Until 2014 the genus Macrochelys was considered to consist of a single, monotypic species, M. temminckii; however, Thomas et al. (2014) described the Suwannee Alligator Snapping Turtle (M. suwanniensis) as a distinct species based on genetic and morphological differences. This finding agrees with the distinct Suwannee genetic assemblage proposed by Roman et al. (1999) and Echelle et al. (2010). Thomas et al. (2014) found Roman’s eastern assemblage (Suwannee lineage) to be the most distinct both genetically and morphologically. Several other studies found M. suwanniensis to be a distinct species (Murray 2014, Folt and Guyer 2015), and it has been recognized by Crother (2017) and TTWG (2021).

Populations of Alligator Snapping Turtles (Macrochelys suwanniensis) may have declined sharply in the Suwannee River since the 1930s due to overharvest; personal communications have indicated that trapping pressure was intense until approximately 1973 in the upper Suwannee River as far upstream as the entrance to Stephen C. Foster State Park and that the Withlacoochee River in Georgia was considered “trapped out” by 1982 (Pritchard 1989). However, there is no evidence of commercial trapping in other portions of the Suwannee drainage, and M. suwanniensis is still present in all large tributaries (including the Withlacoochee River) and many small tributaries. Commercial harvest was prohibited in Florida in 1972 and in Georgia in 1989. All “take” was prohibited in Florida in 2009 and in Georgia in 1992, when the species was listed as Threatened. Subsistence or incidental harvest of the species has probably occurred at low levels for a long time. However, in our opinion, there is no evidence of an observed, estimated, inferred, or suspected population size reduction of at least 30% in the past or future 90 years (three generations) throughout the Suwannee drainage, so we do not believe that the species meets any of the A criteria of population size reduction for ranking as Vulnerable at this time.

The Suwannee drainage basin encompasses 25,830 sq. km, and the historical extent of occurrence (EOO) is just over 30,000 sq. km, which is greater than the 20,000 sq. km EOO criterion for Vulnerable. Regarding area of occupancy, we could not create the recommended grid of 2 km x 2 km cells to determine how many were occupied. However, we calculated the length of all major occupied streams, excluding occupied streams <20 km long (Ichetucknee River, Hunter Creek, and Rocky Creek) and the Okefenokee Swamp (1,770 sq. km), where area of occupancy is unknown. We are excluding the Homosassa River, because we do not know whether this represents a natural population. We used the following publicly available lengths of occupied rivers and streams: Suwannee River (396 km), Alapaha River (325 km), Withlacoochee River (185 km), Little River (169km), Santa Fe River (121 km), Okapilco Creek (101 km), Suwannoochee Creek (79 km), New River (Withlacoochee tributary, 55 km), Willacoochee River (34 km), and Alapahoochee River (23 km). We estimated the lengths of the following occupied streams: Warrior Creek (60 km), Piscola Creek (55 km), Jones Creek (55 km), New River (Santa Fe tributary, 40 km), Olustee Creek (30 km), Toms Creek (30 km), and Cypress Creek (20 km). The estimated total length of all these streams is 1,778 km. If we apply the 2 km x 2 km grid, the minimum current area of occupancy is 3,556 sq. km, which is more than the 2,000 sq. km geographic range B criterion for ranking as Vulnerable. There are at least 17 known locations for the species, which we identified as streams where most of the population could be negatively impacted by a chemical spill from a road or railway crossing near their headwaters. This is higher than the 10 locations for ranking as Vulnerable.

The estimated population size from White Springs to the estuary of the Suwannee River was 1,350 adults or 5.2 adults/river km. If we assume four adults/river km as an estimated average within the entire current area of occupancy, then the extrapolated population size for 1,778 km of occupied streams is 7,112 adults. The upstream reaches of some of these streams may not be occupied, but this is offset by excluding occupied streams <20 km long and the Okefenokee Swamp. Based on this analysis, we estimate that there are <10,000 adult M. suwanniensis in the Suwannee drainage. In the USFWS (2020) Species Status Assessment, two experts estimated a population size of 2,000 individuals (500‒5,000, 50% CI) in the Suwannee drainage based on extrapolation from localized experience; they used a female-only, stage-structured matrix population model to predict a decline in abundance and range, with the species facing extinction in 50 years. Predicted abundances had a >66% probability of dropping below 5% of current abundances within 50 years, and time to quasi-extinction in the Suwannee River basin was between 32 and 42 years. However, this model used an annual adult survival estimate of 0.95, which was based on a long-term mark-recapture study conducted in a different system (Spring Creek, Georgia; see Folt et al. 2016). Instead, annual survival rates in the Suwannee River are much higher (0.99) for adults, based on a mark-recapture study using a similar matrix model. Therefore, we believe that the USFWS estimate is likely inaccurate, and we are of the opinion that the species does not meet the criterion for ranking as Vulnerable under the quantitative analysis E criterion (i.e., ≥10% probability of going extinct in the wild in 100 years).

The population in the Suwannee River during the past 12 years may be slightly declining or possibly stable, but we suspect that at least a 10% decline in populations is likely to occur in the next 90 years (three generations) because of continued incidental bycatch by passive fishing lines for catfish and active fishing by recreational anglers (mortality rates unknown) and reduced minimum flows in rivers decreasing the amount of suitable habitat. Reduced minimum flows will result from increased human population growth and agricultural development, increasing groundwater withdrawal and climate change resulting in more severe droughts. Habitat quality for turtles is likely to decrease because of water pollution from agriculture and reduction in woody structure favoured by turtles. As a result, we assess M. suwanniensis as meeting criterion C1 for a small population size (<10,000 adults) and a projected population decline of at least 10% over three generations, for a ranking as Vulnerable (VU C1). The species was previously provisionally assessed as Vulnerable in 2018 by the IUCN Tortoise and Freshwater Turtle Specialist Group (Rhodin et al. 2018).

Macrochelys suwanniensis is mostly confined to the Suwannee River drainage, which covers an estimated 28,500 sq. km in northern Florida and southern Georgia. The species can be found in several of the Suwannee's major tributaries (i.e., Alapaha, Withlacoochee, and Santa Fe rivers) and in small streams in these systems (i.e., Alapahoochee River, Little River, New River, Cow Creek, Ichetucknee River, New River, Olustee Creek, Okapilco Creek, Piscola Creek, Warrior Creek, and Willacoochee River) (see Jensen and Birkhead 2003, Enge et al. 2021, Johnston et al. 2015, Jackson and Thomas 2018, Enge and Steen 2020, Enge et al. 2021, TTWG 2021).

The estimated historical indigenous range (area of occupancy, AOO) for the species was ca 15,666 sq. km and the estimated historical indigenous extent of occurrence (EOO) as calculated from a minimum convex polygon was ca 30,617 sq. km (TTWG in press). The current AOO is much smaller than the historical estimate, presently estimated at ca 3,556 sq. km based on the lengths of occupied rivers, streams, and creeks. Macrochelys suwanniensis occurs from an altitude of 0 m at the mouth of the Suwannee River in Florida to 105 m asl upstream at the Withlacoochee drainage in Georgia.

Recently, a disjunct population was verified in the Homosassa River, Citrus Co., Florida (Enge 2023), which is >70 km from the mouth of the Suwannee River. Currently, efforts are underway to ascertain whether the origin of this population is an introduction or whether it represents a natural, extralimital population. Most of the individuals in this population appear morphologically similar to M. suwanniensis; but genetic samples have been taken, and results are pending.

Pritchard (1989) speculated that populations of Alligator Snapping Turtles (referring to what later became described as Macrochelys suwanniensis) may have declined sharply in the Suwannee River since the 1930s due to overharvest. Personal communications indicated that trapping pressure was intense until approximately 1973 in the upper Suwannee River as far upstream as the entrance to Stephen C. Foster State Park and that the Withlacoochee River in Georgia was considered “trapped out” in 1982 (Pritchard 1989). However, there is no evidence of commercial trapping in other portions of the Suwannee drainage, and turtles are still present in all large tributaries (including the Withlacoochee River) and many small tributaries (Enge et al. 2021). 

Based on a capture-mark-recapture study at 10 sites along the Suwannee River in Florida, Thomas et al. (2022) estimated a population density of M. suwanniensis as ca seven turtles/river km, indicating a population of 1,709 (1,205–2,694 95% CI) animals from the town of White Springs to the Suwannee estuary (approximately 259 river km). Based on 79% of captures being adults, the estimated adult population size in this stretch of river is 1,350 or 5.2 adults/river km. If one assumes four adults/river km as an estimated average within the entire current area of occupancy, then the extrapolated population size for 1,778 km of occupied streams is 7,112 adults. The upstream reaches of some of these streams may not be occupied, but this is offset by excluding occupied streams <20 km long and the Okefenokee Swamp. Based on this analysis, we suspect that there are <10,000 adults in the Suwannee drainage. Both adult males and females had a very high annual apparent survival rate of 0.99, whereas juveniles had a much lower apparent survival rate of 0.455 (Thomas et al. 2022). 

Catch-per-unit-effort (CPUE) was higher in the middle section than in the upper and lower sections of the Suwannee River in Florida (Enge et al. 2021, Thomas et al. 2023). Interestingly, CPUE was very low in the estuary and upstream of White Springs in Florida and Georgia (Enge et al. 2021, Thomas et al. 2023). Overall, CPUE in tributary streams was apparently lower in Georgia than in Florida and CPUE was higher in the Alapaha River than in the Withlacoochee River (Enge et al. 2021), and subsequent trapping of the Alapaha River yielded an overall CPUE of 0.24 in 420 trap nights (D. Stevenson, unpubl. data). Enge et al. (2021) could not conclude that some streams lacked M. suwanniensis or had a low or high relative abundance because trapping effort in some areas was insufficient, or trapping conditions were poor because of low water levels and stream current. 

The current population trend for M. suwanniensis is unclear. A female-based, stage-structured matrix model suggested an “uncertain” population that could be slightly decreasing or increasing, with the population growth rate being most sensitive to changes in adult survival (Thomas et al. 2022). Based on limited harvest pressure and a population demography that includes juveniles and large adults, populations are probably stable in the Florida portion of the Suwannee River, the Santa Fe River, and the Alapaha River in Georgia (Enge et al. 2021); however, more research is needed to confirm this. The species may never have been common in the upper Suwannee River mainstem in Georgia (Jensen and Birkhead 2003).

Research on populations of Macrochelys suwanniensis in the Suwannee drainage in Florida has provided some insights into its habitat and ecology, which appears to be similar to that of the well-studied M. temminckii (Ewert et al. 2006). The species inhabits blackwater and calcareous, spring-fed streams within the Suwannee drainage. However, habitat use is dynamic and changes with water levels, with turtles extensively utilizing floodplains in flooded conditions (Thomas et al. 2023, 2024). Overall, M. suwanniensis prefers subsurface cover, typically woody debris or undercut banks (Thomas et al. 2023, 2024). During normal water levels, M. suwanniensis uses shallow areas that are typically associated with river bank habitat (Thomas et al. 2023, 2024).

Dobie (1971) found that both sexes of M. temminckii in Louisiana attained sexual maturity in 11–13 years, but other researchers have suggested maturity requires 13−21 years in females and 11−21 years in males (Sloan et al. 1996, Tucker and Sloan 1997). Five juvenile M. suwanniensis in the upper Santa Fe River grew 12.3‒18.9 mm/year, leading to an estimated age of sexual maturity of ca 19 years for females and 22 years for males (Johnston et al. 2012). The estimated mean generation length for M. suwanniensis is 30 years.

The mean SCL (straight-midline carapace length) of adult males in the Suwannee River was 50.0 cm and ranged from 43.1 to 65.0 cm (Thomas et al. 2023). The mean SCL of adult females was 41.5 cm and ranged from 34.4 to 47.0 cm (Thomas et al. 2023, 2024). Adult females were significantly larger (SCL) in the upper Santa Fe River (mean = 43.6 cm, range = 33.6‒49.2 cm) than in the lower Santa Fe River (mean = 40.7 cm, range = 32.9‒44.9 cm), but male size did not differ between river sections, although the six largest males (>60.0 cm SCL) came from the lower section (Johnston et al. 2015). In the Alapaha and Withlacoochee River drainages in Georgia, females measured 34.0‒47.2 cm SCL and males 37.5‒59.0 cm SCL (Stegenga 2019, Stevenson 2019). The maximum size for the species was a turtle from the Suwannee River near White Springs, which had an SCL of 71.3 cm (Johnston et al. 2023); however, this animal had been kept in captivity for an unknown duration.

Two M. suwanniensis clutches that were salvaged because of flooding concerns contained 43 and 47 eggs (Jackson and Thomas 2018). A radiographed female from the Suwannee River contained 32 eggs (Thomas and Enge, unpubl. data). Captive M. suwanniensis deposited a mean of 24.5 eggs (n = 6, range 16–44) (Allen and Neill 1950). Clutch sizes for M. suwanniensis appear comparable to those of M. temminckii along the lower Apalachicola River in Florida, which averaged ca 36 eggs (range 17−52) (Ewert and Jackson 1994).

Research has suggested that turtles in general extensively utilize in-stream woody debris. However, the State of Florida initiated a deadhead log removal programme in 2000, and between 2000–2008, more than 16,000 logs were removed from Florida rivers, but this is likely a conservative estimate (Kaeser and Litts 2008). Removal of any woody debris from the Suwannee River and its tributaries could have a negative impact on Macrochelys suwanniensis because of its importance as primary refugia during low-water periods. Another threat is pollution. For example, the city of Valdosta, Georgia, had major sewage spills of suspended solids into the Withlacoochee River from its wastewater treatment plant in March, July, and August in 2013 and three documented spills in 2023.

Groundwater withdrawal that results in reduced flow of springs and rivers potentially threatens M. suwanniensis. Water levels in the Floridan Aquifer have declined in northern Florida over the past 70 years because of groundwater extraction for human use and reduced groundwater recharge due to surface drainage alterations (Knight 2015). 

While harvest is now illegal, some incidental mortality will continue from accidental ingestion/entanglement of fishing tackle. Ingested fishhooks can perforate the digestive tract lining and eventually cause death in turtles, including Alligator Snappers, as well as population declines (Steen and Robinson 2017). The monofilament or gel spun fishing line attached to the hook can cause severe digestive blockage resulting in injury or death (D. Heard pers. comm.). Of 26 turtles of both sexes and all ages radiographed in the Suwannee drainage, 15.4% had hooks lodged in their upper gastrointestinal tracts (Shook et al. 2023). These ingested hooks may have been from bush hooks (i.e., limb lines), which are single hooks suspended from tree branches, or trotlines set for catfish. Five turtles were caught on about 10 hooks baited with fish in December on the Suwannee River in Florida (Enge and Murray 2021). Trotlines also can catch Macrochelys (Pritchard 1989); recreational trotlines in Florida are restricted to a maximum of 25 hooks. Recreational anglers, particularly those fishing at night for catfish, occasionally catch M. suwanniensis (Enge et al. 2014). However, anglers also catch M. suwanniensis during the day (Shook et al. 2023); a small juvenile near a boat ramp on the Suwannee River contained five hooks (Enge and Thomas, unpubl. data). Enge et al. (2014) trapped a turtle from Dowling Park on the Suwannee River that had a fishing hook embedded in its upper left forelimb, and a juvenile from the Withlacoochee River and two juveniles from the Alapaha River in Georgia had fishhooks in their mouths (D.J. Stevenson, pers. obs.). Another potential threat is injuries or even death from boat propellers in the larger streams, where propeller damage on carapaces has been observed (Enge et al. 2014, Shook et al. 2023).

Harvest of Macrochelys suwanniensis for food or pets is now illegal in Florida and Georgia, but some low level of harvest may still be occurring. Illegal harvest (i.e., “take”) is probably not targeted and likely consists of turtles incidentally captured on passive fishing lines set for catfish (Enge and Murray 2021, Enge et al. 2021, Shook et al. 2023). Hatchling M. temminckii are readily available from turtle farms, so unless a collector specifically wants M. suwanniensis for a pet or exhibit, there is no need to harvest them from the wild. Based on genetic analyses, none of the approximately 40 Macrochelys recently confiscated during two incidents in Florida were M. suwanniensis.

Florida prohibited the sale of Macrochelys in 1972, effectively banning commercial harvest. Georgia prohibited commercial harvest in 1989. Florida listed Macrochelys as a Species of Special Concern until July 2009, when rule changes prohibited the take of all Macrochelys. Florida listed M. suwanniensis as Threatened in December 2018. Georgia listed Macrochelys as Threatened in 1992. In 2006, M. temminckii was included in Appendix III of CITES and in 2023 was uplisted to Apppendix II, and since CITES does not yet officially recognize M. suwanniensis as a separate species, it is also subject to CITES regulations. The draft Species Status Assessment for M. suwanniensis was completed in 2020 (USFWS 2020). The 12-month finding by the USFWS (2021) determined that M. suwanniensis warranted listing as Threatened.

Conservation Needed is as follows: 1. Land/water protection  1.1. Site/area protection = Expanding state/federally owned conservation lands within the basin.   1.2. Resource & habitat protection = Stop the removal of “deadhead” logs (submerged timber) and woody debris in the Suwannee River drainage. Expand conservation areas within the floodplain to limit development.  2. Land/water management 2.1. Site/area management = expand water quality measurements and re-evaluate minimum flow recommendations. Limit sewage spills within the upper drainage near Valdosta, Georgia.  2.2. Invasive/problematic species control = monitor turtles for pathogens.  2.3. Habitat & natural process restoration = manage groundwater runoff from nearby agriculture to remove pollutants.   3. Species management 3.1. Species management = Establish a long-term monitoring programme for the species within the drainage. 3.1.1. Harvest management = all harvest/take should remain illegal.   4. Education & awareness 4.1. Formal education = enhance the awareness of this species and its threats to local schools and universities. 4.2. Training = positively influence the general public’s behaviours to reduce mortality of adults from fishing/turtle interactions. 4.3. Awareness & communications = Utilize public universities extension and outreach networks to engage stakeholders and the general public’s knowledge of this species’ status and threats. 5. Law & policy 5.1. Legislation 5.1.4. Scale unspecified = Provide up to date information on conservation status to state and federal agencies.  5.2. Policies and regulations = Implement, at all levels, conservation actions to conserve this species and its habitat. 5.3. Private sector standards & codes 5.4. Compliance and enforcement 5.4.4. Scale unspecified

Research Needed is as follows: 1.2 Population size, distribution & trends = More accurate apparent survival rates are needed for juveniles and subadults. Hatching survival remains unknown. More information concerning this species distribution is needed in smaller streams and creeks within the drainage. 1.3 Life history & ecology = Only a handful of accounts are available concerning this species’ nesting, and information on important nesting movements and clutch size are lacking. In addition, information on nest success and survivorship is needed in order to produce more accurate models of population status. 1.4 Harvest, use & livelihoods = NA 1.5 Threats = Research is needed to investigate the threat of incidental mortality from passive and active fishing methods. 1.6 Actions = Establishment of studies to assess these threats and how they potentially affect turtle population persistence are needed.