupelo and Baldcypress
trees were scattered throughout the pond, providing almost complete canopy coverage
of the pond’s surface. Duckweed L. (Lemna sp.) was prevalent and, at times, covered almost
the entire surface of the pond. Even though little sunlight penetrated the dense canopy, many
turtle basking logs and branches were available. A recreational walking trail with an observation
deck bordered the western and southern edges of the pond (trail was ~3–10 m away), and
this pond was in closest proximity to the Mississippi Museum of Natural Science (MMNS),
~0.20 km away by trail. Thus, Hammock Pond likely experienced more walking traffic than
the other ponds, but walking traffic was still low on the lightl y used trail.
Armadillo Pond was ~0.92 ha in size (32.32472°N, -90.15162°W). During normal water
conditions, water depths were ≤2 m throughout the pond; the depths were more spatially
consistent across the pond compared to Hammock or Daisy ponds (below). Large Swamp
Tupelo, Baldcypress, and Chinese Tallowtrees were prevalent along the margins of the
pond. The pond had an open canopy, but there were limited basking structures. Baldcypress
trees were sparsely scattered throughout the pond, but higher tree densities on the southern
end of the pond caused this area to be heavily shaded. Similar to Hammock Pond, the same
recreational walking trail and observation deck (~3 m away) occurred along the eastern side
of the pond; the pond was mostly obscured from view on the walking trail (>25 m away)
because of large amounts of understory vegetation. Recreational walking traffic was rarely
observed at Armadillo Pond, ~0.5-km walking distance from MMNS.
Daisy Pond was ~0.82 ha (32.1928° N, -90.0907° W), with several different microhabitats
not present in the other study ponds. Pond margins were shallow (<0.5 m, ~10–15
m wide) and heavily shaded by Baldcypress trees; an area of open canopy occurred in the
center of the pond. Under normal conditions, this middle section was considerably deeper
than the rest of the pond (~1.5–2 m). The substrate was muddy throughout the pond, but
sand was also present because of overbank sand deposition after flooding of the Pearl River
(~25–30 m from the pond’s southern edge). Water level fluctuations in Daisy Pond were
greater than in Hammock or Armadillo ponds because of an overflow stream connection to
the Pearl River. The walking trail approached the northern edge of Daisy Pond, but walking
traffic was minimal because the pond was mostly obscured by thick understory and midstory
vegetation (~0.75-km walking distance from the MMNS).
Turtle Sampling
From May to July 2017, we used 3 different capture methods to capture turtles across 7
weeks. These methods included unbaited fyke nets with leads (Nets and More, Jonesville,
LA), baited hoop nets (Nets and More), and baited collapsible crab traps (Promar Collapsible
Crab Trap, Austin, TX). We used double-throated, unbaited fyke nets (hereafter, fyke
nets) with 0.914-m hoops and 4.8-cm mesh size; the leads of the fyke nets were 7.6 m long
and 0.9 m deep (leads with 5.1-cm mesh size). The leads had weights on the bottom line
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and floats on the top line to ensure the leads were vertical in the water (i.e., functioned as a
fence). We used PVC pipes or available structures to position the cod end of the net away
from the bank and toward the center of the pond. The lead was fully stretched to the bank
and was secured ~1 m away from the water using stakes or available structure. The depth
of the water had to be ~45 cm for the throat to be submerged and allow turtles to enter the
fyke net. The second method was standard turtle hoop nets with 0.9-m wide hoops with a
single throat (5.1-cm mesh size). We set hoop nets with the throat completely in the water
(~45-cm depth). The third method we used was collapsible mesh crab traps (61 × 46 × 20
cm; Promar Collapsible Crab Trap). We used wooden stakes or available structure to set
both hoop nets and crab traps. Crab traps were set on the edge of the water or in shallow
areas to allow a portion of the trap to remain unsubmerged. We baited hoop nets and crab
traps with canned sardines. To maximize sardine scent dispersal, we punctured the top of the
can several times before setting the trap the first day; each day thereafter, the lid was slightly
peeled back (Iverson 1979). If few to no sardines remained in the can after a trap night, the
bait was replaced. For all trap types, we placed small sections of pool noodles inside each
net, allowing the net to float and ensuring that captured turtle s had access to air.
For each sample week in 2017, we set 2 fyke nets, 6 hoop nets, and 8 crab traps. We attempted
to equally sample all parts of the pond by spreading the traps across all sections of the pond
with sufficient water depth. All 16 traps were set on Monday, and they were thereafter checked
for 3 consecutive days. On occasion, inclement weather or rising river levels prevented us from
trapping an entire 3-day period. Also, nets had to be occasionally repositioned to accommodate
changing water levels, and damaged traps had to be removed for repairs. During the summer of
2017, we sampled each pond twice using all 3 trapping methods, but persistent rain and summer
flooding of the Pearl River prevented us from trapping in part of July 2017. Catch per unit effort
(CPUE = total number of turtle captures / trap nights) was used as a measure of trap success.
In 2018, we trapped for 8 weeks between May and July. We used 6 fyke nets per week
with similar-style leads and similar set methods to 2017. However, we tested the efficiency
of 3 different lead lengths (7.62 m, 11.43 m, 15.24 m; 2 nets of each length). We dispersed
nets around the pond in order to sample each section equally, and we checked nets for 3 consecutive
days each week except in cases of rising water levels or net repairs. No crab traps
or hoop nets were used in 2018. In contrast to 2017, the summer of 2018 was characterized
by lower water levels because of semi-drought conditions. Thus, we sampled Hammock and
Armadillo ponds 3 times each during 2018, while Daisy Pond was sampled once as a result
of the pond completely drying during the drought.
For each net/trap, we recorded the number and species of individuals captured per trap
each day. We also collected morphometric and sex data from captured individuals for a
related study. All newly captured individuals were permanently marked by notching or drilling
holes in the marginal scutes using a file or drill, respectively (Cagle 1939). All individuals
were released at their point of capture.
Analysis
We used a Shannon Diversity Index (Hʹ) to calculate and compare turtle diversity across
our 3 study ponds (Shannon and Weaver 1949), with 2017 and 2018 data analyzed separately,
and we also calculated evenness of turtles by site (Krebs 1994). Because CPUE was not normally
distributed, we used a Kruskal–Wallis rank sum test to determine if CPUE (including
all species and all captures/recaptures) was similar across trapping methods (crab trap, hoop
net, and fyke) in 2017. We also used a Kruskal–Wallis rank sum test to determine if CPUE
was similar across fyke net lead lengths (7.62 m, 11.43 m, 15.24 m) for the 2018 data. Finally,
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Kruskal–Wallis rank sum tests were used to determine if CPUE (including all species and
all captures/recaptures) was equal across ponds for the 2017 and 2018 data. In cases where
significant results were found for Kruskal–Wallis rank sum tests, nonparametric Wilcoxon
multiple comparison tests were completed to determine differences among tested groups. All
analyses were performed in JMP 14 (SAS Corporation, Cary, NC).
Results
Species Richness and Diversity
Across both years of sampling, we captured a total of 341 individuals (79 recaptures) of 9
aquatic turtle species. The 9 species were Trachemys scripta elegans (Wied-Neuwied) (Redeared
Slider Turtle), Pseudemys concinna (Le Conte) (River Cooter), Kinosternon subrubrum
(Bonnaterre) (Mud Turtle), Sternotherus carinatus (Gray) (Razorback Musk Turtle), Chelydra
serpentina (L.) (Common Snapping Turtle), Macrochelys temminckii (Troost and Harlan)
(Alligator Snapping Turtle), Sternotherus odoratus (Latreille) (Stinkpot), Chrysemys dorsalis
Agassiz (Southern Painted Turtle), and Apalone spinifera (Le Sueur) (Spiny Softshell) (Table
1). For all captures and all ponds, Slider Turtles dominated the assemblage of turtles in both
years (95.3% in 2017; 88.2% in 2018), while the 8 other species represented minor portions
of the turtle assemblage in both years (from 0–3% in both years; Table 1).
Comparisons of Turtle Diversity by Pond and Movements
Shannon diversity values were low during both years and for all ponds. However, diversity
(Hʹ) and evenness (E) values were lower for all ponds in 2017 (Hammock: Hʹ =
0.29, E = 0.21; Armadillo: Hʹ = 0.13, E = 0.12; Daisy: Hʹ = 0.28, E = 0.25) compared to
2018 (Hammock: Hʹ = 0.61, E = 0.38; Armadillo: Hʹ = 0.43, E = 0.27; Daisy: Hʹ = 0.45, E
= 0.32). Diversity values were similar among ponds each year, with Hammock Pond having
the highest diversity both years.
Of the 355 captures of Slider Turtles in 2017 and 2018, we recaptured 33 individuals.
Of these 33 individuals, 28 were recaptured in their original pond (Hammock—12; Armadillo—
13; Daisy—3), while 5 were recaptured in a different pond in 2018 than where they
were originally captured in 2017. For the latter, 4 individuals (2 females, 2 males) moved
from Armadillo to Hammock (~40 m between the ponds, sometimes with a small overflow
channel connecting them), while a single male moved from Hammock to Armadillo. Further,
only a single male individual was captured in the same year in different ponds (2017—
Hammock to Armadillo). No turtles were found emigrating from Daisy Pond to the other 2
study ponds, which were located on the opposite (west) side of Eubanks Creek.
Trapping Methodology
In 2017, CPUE differed among trapping methods (χ2 = 30.57, p < 0.0001). Wilcoxon nonparametric
multiple comparisons indicated that fyke nets (n = 13 net sets, mean CPUE = 5.33 ±
5.04 SD, range = 0–17.0) captured more turtles than hoop nets (n = 38 trap sets, mean CPUE =
0.19 ± 0.39 SD, range = 0–1.7) or crab traps (n = 46 trap sets, mean CPUE = 0.267 ± 0.47 SD,
range = 0–2.0); there was no statistical difference in CPUE between hoop nets and crab traps.
In 2018, there was no difference in CPUE among fyke nets with different lead lengths (χ2 =
0.36, p = 0.84; 7.62-m lead: mean CPUE = 2.11 ± 1.70 SD, range = 0–5.0; 11.43-m lead: mean
CPUE = 1.72 ± 1.25 SD, range = 0–4.7; 15.24-m lead: mean CPUE = 1.80 ± 1.44 SD, range
= 0–4.3). However, the 15.24-m fyke net captured 6 of the 9 documented species, whereas the
11.43-m fyke nets captured 5 of 9 species, and the 7.62-m captured 4 of 9 species (Table 1).
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Catch per unit effort differed among ponds in 2017 (χ2 = 7.95, p = 0.02). Wilcoxon nonparametric
multiple comparisons indicated a higher CPUE in Armadillo Pond compared to
Daisy or Hammock; CPUE did not differ between Hammock and Daisy ponds. Catch per
unit effort did not differ among ponds in 2018 (χ2 = 2.61, p = 0.27). Armadillo Pond (2017
mean CPUE = 1.28; 2018 mean CPUE = 2.18) was the most species rich pond with 6 species,
whereas Hammock Pond (2017 mean CPUE = 1.02; 2018 mean CPUE = 2.11) and Daisy Pond
(2017 mean CPUE = 0.62; 2018 mean CPUE = 1.49) each had 5 species captured.
Discussion
Urban Aquatic Turtle Richness and Diversity
Our results confirm that ponds within the small natural area of LBSP, a park surrounded by
an urbanized landscape, currently support relatively high species richness of aquatic turtles,
and the threats to turtles in this area appear to be minimal (i.e., no observed collections, no
Table 1. Total captures of freshwater turtles from 3 different floodplain ponds (Hammock, Armadillo,
Daisy) in Lefleur’s Bluff State Park, Jackson, MS, in 2017 and 2018. Effort is shown as the number
of trap days that a capture method was used at that pond for each year. In 2017, methods included
baited crab traps (Crab), baited hoop nets (Hoop), and 7.62-m lead fyke nets (Fyke). In 2018, only
fyke nets with different lead lengths (7.62 m, 11.43 m, 15.2 m) were used. Species abbreviations: A.s.
= Apalone spinifera, C.d. = Chrysemys dorsalis, C.s. = Chelydra serpentina, K.s. = Kinosternon subrubrum,
M.t. = Macrochelys temminckii, P.c. = Pseudemys concinna, S.c. = Sternotherus carinatus,
S.o. = Sternotherus odoratus, and T.s. = Trachemys scripta.
Year Pond Method Effort T.s. C.s. K.s. P.c. C.d. S.c. A.s. M.t. S.o. Total
2017 Hammock Crab 40 6 - 1 - - - - - - 7
Hoop 32 4 - - - - - - - - 4
Fyke 10 51 1 1 1 - - - - - 54
Armadillo Crab 33 13 - - - - - - - - 13
Hoop 33 6 - - - - - - - - 6
Fyke 10 59 - - 1 - 1 - - - 61
Daisy Crab 41 1 - - - - - - - - 1
Hoop 33 1 1 - - - - - - - 2
Fyke 12 42 - - - - 2 - - - 44
Total 183 2 2 2 - 3 - - - 192
2018 Hammock 7.62 m 18 24 - 3 1 2 - - - - 30
11.43 m 18 14 1 1 - - - - - - 16
15.24 m 18 24 3 - - - - - - - 27
Armadillo 7.62 m 16 30 - - - 1 - - - - 31
11.43 m 16 25 - - - 3 - - - - 28
15.24 m 16 21 - - 1 - - 2 - 1 25
Daisy 7.62 m 6 11 - - - - - - - - 11
11.43 m 6 7 1 - 2 - - - - - 10
15.24 m 6 16 - - - - - - 1 - 17
Total 172 5 4 4 6 - 2 1 1 195
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nearby roads, etc.). Turtle richness is known to be high in Mississippi (n = 31 species; Buhlmann
et al. 2008) and the southeast US in general (Buhlmann et al. 2009). One might expect
urban areas to maintain lower species richness than natural areas, a pattern primarily associated
with the extirpation of rare species in urban areas (McKinney 2008). This absence of rare
species was not the case at our study site, as we captured a single juvenile Alligator Snapping
Turtle, a species that is currently proposed for listing under the US Endangered Species Act
(USFWS 2021). Similarly, Munscher et al. (2020) discovered a thriving population of Alligator
Snapping Turtles in the urban center of Houston, Texas. We suspect that the individual in
our study was likely associated with a population in the nearby Pearl River that flows through
Jackson. However, because we only captured a single individual, further research is needed to
document the population status of Alligator Snapping Turtles in the Pearl River near Jackson.
Nonetheless, the findings of this study and Munscher et al. (2020) highlight that urban rivers
and floodplain pond habitats may maintain rare species of turtles.
Diversity and evenness were relatively low for all ponds in both years, and these low
values were associated with capturing few species in each pond and the dominance of Slider
Turtles. The Slider Turtle is a ubiquitous aquatic turtle species that is well-adapted for lentic
environments like our study site and is a native species to our study area (Ernst and Lovich
2009). However, Slider Turtles have also been widely introduced outside of their native
range, and they occur globally in many urban and suburban waterways in high densities
(e.g., Snapp et al. 2021), often competing with native turtles for resources (Cadi and Joly
2004). Along with the more commonly encountered Slider Turtle (MMNS Herpetology
Collection, catalog #16217), historical records of 5 additional lentic turtle species exist for
this region of the Pearl River floodplain (i.e., Hinds and Rankin counties; Southern Painted
Turtle, MMNS #4474; Common Snapping Turtle, MMNS #13000; River Cooter, MMNS
#10853; Stinkpot, MMNS #10827; Mud Turtle, MMNS #1098). During 2017 and 2018
sampling efforts, we captured each of these species. We also captured species usually associated
with lotic environments, including the Spiny Softshell, Alligator Snapping Turtle,
and Razorback Musk Turtle. Similarly, all 3 of these species had previously been found near
our study site (Spiny Softshell, MMNS #1495; Alligator Snapping Turtle, MMNS #4203;
Razorback Musk Turtle, MMNS #4330–4348). However, most of the specimens reported
above were collected before the 1970s.
Since these historical collections of the 9 species were made, there have been substantial
hydrologic changes in the region, including the construction of the Ross Barnett
Reservoir, an impoundment of the Pearl River, upstream of Jackson in 1963 and the levee
protection system around Jackson, which was implemented in the 1960s (Selman 2020).
Also, the area surrounding Jackson has been developed significantly over the last 50 years
for commercial and residential uses, particularly east of the Pearl River (e.g., the towns of
Flowood, Pearl, Brandon). Thus, in spite of these dramatic changes over the last 50 years,
our study demonstrates that these 9 species have persisted in the region. However, the
outlook for a local riverine turtle species not observed in our study, Graptemys pearlensis
Ennen, Lovich, Kreiser, Selman, and Qualls (Pearl Map Turtle), is not as positive. This
species has declined dramatically in the region over the last 30 years (Selman 2020, Selman
and Jones 2017). The future of this diverse turtle assemblage and the greater Pearl
River floodplain may be dependent upon the intensity and rate o f human development in
the region and how it impacts riverine processes. This potential development includes
another impoundment that is planned for the Pearl River, the One Lake Project, which
will significantly impact the river hydrology, the riverine turtles, and the surrounding
floodplain (Selman 2020).
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Floodplain Turtle Assemblages and River Connectivity
Captures of species associated with both ponds and flowing streams/rivers suggest that
our sampling ponds are regularly connected to the Pearl River. The presence of riverine
species points to the importance of river connectivity in these floodplain ponds. In wetlands
associated with a river, resources may vary with alternating periods of connectivity and
disconnectivity between floodplain ponds and rivers during annual flood and drought cycles
(Riedle et al. 2016). Thus, flood pulses are arguably the most important process influencing
stream communities because they permit biotic and abiotic exchanges between the river
and associated terrestrial floodplain habitats. These interactions lead to shifts in species
compositions, nutrient influxes, and changes in chemical processes (Bunn and Arthington
2002, Riedle et al. 2016). During this study in July 2017, flooding connected the Pearl River
to all 3 study ponds, possibly contributing to individuals moving among ponds and between
the river and the ponds. Indeed, 5 of 33 (15%) interannual recaptures (i.e., those individuals
captured in 2017 and recaptured in 2018) exhibited movements between ponds. Further
evidence of the connectivity of the Pearl River floodplain is that 2 marked turtles from our
project in 2017 were found ~0.75 km north of our sites (i.e., upstream) in Maye’s Lake in
2018 (L. Pearson, The University of Southern Mississippi, Hattiesburg, MS, pers. comm.).
Captures of some riverine species in our smaller study ponds also suggest that some of
the river turtle species may be better suited to lentic environments than others. For example,
2 riverine specialists—Graptemys oculifera (Baur) (Ringed Sawback) and the Pearl Map
Turtle—occur within the Pearl River immediately adjacent to the study area (Selman 2020),
but they were not captured or observed during our study. Interestingly, Ringed Sawbacks
were observed in low densities in larger, deeper oxbow lakes (e.g., 2.8 – 8.7 ha) ~0.6 km
northeast of our study site within LBSP, but Pearl Map Turtles were not observed at these
locations (Selman 2020). Thus, even though both Graptemys species are found immediately
adjacent to our study ponds in the Pearl River, and Ringed Sawbacks are found in larger
lakes near our study site, it appears Graptemys species do not use smaller, lentic environments
like our 3 study ponds. In comparison, we found that some lotic species, like the
Spiny Softshell, Alligator Snapping Turtle, and Razorback Musk Turtle, may acclimate to
smaller bodies of water in urbanized areas, such as the ponds in this study.
The turtle assemblage we observed in this study was different across years, and we captured
some species in just 1 of our sampling years. For example, Razorback Musk Turtles were
captured in 2017 but not 2018, whereas Southern Painted Turtles were captured in 2018 but
not 2017. Turtle species exchanges occur during river flood pulses when floodplain and river
habitats are connected (Riedle et al. 2016). Similarly, seasonal droughts may also redistribute
individuals occupying these floodplain ponds. We captured a single juvenile Alligator Snapping
Turtle in Daisy Pond during our first sampling period of 2018. However, because Daisy
Pond dried later in the summer, this individual likely emigrated overland from Daisy Pond
to another waterbody (e.g., Pearl River, Eubanks Creek). In summary, we suspect that some
turtle species may be transient in these floodplain pond habitats, and consequently, some species
may be rare and not be sampled every year. Therefore, multiple years of data are needed
to fully explain the nature of these dynamic floodplain turtle a ssemblages.
Sampling Methodology
When evaluating the best and most appropriate trap type to use, it is important for
researchers to account for the cost, time, effort, and expertise required to achieve the
research goal(s) (Sterrett et al. 2010). Furthermore, most studies similar to ours also
would like to capture a relatively large sample size of turtles for statistical power and a
representative sample of the turtle assemblage. Taking these factors into consideration,
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a variety of methods used together has usually been shown to be most effective (Riedle
et al. 2021, Vogt 1980).
In order to effectively sample the entire turtle assemblage, we utilized 3 different methods
in 2017 to sample our study ponds. Our results from 2017 indicated that fyke net CPUE
was much higher (28×), with ~70% less trap nights, than the CPUE for crab traps or hoop
nets, and the fyke nets sampled the turtle assemblage more effectively, catching all 5 species
observed in 2017. Hoop nets and crab traps each captured only 2 species. This finding
is what led us to further investigate fyke nets during the 2018 field season.
In 2018, we found that fyke net lead length was associated with the number of turtle
species captured (Table 1). The fyke net with the longest lead (15.24 m) captured the highest
number of species (6), including 3 species not detected with other lead lengths (Alligator
Snapping Turtle, Spiny Softshell, and Stinkpot), while the 2 shorter length fyke nets captured
4–5 species. The difference in number of species captured by each lead length may be
due to random chance or related to the pond depth. For example, the 7.62-m fyke net did not
reach the deep, middle portions of the ponds, which could reduce the likelihood of capturing
bottom-walkers, such as Razorback Musk Turtles and Mud Turtles. Conversely, the 15.24-m
lead reached further into the pond and had the ability to catch both the most mobile turtle
species and those that use open, deeper pond microhabitats.
When compared between years, fyke nets demonstrated drastically different mean
CPUEs (2017: 5.33; 2018: 1.72–2.11). It is possible that CPUE was higher in 2017 because
of early 2018 flooding events that may have changed turtle densities and species distributions
among the ponds prior to our 2018 sampling. Alternatively, the employment of 6 fyke
nets in 2018 per sampling week (compared to 2 nets per week in 2017) may have led to an
oversaturation of traps in the relatively small ponds. In the smaller ponds, individuals can
readily move throughout the entire pond; this behavior was observed when individuals were
recaptured within the same day at opposite ends of the pond. Thus, with the deployment of
6 fyke nets in 2018, turtles were more likely to encounter a net compared to 2017. Weekly
mean CPUEs were similar between 2017, when there were only 2 nets (mean CPUE: 5.33),
and 2018, when there were 6 total nets (mean CPUE: 5.63). Further, our 3 most successful
net sets from 2017 had much higher trap rates (CPUE: 5.6–9.3) compared to the 3 most
successful net sets from 2018 (CPUE: 4.7, occurred 3 times). This finding suggests that 2–4
fyke nets per hectare may be sufficient to adequately sample the turtle assemblage; anything
greater may be “overkill” and add additional time, effort, and costs to the study. This ratio
of nets/ha may serve as a guide for future studies.
Trapping Considerations for Researchers
Our results indicate that capture method can dramatically influence the perception of
turtle assemblage composition. Hoop nets have been the standard trapping method since
the 1960s because of their simplicity and low cost (Iverson 1979, Mali et al. 2014, Plummer
1979). However, we found that they recorded a less representative and vastly different
turtle assemblage and were not as cost effective as fyke nets (Tables 1, 2). Because fyke nets
produced a substantially higher CPUE and higher species richness, we agree with Dreslik
et al. (2005) that they provide a better estimation of turtle assemblage dynamics. In general,
fyke nets may be overlooked by researchers because they are more expensive and bulkier
to transport in the field. However, researchers have consistently reported high capture rates
and minimal turtle mortality, and because they are unbaited, they are a less-biased sampling
method (Bury 2011, Dreslik et al. 2005, Selman and Baccigalopi 2012, Vogt 1980, Wallace
et al. 2007). We acknowledge that, while fyke nets are effective in slow-moving rivers and
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Vol. 9, 2022 No. 52
10
ponds, they may be less effective in faster currents because of high flow rates that may dislodge
the nets (Sterrett et al. 2010, Vogt 1980).
Based on our results, fyke nets are capable of capturing more turtles and more adequately
sampling the turtle assemblage with less effort than other trapping methods in a
lentic environment. One remaining question with the study is why the smallest turtle species
(e.g., Mud Turtles and Stinkpots) were rarely captured, even by the fyke nets. This finding
could be the result of our larger mesh size (i.e., smaller individuals escaping from the net),
or it may indicate a habitat with low densities of Kinosternid species. Additional studies
on the roles of bait type and mesh size in accurate documentation of turtle assemblages are
warranted, along with long-term monitoring of the potential homogenization of turtle assemblages
dominated by generalist species like Red-eared Slider s.
Acknowledgements
Funding for this project was provided to GB through a Howard Hughes Medical Institute research
fellowship and to WS through Millsaps College research startup funds. Scott Payton and Bob Jones
(Mississippi Museum of Natural Science) assisted with many logistical aspects of the study. Numerous
Millsaps College undergraduates assisted with this study, including Drew Carter, Aaron Anderson,
Haley Smith, McAulay Jaunsen, Luciano Bartolozzi, Kim Manley, Langston Haden, Richard Murray,
Payton Passantino, Jessica Hackett, and John Houston Robertson. This study was approved by the
Mississippi Museum of Natural Science (Permit 0329181), and vertebrate animal research protocols
were approved by the Millsaps College Animal Care and Use Committee (WS041717).
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