According to the latest Blue Iguana survey, about 750 of the once effectively extinct reptiles now survive in the wild in Cayman.
The next release of the iguanas from the local breeding programme planned this summer will bring the number of the animals in the wild up to 800, edging ever closer to the 1,000 target the Blue Iguana Recovery Programme set for itself some years ago.
The most recent estimates of the iguana population is about 750 in the wild – 400 in the Salina Reserve, 310 in Colliers Wilderness Reserve and 40 in and around the Queen Elizabeth II Botanic Park.
“This summer we should bring that number up well over 800, with our next release. If we rely only on releases, we may be three years away from our 1,000 goal, but we may get there quicker if the rate of wild breeding rises enough to contribute in the same time frame,” said Fred Burton, head of the recovery programme.
“Getting 1,000 out there is only part of the target … we need to know the population is sustaining itself before we can close the captive breeding and headstarting effort,” he added.
Mr. Burton explained that due to the large size of the tracts of land into which Blue Iguanas are released, it is difficult to ascertain exact numbers during the surveys his team carries out, so the population numbers are based on how many iguanas have been released minus how many they know have died.
“We assume that some have died that we don’t get to know about and know that some wild-born hatchlings do make it to adulthood, and maybe these two balance each other out,” he said.
Iguanas that have been released are breeding in the wild, the surveys have found.
“We have evidence that the released Blue Iguanas started breeding in the Queen Elizabeth II Botanic Park in 2001, in the Salina Reserve in 2006, and in the Colliers Wilderness Reserve in 2011. Wild-born hatchlings have been sighted in all three locations most years since,” Mr. Burton said.
However, the Salina Reserve survey last March turned up only iguanas that the team had released, including some that had been living wild there since 2004.
“The iguana population density in the release area has stayed the same since March 2010 when we surveyed it using the same technique and areas as this year. In the time between surveys, we did release a few more young ones into the same area,” said Mr. Burton, adding that most of the iguana releases were into the Colliers Wilderness Reserve in those years.
He said that between 2010 to 2013, in the 650-acre Salina Reserve in East End, “the number of new hatchlings being born was too few to exceed losses to snake predation and dispersal out of the area”.
“As the females get bigger, they will lay more eggs each year and at some point the annual production of hatchlings will reach the critical point where we start to see wild hatched iguanas join the core breeding population. On a much smaller scale, this seems to have happened already in the QE II Botanic Park, but there are issues there with the very small area meaning it can support only 30 to 40 iguanas – not a genetically viable population size,” he added.
The team surveys a small area of the Salina Reserve and part of the 190-acre Colliers, also in East End, which will next be surveyed in March.
“The released iguanas disperse outwards from the release areas, so we can’t easily estimate the total population that way. What we can do is monitor for change – good or bad, and spot the changes in age structure when the population starts to sustain itself,” Mr. Burton said.
There are concerns that invasive green iguanas pose a threat to the native blue by encroaching on its territories and using up local resources.
Mr. Burton reported that no green iguanas have been seen in the Salina or Colliers reserves, but are present in the Botanic Park.
“Hopefully the absence of lakes, ponds and canals in Salina and Colliers shrublands may mean the habitat is too dry for the greens. The park greens congregate especially around the lake there. We and the Park are putting some effort into managing their numbers there, but it’s difficult,” he said.
A survey in 2002 showed that only 10 to 25 blue iguanas existed in the wild and by 2005, the unmanaged wild population was considered to be functionally extinct. Since then, the Blue Iguana Recovery Programme has pulled the species back from extinction.
The species took a formal step back from extinction last year, when its status on the International Union for Conservation of Nature’s Red List was changed from “critically endangered” to “endangered”.