Cyclura rileyi ssp. rileyi
|Scientific Name:||Cyclura rileyi ssp. rileyi Stejneger, 1903|
See Cyclura rileyi
|Red List Category & Criteria:||Critically Endangered B1+2abcde ver 2.3|
|Assessor(s):||Carter, R.L., Hayes, W.K. & West Indian Iguana Specialist Group|
Inhabits six cays totaling 26 ha of marginal to good habitat. Data from 1994 and 1998 indicate that one population has gone extinct since 1994. Three others have declined by 18%, 16% and 32% respectively.
|Previously published Red List assessments:|
|Range Description:||Fossil remains found by Olson et al. (1990) indicate that San Salvador iguanas once occurred throughout the island of San Salvador (area 150 km²). Today, however, sightings on the mainland are exceedingly rare, occurring most often on the eastern side between Great Lake and Storrs Lake. At present San Salvador iguanas appear to be restricted largely to five tiny offshore cays (Gaulin, Goulding, Green, Low, Manhead) and two cays within Great Lake (Guana and Pigeon, Hayes et al. 1995). They were presumably extirpated on at least six additional cays, with two extinctions occurring in recent decades (discounting an unconfirmed sighting on High Cay in 1991). The seven inhabited cays range in size from 1–12 ha and total approximately 26 ha of marginal to excellent habitat.|
|Range Map:||Click here to open the map viewer and explore range.|
|Population:||Recent censuses by Hayes et al. (1995) suggested that approximately 500–600 individuals remain. However they suspected that juveniles were underestimated in their surveys, and have since learned that a moderate population thrives on Pigeon Cay, the one known population they had not yet visited. Nevertheless this subspecies likely numbers fewer than 1,000. Populations on the isolated cays vary from perhaps as few as 10 (Gaulin Cay) to as many as 250 (Green Cay). Several populations are threatened by human-related causes and appear to be declining.|
|Current Population Trend:||Decreasing|
|Habitat and Ecology:||The habitat on cays presently occupied by iguanas varies greatly. Vegetation on offshore cays is similar in varying degrees to coastal rock, sand strand and sea oat, and coastal coppice plant communities described on the mainland (Smith 1993). However, for cays within inland lakes, the vegetation resembles the blacklands coppice (Guana Cay) and mangrove (Pigeon Cay) communities on the mainland. Habitats on the mainland of San Salvador are highly diversified and suitable enough to harbor large iguana populations.
Mean and maximum body sizes of iguanas vary significantly from cay to cay, and are positively correlated with plant diversity. Iguanas are largest on Low Cay and smallest on Manhead Cay. Previously reported measurements of body size (Schwartz and Carey 1977) were limited to samples from cays having low plant diversity. Thus, prior recognition of C. rileyi as the smallest of the rock iguanas may be an artifact of historical extinctions resulting in extant populations being confined today largely to the most inaccessible cays having minimal plant diversity.
Iguanas are locally most common in the vicinity of limestone rock outcrops and/or patches of sea grape (Coccoloba uvifera). On some cays they are numerous in patches of buttonwood (Conocarpus erectus) where they ascend into the foliage to browse. On Pigeon Cay they are frequently encountered basking on the limbs of mangrove trees, often several meters or more above the ground. The iguanas share their habitat with nesting seabirds on several cays, most notably on Gaulin Cay where brown noddies (Anous stolidus) and sooty terns (Sterna fuscata) are extremely dense.
Aspects of feeding and reproductive ecology remain unstudied but are likely similar to other rock iguana species. Adult males appear to be territorial throughout the year. Courtship and mating probably occur in May, followed by nesting and egg-laying in June or July. Hatchlings probably emerge from nest burrows in September or October. Like other rock iguanas, San Salvador iguanas presumably require sandy areas for nest construction. Such habitat appears to be limited on Guana Cay, but the presence of several juveniles in 1994 is indicative of successful nesting there.
Although remote and relatively difficult to access, populations on the cays are still threatened by human-related causes (Hayes et al. 1995). The scarcity of juveniles on Low Cay is probably attributable to the presence of feral rats only recently detected there (Hayes et al. 1995). More recently, rats have also been seen on Guana, High, and Pigeon Cays. Considering the apparent impact of rats on insular populations of the tuatara (Sphenodon punctatus), an iguana-sized burrow-nesting reptile in New Zealand (Cree et al. 1995), rats probably pose a serious threat to survival of iguanas on several Cays and need to be exterminated soon. Rats may also impact iguana populations indirectly by affecting vegetation, especially on cays with low plant diversity.
The once dense population on Guana Cay (Ostrander 1982) has become greatly reduced in recent years. A mysterious die-off due to unknown causes occurred in spring 1994, as evidenced by the discovery of eight adult carcasses and an estimated surviving population of only 24 individuals (Hayes et al. 1995). Although natural disease is a possible cause, so too might be mosquito control efforts, recently implemented for the benefit of the growing tourism industry. The ticks which infest these iguanas have not been found on any other cay, and may have rendered the lizards more vulnerable to agents causing their deaths.
The larvae of a moth (Cactoblastis cactorum) introduced decades ago to the West Indies are now rapidly devastating prickly-pear cacti (Opuntia stricta), an important food source for iguanas, on several cays. The dense population of lizards on Green Cay is especially vulnerable, particularly since destruction of the cacti will be nearly complete within a matter of years, there are no known means of controlling the moth, and the remaining vegetation (nine plant species) represents a meagre diet compared to other rock iguana species (Auffenberg 1982). The impact of this ecological disturbance needs to be closely monitored.
Rapid development on the island of San Salvador will undoubtedly threaten the populations further. Feral dogs and cats are already numerous in local areas, but will increase as more resorts and housing tracts are constructed. This would seriously jeopardize any possible reintroductions of iguanas to the mainland, unless protected areas of considerable size could be set aside. Pollution of Great Lake due to environmentally unsound landfill practices may threaten the fragile mangrove community that harbors a moderate iguana population on Pigeon Cay. Eventually, tourists may discover the attributes of the iguanas themselves, which could increase potentially detrimental human-iguana contacts.
At present, baseline data are being collected on all populations of C. rileyi to aid conservation management decisions. Initial efforts involve population surveys, assessment of threats to survival, and genetic sampling. Genetic analyses are essential to resolve the taxonomic identities of the nominate taxa, to assess the degree of divergence among individual populations, and to evaluate heterozygosity (which may reveal inbreeding depression). Divergence may be sufficient that the genetic identity of most or all populations will need to be maintained.
Further steps include concentrated searches for isolated colonies on the mainland and on the southernmost lakes, as well as reintroductions of iguanas to previously inhabited cays. Further research is necessary to determine the suitability of each cay, and to assess what corrective actions would be necessary to render each suitable for reintroduction (e.g., removal of feral rats or supplementation of nesting habitat). Reintroduction of iguanas on the mainland should be undertaken only if protection of a large area can be assured. Additional comparative research planned for the isolated populations of this taxon includes vegetation analyses and studies of reproductive strategies, seasonal dietary shifts, and behavioral ecology.
At present, no legal captive breeding programs exist outside the Bahamas. The Bahamian government has wisely refused to issue export permits for any rock iguana taxa. However, Ardastra Gardens in Nassau (New Providence Island, Bahamas) currently holds two juveniles and plans to implement an in situ programme. Captive programs could be highly valuable for repatriation efforts, particularly if the genetic integrity of individual populations needs to be preserved.
A public relations campaign is planned to heighten awareness and appreciation among island residents for their endemic iguana.
|Citation:||Carter, R.L., Hayes, W.K. & West Indian Iguana Specialist Group. 2000. Cyclura rileyi ssp. rileyi. The IUCN Red List of Threatened Species 2000: e.T6048A12360803.Downloaded on 22 November 2017.|
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