Abstract

The iguanas of the West Indies are large herbivorous lizards comprising 18 taxa in two genera. Once abundant, West Indian rock iguanas are now the most endangered lizards in the world facing further population declines due to habitat destruction and predation of young by introduced mammalian predators. Emergency conservation efforts for five species of rock iguana are targeted at increasing the recruitment of juveniles into the population through headstart and release. Repatriation programs carry the inherent risk of introduction of pathogens into naïve wild populations. An integral component of the rock iguana headstart programs is comprehensive health assessment of wild and headstarted iguanas in order to generate species databases and to assess the suitability for release of the headstarted individuals. Establishment of a strong veterinary network within range countries is essential for the long-term success of these programs.

Background

The iguanas of the West Indies are large herbivorous lizards restricted to islands in the northern Caribbean archipelago, primarily the Bahamas and Greater Antilles. Comprising 18 taxa in two genera, these lizards are the largest vertebrates endemic to the Caribbean islands. Once abundant, West Indian rock iguana populations have been devastated by habitat destruction and by the deleterious effects of introduced mammalian predators such as feral cats, mongoose and feral pigs, and forage competitors such as goats.³ West Indian rock iguanas are arguably the most endangered lizards in the world. Recent World Conservation Union (IUCN) Red List assessments rank nine taxa as critically endangered, four as endangered, and the rest as vulnerable.^3,9 Several taxa are at risk of extinction, with three species represented by less than 200 individuals. The primary cause of population decline of West Indian rock iguanas is lack of recruitment of juveniles into the population. Recruitment of juveniles is essential if extinction is to be avoided. Headstarting, or captive rearing and release, has been recommended as priority conservation action for six of the 18 taxa of West Indian iguanas.³

The use of captive-bred or captive-held animals to establish or augment wild populations of endangered species has become a popular yet controversial conservation technique.^5,6,11 For reintroduction programs that involve the release of captive-held animals into an existing wild population, the potential for disease or parasite transmission to the naïve wild population is of paramount concern.^2,4,6,10 Introduction of pathogens into naive populations of herpetofauna has proven to be devastating to some species.¹⁰ Unfortunately, no screening system can ever be 100% effective in identifying potential pathogens. Therefore, the release of captive-held animals will always entail a risk to any resident (host) population. Re-introduction programs that involve the release of captive-held animals should be undertaken only in cases where extinction appears otherwise unavoidable. The extinction crisis of the West Indian Rock iguanas demands that reintroduction be regarded as a viable strategy for recovery of these critically endangered taxa.

Currently headstart facilities are in operation in the range country for five of the most critically endangered species including the Jamaican iguana, Cyclura collie (since 1991), the Grand Cayman iguana, Cyclura nubila lewisi (since 1990), the Anegada iguana, Cyclura pinguis in the British Virgin Islands (since 1997), the Mona Island iguana, Cyclura cornuta stejnegeri in Puerto Rico (since 1999), and the Ricord’s iguana, Cyclura ricordi in the Dominican Republic (2002). All of these species face a 50% chance of extinction within the next 10 yr in the absence of immediate and intensive conservation intervention. Veterinarians play a vital role in ensuring the health of the headstart populations and in assessment of risk of introduction of these animals to the wild population. Rigorous health screening prior to release can substantially reduce the potential for disease transmission to wild populations.^7,8 When coupled with comparative data from wild populations, health assessments are invaluable in determining the suitability of headstarted animals for release. The IUCN has well-established guidelines governing reintroductions in general⁸ and specifically for iguanas⁷.

Health Assessment Program

In 2000 the IUCN West Indian Iguana Specialist Group published the first Status Survey and Conservation Action Plan for West Indian Iguanas. The veterinary component of the action plan includes three specific goals: 1) the establishment of baseline biologic and medical data on captive and wild Cyclura; 2) the assessment of the suitability of captive reared individuals for release to the wild through pre-release health screening and 3) maintaining the health of captive Cyclura through consultation on nutrition, environmental conditions, animal density, disease transmission, etc.

The establishment of biologic and medical data on wild iguanas is essential to the health screening programs used in headstart. Without knowledge of “normal” values and endemic infectious agents in wild populations, assessment of the suitability of headstarted animals for release is very difficult. Therefore, health screening of both captive and wild iguanas is being conducted. Each assessment includes:

• Physical assessment of each specimen.
• Body weight, standard measurements, and growth data.
• Collection of whole blood for genetic analysis, white blood cell counts and differentials, screening for blood parasites, and measurement of hematocrit and total solids.
• Collection of plasma for measurement of biochemical parameters and vitamin D levels. Collection of feces or cloacal swabs for assessment of normal intestinal bacterial flora and to screen for bacterial pathogens.
• Collection of feces for assessment of intestinal parasite burdens.

Status of Current Headstart Programs (Jamaican Iguana, Cyclura collei)

The Jamaican iguana was considered extinct for much of the last century, until a remnant population was discovered in the rugged, pristine, dry forest of Hellshire Hills in 1990. As arguably the “rarest lizard in the world”^1,3 this critically endangered species has been the subject of an intensive conservation program. Two active nest areas have been identified. Survey efforts suggest a population containing as few as 50–200 individuals with a highly skewed age structure; juvenile and sub adult animals are not observed, indicating that recruitment is inadequate to maintain a viable population. Predation by the introduced Indian mongoose is considered the single most important factor preventing recruitment into the breeding population. Two emergency conservation measures have been undertaken to alleviate high juvenile mortality: regional predator control and headstarting of hatchlings.

In the 10 yr since the inception of headstarting 142 iguanas have been raised. Five (3.5%) have been lost to disease. The majority of medical concerns result from conspecific trauma in the headstart facility. The health of the headstart C. collei population is excellent. Hatchlings collected at the nest sites are vigorous. They adapt to the captive environment and diet immediately and grow rapidly. Between 1995 and 2001 39 animals had been released to the wild. Successful reproduction in released females was documented in 2001. Ninety-seven iguanas have had comprehensive health assessments performed. These iguanas include animals selected to be released into wild Hellshire Hills habitat, long term inhabitants of the head start facility, and a handful of free ranging iguanas. The data generated from these health evaluations were used to assess the health of animals to be released as well as to establish a database of normal medical and physiologic values for this species.

Grand Cayman Iguana (Cyclura nubila lewisi)

These iguanas are critically endangered with the total number of wild specimens less than 175 individuals scattered in three fragmented populations. Predation by feral cats and habitat loss for commercial development are the main threats to this species. The conservation plan for Grand Cayman iguanas combines research, habitat protection and education using the iguana as the flagship species toward the broader goal of protecting the island’s unique natural environment. Although a headstart program was established for this species, there has only recently been a veterinary component to the program. Thirty-five headstarted yearlings have been released over the past 5 yr with no prior health assessments. Establishing health and nutritional assessment protocols for this program is a high priority for the IUCN Iguana Specialist Group. Comprehensive health evaluations of individuals in the headstart facility were conducted in 2001, with plans to continue health assessments and improve captive management in coming years.

Anegada Island Iguana (Cyclura pinguis)

This critically endangered iguana once ranged over the entire Puerto Rico Bank, but predation by feral cats and habitat destruction have resulted in one remaining population of less than 200 individuals on Anegada Island in the British Virgin Islands. Protection of habitat and predator eradication will be essential to the survival of this species. A headstart program was initiated in 1997 and currently houses 48 individuals. Health assessments of 17 captive and nine wild animals helped to establish a normal values database. However, more veterinary involvement is needed to improve husbandry and nutrition in the headstart facility and to assess the health of animals selected for release. Plans are underway for the first release in 2002. These individuals will be fitted with coelomic transmitters for post-release monitoring of movement, activity and survival.

Mona Island Iguana (Cyclura cornuta stejnegeri)

This iguana is endemic to a remote Puerto Rican island that is located midway between Puerto Rico and Hispaniola. The island is designated as a National Historical Landmark and as such is a protected habitat for these iguanas. Disruption of nests by feral pigs and competition for forage resources with feral goats constitute the largest threats to these animals. Veterinary involvement in this program was initiated following concerns over blindness in wild iguanas. Investigation revealed cataracts in a geriatric wild population, supporting the observation that the population is aging, recruitment of young animals is inadequate to sustain the species in this habitat. Exclusion fences to keep pigs and goats out of the nest areas are in place. This wild population is one of the most thoroughly studied of the rock iguanas. Comprehensive health assessments have been performed on 42 wild animals. Headstarting was initiated in 1999. The facility currently houses 72 individuals. Pre-release health screening and placement of coelomic transmitters will take place in 2002 in preparation for the first release of headstarted animals to the wild.

Ricord’s Iguana (Cyclura ricordi)

Ricord’s iguanas are found only in southwestern Dominican Republic. There are less than 4,000 individuals in two isolated populations, and they are considered critically endangered by IUCN. Ricord’s iguanas are sympatric with another Cyclura species, the Rhinoceros iguana (Cyclura cornuta cornuta). It is interesting to note that although they share the same basic habitats, Rhinoceros iguanas are doing relatively well. Ricord’s iguanas are most threatened by predation from exotic species, although burning for charcoal is also a problem at the Haitian boarder. Comprehensive health assessments of 23 wild individuals have been conducted, and a captive breeding program was initiated in 2000 at Parque Zoologico Nacional, in Dominican Republic with 32 adult animals. The IUCN Iguana Specialist Group is meeting in Dominican Republic in late 2002 to develop an action plan for the conservation of Ricord’s iguanas.

Discussion

Saving the West Indian rock iguanas from extinction requires an immediate, multi-disciplinary, comprehensive effort. Conservation biologists, ecologists and veterinarians must work closely with political, regulatory, and educational groups to secure a future for these animals. The IUCN identified headstarting as a primary conservation strategy for this group of animals. The utility of headstarting is greatest for taxa with indeterminate growth and a large size differential between juvenile and adult stages, and for which high juvenile but low adult mortality rates exist in the wild. This situation is typical of many ectothermic vertebrates. In addition to exhibiting this suite of life history characteristics, rock iguanas do not depend on learning for their requisite survival skills (e.g., food acquisition, refuge site selection). Their innate survival mechanisms remain intact, even after years in captivity. Unlike many birds and mammals, rock iguanas do not require lengthy pre-release conditioning or training.⁷ They are ideal candidates for headstart programs.

Despite the necessity for headstarting in the Cyclura recovery programs, one must acknowledge and seek to reduce the risk inherent in the programs. The role of the veterinarian is critical. Risk cannot be eliminated, but veterinarians skilled in exotic animal and conservation medicine can significantly enhance the chances for successful outcome. It is important to note that to date veterinary involvement in the West Indian rock iguana programs has been initiated and conducted primarily by veterinarians based in the United States. The importance of providing a solid program of in-country training for local veterinarians cannot be overstated. Ultimately, these animals must be conserved in the countries where they naturally occur. For the five headstart programs discussed in this paper, training of local veterinarians and technology transfer is taking place. The goals are to generate consistent, sustained interest in the programs by veterinarians in the range countries, to provide appropriate training in technical and diagnostic reptile medicine, to create an infrastructure of facility and laboratory support necessary for continuation of these programs. It is only through local capacity-building that these programs can continue until the day that populations recover and intensive headstarting is no longer needed.

Literature Cited

1.  Alberts AC. 1993. The most endangered lizard in the world: the Jamaican iguana, Cyclura collei. Vivarium. 5:12–14.

2.  Alberts AC, ML Oliva, MB Worley, SR Telford, Jr., PJ Morris, DL Janssen. 1998. The need for pre-release health screening in animal translocations: a case study of the Cuban iguana (Cyclura nubila). Animal Conservation. 1:165–172.

3.  Alberts A. 2000. Status Survey and Conservation Action Plan: West Indian Iguanas. (ed). IUCN/SSC West Indian Iguana Specialist Group. IUCN - the World Conservation Union, Gland, Switzerland.

4.  Cunningham AA. 1996. Disease risks of wildlife translocations. Conservation Biology. 10:349–353.

5.  Dodd DK, Jr., RA Seigel. 1991. Relocation, repatriation, and translocation of amphibians and reptiles: are they conservation strategies that work? Herpetologica. 47:336–350.

6.  Griffith B, JM Scott, JW Carpenter, C Reed. 1993. Animal translocations and potential disease transmission. Journal of Zoo and Wildlife Medicine. 24:231–236.

7.  Hudson R. 2000. Reintroduction guidelines. In: A Alberts, ed. Status Survey and Conservation Action Plan: West Indian Iguanas. IUCN/SSC West Indian Iguana Specialist Group. IUCN - the World Conservation Union, Gland, Switzerland

8.  IUCN. 1995. Guidelines for Re-Introductions. IUCN/SSC Re-Introduction Specialist Group, IUCN - the World Conservation Union, Gland, Switzerland.

9.  IUCN. 1996. IUCN Red List of Threatened Animals. IUCN - the World Conservation Union, Gland, Switzerland.

10.  Jacobson ER. 1993. Implications of infectious diseases for captive propagation and introduction programs of threatened/endangered reptiles. Journal of Zoo and Wildlife Medicine. 24:245–255.

11.  Reinert HK. 1991. Translocation as a conservation strategy for amphibians and reptiles: some comments, concerns, and observations. Herpetologica. 47:357–363.