Black-knobbed Sawback

Photo By: Michael Bloxom
 

SCIENTIFIC NAME: Graptemys nigrinoda ssp.

DESCRIPTON: The black-knobbed sawback (Graptemys nigrinoda spp.) is a small to medium size turtle. Adult males are three to four inches in length while adult females are six to eight inches long. It has a narrow head with broad, rounded, black, knoblike vertebral projections on the carapace (back) and strongly posterior carapacial rim. The carapace is dark olive in color and each scute has semicircular or circular markings. The plastron (belly) is yellow and commonly tinted with red and has a black, branching pattern. The skin is black, with yellow stripes on the head, limbs, and tail. The dorsum (top of the head) is marked with a vertical crescent connecting with the other side to form a Y-shaped mark that is postorbital (behind the eyes). The sides of the neck have two to four stripes and the interorbital (between the eyes) strip is narrower than the neck stripes. Two subspecies, G. nigrinoda nigrinoda (Northern black-knobbed sawback) and G. nigrinoda delticola (Southern black-knobbed sawback) occur in Alabama. 
   
DISTRIBUTION: Found in Alabama and Mississippi, the Northern back-knobbed sawbackinhabits the Coosa, Tallapoosa, and Cahaba rivers from the Fall Line southward to approximately the Wilcox-Monroe County line in Alabama. The Southern black-knobbed sawback is an endemic of Alabama where it is found primarily in the rivers, lakes and streams located in the Mobile-Tensaw Delta.
 
HABITAT: Black-knobbed sawback turtles are associated with sand and clay-bottomed streams with moderate currents and abundant basking sites of brush piles, logs, and other debris. 
 
FEEDING HABITS: Black-knobbed sawbacks feed mostly on insects, but are opportunistic and have been reported eating crustaceans such as mollusks as well as small fish.   
 
LIFE HISTORY AND ECOLOGY: Several nesting observations have been conducted on Gravine Island which is located in the Mobile-Tensaw Delta in Baldwin County. At this site, nesting season begins in May and peaks from mid-June to mid-July and ends in early August lasting about 72 days. Nesting habitat is found on beaches near deep water. Clutch size ranges from three to seven eggs and incubation lasts close to 63 days. Three clutches may be produced annually. Nest depredation by fish crows has been reported to be as high as 82%. Captive wild black-knobbed sawback turtles have been known to live for 13 years.
 
CONSERVATION STATUS: In Alabama, G. nigrinoda nigrinoda and G. nigrinoda delticola are protected under the Nongame Species Regulation 220-2-.92, stating “It unlawful to take, capture or kill; possess, sell, trade for anything of monetary value, or offer to sell or trade for anything of monetary value…” 
 
 
REFERENCES:
 
Ernst, C.H., J.E. Lovich, and R.W. Barbour. 1994. Turtles of the United States and Canada. Smithsonian Institution Press., Washington D.C. 578 pp.
 
Mount, R.. 1975. The Reptiles & Amphibians of Alabama. Auburn Printing Co., Auburn, AL. 347 pp.
 
AUTHOR: Steve Barnett, Wildlife Biologist, Division of Wildlife and Freshwater Fisheries

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