Counting the blue iguanas

Matt Goetz, Durrell and Fred Burton, Blue Iguana Recovery Programme

Last December saw the sixth annual release of young Blue Iguanas (Cyclura lewisi) into Grand Cayman’s Salina Nature Reserve brought the total number of iguanas released back into the wild on Grand Cayman to over 300. It was now time to take a detailed look at how all those iguanas were doing. We knew they started breeding in the wild in 2006, but how successful had this natural breeding been in raising the total wild population even further?

Permanent artificial retreats, ranging in size, have been placed throughout the core area of the release site. We wanted to know whether these have had a positive effect on the population density within the protected area. We also wanted to know how many iguanas have dispersed out of the release area and how far have they have travelled. These are the sort of specific questions that will help us address the most important question, especially in light of the forthcoming planned releases into the new second big nature reserve, Is the release strategy actually working?

With a methodology specifically designed for this project, three survey teams were formed to stealthily walk every trail in the Salina Reserve, scanning intensely for iguana sightings twice a day, six days a week for over three weeks, for a total of 18 survey days and 108 individual survey walks.

I joined the survey for the first two weeks in March to lead and instruct an additional “catch-and-tag” team. This team would back up the survey party with focused attention on any un-tagged or elusive iguanas which the survey teams were unable to identify as they passed. Besides identifying such individuals we were also recapturing iguanas which had lost their markings. At the same time we took the opportunity to take morphometric data. Additionally any hatchlings from the previous year were caught for marking and samples were taken for genetic analysis.

The thing is that whilst most of the iguanas are generally easy to catch with the right method, this only works for the first attempt. Once these astonishingly smart reptiles got the idea of what we were up to, they would instantly avoid a second such situation. So we had to make sure to have a couple of catching methods available to ensure capture success the first time round.

With a lot of hard work the teams were able to complete the survey of the Salinas reserve by the end of March, and now the number crunching and mapping work begins. All in all we had 162 total survey walks, 945 person-hours of survey work, 466 iguana sightings in total and 46 individual iguanas identified in the survey area. By early May the results of the analysis should be clear enough to guide the Blue Iguana Recovery Programme in it’s next big endeavor of the year – the first iguana release into the new Blue Iguana Reserve!