Cattle Tanks Prevent Extinction of the Dusky Gopher Frog
By Linda LaClaire
The dusky gopher frog is a native to the longleaf pine forests of the southeastern United States. This federally endangered animal depends on temporary shallow ponds embedded in this landscape for breeding. Unfortunately, the open longleaf pine habitat where rainwater collects to create the ideal setting for breeding has dwindled as a result of development and fire suppression. For years, the survival of the frog has primarily depended on a single breeding pond – Glen's Pond – located within the DeSoto National Forest in southern Mississippi. This site has been monitored continuously since it was discovered in 1988. Since then, severe drought events and a disease outbreak in 2003 resulted in several back-to-back years where there was little to no breeding success. With few frog tadpoles surviving to adulthood, the species was in jeopardy.
Since 2002, the U.S. Fish and Wildlife Service's Mississippi Field Office has supported a project to help bolster this dusky gopher frog breeding population. Staff collect a portion of the available egg masses at each breeding event to be hatched and reared to metamorphosis in the safety of a controlled captive setting. As a result, between 2002 and 2009, more than 2,000 metamorphic frogs raised in captivity were released at Glen's Pond. This intervention has resulted in recruitment to the population during years when natural development of tadpoles into frogs did not occur at the pond.
Since normal natural mortality of dusky gopher frog eggs and tadpoles is approximately 95 percent, collection of a comparatively small number of eggs does not represent a threat to the Glen's Pond population. The eggs are then transported to a laboratory provided by the U.S. Forest Service's Southern Research Station Institute of Forest Genetics where they will hatch. Once the tadpoles completely absorbed their yolk sacks and begin foraging on their own, they are then transferred to large, 350-gallon outdoor cattle tanks where they will develop into metamorphic frogs. Cattle tank set-up includes filling the tanks with well water, adding the desired amount of leaf litter used as substrate, and inoculating them with plankton as a food source for the dusky gopher frog tadpoles. An untreated pine board is added at an inclined position at the surface to give metamorphic frogs a place to rest out of the water. The end result is a perfect artificial pond.
Tadpole metamorphosis is triggered by warming temperatures. Tadpoles are monitored for emergence of forelimbs and absorption of their tails. After approximately three to four months, depending on temperature, the transformation of the tadpoles into frogs is complete, and the animals are then released back at the breeding site.
Prior to their release, the frogs are marked with fluorescent dye for identification and monitoring. The predominance of adult frogs with dye marks that have entered Glen's Pond to breed indicates that raising frogs in tanks is a successful technique for head-starting dusky gopher frogs. Population analyses demonstrates that using the cattle tanks for supplemental recruitment has helped lift the dusky gopher frog back from the brink extinction by stabilizing the population. Due to the effects of drought and disease, natural metamorphic recruitment alone would not have been sufficient to maintain the Glen's Pond population in the absence of this supplemental recruitment.
Cattle tanks are now also used to raise metamorphic frogs for introduction to restored sites as partners attempt to establish new dusky gopher frog recovery populations. The same technique as described above is being used by the Mississippi Department of Wildlife, Fisheries, and Parks and cooperators to provide frogs for release at these sites. Due to the extensive habitat restoration efforts of the U.S. Forest Service, there are ongoing projects to establish new populations at rehabilitated ponds in other areas of the DeSoto National Forest. Additionally, metamorphic frogs are released on sites owned by cooperating private landowners and on the Mississippi Sandhill Crane National Wildlife Refuge. As the dusky gopher frog moves toward recovery, partners will continue to rely on cattle tanks to protect against catastrophic loss and to provide frogs for establishment of new populations.
Linda LaClaire, a wildlife biologist in the Service's Mississippi Ecological Services Field Office, can be reached at firstname.lastname@example.org or 601-321-1126.
Wildlife and Habitat Conservation
- Conservation Planning