Archives of The Cold Blooded News

The Newsletter of the Colorado Herpetological Society

Volume 33, Number 2;   February, 2006

Map Turtles (Genus Graptemys) in the Hurricane Belt of the Gulf Coast

by Chris Lechowicz
Technical Coordinator/Herpetologist
Sanibel-Captiva Conservation Foundation
3333 Sanibel-Captiva Road, Sanibel, FI 33957
chris@graptemys.com

From a human perspective, hurricanes are natural disasters: negative effects include loss of individual lives, property and in some cases livelihoods. But even though it is hard to look at a hurricane as a "good thing" when considering people, there may be some beneficial effects to the environment. The natural ecosystems in the Hurricane Belt are adapted to this kind of stress. The physical environment may sustain considerable damage, but the plants and animals have been through hurricanes many times before and are adapted for survival. The map turtles (genus Graptemys) of the southeastern United States certainly exemplify this. Here I report on several post-hurricane effects I observed on Graptemys species and their habitat during a spring 2005 trip to the Gulf Coast.

A positive effect of hurricane Ivan (16 September 2004 landfall over Mobile, Alabama) was the large amount of habitat created in rivers by falling tree debris. Branches, and in some cases entire trees, which fell into the water ended up as brush piles or snags. Brush piles are very important to Graptemys because they provide shelter from predators, basking sites and areas to feed (Cagle, 1952; Ernst et al., 1994; Lindeman, 1997, 1998). Graptemys generally stay in close proximity to such areas (Carr and Marchand, 1942; Jones, 1996). These piles also help to prevent shoreline erosion, give shelter and shade to fish, and create unique river habitats for other organisms by either slowing down the flow of water or causing riffles.

Brush piles are a dynamic system in these fast-moving Gulf Coast rivers. They may break apart or come loose, in which case the current moves them downstream. They usually get caught in other brush piles or in sharp bends of the river. Over time they slowly break down and/or end up in the Gulf of Mexico. Some people who live along these rivers remove brush piles for better boat access. This, of course, is a disadvantage to basking riverine turtles.

Over the past 14 years, I have noticed differences in the quantity and quality of brush piles in certain locations. When there is a long gap between hurricanes, tropical storms or severe storms, the brush piles thin out. This forces the turtles to become more concentrated in the remaining piles. In the aftermath of a hurricane, turtles are able to spread out because of more suitable habitat.

Nesting and egg incubation are also affected by hurricanes. The Gulf Coast Graptemys mostly nest on large sandy beaches along the river corridor. The adult females generally lay eggs from the beginning of June until August (Shealy, 1976). These females do not always lay their eggs high enough on the beach to be safe from flooding. It is not uncommon for many nests to be lost from long-lasting flood events. I found this to be the case in spring of 2005 with the Escambia map turtle (G. ernsti) on the Escambia and Conecuh rivers and the Barbour's map turtle (G. barbouri) on the Chipola and Apalachicola rivers, at least in the southern part of their range. My monitoring sites near the landfall and path of hurricane Ivan yielded no sightings of hatchling Graptemys in the spring of 2005. In recent years, these areas have always had moderate to high numbers of neonates, even during some moderate flood events. However, adults were still present, even though the river was high over the banks and the nearby forested areas were totally inundated.

Map turtles are able to survive as species because of the long life of the adults. It takes the Gulf Coast female Graptemys a long time (approximately 8 to 20 years) to reach sexual maturity. Once mature, however, they can lay multiple clutches of eggs per season and reproduce very late in life (Sanderson, 1974). Hatchlings have relatively low survivorship, mostly due to predation. If a year or two of production is lost due to flooded nests, the population will still be sustainable assuming that the adult population survived the event.

Also in spring 2005 we monitored map turtle populations on the Pearl and Pascagoula Rivers in Mississippi, and the Tallapoosa, Tensaw and Coosa Rivers in Alabama. In these river systems the ringed map turtle (G. oculifera), yellow-blotched map turtle (G. flavimaculata), Pascagoula map turtle (G. gibbonsi), black-knobbed map turtle (G. n. nigrinoda), delta map turtle (G. n. delticola) and the Alabama map turtle (G. pulchra) appeared to experience very similar situations and outcomes. All of these rivers flooded, and most of them were almost inaccessible. Hatchlings of all the above species were seen, which proves some reproductive success following hurricane Ivan and flooding that year. It was only with G. barbouri in Florida and G. ernsti in Florida and extreme southern Alabama that hatchlings were not observed.

When these rivers flood, (the Pascagoula in Mississippi, for example) the water fills the nearby floodplain. This can sometimes extend as far as a mile from the normal river channel. The Gulf Coast Graptemys generally do not wander too far from the actual corridor of the river during flood events (Ernst et al., 1974). Many attempts to spot turtles in the flooded forests resulted in failure. However, during flood stages you can still see adult turtles basking alongside the original river channel at the tops of trees (now at the surface of the river) that lined the previously exposed banks. Smaller turtles were also observed alongside the main corridor during flood conditions, but in the calmer areas such as behind large brush piles, bridge pylons or houseboats (Ernst et al., 1994).

In summary, I reiterate that Graptemys populations in the Gulf Coast region are adapted to hurricane conditions. Even with the loss of a single or multiple years' offspring due to flooding, stable populations can be sustained given the survival of the adults. Hurricanes reconstruct Graptemys habitat by causing trees to fall in the water to form new brush piles. Numerous brush piles provide these turtles with more shelter from predators, more surface area to feed from, and more areas to bask. An increase in the amount of brush piles enables the entire population to spread out in the river system, as opposed to being concentrated in a few areas.

On August 29, 2005, the Gulf Coast region experienced another hurricane, Katrina, as it struck Louisiana, Mississippi and Alabama. This deadly and devastating storm was more powerful than Ivan from the previous year and did unspeakable damage to the people of that area. The path of Katrina was just a little west of Ivan's path. This Category 4 hurricane has undoubtedly affected the river systems containing the yellow-blotched map turtle (G. flavimaculata), ringed map turtle (G. oculifera), and the Pascagoula map turtle (G. gibbonsi) in Louisiana and Mississippi. Many pollutants will find their way into these rivers when the water recedes from towns and neighborhoods. The combination of noxious, even toxic substances, such as lead and bacteria, that ends up in the river can be as detrimental to riverine species as to humans. Monitoring trips to this area will be conducted in the near future in order to document the effects on the turtles and their habitat.

Acknowledgments
I thank everyone who helped with the monitoring and observations, especially Ron and Dottie Humbert, John Archer, Shane Johnson, Pete Wilson and Nicole Lechowicz.

Literature Cited and Other References Cagle, F. R. 1952. The status of the turtles Graptemys pulchra and Graptemys barbouri Carr and Marchand, with notes on their natural history. Copeia 1952:223-234.
Carr, A., and L. J. Marchand. 1942. A new turtle from the Chipola River, Florida. Proc. New England Zool. Club 20:95-100.
Ernst, C. H., R. W. Barbour, E. M. Ernst and J. R. Butler. 1974. Subspecific variation and intergradation in Florida Kinosternon subrubrum. Herpetologica 30:317-320.
Ernst, C. H., J. E. Lovich and R. W. Barbour. 1994. Turtles of the United States and Canada. Washington, D.C. Smithsonian Institution Press.
Jones, R. L. 1996. Home range and seasonal movements of the turtle Graptemys flavimaculata. J. Herpetology 30(3):376-385.
Lindeman, P. V. 1997. Effects of competition, phylogeny, morphology, and ontogeny on structuring the resource use of freshwater turtles. Ph.D Thesis, Univ. Louisville, Kentucky.
_______. 1998. Of Deadwood and map turtles (Graptemys): An analysis of species status for five species in three river drainages using replicated spotting-scope counts of basking turtles. Linnaeus Fund Research Report. Chel. Conserv. Biol. 3(1):137-141.
Sanderson, R. A. 1974. Sexual dimorphism in the Barbour's map turtle, Malaclemys barbouri (Carr and Marchand). Master's Thesis, University of South Florida, Tampa. 94 pp.
Sanderson, R. A., and J. E. Lovich. 1988. Graptemys barbouri. Catalog. Amer. Amphib. Rept. 421.1-421.2.
Shealy, R. M. 1976. The natural history of the Alabama Map Turtle, Graptemys pulchra (Baur) in Alabama. Bulletin of Florida St. Mus. BioI. Sri. 21:47-111.