THE THREATS TO FIJI’S NATIVE IGUANAS FROM THE EXOTIC GIANT INVASIVE IGUANA (GII)
The Giant Invasive Iguana (GII), scientifically known as Iguana iguana is a declared pest in Fiji. It is a herbivorous exotic pest brought illegally into Fiji and introduced on Qamea Island in early 2000. GII is now also found on the Matagi, Laucala, Taveuni and Viubani islands. GII is a large arboreal (tree-dwelling) species of lizard and is native to Central/South America and the Caribbean. Adults can reach more than 2 meters in length and weigh an average of 9 kilograms. Most GIIs are predominantly green in colour. However, the coloration is variable including black, grey, whitish, bluish and brown hues. GII has a very long tail which is 2 to 3 times the length of its body. The toes are long with thin curved claws for climbing. GII has spines along the head, neck and back, reaching up to its tail. It has a fold of loose skin hanging below the throat which is called the dewlap. GII also has large scale (leathery covering of their eardrums) on both sides of the neck. The large scale and the dewlap are key ways to differentiate between GII and the native Fijian iguanas. In this week’s article we look at GII in detail and the threats they present to Fiji’s native species of iguana. GII spends most of its time on trees amongst the canopy, descending only to mate, lay eggs or change trees. It also inhabits mangrove forests and saltwater habitats. GII also burrows into the ground usually close to the seashores or close to water. Although they prefer sun and seashores, they can invade inner lands and forests. GII can also sleep in available vegetation and occasionally they are seen sleeping in tunnels constructed in the ground. This behaviour may cause damage to infrastructure such as seawalls, concrete/tarsealed roads and even lead to small landslides causing damages to buildings. GII prefers a tropical to subtropical climate. They are excellent swimmers and can remain submerged in water for a long time. GII has excellent ability to migrate and multiply. It breeds rapidly and a female can lay 17 to 76 eggs in a nesting period. As herbivores, GII mainly eats a wide variety of plant foods. It has very sharp teeth and is able to shred leaves and branches with great ease. Further, GII has the ability to escape predators or captivity when kept as pets (interestingly, GII are popular in the pet trade). GIIs are hard to spot since they camouflage well, capable of running fast and can dive into water to escape predators. These features make it difficult to capture and eradicate these nuisance pests. Fijian Native Iguanas There are 4 different species of Fijian native iguana. These are the Fiji crested iguana (Brachylophus vitiensis), Lau banded iguana (Brachylophus fasciatus), Fiji banded iguana (Brachylophus bulabula) and the newly discovered Gau banded iguana (Brachylophus gau). Fiji native iguanas are very small in size compared to GII. These iguanas prefer to eat leaves, fruits, flowers and buds. This means that the GII are in direct competition with Fiji native iguanas for food. All the Brachylophus iguanas (that is, the Fijian species) are very difficult to observe during the day and occupy the highest levels of the tree canopy on the islands. Let’s look at the four native Fijian iguana species in more detail: Fiji crested iguanas are reportedly found on Yadua Taba and Macuata islands and the Yasawa and Mamanuca groups. They are the largest South Pacific iguanas with a maximum snout to vent length of 25 centimetres and have large spines on the back as opposed to the other three species of banded iguana. Both male and female Fiji crested iguanas have dorsal spines. Females lay 2 – 4 eggs in a clutch and their eggs are known to have the longest incubation times than any other lizards, taking approximately nine months to hatch. Lau banded iguanas are found only on the Lau group in Eastern Fiji. This species is also herbivorous although a comprehensive study of its diet in the wild has never been studied (because this iguana is so rare). They are the smallest South Pacific iguanas with snout to vent length of 18 centimetres thus different from the other three Brachylophus iguanas genetically with a smaller body size, higher number of dorsal crest spines, low number of femoral spines and different nostril colour, different body shape and overall colour pattern. Females lay an average of 5 eggs per clutch. Fiji banded iguanas are reported from Mali and Cikobia with verbal reports of presence on other smaller islands. This species is also her- bivorous. They are assumed to prefer the same food plants as the better studied Fiji crested iguanas. In wild they are not successful in reproduction until they are four years of age and lay 5 eggs per clutch on average. Gau banded iguanas are restricted to the island of Gau in the Lomaiviti group. Both males and females are either unicolor or with small spots. They have a maximum snout to vent length for both sexes at 15.3 centimetres. Gau banded iguanas most identifiably differ from other local species in that males and females have green throats whereas in other species males have throats that are coloured white solid or white with green/grey spots or blotches, as do the females in most populations. Gau banded iguanas additionally differ from the other three species by having a primarily green coloured nasal scale. Impact of GII on local iguana GIIs have shown the potential to become a significant pest in a wide variety of agricultural settings and cause immense damage to Fiji’s fauna and flora. GII is also said to pose threats to a variety of native animals, including the four native iguana species, through direct competition, predation and the introduction and spread of disease and parasites which may affect these vulnerable native reptile species. GII can spread salmonella disease.