The Alligator Snapping Turtle, Macrochelys temminckii, was initially placed in the genus Macroclemys throughout much of the late 20th century until it was revised due to the genus Macrochelys having nomenclatural priority (Webb 1995).

Genetic research found significant divergence in the Suwannee River populations (Roman et al. 1999, Echelle et al. 2010), further supported by morphological analyses (Murray et al. 2014, Thomas et al. 2014), which led to taxonomic revision recognizing the Suwannee River populations as M. suwanniensis (Thomas et al. 2014).

Distinctions were also noted for the Apalachicola River population, prompting description as M. apalachicolae (Thomas et al. 2014). The taxonomic distinctiveness of M. apalachicolae was contested, and the recommendation was to subsume M. apalachicolae back into M. temminckii (Folt and Guyer 2015). However, the genetic lineage representing the Alligator Snapping Turtle populations in the Apalachicola River and adjacent drainages has been further confirmed by next-generation sequencing of a large, range-wide sample of Macrochelys specimens (Apodaca et al. 2023), although no taxonomic or nomenclatural recommendations were made. The current nomenclatural arrangement recognizes only M. temminckii and M. suwanniensis (TTWG 2021).

The Western Alligator Snapping Turtle, Macrochelys temminckii, has experienced a significant decline exceeding 50% across its historic distribution within the last ca 100 years, equivalent to three generations. Although more precise quantification in distributional status and abundance estimates are needed, the decline has been influenced by commercial and recreational overharvesting, habitat degradation, loss, and fragmentation, and increased nest and juvenile turtle predation, particularly from subsidized mesopredators. The chronic synergistic and cumulative impacts of such factors since the 1950s suggest a substantial population reduction by at least 50% (criterion A2). The declines, characterized by reversible and irreversible impacts, are significant enough to categorize M. temminckii as Endangered (EN) under criteria A2bcd+4bcd, considering the past three generations or the ongoing last two generations with projections for the next generation (criterion A4). Furthermore, an assessment conducted by the USFWS (2021a) indicated that M. temminckii qualifies for listing as Threatened under the U.S. Endangered Species Act, implying a high likelihood of the species becoming Endangered in the foreseeable future across its entire range or a substantial portion thereof. The current assessment reflects the precarious status of M. temminckii and the urgency of needed conservation efforts. The species was previously assessed in 1996 as Vulnerable (VU) (TFTSG 1996) and provisionally re-assessed in 2011 as Vulnerable (Rhodin et al. 2018, TTWG 2021).

The distribution of Macrochelys temminckii is centred in the south-central and southeastern United States within river systems draining into the Gulf of Mexico, from the Apalachicola River system in Florida and Georgia westward to the Buffalo Bayou, Brazos, and San Bernard drainages in Texas. Its range formerly extended upstream within the Mississippi River system, reaching western Illinois and Indiana, northern Missouri, and potentially Iowa, with Alabama, Mississippi, and Louisiana representing the core of its range (Iverson 1992, Ernst and Lovich 2009, TTWG 2021). Specifically, the states historically inhabited are Alabama, Arkansas, Florida, Georgia, Illinois, Indiana, Kansas, Kentucky, Louisiana, Mississippi, Missouri, Oklahoma, Tennessee, and Texas. Extralimital records within the United States have been recorded for Arizona, California, northern Indiana, northeastern Virginia, Oregon, Puerto Rico, southwestern Michigan, and Washington D.C. (USGS 2023). In addition, the species has been found introduced or as pet releases in the following countries: China (Liu et al. 2021), Italy (Esposito et al. 2022), Japan (Ekawa 2005, Nambu 2001, Yoshinori and Tomomi 2022), Reunion Island (Boulay and Probst 1998), Spain (Poch et al. 2020), Republic of Korea (Kim et al. 2020, Koo et al. 2020, 2021), Taiwan, Province of China (Lee et al. 2019), United Kingdom (Langton et al. 2011).

The estimated historical indigenous range (area of occupancy, AOO) was 505,589 sq. km, as calculated using all HUC-12 watersheds with recorded or estimated historical occupancy (TTWG in press). The current AOO, reflective of records after 1990, is significantly decreased, with Indiana, Illinois, Kansas, northern Missouri, northeastern Oklahoma, and many peripheral historical populations apparently extirpated (Carr et al. 2023). The estimated historical indigenous extent of occurrence (EOO) was 1,406,452 sq. km, as calculated using a minimum convex polygon around all HUC-12 watersheds with recorded or estimated historical occupancy (TTWG in press). The current EOO is ca 1,051,342 sq. km, as calculated using a minimum convex polygon around all post-1990 locations, excluding likely extirpated populations (Carr et al. 2023; TTWG in press), a ca 25% reduction. Contraction of the EOO has occurred at the periphery of the range, notably with extirpations in Indiana, Illinois, northern Missouri, Kansas, and northeastern Oklahoma. The species has been recorded post-1993 at nearly 1,400 native locations, but of those, as many as about 400 no longer have contemporary observations, indicating a ca 29% recent decline in known locations (Carr et al. 2023).

Knowledge concerning population densities of Macrochelys temminckii is somewhat limited, with catch per unit effort approaches dominating. Within habitats unaffected by anthropogenic pressures, the species can attain high densities, as high as 28–34 individuals per stream km (Riedle et al. 2008a). Studies from Texas estimate densities at ca 4.43 turtles/river km with a population estimate of 173 individuals over a 39 km stretch of habitat during five years of study (Munscher et al. 2023). Contrastingly, populations influenced by chronic anthropogenic factors exhibit reduced population sizes relative to their unimpacted counterparts (Trauth et al. 1998, Shipman and Riedle 2008, Riedle et al. 2008a). In the western portion of its distribution, fragmentation from impoundments has impeded recruitment and movements, as observed by extirpations in Kansas due to such barriers in northern Oklahoma (Riedle et al. 2008b). The phenomenon of restricted movements and dispersal within watersheds warrants thorough investigation. The USFWS (2021a) has proposed a total range-wide population estimate for M. temminckii of between 68,154 and 1,436,825 adults, with a mean estimate of 361,213, with little supporting evidence of how these estimates were derived (USFWS 2021a).

The available population data illustrates that M. temminckii has historically constituted a substantial proportion of turtle populations within aquatic ecosystems within its range. The assertion is substantiated by historical data indicating the species constituted between 4–12.5% of the total turtle catch across four sites in Louisiana in 1947 (Cagle and Chaney 1950). Across three sites in Alabama, it comprised 18% of the trapped turtle specimens (Godwin 2004). At 70 sites across Mississippi, the species comprised only 2.3% of trapped turtles in the Tombigbee River drainage, but up to 50% of trapped turtles in the Mississippi River alluvial plain (Berry 2019, Haralson 2022). Notably, in Oklahoma, it comprised only 2–6% of turtle captures (Riedle et al. 2009). Comparatively, trapping efforts in Florida yielded threefold higher capture rates of larger individuals per unit effort than the extensively exploited Flint River in Georgia (Ewert et al. 2006).

Notable population declines have occurred in Oklahoma and Missouri, with the causative factors attributed to a dual impact of extensive harvesting and alterations to the habitat through channelization, cold water release, and agricultural drainage (Riedle et al. 2005, Shipman and Riedle 2008, Riedle et al. 2009). The species' distribution has contracted from ca 60–70% of its former range in Oklahoma, alongside parallel findings in southeastern Missouri (Shipman and Riedle 2008); however, recently there appears to be some increase in sightings in Missouri (J.T. Briggler, Missouri Department of Conservation, pers. comm.) and in Oklahoma a few new populations have recently been documented, and repatriation efforts are underway in other areas (M. Howery, Oklahoma Department of Wildlife Conservation, pers. comm.). The species has been extirpated from Kansas (Riedle et al. 2008b) and apparently from Indiana and most of Illinois. Declines have also been noted in Arkansas (Trauth et al. 1998) but have not reached the same magnitude observed in Kansas, Missouri, or Oklahoma. In Texas, the species has apparently been nearly extirpated from the Brazos River watershed, although scattered records persist (Gordon et al. 2023a, Rosenbaum et al. 2023) and the species has recently been recorded in the San Bernard R. southwest of the Brazos (Ross et al. 2023).

Evidence from recent studies indicates a discernible decline in the adult turtle population at a site in Oklahoma, with comparisons between sampling in 2010 and surveys conducted between 1997–2000 affirming the trend (Riedle et al. 2008a). A comprehensive understanding of the population dynamics is provided from numerous literature sources, including Pritchard (1989), Trauth et al. (1998), Reed et al. (2002), Jensen and Birkhead (2003), Riedle et al. (2005), Ewert et al. (2006), Shipman and Riedle (2008), Ernst and Lovich (2009), Folt and Godwin (2013), Folt et al. (2016), Huntzinger et al. (2019, 2020), Garig et al. (2021), USFWS (2021a), and Munscher et al. (2023).

Historically elevated levels of commercial exploitation during the 1960s and 1970s significantly depleted populations (Reed et al. 2002). Population recovery is partially hindered by increasing fragmentation of rivers by impoundments, at least in the western portion of the species' range, leaving fragmented populations with little chance of up or downstream recruitment (Riedle et al. 2008b). Declines in Oklahoma and Kansas were simultaneous with the commercial overexploitation, although anecdotal evidence exists that illegal take continued through the early 2000s in southeastern Oklahoma.

The contemporary population trajectory indicates substantial reductions, as evident from the extirpations in Kansas (Riedle et al. 2008b), Indiana, Kentucky (Baxley et al. 2014), and Illinois, and the continued range contraction in Oklahoma (Riedle et al. 2005). Comparable declines have occurred in southeastern Missouri (Shipman and Riedle 2008), likely related to the associated decline in Arkansas. While a decline had occurred in Arkansas based on sampling in three streams, it did not reach the same level as other states as based on catch per unit effort (Trauth et al. 1998). A later study of one of the three streams, Salado Creek (Trauth et al. 2016), found the population size estimates had increased, and average male and female sizes had increased, indicative of a partial recovery from depressed levels from prior turtle harvesting in the area.

Data available for M. temminckii populations in Georgia (including estimations of abundance from catch-per-unit-effort [CPUE] survey data as well as population modelling from a long-term data set collected from a natural population) neither indicate precipitous population declines, nor population growth or recovery over the last ca 20 years (Folt et al. 2016, King et al. 2016; T.M. Floyd pers. comm.). Instead, taken as a whole, the data suggest a slow gradual recovery of populations; the lack of an increase in estimated relative abundance in Georgia for such a long-lived species that takes so long to reach sexual maturity is hardly surprising, since the enactment of conservation measures, such as harvest prohibition, have only been in place in Georgia for a small fraction of the species’ life span (T.M. Floyd pers. comm.).

Although quantifiable data are sparse, an emerging concern centres around using setlines (such as trotlines and limblines) in recreational fishing activities (USFWS 2021). A preliminary investigation in Oklahoma suggested a correlation between the increase in setline fishing and declines in adult populations of M. temminckii (Riedle, unpubl. data). Both recent (2020–2021) and historical (1999–2001) surveys in Texas have documented a significantly lower M. temminckii catch per unit effort (CPUE) at sites with trotlines present as opposed to those without (Rosenbaum et al. 2023). Both single-hook fixed line and trotline fishing gears have been identified as significant sources of mortality across the entire range of M. temminckii (Shook et al. 2023). Further comprehensive analysis is warranted to ascertain the extent of this hazard and its potential implications for the species' population viability.

The Western Alligator Snapping Turtle primarily inhabits rivers and flooded channels within floodplain swamps (Ernst and Lovich, 2009). Additionally, it is found in various aquatic environments, including creeks, bayous, floodplain lakes, oxbows, and swamps, with a preference for permanent water bodies (Dundee and Rossman 1979, Boundy and Carr 2017). An overview of movement and habitat use suggests that Macrochelys temminckii uses habitats with deeper water depths than other turtles (Riedle et al. 2015). Ambient temperature regimes can influence the depth used within sites (Fitzgerald and Nelson 2011). Deeper depths provide the depth variation required for thermoregulation in M. temminckii (Riedle et al. 2006, Fitzgerald and Nelson 2011). Additionally, there are ontogenetic shifts in depth use, with smaller age classes using smaller, shallow tributaries or shallower depths in lentic habitats (Bass 2007, Hyder et al. 2021, Brown 2023). Hatchling-sized M. temminckii were found at depths significantly more shallow than random points, with a mean of 34 cm and median of 12 cm in Louisiana (Bass 2007) and Oklahoma (Spangler et al. 2021), respectively. The same was true for a group of translocated, head-started juveniles (2-, 3-, and 4-year-olds) in Louisiana in oxbow lakes (Townsend 2016), with mean depths of 38, 43, and 52 cm deep selected, respectively. Mean water depths used by subadults (mean CL = 26.5 cm) were 111 and 125 cm for males and females, respectively, in an impounded, linear bayou habitat (Harrel et al. 1996). Depths up to 9 m (P. Delisle, unpubl. data), shallow and heavily vegetated backwaters, and smaller tributaries are all important.

Movement: Distinct movement patterns are exhibited by the species, primarily among submerged structures, and it displays high site fidelity, often residing at specific sites for extended durations, potentially spanning several months. Extensive movements have been recorded, with documented cases of individuals moving up to 24.1 km within two months (Harrell et al. 1996, Trauth et al. 1998, Riedle et al. 2006, Howey and Dinkelacker 2009; P. Delisle, unpubl. data). Additionally, evidence suggests short-distance terrestrial forays among wetlands occurs (Shipman et al. 1991, Riedle et al. 2015; P. Delisle, unpubl. data). Notable examples of extreme movements include 22.5 km in 6 weeks in Mississippi (P. Delisle, unpubl. data), a 16 km displacement in two months in Oklahoma (Riedle et al. 2006), and a significant 22.5 km migration within one year by a large male in Texas (Munscher et al. 2021a). Historical data indicate such movements were likely influenced by stream dynamics preceding impoundments (Riedle et al. 2008, 2018).

Home Range: Spatial patterns using multiple methodologies show variation in home range across regions and illustrate the species' required area. Stage-specific patterns exist whereby adults use larger areas than younger turtles; however, no sex-specific patterns are apparent. In Florida, a translocated population demonstrated a minimum linear home range of 12.9 km for males and 10.6 km for females (Cozad et al. 2023). Work on a natural population in Louisiana revealed much smaller linear home ranges of 890 m for males and 389 m for females (Harrel et al. 1996), similar to the 481 m for males and 878 m for females in Oklahoma (Riedle et al. 2006). Linear home ranges of 1.3 km for males and 2.2 km for females in Missouri (Shipman and Riedle 2008) were similar to those in Texas, where linear home ranges were estimated as 1.6 and 2.3 km for males and females, respectively (Munscher et al. 2021b). In Mississippi, individuals exhibited linear home ranges of approximately 6 km for males, 5 km females, and 1.8 km for juveniles (P. Delisle, unpubl. data). Using Minimum Convex Polygon methodology (MCP), home ranges varied from 0.00945 ha for hatchlings in lentic/lake environments in Louisiana (Bass 2007) to 28.2 ha for males and 44.8 ha for females in natural populations (Ray 2010). Additionally, translocated and hatchery-raised individuals in a lentic/oxbow habitat in Louisiana had an MCP of 0.55 ha for juveniles (Townsend 2016). The most extensive spatial coverage was recorded in a mixed setting of translocated and natural adults in Louisiana, where home ranges varied from 0.7 to 247 ha (Sloan and Taylor 1987).

Body Size: The largest recorded M. temminckii was a male, achieving 74.0 cm in carapace length (CL) (Rosenbaum et al. 2023). Males consistently are larger in CL than females. In Alabama, males reach a mean CL of 52.8 cm, while females have a mean CL of 42.5 cm (Folt and Godwin 2013). Statewide sampling in Arkansas found turtles had an overall mean CL of 33.8 cm (Wagner et al. 1996). Sampling in Georgia found mean CL was 51.3 cm for males and 42.1 cm for females (Folt et al. 2016). A study across multiple sites in Louisiana found adults had a mean CL of 46.3 cm and 40.2 cm for males and females, respectively (Dobie 1971). In the northern regions of Louisiana, adult male mean CL ranged from 49.5–50.8 cm, with corresponding female CL ranging from 40.2–43.1 cm (Douglas 1989, Sloan et al, 1996, Tucker and Sloan 1997, Johnson et al. 2023b, Woosley 2005). In southeastern Louisiana, males have a mean CL of 47.2 cm, and females have a mean CL of 39.6 cm (Boundy and Kennedy 2006). In addition, immature males and females had mean CL of 34.5 and 33.8 cm, respectively (Tucker and Sloan 1997). In Mississippi, males had a mean CL of 46.5 cm, and females had a mean CL of 40.1 cm (Pearson, unpubl. data). Finally, two studies in Texas reported mean CL of 52.1– 51.6 cm and 42.1–42.8 cm for males and females, respectively (Munscher et al. 2023, Rosenbaum et al. 2023).

Following suit with body size, masses for M. temminckii can be high, with the largest recorded being 95.8 kg (Rosenbaum et al. 2023). Sexual dimorphism exists, with females weighing less than males; regionally, M. temminckii from Texas tends to be heavier than in the rest of the range. In Alabama, females average about 20 kg, with the largest reaching 55.3 cm CL (Godwin et al. 2023). In Arkansas, males had a mean mass of 25.6 kg, whereas females averaged 13.4 kg (Howey and Dinkelacker 2013). In northern Louisiana, adults averaged 20.4 kg (Douglas 1989); more specifically, mean masses for males ranged between 29.9–32.7 kg and for females 18.7–19.2 kg (Woosley 2005, Johnson et al. 2023b). In southeastern Louisiana, mass averaged 21.3 and 13.4 kg for males and females, respectively (Boundy and Kennedy 2006). Surveys in Mississippi documented mean masses of 26.3 and 16.4 kg for males and females, respectively (Pearson, unpubl. data). Research on Texas populations reported mean masses of 25.3–34.9 kg and 19.0–19.2 kg for males and females, respectively (Munscher et al. 2023, Rosenbaum et al. 2023).

Diet: Diets and foraging habits of M. temminckii show distinct ontogenetic shifting across life stages. Juveniles are ambush predators, primarily targeting fish for sustenance (Harrel and Stringer 1997). In contrast, the diets of larger individuals comprise numerous prey items, predominantly vertebrate animals, carrion, fruits, acorns, and other plant materials (Elsey 2006). Examination of stomach contents from 65 individuals identified the diet composition included acorns (43%), fish (57%), wood, and crayfish (Sloan et al. 1996). Another study analyzing 109 digestive tracts identified dietary categories with over 25% frequency, featuring crayfish, molluscs, insects, fish (80%), turtles, vegetation (99%), and non-food items such as fishing gear, rocks, and aluminium foil (Elsey 2006). Identifiable fishes corresponded with the most common species in the north Louisiana environment turtles occupied, i.e., various sunfishes (60% Centrachidae) and Gizzard Shad (Harrel and Stringer 1997). Being a large species requiring and having a broad diet, M. temminckii provides ecosystem services as predator, scavenger, and (possibly) a seed and plant disperser (Sloan et al. 1996, Elbers and Moll 2011).

Life History: More research is needed to understand some of the life history traits of the species. However, the existing work illustrates it follows the typical pattern of delayed sexual maturity as observed in many turtle species, making it extremely susceptible to chronic threats. Males mature at 11–13 years at a CL of ca 37.0 cm, whereas females mature between 11–16 years at ca 33.0 cm CL (Dobie 1971). Additional studies indicate males mature between 11–21 years and 37.8-41.0 cm CL and females between 13–21 and ca 32.7–37.0 cm CL (Tucker and Sloan 1997). Notably, these age and size thresholds mark key milestones in the reproductive lifecycle of the species. Longevity assessments suggest turtles may lie beyond 80 years (Ewert et al. 2006). Additionally, generation time calculations range from 31–49 years, with the former being derived from a demographic study in Georgia (Reed et al. 2002, Folt et al. 2016).

Reproduction: Current work indicates that M. temminckii has relatively low fecundity for its body size and thus likely lack resiliency to chronic and severe threats. Females deposit a single clutch annually (Dobie 1971, Tucker and Sloan 1997). Clutch size varies geographically, ranging from a mean of 24.5 eggs (range = 16–52) in Louisiana (Dobie 1971) to a mean of 35 eggs (range = 17–52) in the Apalachicola River region (Ewert et al. 1971, Jackson and Ewert 2023). A translocated population in Oklahoma had a mean clutch size of 22.4 eggs (range = 15–41) (Miller and Ligon 2014). Incubation periods observed for the translocated population spanned 79–96 days (Miller and Ligon 2014), whereas the interval from oviposition to emergence from nests in Louisiana averaged 115.3 days (range = 97–143) (Holcomb and Carr 2011). Louisiana hatchlings were 37.4 mm in CL and had a mass of 17.3 g (Bass 2007). Although foundational work exists, further work is needed to examine reproductive traits range-wide to help determine if clinal variation exists, what the drivers of fecundity are, and how such information translates to population resiliency.

The recent Species Status Assessment of Macrochelys temminckii by USFWS (2021a) identified four main threats to the species: legal and illegal harvest, fishing bycatch, habitat alteration, and nest predation. The conclusions were reached based primarily on expert elicitation. The top four threats identified within the IUCN Threat Scheme based on first-hand field observations and literature reports included, in descending order: (1) recreational fishing bycatch with hook-bearing gear; (2) intentional persecution by humans; (3) human infrastructure encounters; and (4) fishing bycatch with net devices (Shook et al. 2023). Human-turtle interactions threatening populations varied in the degree to which encounters were lethal—among the most dangerous were intentional shooting and bycatch by trotlines, a type of multi-hook fishing device (Shook et al. 2023). Demographic analyses concluded delayed maturation and high adult survivorship traits can confound recovery and exacerbate declines (Reed et al. 2002). Even less than a 2% annual harvest rate is unsustainable, and there is no evidence of sustainable adult harvest rates (Reed et al. 2002).

Harvest: Targeted exploitation has depleted populations in the Flint River, Georgia (Johnson 1989, King et al. 2016), across Louisiana (Sloan and Lovich 1995), and elsewhere (see USFWS 2021a) based on past commercial harvest of the species for consumption (Pritchard 1989). Personal, recreational harvesting is legal only in Louisiana and Mississippi (Shook et al. 2023, USFWS 2021a). Poaching is reported occasionally (e.g., DOJ 2017, Shook et al. 2023), but there is no single repository of information for federal (interstate or federal lands) and state-level cases. A recent study by Easter et al. (2023) identified 54 cases of illegal turtle trade from 1998–2021 (United States Department of Justice cases). Several violations were identified, but most were charged under the Lacey Act (interstate violations). In 47 of those cases with associated news articles, those with information about the driver of the illegal activity most often mentioned profit motives (38%) and the demand for pet turtles (40%), which was primarily international (43%) and originating from eastern Asia. In general, they recorded more cases throughout the study, and of the 34 turtle species identified, Macrochelys were recorded in six cases.

Pet trade for the species exists at domestic and international levels (CITES 2022). Exports from the United States have averaged around 34,000 individuals annually since 2006, when the species was added to Appendix III of CITES (CITES 2022). The three principal destinations reported through part of 2021 were (97%) China, Hong Kong SAR, and Macao SAR (CITES Trade Database 2023). Of approximately 515,500 reported individuals from the USA (2006–2021), virtually all were exported alive, and 98% were reportedly sourced from the wild (CITES Trade Database 2023). The live exports are undoubtedly primarily originating from captive facilities, so the impact on wild populations is unknown (CITES 2022).

Persecution is often associated with fishing when humans and turtles are brought into proximity, with shooting and blunt trauma being the main means of harming turtles (Shook et al. 2023). Fishing bycatch and the consequences of hook ingestion were identified by USFWS (2021a) as among the most serious threats (see Steen and Robinson 2017). Bycatch and commercial fishing for catfish and buffalo were specifically identified. Fishing net devices such as hoop nets and gill nets are more commonly associated with commercial fishing, and there is evidence of individual M. temminckii being captured and drowned in such gear (Shook et al. 2023).

Habitat Alteration & Destruction: Although M. temminckii is highly adaptable in habitat usage, significant threats exist from habitat degradation driven by river engineering practices. Such anthropogenic alteration, notably the reduction of silt load below dams, lowers the main channel, negatively impacting connectivity among swamp forest channels. Consequently, habitat quality, extent, and carrying capacity become degraded. The species experiences overwintering mortality due to flood control measures in pulsed systems, further accentuating the detrimental effects of habitat alteration (Dreslik et al. 2023; Kessler 2020, 2023). In Houston, Texas, no direct evidence of mortality has been observed within Buffalo Bayou due to flooding and being a pulse system (Munscher et al. 2021c). However, urban pulse systems are routinely altered and "improved" to limit flooding. Notably, the species encounters numerous additional anthropogenic threats associated with infrastructure related to various types of roads, occasional interactions with railroads, and structures related to water, such as swimming pools and cooling-water intakes (Shook et al. 2023). Additional threats highlighted encompassed recreational boat strikes, which may be on the rise, and encounters with industrial equipment such as dredging-type machinery (Shook et al. 2023). The findings illustrate the range of anthropogenic threats impacting populations and emphasize the urgency of conservation measures to mitigate habitat degradation and associated risks (Shook et al. 2023).

Nest Predation & Mortality: Nesting success is also under heavy ecological pressure from anthropogenically induced sources. Specifically, nest predation rates were notably high in Louisiana and Florida, reaching 87% in the latter (Ewert et al. 2006). Raccoons are the prominent nest predators, contributing to high nest predation rates (Redmond, 1979, Ewert et al. 2006). Mammalian nest predators in Louisiana included raccoons, armadillos, opossums, bobcats, and river otters (Holcomb and Carr 2013). The resurgence of river otters, attributed to targeted reintroductions in various regions, has been noted as impacting Alligator Snapping Turtles negatively, with growing otter populations posing an additional threat (Ligon and Reasor 2007; J. Kath, Illinois Department of Natural Resources, pers. comm.). Invertebrate predation on eggs and neonates from invasive Red Fire Ants and the Scaled Hump-backed Fly illustrate the additional threats to survival (Pritchard 1989; Ewert et al. 2006; Holcomb and Carr 2011a, 2011b, 2023). Additionally, non-biological factors, such as heavy rainfall leading to nest flooding, contribute to egg mortality within nests (Holcomb and Carr 2023). Collectively, these stressors underscore the pervasive threats to recruitment.

Genetic Loss: Genetic studies have revealed a history of population bottlenecks and remarkably low female dispersal rates across drainage basins (Echelle et al. 2010, Apodaca et al. 2023). The findings suggest restricted gene flow and limited genetic connectivity among populations, raising concerns about potential impacts on genetic diversity and adaptability. A more detailed genetic analysis conducted within the Yazoo River system in Mississippi further highlights significant genetic bottlenecks (Pearson 2021). The observation may explain the lower genetic diversity in western Mississippi compared to the eastern region (Pearson 2021). Unfortunately, more work should be conducted to examine additional population genetic patterns, critical for developing effective conservation strategies.

Macrochelys temminckii has experienced substantial anthropogenic pressures primarily through intense exploitation for subsistence consumption and trade (Pritchard 1989, Boundy and Kennedy 2006, Howey and Dinkelacker 2013, USFWS 2021a). Juveniles have been subjected to extensive trade within the pet industry, catering to the demand for exotic pets and supplying East Asian aquaculture enterprises. Furthermore, commercial farming activities targeting this species have been established in specific regions, including Arkansas, Florida, Louisiana, and Missouri (Hughes 1999). The species is consequently listed in CITES Appendix II as of February 2023 (CITES 2023), meaning although they are not imminently threatened with extinction in the wild, international trade must be regulated to avoid overexploitation. With this designation, an export permit is required for trade and issued by the CITES Management Authority (USFWS) only when the specimen was deemed legally obtained and its export not detrimental to the species' survival.

Macrochelys temminckii is protected through various state legislative regulations and is currently protected from commercial exploitation in all states and recreational take in all states except Louisiana and Mississippi. It has recently been assessed and recommended for inclusion under the U.S. Endangered Species Act as a Threatened species (USFWS 2021a, b). It was included in CITES Appendix III from 2004 to 2022 and transferred to Appendix II in February 2023 (CITES, 2023). NatureServe ranks it as G3 – Vulnerable, with the United States also being N3 – Vulnerable (NatureServe, 2023). By state ranks, it is S1 – Critically Imperiled in Illinois and Kentucky, S2 – Imperiled in Missouri, Oklahoma, and Texas, S2S3 Imperiled-Vulnerable in Tennessee, S3 – Vulnerable in Alabama, Florida, Georgia, Louisiana, and Mississippi, S3S4 – Vulnerable-Apparently Secure in Arkansas, and SH – Possibly Extinct in Indiana and SU – Unrankable in Iowa (NatureServe 2023). NatureServe does not provide an S rank for Kansas, but it would be SX – Presumed Extinct.

The species occurs in many protected areas throughout its range. Alabama: Choctaw NWR; Bon Secour NWR; Conecuh National Forest; Tuskegee National Forest, Fort Benning (Godwin et al. 2023). Arkansas: White River NWR; Cache River NWR; Holla Bend NWR; Big Lake NWR; Felsenthal NWR; Fort Chaffee, Little Rock Air Force Base, Camp Robinson Maneuver Training Center (Wagner et al. 1996; Trauth et al. 2004; DoD PARC 2021). Florida: The species occurs in several protected areas in Florida (Eglin AFB, Tyndall AFB, NAS Pensacola-NOLF Bronson Field; NAS Pensacola-Saufley Field NETPDTC; NAS Whiting Field; DoD PARC, 2021; Ewert et al. 2006). Georgia: Moody AFB, Fort Benning. Louisiana: Black Bayou Lake NWR (Sloan and Taylor 1987, Woosley 2005); Red River NWR (Bogosian 2010); Tensas River NWR (Johnson et al. 2023); Upper Ouachita NWR (Johnson et al. 2021); Barksdale AFB, Fort Johnson, Naval Air Station Joint Reserve Base New Orleans (DoD PARC 2021). Natchitoches National Fish Hatchery has been raising hatchlings for eventual release. Mississippi: Theodore Roosevelt NWR Complex; Tallahatchie NWR; Camp Shelby Joint Forces Training Center; Naval Construction Battalion Center Gulfport Stennis Western Maneuver Area; Bogue Chitto NWR; Mississippi Sandhill Crane NWR; DeSoto National Forest; Delta National Forest; Holly Springs National Forest (Pearson et al. 2023. Feist et al. 2018; J. Lee pers. comm.). Oklahoma: Little River National Wildlife Refuge, Tishomingo National Wildlife Refuge, Sequoyah National Wildlife Refuge, Deep Fork National Wildlife Refuge. A captive hatchery was established at Tishomingo National Fish Hatchery, and trial releases were conducted in Oklahoma, Louisiana, and Illinois (Dreslik et al. 2017). Texas: Red River Army Depot, Big Thicket National Preserve, Sam Houston National Forest, Trinity River National Wildlife Refuge, Buffalo Bayou Park System (Gordon et al. 2023, Munscher et al. 2023, Rosenbaum et al. 2023).

Conservation Actions by State:

Alabama: Designated as S3 (Vulnerable) by NatureServe (2023), the Alabama Department of Conservation and Natural Resources (ADCNR) listed M. temminckii as a protected non-game species in 1990 (Alabama Administrative Code r.220-2-.92; Folt and Godwin 2013). Originally assigned a P3 rank (moderate conservation concern) in the Alabama Wildlife Action Plan (ADCNR 2015), in 2002, the ADCNR Amphibian and Reptile Committee upgraded the rank to P2 (high conservation concern) for the species because of its low apparent abundance (Soehren and Godwin 2004). The first major status survey for the species sampled 11 major rivers in the state's southern portions and detected 93 turtles from seven of the systems (Folt and Godwin 2013). Targeted survey work in Alabama sampled 18 sites from 1995–2021, resulting in 174 individuals detected at six sites, thus helping fill gaps within the state's distribution (Godwin et al. 2023). Among the newly documented locations were urban habitats around Birmingham. Additional occurrence records were contributed based on captures during fisheries surveys, data which also contribute to our understanding of fishing gear interactions by documentation of the rates of capture of the species with trotlines and gill nets (Rider et al. 2023).

Arkansas: Designated as S3/S4 (Vulnerable/Apparently Secure) by NatureServe (2023), the species was protected against all harvest as of 1993 (Trauth et al. 1998, Wagner et al. 1996). It is not listed as an SGCN species within the Arkansas Wildlife Action Plan (Fowler 2015). A status survey conducted from 1994–1995 captured 445 individuals in 1,905 trap nights, which expanded its known range by 41 counties and affirmed its presence in 61 (Wagner et al. 1996). No statistical size differences were noted between counties open and closed to commercial harvest (Wagner et al. 1996). One population with historical harvest exhibited female-biased sex ratios (Howey and Dinkelacker 2013), whereas others had equal or male-biased adult sex ratios (Trauth et al. 1998, 2016). Density estimates for a northeast Arkansas population averaged 26 turtles per river km, ranging from 21.9–290 turtles per river km (Trauth et al. 2016). No recent species status surveys have been conducted in Arkansas since 1995, and current occurrence records rely on opportunistic observations, underscoring the necessity for updated assessments (Wagner et al. 1996).

Florida: Restricted to just the Panhandle populations, the species is designated as S3 (Vulnerable) by NatureServe (2023). Florida does not provide a protected status for the species; however, it is listed as SGCN (FWC, 2019). Recent surveys in the Ochlockonee, Apalachicola, Choctawhatchee, and Escambia River systems reported a CPUE of 0.21 (Enge et al. 2023), comparable to the 0.25 CPUE from a prior survey (Moler 1996). The recent survey confirmed its presence in 23 out of 26 surveyed streams, with additional records indicating its occurrence in another 21 untrapped streams (Enge et al. 2023). The comprehensive survey suggests similar population abundances and distributions between the 1996 and 2019 assessments.

Georgia: Designated as S3 (Vulnerable) by NatureServe (2023), the Georgia Department of Natural Resources (GDNR) protects the species as Threatened and lists it as SGCN in their wildlife action plan (GDNR 2015). Status surveys have shown no recovery following the closure of the commercial harvest, with a CPUE of 0.09 in the Flint River, comparable to surveys conducted 22 years earlier (King et al. 2016, Johnson 1989). Further, additional surveys in the Apalachicola and Ochlockonee rivers reported a low CPUE of 0.40 (Jensen and Birkhead 2003). For all surveys, CPUE values were well below the 1.0 CPUE anecdotal reports from the 1970s when commercial harvesters would capture 1,000 pounds (455 kg) of Macrochelys from a single hoop net (Johnson 1989, George 1988).

Illinois: Designated S1 (Critically Imperiled) by NatureServe (2023), listed as a Species in Greatest Need of Conservation (SGCN), and protected as Endangered (ILESPB 2020; IDNR 2005, 2015). A species status survey was conducted throughout the historical range, and no turtles were found (Bluett et al. 2011). Work then led to the forming of a recovery team and a plan to reintroduce the species from the appropriate mtDNA haplotype stock from Tishomingo National Fish Hatchery, supplemented with captive-reared and confiscated animals (Dreslik et al. 2017, Kessler et al. 2017). The initial pilot study was unsuccessful, as tracked turtles suffered mortality through anoxic conditions at a lentic site (Dreslik et al. 2017, Kessler et al. 2017). A second pilot study in a lotic system met with better success, barely achieving the survival performance metrics (Dreslik et al. 2017, Kessler et al. 2017). A formal 8-year reintroduction project commenced at the last known lotic habitat site for the species in Illinois (Dreslik et al. 2017, Kessler et al. 2017, Kessler 2020). Results from the study found mortality rates were too high, and the threats were high juvenile predation rates, overwinter mortality due to flooding and exposure, and bycatch in illegal trapping. Growth rates were also too slow, suggesting insufficient food resources, maladaptability of captive-reared stock, or the overall unsuitable climate (Kessler 2020, Dreslik et al. 2023). There has been a formal Illinois species status assessment (Ballard 2022) and species guidance document geared toward conservation and best management practices (Kessler 2023). After eight years of release, the reintroduction project was shuttered because it did not meet performance goals (Kessler 2020, Dreslik et al. 2023).

Indiana: Designated as SH (Presumed extirpated) by NatureServe (2023), and the Indiana Department of Natural Resources (INDNR) protects the species as Endangered and lists it as SGCN (INDNR 2015). Exploratory eDNA surveys have been conducted at sites in southwestern Indiana in the Patoka and White River watershed, where one positive result was detected. Subsequent trapping did not yield any captures, and systematic eDNA surveys throughout southwestern Indiana did not result in any detections (Kessler and Dreslik 2018, 2019, 2021).

Kansas: Not designated by NatureServe (2023), the Kansas Department of Wildlife and Parks currently lists it as a species in conservation need (SICN) Tier 2 SGCN (Rohweder 2022) due to a lack of known breeding populations in the state. The species is currently covered under a multi-species Candidate Conservation Agreement with Assurances/ Safe Harbor Agreement to allow for release in private waterways in Kansas (Riedle pers. comm.).

Kentucky: Designated as S1 (Critically Imperiled) by NatureServe (2023) and the Kentucky Department of Fish and Wildlife Resources (KDFWR) lists it as SGCN in their wildlife action plan but notes that it is a data deficient priority group (KDFWR 2023). Status surveys conducted at 24 sites for over 800 trap nights detected no individuals (Baxley et al. 2014). The current population status in Kentucky is unknown, with only three counties having records within the last 21 years (Caldwell, Calloway, and Hickman counties; USFWS 2021a).

Louisiana: Listed as SGCN (Holcomb et al. 2015) and designated S3 (Vulnerable) by NatureServe (2023). Louisiana allows the take of one individual per person per vehicle per day with a recreational fishing license (LDWF 2021). A translocation effort in a 3-state project was initiated over four years (2013–2016) to augment populations at two sites within Boeuf Wildlife Management Area in Caldwell Parish (Townsend 2016, Dreslik et al. 2017). Turtles have been recovered from those translocations and other translocated, head-started animals from the Monroe Fish Hatchery (Johnson et al. 2023a, Schwartz in prep.). Another augmentation with head-started turtles (2015–2016) from the Monroe Fish Hatchery involved releases into the Calcasieu River (Beauregard Parish) drainage in southwestern Louisiana (Glorioso et al. 2020). Status surveys in two portions of the state were completed in the last 12 years. Trapping was conducted in 2012–2013 at 15 sites in southwestern Louisiana for 731 trap-nights and yielded 14 captures (Huntzinger et al. 2019). Similar surveys in the northern part of the state (2018–2020) for 615 trap-nights at 19 sites yielded 66 individuals (Johnson et al. 2023a).

Mississippi: Classified as S3 (Vulnerable) by NatureServe (2023), and although not formally protected, the Mississippi Department of Wildlife Fisheries and Parks (MDWFP) classifies it as SGCN (MDWFP 2015). The species is continually monitored by the Mississippi Natural Heritage Program (MNHP 2018). Regulations permit the recreational harvest of one turtle per person annually, at a minimum CL of 61.0 cm, to protect mature females (MDWFP 2021). Status surveys in 2017 yielded 154 confirmed localities across 60 counties (Pearson et al. 2023). A CPUE analysis indicated higher abundance in larger river systems with adjacent wetlands, decreasing towards headwaters (Pearson et al. 2023). Populations in the Mississippi alluvial plain comprised more adults in better body condition, whereas Gulf coastal river drainages predominantly had more juveniles, constituting up to 80% of captures (Pearson 2021, Pearson et al. 2023). Surveys using eDNA detected the species in six of nine National Wildlife Refuges and traditional capture surveys detected turtles at a site with no eDNA detection (Feist et al. 2018, Pearson et al. 2023). Genetic assessments delineated discrete populations in each river drainage, with fine-scale intra-drainage genetic structuring present (Pearson 2021). A radio-tracking project in the Mississippi alluvial plain aims to provide data on home ranges, movement patterns, habitat use, and nesting locations (P. Delisle, unpubl. data). Notably, preliminary observations include the discovery of two dozen depredated nests, with an average conservative clutch size of 24 eggs from five nests (L. Pearson, pers. obs.). In addition, trapping efforts have been consistently applied at five selected sites to facilitate long-term monitoring since 2017.

Missouri: Designated as S2 (Imperiled) by NatureServe (2023), the Missouri Department of Conservation (MDOC) lists the species as SGCN (MDOC 2015). Some status surveys and spatial ecological work have occurred in the state (Lescher et al. 2013, Shipman and Riedle 2008). A status survey covering fifty sites with potential suitable habitats were visited in 1994, and 19 were trapped in Dunklin, Mississippi, New Madrid, and Pemiscot counties (Shipman and Riedle 2008). The surveys captured 37 turtles 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 (six males, four females, one unknown sex). Radio-equipped turtles used microhabitats with more cover, high-density canopy, and lower gradient banks than random locations (Shipman and Riedle 2008. There were significant differences in turtle size between sites with and without historical harvest, particularly along the Arkansas Border (Shipman and Riedle 2008). Lescher et al. (2013) resampled six sites in 2009 where the occurrence of M. temminckii had been documented in 1993 (Santhuff 1993) or 1994 (Shipman and Riedle 2008). They documented a decline in their measure of relative abundance (CPUE) and a decrease in the size structure of those populations with fewer adults of both sexes and more juveniles.

Oklahoma: Designated as S2 (Imperiled) by NatureServe (2023), the Oklahoma Department of Wildlife Conservation (ODWC) lists it as Tier I SGCN (ODWC 2016). The Natural Heritage State Rank for Oklahoma (S2) was last updated in the early 2000s and does not reflect the results of surveys since at least 2010 (M. Howery pers. comm.). Conservation work includes status surveys and work associated with a reintroduction programme. From 1997 to 1999, a status survey was conducted to identify extant populations and assess relative densities and viability (Riedle et al. 2005). Sixty-seven sites in 15 counties were surveyed across the historic distribution within the state, and 63 turtles were captured at 11 sites, all in the state's southeastern quarter and only in protected or isolated locations (Riedle et al. 2005). The authors concluded there appeared to be a significant range contraction in Oklahoma, and with so few sites exhibiting capture rates indicative of healthy populations, population declines had occurred in Oklahoma (Riedle et al. 2005). A mark-recapture project at Sequoyah National Wildlife Refuge between 1997–2000 found the population had equal sex ratios, marked sexual-size dimorphism, and population densities between 28 and 34 animals per km of stream (Riedle et al. 2008). The lack of large adults and an underrepresented cohort of subadults were hypothesized to be evidence of past population perturbations (Riedle et al. 2008). Follow-up sampling from 2010–2011 on the Sequoyah NWR revealed juveniles dominated the population, and the population lacked detections of large adult-size classes and small juveniles (East et al. 2013). A retrospective analysis of 1997–2001 data (Riedle et al. 2008) revealed that the population was likely to decline even at that time despite high capture rates, a concerning finding given the protection afforded by the national wildlife refuge (East et al. 2013). A reintroduction project in the Caney River and its tributary, Pond Creek, released 246 juveniles from 2008–2010. All turtles exhibited measurable growth by their first recapture 1–3 years after release, and no decline in body condition was observed (East et al. 2013). Apparent survival and recapture probabilities increased with age, and apparent survivorship was higher for turtles released in the main channel, whereas recapture probabilities were higher in the tributary (Anthony et al. 2015). The releases of captive-reared juveniles have continued through the present at the sites on the Caney and Verdigris rivers and the reintroduction effort on the Washita River has resulted in the successful hatching and growth of multiple size classes of juvenile turtles (M. Howery pers. comm.).

Tennessee: Designated as S2 by NatureServe (2023), and the Tennessee Wildlife Resources Agency (TWRA) lists the species as SGCN and Deemed in Need of Management (TWRA 2015). Limited conservation efforts have occurred. Status surveys conducted in western Tennessee spanning 65 sites yielded 22 turtles, nine of which were likely recaptures of turtles reintroduced in the early 2000s (Garig et al. 2021). The survey further concluded the species occurs at low densities within the region, potentially attributed to historical habitat modification (Garig et al. 2021). Despite the findings, the status of M. temminckii in central Tennessee rivers remains unknown due to a lack of contemporary surveys. However, recent observations near Saltillo in the Tennessee River suggest the species' presence, emphasizing the need for further investigation (R. Colvin pers. comm.).

Texas: Designated as S2 (Imperiled) by NatureServe (2023), the species has been protected as State Threatened since 1987 (Texas Register 1987), and it is listed as SGCN by the Texas Parks and Wildlife Department (TPWD 2005). It is unlawful to take or possess any freshwater turtle from the wild for commercial purposes and to possess more than six individuals of any freshwater turtle species. Texas Parks and Wildlife has rewards of up to $1,000 for any poaching report. Although there are prohibitions on take, there is a challenge to monitoring illegal harvest because most of Texas is private land (94%). An initial status assessment was conducted at 23 sites across the major river drainages of east Texas and detected 48 individuals at 17 sites, including the Sabine, Trinity, San Jacinto, and Brazos rivers (Rudolf et al. 2002). Follow-up surveys of these sites from 2020–2021 detected individuals at 18 of 22 historic sites and 29 additional, resulting in 221 turtles captured from 51 sites (Rosenbaum et al. 2023). A recent survey from 2021–2022 detected 69 individuals at 24 of 34 locations across 25 counties, with supporting genetic analyses revealing three metapopulations, one spanning the Red, Cypress, and Sulphur River basins, a second covering the Sabine and Neches River basins, and the third covering the San Jacinto and Trinity River basins (Gordon et al. 2023a). Detailed population research at Buffalo Bayou began in 2016 after discovering this urban population (Munscher et al. 2020, 2023). Work has identified 142 marked individuals at a density of 4.43 turtles/river km and biomass estimates of 89.9 kg/km. Capture rates remain high at 0.267–0.547 turtles per trap night, with a population estimated at 173 turtles (95% CI:138–250) and a sex ratio of 1.00M:1.28F (Munscher et al. 2023). The main issue with determining the extent of the species' presence and population status in the landscape is the limited access of wildlife research to private lands (Texas Center for Policy Studies 2000, Texas General Land Office 2019).