Figure 2. Inagua is an island in the Bahamas.
The Inagua slider arguably has the most restricted geographic range of any turtle. Inagua is the third largest island in the Bahamas (Fig. 3). Thus, while this turtle is confined to an island of 1,551 km2, habitat limitations restrict it to the extreme eastern portion of the island. We would estimate that 95% of the total population lives in a 50 km2 area. Here freshwater habitat is limited. Lake Windsor (saline) and salt evaporators of Mortonís Bahama Salt Works (28,000 acres) occupy the majority of the land.
Additionally a network of old salt pans from a previous salt industry, the salt plant, pump stations and canals, 59 crystallizers covering 2,169 acres, an airport, Matthew Town, roads, natural brackish ponds, and coastal plant communities occur on this end of the island. The turtles occupy about 100 scattered pools covering less than 50 to 100 acres, with many pools being interconnected during periods of high water. At any given time many of these pools are dry, saline, or so shallow that they become too warm to support turtles. It appears that 10-20% of these pools are natural and the remainder are borrow-pits formed during the construction of the airport and the various roads and dikes which are prevalent on the west end of the island. On our visit to the Island (May 2000) many of the freshwater pools used by these turtles (50-60% of the ones containing water, ca. 30) were saline and were uninhabited by turtles (Fig. 4). It is not known if pools typically become saline during periods of drought, or if this is a result of salt intrusion from hurricane Floyd (fall of 1999).
Fresh water is at a premium on Inagua. Hurricanes are probably important in reviving freshwater systems. During years of drought it is assumed that the turtles remain inactive for long periods, finding shelter where they can on land. On rainy nights the turtles often walk around on land. The Oxford Expedition (Bostock 1988) found that only one of the dozen animals that they monitored traveled any significant distance from the point of capture (one male went 2 km). We found adult males to be much less common than females, as did the Oxford Expedition, and Hodson and Person (1943). Whether this is related to behavior or higher hatch rates of females caused by the high temperatures of the southern Bahama region and temperature dependant sex determination is unclear.
The Inagua sliderís total population size is unknown, but believed to be small. We estimate that the total population is less than two thousand individuals, but it is more likely to be half that. For two months in 1988 four people from the Oxford Expedition collected only 102 turtles despite extensive field efforts. This yielded a maximum density of approximately one turtle per 20 acres. Unpublished mark-recapture data from their study indicated a total population of 492 turtles at the three most heavily populated sites. We saw about 50 individuals after examining all ponds of known occurrence during our 5 day visit. The turtleís habit of spending long periods of time on land makes surveys focused on freshwater sites difficult to evaluate.
Issues affecting population stability
These turtles are living on the edge. The continued existence of the Inagua slider is to some degree dependent on hurricanes and other major weather events, which bring freshwater to the island. The pools in which they live are constantly drying or becoming saturated with saline water. Many of the shallow pools become overheated during the day forcing the turtles to move onto land. Because of this the turtles are typically on land more than they are in the water and the locals refer to them as land turtles (in part this is to distinguish them from marine species). Under normal weather conditions the turtles must spend much of the year on land hiding in leaf litter and under rock ledges (Fig. 5). In drought years, and drought is not uncommon on Iguana, these turtles may have periods of aquatic activity which may last only for a few months of the year.
The majority of Great Inagua is protected within the boundaries of the Inagua National Park, but no turtle populations are known from within the park. The majority of sites where turtles occur is on the developed northwest portion of the island and is adjacent to the salt production area. Ownership of much of the lands occupied by the turtles is unclear. Despite being listed as endangered by the US Fish and Wildlife Service the Inagua slider is not protected by the Bahama government. There are no regulations against removing the turtles from the island and there are no current plans for long-term habitat protection. This turtle has not been considered as a species of conservation concern nor is its endemic status well known either in the Bahamas or on Inagua.
The movement of Trachemys from island to island has become a problem throughout the Bahamas. Visitors to the various outer islands often bring home cultural, geological or biological elements unique to particular islands as souvenirs. This has lead to hybridization of Trachemys on New Providence. A number of locality records for Trachemys on other islands which represent native species are actually stocks of questionable origin.
Electricity has been available to the public on the island for only a few decades. Prior to electric pumps groundwater was less accessible and its use was more conservative since it had to be pumped by hand. In addition most residents relied on cistern systems to capture rainwater. To what extent the water table has been lowered, and how this effects the hydrology of the pools in which the turtles live is unknown. The recent drilling of one large well-field resulted in the invasion of seawater into the aquifer when the drilling went too deep. This well-field is centered in the area inhabited by the turtles. The long-term effect of this on the turtles is unknown.
Few natural pools now exist on the island. To what extent they were destroyed in the mid 1900s by the expanding salt industry is unknown, but the proximity of the salt works to the existing population suggests that the area developed was the former core of the turtleís distribution. Today, most occupied sites are freshwater pools formed by borrow pits associated with road, dike, and airstrip development. This places the majority of the population in areas that are vulnerable to brine overflow from the salt processing pools, and makes the turtles vulnerable to road traffic. The turtles commonly walk about on the roads on rainy nights and probably use the roads and dikes as nesting sites since other high ground is often limited. The good news is that a present there is extremely little vehicle traffic on Inagua.
Feral hogs occur throughout Great Inagua and have been present since at least the early 1900s. While we have no direct evidence of their impact on the turtles they almost certainly destroy nests and probably consume turtles they root out on land. Because of the scarcity of fresh surface water on Inagua the distribution of the feral hogs is concentrated around freshwater and contact with the turtles is assumed to be high.
Saltwater does intrude occupied sites. One of the major collecting sites described by the Oxford Expedition was highly saline during our visit. Connection to the sea was evident by the presence of tarpon in several of the occupied pools. How much of this is natural and how much is the result of massive landscape alteration around the salt works is unclear. Brine overflow from the salt evaporation ponds is a problem. The close proximity of the occupied sites suggests a potentially persistent problem and one site of more than 100 acres of natural vegetation and freshwater pools was saturated with salt when one of the discharge pumps was left unattended. Although it has been a decade since the accident, the site shows no sign of recovery.
Unlike Cat Island where another species of freshwater turtle occurs, no one on Inagua eats fresh water turtles.
The current conservation effort:
The Inagua slider population is vulnerable to any number of factors. We believe that a few simple remedies would provide reasonable buffers against unexpected events that could jeopardize the turtleís future. Research on the Inagua slider to understand the effects of shifting hydrology and varying salinities is needed for the creation of long-term management plans, but there are a number of conservation issues that can be addressed immediately. At the suggestion of The Tortoise Reserve, the Bahama government is now considering listing native freshwater turtles as a Crown-protected species. Local educational programs will be developed and posters can be placed at key sites, such as airports to the outer islands. Additionally, regulations are now being considered to ban the import of red-eared sliders (T. scripta elegans) for the pet trade. The release of these turtles on Inagua could genetically alter the indigenous Trachemys population. The key to conservation will rely on work done on Inagua itself. We propose the creation of additional artificial ponds, expansion of the Inagua National Park to include existing sites inhabited by the turtles, and an ongoing island educational effort to raise awareness about the endemic fauna of the island. A number of other reptiles and a subspecies of the Bahama woodstar are also Inagua endemics.
A small park in the middle of Mathewtown has been proposed and a number of the islandís endemic species already live at this site. A large pool is already in place, and with minor fencing, a small number of turtles can be exhibited. Young hatched from this group can be used to help stock the proposed new ponds constructed in protected areas. This park would be created largely as a focused educational effort for the people of Inagua, in that tourism on Inagua is all but non existent. Additionally, a small breeding group of Inagua sliders has been established in the National Botanical Garden in Nassau. All the Inagua sliders exhibited have been marked for identification. The turtles are kept in an enclosed concrete pond in the public area. The endemic freshwater Bahama pupfish (Cyprinodon laciniatus) and a New Providence endemic race of the Caribbean gambusia (Gambusia puncticulata manni), Bahama pintails (Anas bahamensis) and the regionally endangered West Indian Whistling-Duck (Dendrocygna rborea) will also be exhibited (and bred) in the same exhibit. Educational signs explaining the importance of these animals to the country are being designed. The main purpose of the slider-breeding group is educational, but students at the College of the Bahamas will also use it for studies on the reproductive biology of the species. Offspring will be available for restocking ponds on Inagua, if that becomes necessary, and the turtles will serve as a backup stock of known genetic history if the wild populations become contaminated through introduction of exotic North American Trachemys.
We thank the staff of the Bahama National Trust for help with our field studies and for information provided.
Bostock, C. 1988. Oxford University Expedition to Inagua Island, Bahamas. 14 July- 19 September 1987. Sponsorsí Report. 35 pages. unpublished.
Hodsdon, L. A. and J. F. W. Pearson. 1943. Notes on the discovery and biology of two Bahamian freshwater turtles of the genus Pseudemys. Proc. Fla. Acad. Sci. 6(2):17- 23.