Relocation-Site Selection

In January 1999 we examined potential targets for iguana translocation. Because the iguana is fecund, we assumed that all islands currently supporting iguana populations would be at carrying capacity under the existing environmental conditions on each. We therefore opted to select among islands without iguanas. We found that most islands without iguanas were either extremely small (<0.1 ha) or supported populations of feral cats or grazing ungulates (goats, cattle, donkeys, etc.). Islands were either too small to be suitable (iguana populations there would be small and vulnerable to extinction) or islands needed restoration and management before they became suitable.

In view of these realities, Long Cay, Caicos Bank, part of the Admiral Cockburn Nature Reserve, stood out as the best candidate for a relocation site. It is large (111 ha), and could support a large iguana population (thousands). The drawback was the population of feral cats that lived there.

Cyclura c. carinata formerly lived on Long Cay (Schwartz and Thomas 1975), and had been seen there by John Iverson in visits between 1974 and 1977 (pers. com.), but had been since extirpated, presumably by cats. Rats and mice (Rattus rattus and Mus musculus) also were in evidence on the cay but we did not consider them a threat to the iguanas as they occur on most islands in the TCI including those with healthy C. c. carinata populations. There were no other feral mammals on Long Cay, though goats and pigs had ranged there in the recent past. We decided to restore Long Cay to suitable iguana habitat through cat eradication and focus the iguana relocation there. As our work progressed we considered that we might relocate individuals to nearby smaller islands as well.

Long Cay Cat Eradication

We chose to conduct an intensive cat poisoning campaign on Long Cay using 1080 (sodium monofluoroacetate) with follow-up trapping as needed. We collaborated closely with experts Dick Veitch (Papakura, New Zealand) and Charles Wigley (Tull Chemical Company, Oxford Alabama) who gave us guidance on dosage and handling. 1080 was chosen because it has been used, along with trapping, to successfully to eradicate cats on islands in New Zealand.

We carefully considered possible effects of the poison before conducting the cat removal work. Long Cay was an unusual island that lent itself to use of 1080: the island had no iguanas, no native mammals, few scavenging birds, and no nesting colonies of scavengers. We judged that it was possible, but unlikely, that incidental bird deaths would occur. There were few scavenging birds (birds likely to hunt for scraps of fish in the bush, e.g., gulls, terns) on Long Cay; there are birds that use the habitat but no nesting colonies of scavengers.

Cats are extremely susceptible to minute quantities of 1080, 20 times more susceptible than humans, 10 -30 times more susceptible than birds. Sub-lethal doses are metabolized and excreted. This chemical is broken down into non-toxic by-products by bacteria in soil or water. In freshwater the compound is 70% degraded after 24 hours. We also planned and equipped ourselves for supplemental cat trapping if it was necessary after the poisoning effort was concluded. Work was conducted in July 1999.

Though the cats seemed localized in certain parts of Long Cay, we set up bait stations that allowed us to systematically distribute the poison baits uniformly over the 3.5 km long island. Bait stations were flagged with surveyor's tape, numbered, and spaced 25 m apart in roughly parallel lines 50-100 m apart. The northeast section of the island is 50m or less in width and therefore had only one line of bait stations, wider mid-sections of the island had 4 parallel lines of bait stations, and so on, depending on the width of the cay.

Fish chunks (Clupeidae) or whole minnows (Atherinidae) injected with 0.009 ml of 1080 in a 22% solution was used as bait. Most of the bait was placed or skewered on branches overhanging clearings or trails at a height of about 15 cm. This placed the bait at cat nose-height out of the reach of land crabs. On the beach, or in areas without vegetation, bait was placed on inverted plastic cups (15 cm high) that were filled with sand to prevent them from being displaced by wind. Thorough and even coverage of Long Cay required more than 460 bait stations. Bait was laid at the stations between 1600-1900 h to minimize exposure to heat and scavenging birds. Old baits were collected when fresh bait was deposited daily for 5-6 days. At the end of the week, leftover toxin and contaminated items were diluted to non-toxic levels and disposed of or burned, respectively.

Cats Gone, Iguana Relocation Begins

In November 1999, we examined the island carefully for tracks or signs of cats. In three days of surveys no evidence of cats was seen anywhere on the cay. No follow-up trapping appeared necessary. This result allowed us to proceed with the next step: iguana relocation.

In mid-November 1999, the first iguanas, a test-group of 25, was taken from Big Ambergris Cay to Long Cay. Survivorship of this small group, which included age classes susceptible to cat predation (75 g), would provide a second test for presence/absence of cats. If this translocation was successful, future groups to be relocated would be larger (200 individuals) and would consist primarily of larger animals (500-1200g).

Between November 1999 and January 2000, during our field sessions and weekly radio tracking, no cat tracks were seen on Long Cay and survivorship of radio-tagged iguanas was 100%. On 23 January, however, we found tracks from a cat that one of us (Wesley Clerveaux) confirmed had been recently released on Long Cay by its owner from South Caicos. We succeeded in trapping and removing the cat from Long Cay within two weeks.

This event reinforced the necessity of increasingly involving the community of South Caicos and reaching everyone with the message that unwanted animals should not be dropped off on uninhabited cays - particularly Long Cay. DECR patrols and courtesy visits to vessels cruising the area are underway, and informational signs for Long Cay have become a priority. One sign has already been placed in the village. The DECR is also placing signs on all Long Cay beaches.

We began production of a series of informational public announcements for local cable TV. In this regard we were lucky enough to have the services of a professional filmmaker, Vladimir Bibic. He donated time, equipment, and materials and has completed two public service announcements which were aired in May 2000. In June, Julia Jones, the Governor's wife presided over a ribbon-cutting ceremony on Long Cay.

During January and February 2000, radio-collared iguanas in the test group of 25 animals were recaptured and radio collars were removed. Animals were weighed and measured. All appeared healthy and each had established one or more burrow sites. 2 collars malfunctioned (stopped transmitting), however, and were not recovered during this session. We will attempt to recapture the iguanas and remove the collars as the weekly monitoring continues.

We captured and moved 208 iguanas from Big Ambergris to Long Cay during the January-February field-session. We attempted to collect as many females as possible because the first group of 25 animals appeared to be male-biased (16:9). We took all low-crested, 250-500g, iguanas we encountered with the hope that they would prove to be female. We took animals from the same area on the north end of the cay in three separate missions. In spite of our focus on targeting females, probing (an internal check for presence/absence of hemipenal pouches using thin lubricated rods) demonstrated the group again appeared heavily male-biased (154:54). Most individuals we captured with what one might consider "female qualities" (low crests, small femoral pores, no visible hemipenal bulge or pouch) were judged by probing to be immature males. We have found that we cannot distinguish young males from females without probing.

We suspect that our catch is representative of the population in the area we hunted and, if probing is a reliable way of determining sex in C. c. carinata, reflects a true male-biased population in this area of Big Ambergris. A sex-bias would be extremely interesting as the existing literature on Cyclura carinata populations, including the Big Ambergris population, reports 1:1 sex ratios. We will track these data closely as we continue to capture iguanas on the cay in different areas and, if the trend continues, will be preparing a manuscript describing this apparent anomaly later this year.

In order to monitor the animals on Long Cay, relocated iguanas are permanently marked with PIT tags (which allows animals to be identified with a bar-code reader). The sex of all iguanas is confirmed by probe, animals are weighed, snout vent length is recorded, and distinguishing features (e.g., regenerated tails, pigmentation, dorsal spine anomalies) are noted. 10 individuals in each group relocated are fitted with radio collars and are monitored weekly until the next translocation.

During weekly checks of radio-tagged iguanas we record animal location using D-GPS, as well as habitat and behavior variables. Most animals allow us to approach them closely. Plant species within a 0.5 m radius of each animal are recorded. Most iguanas are seen basking on rocks, climbing in shrubs, or hidden in burrows. We note the condition of all radio-collared animals and uncollared animals opportunistically. On return to the lab, data are transferred to a GIS data base.

Future Plans

Since our first translocation in November 1999 we have relocated a total of 404 iguanas.   Cats are no longer present on Long Cay.  We continue to collect data on iguana habitat use, burrow location, home range dynamics, and will soon be collecting information on reproduction and recruitment of young.  Since all Long Cay founders are PIT tagged, and dispersal to the cay is unlikely, we can be reasonably sure that untagged iguanas were born there.  In January 2001 we confirmed the presence of Long Cay hatchlings.  Volunteers are always welcome and should contact Numi Mitchell regarding expedition schedules.

Numi Mitchell, Ph.D. (Biologist, The Conservation Agency, 67 Howland Avenue, Jamestown RI, USA, 02835), Michelle Fulford-Gardner (Chief Scientific Officer, DECR, South Base, Grand Turk, Turks and Caicos Islands, BWI), Rick Haeffner (Curator, Denver Zoological Gardens), Wesley Clerveaux (Fisheries Biologist, DECR Fisheries Office, South Caicos, Turks and Caicos Islands, BWI), Glenn Mitchell (Biologist, The Conservation Agency, 67 Howland Avenue, Jamestown, RI, USA, 02835)