Report submitted by Ashley Campbell, Florida Atlantic University
The Roatán Spiny-tailed Iguana (Ctenosaura oedirhina) is listed as Endangered by the IUCN and as threatened by the Honduran government. This endemic species is found in high densities within pockets of protected habitat on Roatán. The protection offered in these areas is at the grassroots level and is very unstable; there is no enforced protection by local authorities. Outside of the protected areas, the iguanas are illegally harvested and found only in very low densities, if at all. The small, high-density areas are critical for the survival of this species on the island. Aside from hunting, these iguanas are threatened with habitat loss and fragmentation, predation from domestic species, and the potential encroachment of a related, invasive ctenosaur, C. similis.
This study continued to build on the past five years of research, began by S. Pasachnik and continued by A. Campbell. The objectives for 2015 were to continue the morphometric and demographic mark-recapture survey and to begin health and fitness evaluations from iguanas found in study sites. In future years, we hope to continue with this demographic work through training workshops, transforming this project into a long-term study of population dynamics in ctenosaur iguanas and a progressive education program.
As in previous years, life history and morphometric data were collected. In 2015, 100 new individuals were captured and tagged and 21 individuals were recaptured. Now 869 individuals have been tagged (~20% of the entire population). Analysis of all mark-recapture data indicated a very high adult mortality (potentially up to 80%) and analysis of distance sampling data indicate that densities have decreased over the course of this five-year study. The total population on the island is estimated at 4,130-4,860 iguanas. A population viability analysis shows the population declining towards extinction within the next decade and sensitivity analysis suggests that female mortality is a main factor in the decline.
As part of the new objectives this year, 50 flight distance surveys were conducted at three of the main study locations. Two of the locations could not be surveyed in this aspect because ofsteep cliffs and thick underbrush. Flight distance may indicate both habituation to human disturbance and increased predation risk (mostly from humans, in this case). Habituation to human disturbance could affect health, as seen in Hines (2011), where habituated iguanas were fed unnatural foods. A decrease in flight distance could also affect predation attempts making the species increasingly vulnerable to humans and other predators.
In 2013, ectoparasites (ticks and mites) were surveyed on all captured iguanas via handheld magnifier and forceps. Preliminary analysis of this data shows that there is a difference in ectoparasite load between study locations. To better understand this difference, this protocol was continued in 2015. Endoparasites had not previously been systematically surveyed in this species and were only known from post-mortem examination of car strike carcasses. Fecal samples were collected opportunistically from the ground or from the holding bags iguanas are placed in immediately after capture. They were analyzed for eggs, cysts, larva, and adult parasites using the standard veterinary techniques of floatation and smear slides. Blood samples were taken from the caudal vein and used to prepare a blood smear, which was analyzed under oil immersion for eggs, larvae, and adult parasites. Fifty fecal samples and 80 blood samples were analyzed. Fecal samples from I. iguana were also analyzed for comparison, as they are broadly sympatric with C. oedirhina. The C. oedirhina samples were generally free of internal parasites, with only two found with pinworm egg cases in the fecal float samples and three with microfilaria in the blood smears. The I. iguana fecal samples however were heavily infested with pinworm and flukes. The occurrence of external parasites on C. oedirhina appears to be related to substrate at the locations. Both flight distance and health data will be analyzed and summarized in a manuscript to be submitted in the summer of 2016.
This year, management at one of the study locations changed. Previously, we had relatively unrestricted access to this park during daylight hours, however this year we were unable to gain entrance on days when the park was closed to tourists (sometimes up to five days a week). This impacted the study because we could only reliably gain access when the park was full of tourists and some of the trails were being used for 4×4 off-road vehicles, making surveys dangerous and generally unproductive. We were unable to make contact with the new manager after multiple attempts, phones calls, and emails. While the estimated density at this location is similar to last year’s, we do not know if this population is still being protected the way it was before, making it potentially vulnerable. We will continue to reach out to this organization in hopes of once again gaining access, but more importantly in hopes of ensuring that this population is still protected. This situation demonstrates the vulnerability of this species as all stable populations of C. oedirhina are in privately owned areas that are protected by grassroots efforts and thus with a change in management the level of protection afforded at a given site can quickly change.
Milestones for 2015
• “Habitat Utilization of Roatán Spiny-tailed Iguanas (Ctenosaura oedirhina) and Its Implications for Conservation” was accepted for publication in the “Iguanas of the World” monograph volume of Herpetological Conservation and Biology.
• “Population genetics of Roatán Spiny-tailed Iguanas, Ctenosaura oedirhina” was accepted for publication in the “Iguanas of the World” monograph volume of Herpetological Conservation and Biology.
• “Piebaldism in Roatán Spiny-tailed Iguanas, Ctenosaura oedirhina” was submitted to the Journal of Herpetology for review.
• 50 fecal samples and 80 blood samples were analyzed.
• 100 new iguanas were captured and 21 were recaptured.
• Adult mortality was estimated at 81% for one of the locations using software Program Mark. The mortality at the other four locations could not be reliably estimated because of lack of resightings.
• Densities estimated from distance sampling at the study locations have declined 36% since 2012.
• The data show that the high-density populations have been decreasing since the beginning of the study. The current population size is estimated to be 4,130-4,860 individuals as of 2015.
• “An analysis of habitat usage and demography of the Roatán Spiny-tailed Iguana (Ctenosaura oedirhina)” Ph.D. dissertation by Campbell was written and will be defended on October 26, 2015.
• All data gathered and analyzed thus far will be used to complete a IUCN Redlist update during the 2015 annual ISG meeting.
• Additional manuscripts will be submitted:
o “Demography of the Roatán Spiny-tailed Iguana (Ctenosaura oedirhina)” – to be submitted spring of 2016.
o “Population Viability Analysis of the Roatán Spiny-tailed Iguana (Ctenosaura oedirhina)” – to be submitted summer 2016.
o “Conservation of an Endemic Iguana in Honduras” – to be submitted summer 2016.
o “Anthropogenic Influences on Health in Ctenoasaura oedirhina Populations” – to be submitted fall 2016.
Hines, K.N. 2011. Effects of Ecotourism on Endangered Northern Bahamian Rock Iguanas (Cyclura cychlura). Herpetological Conservation and Biology 6(2):250-259.