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Cambarus unestami Hobbs and Hall, 1969

Blackbarred Crayfish

Federal Protection: No US federal protection

State Protection: Threatened

Global Rank: G2

State Rank: S3

SWAP High Priority Species (SGCN): Yes

Element Occurrences (EOs) in Georgia: 14

Habitat Summary for element in Georgia: Medium-sized streams from beneath rocks or within leaf litter in slow to moderate current


Description

The overall color of the Blackbarred Crayfish is brownish with dark barring on the abdomen giving the impression of longitudinal stripes. The areola is wide and the rostrum tapers gradually. There are two rows of tubercles on the mesial margin of the palm. This species reaches a maximum total body length of about 80 mm (3.1 in).

Similar Species

The Blackbarred Crayfish has been collected with the somewhat similar Mountain Midget Crayfish (Cambarus parvoculus) a few times. The latter has a slightly narrower areola and a fairly blunt rostrum compared to the longer tapered rostrum of the Blackbarred Crayfish. Additionally, the Blackbarred Crayfish has a mottled appearance while the Mountain Midget Crayfish is more uniformly colored.

Habitat

The Blackbarred Crayfish is usually collected in medium-sized streams from beneath rocks or within leaf litter in slow to moderate current (Kilburn et al. 2014).

Diet

No studies of the Blackbarred Crayfish 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.

Life History

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. Male Blackbarred Crayfish in reproductive condition have been collected in April, May, October, and November and females carrying eggs were found in April and May. The number of eggs for two individuals ranged from 124 to 194, with egg diameters averaging 2.5 mm. The smallest breeding male is about 54 mm (2.1 in) and the smallest female with eggs about 65 mm (2.6 in) in length (Hobbs 1981).

Survey Recommendations

Since this species is usually found in moving water, it is most easily collected by holding a net perpendicular to the current downstream of a large rock, then lifting the rock and disturbing the substrate beneath it. If a crayfish is hiding underneath the rock, it will likely move into the net. Shocking downstream into a seine net with a backpack electroshocker and setting baited minnow traps overnight may also be effective. Collections in spring or fall are more likely to produce males in reproductive condition, which can be helpful with identifications.

Range

The Blackbarred Crayfish is known from at least 9 sites (7 in GA) in the Cumberland Plateau and Ridge and Valley physiographic provinces in northwestern Georgia and extreme northeastern Alabama. It has been collected from streams in the Tennessee River drainage and Little River tributaries of the Coosa River system (Kilburn et al. 2014).

Threats

The small range size of this species makes it vulnerable to extirpation. Heavy sedimentation resulting from poor development, land management, and agricultural practices may cover substrates and other daytime hiding places on which crayfishes rely to avoid predation. The introduction of non-native crayfishes is a threat to all native crayfishes.

Georgia Conservation Status

The species is considered stable at this time. It likely occurs in streams in Cloudland Canyon State Park which would be somewhat protected.

Conservation Management Recommendations

Conserving populations of the Blackbarred Crayfish will require general watershed level protection measures, including the protection of riparian zones, control of sediment and nutrient runoff from farms and construction sites, and limiting the amount of impervious cover (e.g., pavement) within occupied watersheds. 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.

References

Hobbs, H.H., Jr. 1981. The crayfishes of Georgia. Smithsonian Contributions to Zoology 318:1–549.

Hobbs, H.H., Jr., and E. T. Hall, Jr. 1969. New crayfishes from Georgia (Deapoda: Astacidae). Proceedings of the Biological Society of Washington 82:281–294.

Kilburn, S.L., C.A. Taylor, and G.A. Schuster. 2014. Conservation assessment and habitat notes for three rare Alabama crayfishes: Cambarus cracens, Cambarus scotti, and Cambarus unestami. Southeastern Naturalist 13:108–118.

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.

Authors of Account

Christopher E. Skelton

Date Compiled or Updated

C. Skelton, 2008: original account

C. Skelton, January 2019: general update of account.

Photo by Georgia DNR – Wildlife Resources