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Procambarus gibbusMuckalee Crayfish
Federal Protection: No US federal protection
State Protection: Threatened
Global Rank: G3Q
State Rank: S2
SWAP High Priority Species (SGCN): Yes
Element Occurrences (EOs) in Georgia: 18
Habitat Summary for element in Georgia: Flowing waters with rocks, woody debris, leaf litter, or undercut banks
The carapace of the Muckalee Crayfish ranges from pale to dark brown. A dark saddle crosses the top of the carapace just before the abdomen and extends forward along the sides of the carapace. The rostrum is long and sharply pointed. There are two distinctive cervical spines on either side of the carapace. The dorsal surface of the abdomen is tan with a dark margin along the posterior edge of each segment. The abdominal segments have green or black U-shaped stripes on the sides, the first four of which are bordered above by a scarlet to orange spot. These scarlet to orange markings are located more dorsally on the last abdominal segment and have irregular outlines. The telson alternates between tan and brown, has black spots, and its margins have an orange tinge. The claws are dark with a prominent row of light tubercles on the mesial margin of the palm. The tips of the fingers are red or orange. The areola is 2.8–3.5 times as long as broad and comprises 24–wh28% of carapace length. Adult Muckalee Crayfish may reach a maximum total body length of over 100 mm (>4 inches).
The presence of two cervical spines separates the Muckalee Crayfish from all Georgia species except other members of the subgenus Pennides. The White Tubercled Crayfish (Procambarus spiculifer) is very similar and occurs in the mainstem Flint River near the tributaries where Muckalee Crayfish live. Details of the male reproductive structure is required to separate these two species. All specimens resembling Muckalee Crayfish and White Tubercled Crayfish collected in the lower Flint River system should be examined carefully.
The Muckalee Crayfish is found in a wide array of flowing water habitats across its range. Depending on the substrates available it can be found hiding beneath rocks, within woody debris or leaf litter, and beneath undercut banks.
No studies of the Muckalee Crayfish diet are known. Crayfishes are considered opportunistic omnivores and are likely to feed on live and decaying vegetation, aquatic insect larvae, small fishes, and dead animal matter.
Stream dwelling crayfishes typically hide during the day and come out at night to feed. Reproduction usually occurs during the spring and fall, but males in reproductive condition may be found at any time during the year. When female crayfish are ready to lay eggs, they usually find a secure hiding place and hence are rarely encountered. When the eggs are released, the female attaches them to her swimmerets and is said to be “in berry.” Upon hatching, the juvenile crayfish are attached to the mother by a thread. After the juveniles molt for the second time, they are free of the mother, but stay close and will hold on to her for some time. Eventually they move off on their own. Crayfishes molt 6 or 7 times during their first year of life and most are probably able to reproduce by the end of that year. They molt once or twice a year for the remainder of their lives and live about 3 years. Males in reproductive condition have been collected in April and August and no females with eggs have been found. The smallest male breeding male is about 60 mm (2.4) in length (Hobbs 1981).
Since this species is usually found in flowing water, it is most easily collected by holding a net perpendicular to the current downstream of vegetation or woody debris and kicking to dislodge and scare crayfish into the net. If there are rocks or logs in the creek, they may be carefully lifted and crayfish may be pinned by hand or coaxed into a dipnet. Using a backpack electroshocker or minnow traps can be effective as well. Collections in spring or fall are more likely to produce males in reproductive condition which can be helpful with identifications.
Most records for this species are from Muckalee Creek and tributaries (Flint River system) in both the Fall Line Hills and Dougherty Plain physiographic provinces in southwestern Georgia. It is also reported from a single locality in Coolewahee Creek, a tributary to the Flint River that lies south of Muckalee Creek. Hobbs (1981) listed a single collection from a small tributary to the Flint River in Crawford County.
The small geographic range of this species makes it vulnerable to extinction. The Muckalee and Coolewahee creek watersheds are primarily agricultural and threats include inadequate riparian buffers, nutrient and pesticide runoff, stream impoundment, and excessive groundwater pumping that can reduce stream flows. Of perhaps greatest concern is the presence of a non-native invasive species (Gray-speckled Crayfish, Orconectes palmeri) that is established in the lower Flint River system. This species appears to be displacing the White Tubercled Crayfish in the Flint mainstem (Sargent et al. 2011) and there are records of this invader in lower portions of Muckalee and Coolewahee creeks. Since Muckalee Crayfish is very closely related to White Tubercled Crayfish, it seems likely that Muckalee Crayfish will be in jeopardy if the Gray-speckled Crayfish is able to establish itself in Muckalee and Coolewahee creeks.
Despite the narrow range of this species, it is considered stable at this time.
Additional surveys are needed to better define the range of the Muckalee Crayfish in the Coolewahee Creek system. Additional taxonomic study is needed to better differentiate the Muckalee Crayfish from the similar appearing White Tubercled Crayfish. Incentive programs to help farmers implement best-management practices could improve instream habitat by decreasing sediment, nutrient, and chemical runoff and increasing riparian forest cover. Non-native crayfishes should never be used for bait. Instead, anglers should use crayfishes collected from the river system they will be fishing in and should never release unused bait crayfish back into Georgia waters.
Hobbs, H.H., Jr. 1969. Two new species of the crayfish genus Procambarus (Decapoda, Astacidae). Proceedings of the Biological Society of Washington 83:329–348.
Hobbs, H.H., Jr. 1981. The crayfishes of Georgia. Smithsonian Contributions to Zoology 318:1–549.
Sargent, L.W., S.W. Golladay, A.P. Covich, and S.P. Opsahl. 2011. Physicochemical habitat association of a native and a non-native crayfish in the lower Flint River, Georgia: implications for invasion success. Biological Invasions 13:499–511.
Stanton, G.E. 2006. Evaluation of conservation status of six west Georgia, Chattahoochee-Flint River crayfish species. Columbus State University, report to the Georgia Department of Natural Resources, Georgia Natural Heritage Program. 60 pp.
Taylor, C.A., G.A. Schuster, J.E. Cooper, R.J. DiStefano, A.G. Eversole, P. Hamr, H.H. Hobbs III, H.W. Robison, C.E. Skelton, and R.F. Thoma. 2007. A reassessment of the conservation status of crayfishes of the United States and Canada after 10+ years of increased awareness. Fisheries 32:372–389.
George E. Stanton
G. Stanton, 2008: original description
C. Skelton, January 2019: general update of account.