Population Structure and Body Size of the Suwannee Alligator Snapping Turtle (Macrochelys suwanniensis) in Northern Florida

Abstract

Macrochelys suwanniensis is a newly described species endemic to the Suwannee River drainage in the southeastern United States. We conducted a study of M. suwanniensis in the Santa Fe River (SFR), the major Florida tributary of the Suwannee River, between 2004 and 2011. We captured 109 individuals (24% immature, 44% adult female, 32% adult male). Adult males (mean straight midline carapace length [CL] = 530.7 mm, mean mass = 34.0 kg) were significantly larger than adult females (mean CL = 424.0 mm, mean mass = 17.2 kg), with a sexual size dimorphism index of 20.25 based on mean CL. The largest turtle in our study was 623 mm CL and weighed 54.4 kg. Adult females were significantly larger (CL) in the lower SFR than in the upper SFR (these reaches are separated where the river flows underground for 5 km). All adult males . 600 mm CL were captured in the lower SFR. Adult females were proportionately heavier in the upper SFR than in the lower SFR; males did not show this difference. We hypothesize that these differences in body size are related to habitat. The M. suwanniensis population in the SFR presently appears healthy, but we suggest this species requires continued protection because of vulnerability of adults to harvest.

Distribution and Relative Abundance of Macrochelys (Alligator Snapping Turtles) in the Florida Panhandle

“…Our sex ratio was skewed significantly towards males and was similar to the sex ratio found in northeastern Arkansas (Trauth et al 1998). Even adult sex ratios, which are consistent with predictions for long-lived turtles (Folt et al 2016), were found in Georgia (Jensen and Birkhead 2003), southeastern Louisiana (Boundy and Kennedy 2006), Oklahoma (Riedle et al 2008), and the lower Santa Fe River in Florida (Johnston et al 2015). In contrast, the Suwannee River had a highly malebiased sex ratio (3.8:1; Thomas et al 2023 [this issue]), whereas female-biased sex ratios (1:2) were found in the lower Apalachicola River (Ewert and Jackson 1994), upper Santa Fe River in Florida (Johnston et al 2015), and in Alabama (Folt and Godwin 2013).…”

“…Small and large streams contained all sizes of Macrochelys , but only 8.1% of our captures were juveniles. This is the smallest proportion of juveniles of any Macrochelys trapping study, although most surveys in Florida and Georgia found fewer than 25% juveniles (Jensen and Birkhead 2003, Johnston et al 2015, Moler 1996, Thomas et al 2023 [this issue]). However, 55% of Macrochelys trapped in the Flint River in Georgia were juveniles, possibly because of past commercial harvest of adults (King et al 2016).…”

Movements of marine and estuarine turtles during Hurricane Michael

“…Although reptiles are occasionally displaced by storms those dislocations are typically farther (i.e. tens of kilometers) than the small distance (~ 1.5 km) observed here 2 , 19 , 49 . Flooding from SJB eastward was severe during and immediately after Hurricane Michael 11 and this may have pushed the terrapin landward.…”

“…The diamondback terrapin is the smallest of all species tracked during the hurricane however this individual did not appear to be impacted during the storm's passage. While displacement of aquatic turtles, such as wood turtles (Glyptemys insculpta) and Johnstone River snapping turtles (Elseya irwini), has been documented during extreme flooding, the majority of individuals in these studies were not impacted by the floods 20,49,50 . It has been suggested that individuals bury themselves or remain on the bottom in deep water to avoid extreme surface currents 20 and this may have been the strategy utilized by the terrapin in SJB.…”

New Location Records for Alligator Snapping Turtle (Macrochelys temminckii) Captured during Fishery Surveys in Alabama

“…However, a taxonomic assessment of western, central, and Suwannee Alligator Snapping Turtle lineages described 2 new species: Macrochelys suwanniensis Thomas, Granatosky, Bourque, Krysko, Moler, Gamble, Suarez, Leone, Enge, and Roman (Suwanee Alligator Snapping Turtle) and Macrochelys apalachicolae Thomas, Granatosky, Bourque, Krysko, Moler, Gamble, Suarez, Leone, Enge, and Roman (Apalachicola Alligator Snapping Turtle) (Thomas et al 2014). The newly described Suwanee Alligator Snapping Turtle is endemic and restricted to the Suwanee River drainage in northern Florida and southeastern Georgia (Johnston et al 2015). The proposed Apalachicola Alligator Snapping Turtle of the central lineage occurs from the Apalachicola and Chattahoochee River drainages of Alabama, Georgia, and Florida (Thomas et al 2014).…”