|Scientific Name:||Cyclura lewisi|
|Species Authority:||Grant, 1940|
Cyclura macleayi subspecies lewisi Grant 1940
Cyclura nubila subspecies lewisi Grant, 1940
|Taxonomic Notes:||Previously listed as Cyclura nubila lewisi, this taxon has recently been recognized as a full species, Cyclura lewisi by the IUCN SSC Iguana Specialist Group, in light of genetic data (Malone et al. 2000) and a review by Burton (2004). The Reptile Database (see http://www.jcvi.org/reptiles/species.php?genus=Cyclura&species=nubila) treats it as a subspecies of C. nubila.|
|Red List Category & Criteria:||Endangered B1ab(iii)+2ab(iii) ver 3.1|
|Reviewer/s:||Grant, T. & Hilton-Taylor, C.|
Due to ongoing conservation actions, the Grand Cayman Blue Iguana population is currently increasing and expected to continue to increase. However, the small extent of occurrence (15.6 km²) reflects the fact that the species is now effectively restricted to managed protected areas. The surrounding and intervening land, once also occupied by iguanas, is inexorably declining in quality as roads, housing, and other human infrastructure expands bringing associated invasive alien predators (dogs, cats, and rats). The loss of recolonization options may eventually impact the population, hence this is treated as a continuing decline.
Within the three protected areas suitable habitat is quite restricted. The estimated current area of occupancy is 0.5 km²based on the summation of monitored iguana locations. This area may increase slightly in the next decade, but is currently not predicted to reach one km² (using the recommended grid size of 2x2 km for estimating AOO increases the area to 12 km², a figure which is well within the Endangered threshold and very close to the Critically Endangered threshold). The species does not qualify as Critically Endangered under criterion B2 because it is known from more than one location, and is not severely fragmented.
The three protected areas (QE II Botanic Park, Salina Reserve, and Colliers Wilderness Reserve) support the entire three subpopulations, the largest of which is approximately 319 adults in the Salina Reserve. The subpopulation structure is predicted to remain stable, and the number of breeding age iguanas within the Salina Reserve and Colliers Wilderness Reserve is expected to increase. Future population growth is not likely to be possible beyond a total of approximately 1,000 adults, unless additional protected habitat is secured.
|Range Description:||The Grand Cayman Blue Iguana is endemic to the island of Grand Cayman, Cayman Islands, and currently is only found in the districts of North Side and East End. It occurs from 1-6 m above sea level. Formerly believed (from fossil evidence) to have occurred in suitable habitats throughout Grand Cayman, by 2002 this iguana’s distribution had contracted to a four km² area of occurrence in the east interior. Since then, repatriation of captive-reared and head-started juveniles to protected areas has expanded its extent of occurrence to 15.6 km² in three subpopulations located in the QE II Botanic Park, the Salina Reserve, and the Colliers Wilderness Reserve (Burton 2011). The area of occupancy within these areas is 0.5 km². Significant breeding populations of Cyclura lewisi no longer occur outside these protected areas.|
|Range Map:||Click here to open the map viewer and explore range.|
The wild population of Grand Cayman Blue Iguana is currently estimated at 443 adults, based on known number of iguanas released to the wild and with ongoing monitoring. This is a significant increase compared to three generations ago (78 years) when the population may have been of the order of 250 adults. By 2002, that estimate had further reduced to less than 25 adults surviving in the wild (Burton 2002).
The Blue Iguana Recovery Programme (a programme of the National Trust for the Cayman Islands with local and international partners) maintains a captive breeding and head-starting facility that currently houses an additional 175 iguanas (Grant 2009). With ongoing conservation work, we anticipate the wild population will rise to 1,000 iguanas and stabilize within the next three generations. As a long-lived species with an extended reproductive life, Cyclura lewisi is not subject to extreme population fluctuations.
As a direct result of conservation action, plus natural reproduction in protected areas, the population of Grand Cayman Blue Iguana is increasing.
|Habitat and Ecology:||
Comparison with other rock iguana species in the region strongly suggests there was once a coastal population of Cyclura lewisi, which was gradually displaced or extirpated by human settlements and the construction of a perimeter highway. The sparse interior population is believed to have attracted iguanas to agricultural clearances, where, by 1993, the remnant wild population was occupying the intergrade between dry forest/shrubland and traditional fruit farms. The farms provided thermoregulatory opportunities, herbaceous browse, fallen fruit, and nesting soil, but also brought the iguanas into harmful contact with people.Like all Cyclura, the Grand Cayman Blue Iguana is an annual breeder, laying one to 22 eggs depending on the female’s age and size. Hatchlings are vulnerable to native snakes (Cubophis caymanus) and naturally have a very high mortality rate. Head-starting young through the first two years increases survival greatly, and is proving an effective medium-term conservation strategy. This is one of the larger rock iguana species, with the biggest males known to exceed 10 kilograms in mass. Breeding begins in the third year, assuming adequate nutrition. The estimated generation length is approximately 26 years. Average longevity is not known, but may be in excess of 50 years. One male, whose final home was at a US zoo, was known to have lived for at least 69 years.
Feral and free-roaming dogs and cats kill adults and juveniles respectively and have been shown to be capable of causing local extinction of other Cyclura species in absence of other threats (e.g., Iverson 1978). Norway Rats (Rattus norvegicus) have also been observed to cause severe injury to Grand Cayman Blue Iguana hatchlings and may cause mortality. Cats, rats, and dogs have been observed throughout all areas of remaining Grand Cayman Blue Iguana occurrence. In 2002 dogs were seen in areas that had supported nesting as recently as 1993. Dog attacks have resulted in observed deaths of adult free-roaming iguanas in the QE II Botanic Park. Predation by feral species generally is regarded as one of the major ongoing threats to this iguana.
Habitat conversion is the second-most major threat to the Grand Cayman Blue Iguana. Traditional fruit farms have been converted to grassland for cattle grazing on a large scale over the last two decades. The loss of fruit trees and herbaceous browse, combined with soil compaction, means this conversion has drastically reduced the extent of suitable habitat for the iguanas. Increasingly, land is also being converted for human residential purposes, which brings an increase in rats, cats, and dogs.
Vehicular road access to farms in inland residential subdivisions has brought fast-moving traffic into remnant iguana areas. Deaths of iguanas dispersing out of protected areas and encountering fast-moving vehicles are now documented every year.
Although Cyclura lewisi is protected under local legislation, occasional illegal captures (not involving international trade) do occur.
A large breeding population of alien Common Green Iguana (Iguana iguana) from Central America has become established on Grand Cayman. While no resulting direct threats to native iguanas have become evident, the presence of another iguana species confuses public awareness effort for conservation of Cyclura lewisi. Occasional specimens of the closely related Sister Isles Rock Iguana (Cyclura nubila caymanensis) from Little Cayman have been found free in western Grand Cayman as a result of deliberate or accidental transport of hatchlings on boats and aircraft. No sightings have occurred in eastern Grand Cayman where C. lewisi persists, but there is clearly a potential risk of hybridization.Despite a historic tradition of consuming the tail meat of iguanas, modern-day Caymanians do not generally eat iguanas. However, an increasing Central American immigrant human population has brought a tradition of consuming Iguana iguana to Cayman, and there is a danger that this practice could be redirected to native species and threaten Grand Cayman Blue Iguanas.
The National Trust for the Cayman Islands owns and protects a substantial network of terrestrial protected areas, but within Grand Cayman suitable protected land for the Grand Cayman Blue Iguana is relatively scarce. The Blue Iguana Recovery Programme is successfully breeding these iguanas in captivity, head-starting them to two years old (along with hatchlings from selected wild-laid nests), and releasing them all into protected areas on Grand Cayman. After initial pilot releases into the QE II Botanic Park, the main release effort has been to the Salina Reserve and the Colliers Wilderness Reserve, both in the east interior of Grand Cayman.
These restored populations have all started breeding in the wild. Long term, the programme seeks to restore a genetically diverse, self-sustaining population of approximately 1,000 adult iguanas. Control of feral predators will be required in perpetuity, and to this end nature tourism activities in the Colliers Wilderness Reserve are being developed to generate the necessary sustainable income.
The Grand Cayman Blue Iguana is fully protected under local legislation and is effectively kept out of international trade by inclusion in Appendix I of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES).Grand Cayman Blue Iguanas today are recognized as a significant nature tourism attraction for Grand Cayman. Although the population was restored for conservation reasons, it now constitutes one of the main visitor attractions to the QE II Botanic Park. Under this controlled setting with exclusion of dogs and cats, this synergy is proving beneficial to both the Park and the iguanas.
|Citation:||Burton, F.J. 2012. Cyclura lewisi. In: IUCN 2012. IUCN Red List of Threatened Species. Version 2012.2. <www.iucnredlist.org>. Downloaded on 25 May 2013.|
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