articles

ARTICLES Chelonian Conservation and Biology, 2007, 6(2): 163–169 Ó 2007 Chelonian Research Foundation

Abundance, Population Structure, and Conservation of Kinosternon scorpioides albogulare on the Caribbean Island of San Andre´s, Colombia GERMA´N FORERO-MEDINA1, OLGA VICTORIA CASTAN˜O-MORA2,

AND

OLGA MONTENEGRO3

1

Laborato´rio de Vertebrados, Universidade Federal do Rio de Janeiro, CP 68020, Brazil [[email protected]]; 2 Instituto de Ciencias Naturales, Universidad Nacional de Colombia, Ciudad Universitaria, Bogota´, Colombia [[email protected]]; 3 Instituto de Ciencias Naturales, Universidad Nacional de Colombia, Ciudad Universitaria, Bogota´, Colombia [[email protected]]

ABSTRACT. – We estimated population sizes, densities, structure, and the sex ratio of a locally endangered species of mud turtle, Kinosternon scorpioides albogulare, on the Caribbean island of San Andre´s, Colombia. We estimated the population size at 4343 turtles on the island in 2002, inhabiting both freshwater ponds and mangroves. Densities for the main populations varied from 77 to 254 turtles/ha. The population structure showed that most of the individuals belong to intermediate size classes (110- to 140-mm carapace length) and a few belong to the smaller or larger size classes (, 110- or . 140-mm carapace length). The sex ratio was significantly different from 1:1 and was skewed toward females, 1 male per 1.97 females. No common use was found for the species among native islanders, although people from the continent living on the island use it for diverse purposes. Some threats were identified, such as mangrove pollution and the presence of the introduced species Tupinambis teguixin. KEY WORDS. – Reptilia; Testudines; Kinosternidae; Kinosternon scorpioides; abundance; population structure; sex ratio; threats; San Andre´s Island; Colombia The swanka turtle (Fig. 1), as Kinosternon scorpioides albogulare is known on the Caribbean island of San Andre´s, Colombia, is a subspecies of mud turtle that ranges from Honduras to Panama´ (Ernst and Barbour 1989) that also occur on San Andre´s. In Colombia, it can only be found on this island, where it has been poorly studied; data on habitat use, abundance, and population structure are lacking. It is the only freshwater turtle present on the island, and, according to Pritchard (1979), populations on the island decreased because of a drought that occurred during the 1970s. Apart from this possible reduction, there have been recent introductions of wild animals to the island such as Caiman crocodilus and Tupinambis teguixin, which could be feeding on eggs, hatchlings, and even adult turtles. The first reports of the species on this island were by Dunn and Saxe (1950) and later by Tamsitt and Valdivieso (1963). In 1988, Castan˜o-Mora found only 1 pair of turtles in a large pond, where these turtles were considered to be abundant, and dense populations in the mangroves, suggesting that it had abandoned the freshwater ponds, possibly because of the introduction of C. crocodilus to those places (Castan˜ o-Mora 1992). This study also reported a sex ratio of 1 male per 14 females; however, this ratio could have been skewed because of the low number of animals for which sex was determined and a lack of complete sampling in every possible habitat,

because only animals from certain parts of the mangrove forest were studied. Despite the restricted distribution of the species, the vulnerability of this turtle’s populations because of insularity, and the possible risks it faces on the island, no research had been conducted apart from casual observations. The island is now a biosphere reserve, and local authorities need information on the population biology of the different species of fauna and flora to monitor this fragile ecosystem.

Figure 1. The swanka turtle, Kinosternon scorpioides albogulare, in a mangrove forest on San Andre´s Island, Colombia. Photograph by G. Forero-Medina.

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Figure 2. San Andre´s Island and localities where Kinosternon scorpioides albogulare was found to occur.

Our goals were to determine the distribution of the different populations of mud turtles present on the island, estimate the abundance and density of the species in each of these populations, study the population structure on the island, and evaluate the uses of the turtle by the human community. One of the main objectives was to start longterm monitoring of the population to better understand its dynamics and the possible effects of humans and introduced species. The island presents appropriate conditions for a long-term study because it is small, individuals are easily found during the dry season, and the population is isolated from other continental populations. METHODS We studied the population of turtles on San Andre´s Island, which belongs to the archipelago of San Andre´s, Providencia, and Santa Catalina. It is located in the Colombian Caribbean, between 12828 0 55 00 N and 12835 0 37 00 N and 81840 0 49"E and 81843 0 23 00 E, and has an approximate area of 27 km2 (Fig. 2). The average temperature is 27.38C (IGAC 1996), and annual precipitation is around 1800 mm (Barriga et al. 1969). The different ecosystems on the island are mainly tropical dry forest, xerophytic habitats, freshwater ponds, and mangrove forests (Barriga et al. 1969). The freshwater ponds vary in size from 0.33 to 1.85 ha (Machaco´n-Guzman and Ward-Bolivar 2004), and only a few of them are permanent, whereas others only appear during the rainy season. Some of the mangrove forests are connected to the sea, and others are isolated (Garcı´a-Hansen and GaviriaChiquazuque 1996). Although there is no massive

exploitation of mangrove forests, all of them are affected or influenced by urban expansion and tourist development. The terrestrial herpetofauna consists of 18 species (Rueda 1999), with only 1 amphibian present and a dominance of lizards over snakes. There also have been recent introductions of reptiles and mammals, some of them predators, such as T. teguixin and C. crocodilus. The study was conducted during the dry season, from March to June 2002, when only the permanent ponds remain and when most of the isolated mangroves are dry. To identify the localities where the species occurred on the island, different ecosystems were searched. Information from the human community was also very helpful for finding turtles. To estimate the abundance in each locality, we used the Lincoln-Peterson method for closed populations (Krebs 1999). We assumed closure because, even though the hatching season is not known for the species on the island, no eggs or hatchlings were found during these months. Also, only 1 turtle was found dead, and no movements between the localities were recorded during the study. Thus, we assumed that there was no breeding, recruitment, mortality, immigration, or emigration during the sampling periods. Individuals in each locality were hand captured, measured, marked by using the marginal scute notching method (Cagle 1939), and released. The length of the capture and marking period was 1.5 months. We conducted the recapture activities approximately 1 month later, by using the same sampling effort, and estimated population sizes by using 95% confidence intervals. These intervals were estimated by using the normal, binomial, or Poisson distribution according to the number of captures and

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Table 1. Estimated population sizes of Kinosternon scorpioides albogulare at different sites on San Andre´s Island. Site

Estimated population size

95% Confidence intervals

4343 1364 964 2360 38

3569–5800 816–2589 686–1440 1648–3587 27–92

Total Island Smith Channel Salt Creek Sound Bay Big Pond

recaptures in each locality, following recommendations by Krebs (1999). We estimated the density in each locality by dividing the population size estimate by the sampled area. Individuals were measured for carapace length (CL; straight line in mm from the nuchal scale to the midpoint of the contact between marginals 11), by using calipers, to the nearest 0.1 mm; sex was determined by distinguishing males from females by using the sexual dimorphism described for the species (Berry and Iverson 2001). The male has a longer tail than the female, and the cloacal aperture is at or posterior to the shell margin in males, whereas, it is anterior to the shell in females. Sex determination was not possible for individuals under 90mm CL. Plastron length was not measured; it was not considered reliable for this species, because they present differing responses to handling, thus opening their hinged shells to varying degrees and making it difficult to measure and compare. For studying the population structure on the island, we constructed size classes, each spanning 10-mm CL and compared the number of individuals in each class. Sex ratios were examined by using Pearson’s v2 test with a level of significance of 0.05. The uses and importance of the species for the human community were studied through direct contact with people from the island via interviews and informal conversations, where people were asked if the turtle was collected, consumed, or traded. RESULTS We found mud turtles at 7 different localities on the island, occurring in mangrove forests and freshwater ponds (Fig. 2). These localities were separated in some cases only by unpaved roads and in other cases by main roads. The mangrove forests were separated from the ponds by roads, houses, and crop fields. Given the proximity of the several localities, we considered the whole island as 1 single population distributed in several localities of appropriate habitat. This could also represent a metapopulation, following Hanski and Simberloff (1997), but only studies on the frequency of movement among localities could help to define this condition. The mangrove forests where the species was found were the southern forests (Fig. 2), which are not permanently connected with the sea, thus being less saline than the northern ones. Salinity levels in these southern mangroves are in the range of 0% to 31.7% (Garcı´a-

Distribution Binomial Poisson Binomial Poisson Binomial

Hansen and Gaviria-Chiquazuque 1996). The principal mangrove trees that occur in these forests are Rhizophora mangle, Laguncularia racemosa, and Avicennia germinans; in some of these forests, the mangrove fern (Acrosticum aureum) is also very abundant. The ponds where K. scorpioides albogulare was found were permanent freshwater ponds no bigger than 1.85 ha, with varying degrees of vegetation at the edges and with some aquatic macrophytes belonging principally to the families Cyperaceae, Poaceae, Polygonaceae, Onagraceae, and Lemanceae (Machaco´n-Guzma´n and Ward-Bolı´var 2004). Besides these localities, we found solitary individuals in a few other places. Other sites that were searched and where we thought turtles could occur, but no individuals were found after many searches, were the northern mangrove forests, which are permanently connected with the sea, and the only permanent stream that occurs in the island. Abundance. — A total of 1229 individuals were captured during the study period, with 81 recaptures. The number of recaptures permitted an estimation of population sizes in most of the localities (Table 1), except in Small Pond and Jack Pond, where captures were fewer than 10 and reliable estimates could not be done according to Krebs (1999). A population of 4343 turtles (3569–5800, 95% confidence limits) was estimated for the entire island. According to the population size estimates, more than 95% of the population is concentrated in the southern mangroves, whereas the freshwater ponds account for less than 5% of the population. Apart from these localities, a few (, 50) turtles were found in a small relict of mangrove forest called Hoffie Swamp. This was the only place where, because of logistic difficulties, mark and recapture was not conducted. However, the number of turtles at this site is comparatively low compared with the total population in the island. Densities in the mangrove forests varied from 77 to 254 turtles/ha (Table 2). The smallest mangrove forest, Salt Creek, had the highest density, whereas the largest, Smith Channel, had the lowest density of the 3. Population Structure. — The smallest individual captured had a 61.1-mm CL, and the largest was a male had a 157.7-mm CL. Most of the individuals were in the middle size classes and few appeared in the smaller or largest size classes (Fig. 3). Of the 1229 turtles captured, 41.9% belonged to the 120–130 mm class, 31.3% to the

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Table 2. Densities (turtle/ha) of Kinosternon scorpioides albogulare at different sites on San Andre´s Island. Site Salt Creek Sound Bay Smith Channel

Area (ha)

Density (no. turtles/ha)

3.79 12.46 17.77

254.4 189.4 76.7

110–120 mm class, and 16.8% to the 130–140 mm class. The other size classes had abundances representing less than 5% of the sample. Most males and females belonged to the middle size classes. However, as seen in Fig. 3, there were more females than males. We found a skewed sex ratio of 1.97 females per male. This ratio was significantly different from 1:1 (v2 ¼ 120.18, df ¼ 1, p , 0.05). We tested the sex ratio in the mangrove forests and the largest pond. In the 3 mangrove forests, the skewed sex ratio was maintained (v2 ¼ 9.49, v2 ¼ 38, v2 ¼ 73.02; df ¼ 1, p , 0.05) and only in the pond was it not significantly different from 1:1 (v2 ¼ 0.57, df ¼ 1, p . 0.05). Human Use and Possible Threats. — People that lived near the mangrove forests and the ponds identified this turtle and knew where it lived, whereas many islanders who did not have the same contact with these places did not recognize it and confused it with a marine turtle or with an introduced tortoise (Geochelone carbonaria), thus giving names that do not correspond to its native name swanka. This name apparently comes from the word ‘‘swamp’’, the name given to the mangroves where the turtle lives. For native islanders, it has no economic value, and they do not eat the species; however, some people from the Colombian mainland, where turtle eating is a very common practice, occasionally eat some individuals or use them for medicinal purposes, e.g., treating asthma. Some possible threats identified were 1) introduced species, especially T. teguixin, which is an active predator and is very abundant in the mangrove edges where the turtles lay

BIOLOGY, Volume 6, Number 2 – 2007 their eggs, and 2) contamination by industrial and domestic wastes, which is high, especially in the Sound Bay forest. DISCUSSION The species K. scorpioides has not been reported earlier in saline habitats, even though studies for K. scorpioides cruentatum (Acun˜a-Messen 1998) in Costa Rica, showed that it inhabits water with varying degrees of hardness, from soft (54.78 ppm) to hard water (125 ppm). On San Andre´s Island K. scorpioides albogulare inhabits mangrove forests, where salinity can reach up to 31.7% in some months of the year, even though the average can be much lower (Lasso et al. 1998). Other species from the genus Kinosternon have been reported to occur in saline environments, such as Kinosternon baurii palmarum and Kinosternon subrubrum steindachneri on Meritt Island in Florida (Neill 1958), K. subrubrum hippocrepis in Texas (Neill 1958), K. subrubrum subrubrum on Ocracoke Island in North Carolina (Engels 1942) and K. baurii baurii in South Florida (Duellman and Schwartz 1958). This last species is not an estuarine specialist (Dunson 1979), and, to survive in saline habitats, it uses a behavioral osmoregulation (Dunson 1981). The mechanisms by which K. scorpioides albogulare could be acclimating to high levels of salinity on San Andre´s Island are not known. It is important to evaluate the salinity tolerance of the species to determine the strategies used, especially during the dry season when water levels in the mangrove forests fall and salinity increases considerably. When this happens, turtles are frequently found buried in the mud or under the roots of mangrove trees, so it is possible that they could be carrying out a similar strategy to the one used by K. baurii baurii. Salinity tolerance could also help to identify if this variable is regulating the dispersal and distribution of the turtle on the island, because the turtle is not present in the

Figure 3. Population size structure of Kinosternon scorpioides albogulare on San Andre´s Island.

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northern mangrove forests, where salinity levels are much higher because of the permanent influence of the ocean. Abundance. — Population densities in freshwater turtles are very variable and depend on the species and the environmental conditions during sampling, especially in open populations. Moll (1990) found that in a freshwater stream in Belize, during a 4-month interval, population sizes for K. scorpioides and K. leucostomum increased, probably because of emigration from surrounding ephemeral aquatic habitats. There is also a marked variation in the estimated densities of freshwater turtles from different aquatic ecosystems and geographic areas (Bury 1979). The densities estimated in this study are within the range of other values reported for the genus Kinosternon. These values have been recorded to be as low as 10 turtles/ ha for K. leucostomum in a Belize stream (Moll 1990) and as high as 20,000 turtles/ha for Kinosternon integrum (Berry and Legler 1980), even though this value is certainly exaggerated (Iverson 1982). However, Iverson (1982) reported values of up to 1196 turtles/ha for this same species. For the species K. scorpioides, some densities found are 14 and 21 turtles/ha (Moll 1990), 48 turtles/ha for K. scorpioides cruentatum (Iverson 1982), and 272 turtles/ha for K. scorpioides abaxillare (Iverson 1982). The values found for San Andre´s Island seem to be near the higher values for the species K. scorpioides; however, it is important to note that all of the other density values have been estimated for mainland populations and that there are no reports for island populations of this species. This might make comparisons among the different population estimates even more difficult. Langtimm et al. (1996) suggested that population size of Terrapene carolina bauri on Egmont Key island could be higher than those on the mainland because of reduced predation. A continued study of the dynamics of the population of San Andre´s Island would make a significant contribution to the understanding of the ecology of island populations of freshwater turtles. The locality with the highest number of individuals was Sound Bay mangrove forest, followed by Smith Channel; however, the highest density occurred in Salt Creek mangrove forest, the smallest of the 3. There is no evident explanation for this higher density. These mangrove forests are apparently similar in their structure, however, there could be differences in salinity of the water, resource availability, or any other condition that could be related to this difference in densities among them. Population Structure. — The body sizes found on San Andre´s are all within the range described by Berry and Iverson (2001) for K. scorpioides. The largest male captured (157.65-mm CL), was the biggest individual of this subspecies reported for Colombia. The population structure on the island was very similar to that for other populations of species of the family Kinosternidae. For example, studies of Sternotherus odoratus (Bancroft et al. 1983; Ernst 1986; Dodd 1989) showed that most of the turtles belonged to medium-size classes, whereas, smaller

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and larger size classes represented a smaller proportion of the population. Not surprisingly, no hatchlings were found, and size classes of less than 90-mm CL were underrepresented. Very small turtles are hard to find on the mangrove floor because of the large number of holes, roots, and leaves. It has been suggested that the fact that juveniles represent a small proportion of the population in such studies might be because of the high mortality of eggs and neonates, opposite to what occurs with juveniles and adults, where the increase in size and hardness of the shell makes them less vulnerable to predators, desiccation, and other factors affecting neonates (Bury 1979). It would be very important to evaluate the survivorship of eggs and hatchlings on the island, because, apart from the factors mentioned above that reduce recruitment into the juvenile age class, there might be other problems. Introduced species, especially T. teguixin, which is very abundant in the mangrove forests, could be preying substantially on eggs and hatchlings, and could cause a population decline in the future. Sex ratios on San Andre´s Island appear to be different from 1:1. Both even and unbalanced sex ratios were reported for natural populations of turtles (Bury 1979). There are various reports of skewed sex ratios for freshwater turtles, generally with females outnumbering males (Bury 1979), even though it was suggested that these differences might be because of inadequate methods and selective sampling (Gibbons 1970). The sex ratios found in the present study for the island represent the ratios during a single sampling event; therefore, there is no reason to necessarily expect a 1:1 ratio. Some studies showed that sex ratios for turtles with temperaturedependent sex determination can change seasonally and by collecting site (Dodd 1989) and that they can vary from 1:1 in any one year, although being 1:1 over a longer period of time (Gibbons 1983). Reports for the genus Kinosternon (Gibbons 1983; Carr and Mast 1988; Iverson 1991) are inclined toward a 1:1 sex ratio. However, in the only previous work conducted on San Andre´s Island with K. scorpioides albogulare, Castan˜o-Mora (1992) found a sex ratio of 14 females per male. Even though this ratio might be skewed because of sampling error, because not all the habitats were sampled and only individuals from the mangrove forests edges were caught, it shows that sex ratios on the island can also change in different years or by collecting site. Long-term studies will be needed to determine the variation of sex ratios on the island. Conservation. — The fact that native islanders do not consume the turtle is important for its conservation on the island. Even though some people who inhabit the island occasionally take some individuals from the mangrove forests for food or for medicinal purposes, this extraction seems to be of minor importance. However, there are other indirect problems, e.g., contamination of the mangrove forests. Because people do not value the turtle, they throw garbage and domestic wastes in the mangroves that the turtle inhabits. The levels of contamination in some of

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these places can be very high, with turtles swimming among all sorts of garbage. This clearly diminishes habitat quality and affects the species. Recommendations for the conservation of the species on the island include the following. 1. Local authorities should take measures related to introduced species without delay. Simberloff (2003) suggested that the information needed to manage introduced species is often minimal, and that waiting to do more can make control more difficult or impossible in some cases. 2. Conduct environmental education programs to help increase the importance of the turtle for the islanders. 3. Stop pollution and contamination in the mangrove forest. 4. Conduct studies on the reproductive cycle of the turtle to help management plans. ACKNOWLEDGMENTS We would like to thank John Iverson who kindly corrected this article and contributed with suggestions and the bibliography. We also thank an anonymous reviewer and C. Kenneth Dodd Jr. who made important contributions and corrections to the text, and to A. Rhodin who helped us improve the final version of this paper. Special thanks to the people in San Andre´s Island and to Whadyd Jimenez Morales for his help during the field work. Thanks to the Universidad Nacional de Colombia and the Instituto Alexander von Humboldt for sponsoring the project. LITERATURE CITED ACUN˜A-MESSEN, R.A. 1998. Las Tortugas Continentales de Costa Rica. Costa Rica. San Jose´: Editorial de la Universidad de Costa Rica, pp. 41–48. BANCROFT, G.T., GODLEY, J.S., GROSS, D.T., ROJAS, N.N., SUTPHEN, D.A., AND MCDIARMID, R.W. 1983. The herpetofauna of Lake Conway: species accounts. U.S. Army Corps Eng., Miscellaneous Papers, A-83-5:164–207. BARRIGA, E., HERNA´NDEZ, J.H., JARAMILLO, I.J, JARAMILLO, R., MORA, L.E., PINTO, P., AND RUIZ, P.M. 1969. La isla de San Andre´s, contribuciones al conocimiento de su ecologı´a, flora, fauna y pesca. Bogota, D.E.: Instituto de Ciencias Naturales, Universidad Nacional de Colombia. Direccio´n de divulgacio´n cultural publicaciones, 50 pp. BERRY, J.F. AND IVERSON, J.B. 2001. Reptilia: Testudines: Kinosternidae, Kinosternon scorpioides. Catalogue of American Amphibians and Reptiles 725:1–11. BERRY, J.F. AND LEGLER, J.M. 1980. A new turtle (genus Kinosternon) from northwestern Mexico. Contributions in Science, Natural History Museum of Los Angeles County 325: 1–12. BURY, R.B. 1979. Population ecology of fresh water turtles. In: Harless, M. and Morlock, H. (Eds.). Turtles: Perspectives and Research. New York: John Wiley and Sons, pp. 571–602. CAGLE, F.R. 1939. A system for marking turtles for future identification. Copeia 1939:155–162.

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generada por la introduccio´n de ‘‘Rana Toro’’ a Colombia. Revista de la Academia Colombiana de Ciencias Exactas, Fı´scas y Naturales. Volumen XXIII, Suplemento Especial, diciembre. Bogota´. pp. 367–393. SIMBERLOFF, D. 2003. How much information on population biology is needed to manage introduced species? Conservation Biology 17:83–92. TAMSITT, J.R. AND VALDIVIESO, D. 1963. The herpetofauna of the Caribbean Islands San Andres and Providencia. Revista de Biologia Tropical 11:131–139. Received: 25 December 2004 Revised and Accepted: 17 February 2006