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Update on the Cyclura c. carinata Rescue and
Relocation Project:
Big Ambergris Cay to Long Cay, Turks and Caicos Islands,
British West Indies
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The
Big Ambergris Cay iguana relocation project being conducted by the
Department of Environment and Coastal Resources, Turks and Caicos
Island (TCI), The Conservation Agency (TCA), and the Denver Zoo
continues to progress well in its third year. The iguanas on Big
Ambergris Cay are currently being displaced by an expansive
development project there. The island is populated by an estimated
15,000 Cyclura c. carinata (Coastal Systems International, Inc.1998.
Strategic Environmental Assessment for Big Ambergris Cay). The
developer's planned build-out leaves only small areas of the cay
undeveloped and it is his desire and that of the DECR that as many of
the iguanas as possible be moved before they are killed.
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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.
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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.
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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.
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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)
Participation from the staff at Denver
Zoo (www.denverzoo.org) and funding from the Denver
Zoological Foundation, private donations and volunteers to The
Conservation Agency, and the generosity of our hosts and partners at the
Department of Environment and Coastal Resources have been critical to
the success of the iguana relocation project to date.
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