Invasive Species Threat Summary
Fiji’s endemic crested iguana (Brachylophus vitiensis) or vokai is classed as Critically Endangered according to the IUCN Red List. This arboreal species is herbivorous and consumes leaves, buds, fruit, and flowers. Its abundance has been correlated with the presence of food plants (Harlow, Fisher & Grant 2012). Yadua Taba (where the crested iguana is legally protected) represents the last strong hold for the species with an estimated 6 000 to 12 000 individuals; populations on all other islands are barely detectable (apart perhaps from Macuata) (National Trust for Fiji 2008; Harlow, Fisher & Grant 2012). According to one vegetation survey nine out of ten vegetation quadrats on Yadua Taba contained with the iguana’s preferred food source (the cevua tree; Vavaea amicorum) (Harlow, Fisher & Grant 2012). In comparison cevua was not detected in similar surveys on Monuriki which has experienced three decades of intensive goat (Capra hircus) grazing and dry season fires.
Habitat loss and introduced predators are the two key factors influencing the survival of Fijian crested iguana populations. Crested iguanas are dependent on healthy beech and tropical dry forests. Unfortunately these are rare in Fiji being the island group’s most critically endangered habitat types (Morrison et al. 2009). Very few islands contain significant patches of dry forest and remnant populations of crested iguanas are threatened by the continuing degradation of native forest due to conversion into plantations and grassland, goat grazing, invasive alien plants and village and tourism development (Harlow, Fisher & Grant 2012). Habitat loss due invasive species is discussed in detail in the Invasive-Plant Assessment and Weed Management Plan for the Fijian Crested Iguana Sanctuary Island of Yadua Taba, Bua (Taylor, Harlow & Niukula 2005). Plants of most concern are vaivai moce moce (Samanea saman), wedelia (Sphagneticola trilobata), guava (Psidium guajava) and lantana (Lantana camara). Other species of concern are vaivai (Leucaena leucocephala) and mile-a-minute vine (Mikania micrantha). Wedelia and lantana have been listed among the world’s worst 100 invasive weeds by the IUCN (2010) and as dominant invaders in Fiji (Meyer 2000, in Taylor, Harlow & Niukula 2005). Rain tree (Albizia saman) and guava are listed as moderate invaders in Fiji (Meyer 2000, in Taylor, Harlow & Niukula 2005). None of these species appear to provide sufficient habitat for crested iguanas (Harlow & Biciloa 2001).
Feral predators are infamous for their ability to reek havoc on native fauna. While crested iguanas are still occasionally encountered on four of the five inhabited islands surveyed (Nacula, Matacawa Levu, Naviti and Waya) these populations cannot be expected to survive in the long-term because of the presence of feral predators and continuing forest degradation (Harlow et al. 2007). For example the probable extirpation of crested iguanas from Viti Levu and Vanua Levu was likely due to predation by the small Asian mongoose (Herpestes javanicus) as well as the conversion of dry forest into sugarcane plantations and for urban development. The small Asian mongoose was introduced to Fiji in the 1800s to control rats (Gorman, 1975, in Morley 2004) but prefers to prey on other species such as iguanas. The potential introduction of feral cats (Felis catus) from Yadua to Yadua Taba (only 120m across the sea) is of great concern (Harlow & Biciloa 2001) as cats were regarded as the predominant reason for the decline of Fijian iguanas (Gibbons 1984, in Harlow & Biciloa 2001). Crested iguanas of all life stages are vulnerable to predation by feral cats and younger life stages are also perhaps vulnerable to black rats (Rattus rattus) (Gibbons 1984, in Harlow, Fisher & Grant 2012).
In terms of invasive competitors the potential future impact of the American or green iguana (Iguana iguana) is unclear. First detected in the country in 2000 the lizard is currently absent from Yadua Taba however should it be introduced detrimental impacts to the native crested iguana would be likely as the American iguana is significantly more fecund and aggressive than the native Fijian iguanas (Harlow, Fisher & Grant 2012).
Exotic herbivores have also impacted populations of Fijian crested iguana. Exotic herbivores can impact island vegetation dramatically by impoverishing the quality and quantity of the indigenous flora (North et al. 1994, in Harlow & Biciloa 2001). The combination of goat introduction and fire may have reduced the abundance of iguana food tree species on Monuriki. Selective browsing by goats on the seedlings of tree species palatable to iguanas has resulted in an increase of inedible species (Harlow & Biciloa 2001).
While the population on Yadua Taba is currently secure and there are no introduced predators there are obvious risks in having only a single secure population and the accidental introduction of exotic predators, disease or wildfire could decimate the population. As well as this there is the on-going struggle against invasive plant species (Harlow & Morrison et al. 2006; Morrison et al. 2007). Finally the introduction of the yellow crazy ant (Anoplolepis gracilipes) on Yadua Taba may threaten the remaining main population of crested iguanas (FCIP 2008). Yellow crazy ants have been responsible for severe damage on other South Pacific islands and are listed in the 100 worst invasive species globally (IUCN 2010). These ants are sometimes triggered to form “super colonies” which can have a very great impact on the ecosystem.
Invasive Species Management Summary
Funding and support for the Fijian crested iguana and native iguana conservation in Fiji is extremely high. An International Conservation Fund for the Fijian Crested Iguana (ICFFCI) was established in January 2000 (involving the National Trust for Fiji, Kula Eco Park, Fiji and the Zoological Parks Board of NSW). The Taronga Foundation Crested Iguana Fund has also been established. The National Trust of Fiji Islands has had increased financial support for wildlife conservation projects and The Wildlife Conservation Society have recently increased their presence in Fiji. Despite this a lack of technical and financial resources and expertise on and knowledge about iguana biology impedes conservation work.
The last viable population of the Fijian crested iguana remains on Yadua Taba island which was declared a national sanctuary in 1980 and is protected as a Fiji Biodiversity Strategy and Action Plan Site of Biological Significance. The crested iguana is protected by the Endangered and Protected Species Act 2002. The Fijian Crested Iguana Sanctuary on Yadua Taba is administered by the National Trust of Fiji Islands and a full-time ranger has been employed in the sanctuary since the 1990s (National Trust for Fiji 2008). Fires have been banned on the island and anthropogenic activities restricted in order to preserve the tropical dry forest which is the crested iguana’s only viable habitat (Taylor et al. 2005, in Harlow et al. 2007; Morrison et al. 2009). Previous awareness and education projects include several endangered species education programs within Fiji and the distribution of posters and children’s books (National Trust for Fiji 2008). Research on the diet and habitat preferences of Fijian crested iguanas on Yadua Taba has been conducted and a reproductive and life history study is nearing completion (Morrison et al. 2008; S. Morrison pers comm., in National Trust for Fiji 2008).
The National Trust for Fiji is monitoring, poisoning and removing the most invasive plants on Yadua Taba in an effort to maximise the native forest available to the Critically Endangered crested iguana and Endangered Fijian banded iguana (Brachylophus fasciatus) (Harlow & Morrison 2006). A recent vegetation survey identified several invasive plant species of concern (Olson et al. 2002). An invasive plant assessment and experimental control plan was formulated in 2003 and a follow up evaluation and training project was undertaken in October 2004 (Tarona Foundation 2008a). An invasive-plant assessment and weed management plan for Yadua Taba is now in its third year of implementation (Taylor et al. 2005, in National Trust for Fiji 2008). In July 2003 a team undertook field work on Yadua Taba to identify, assess and map the status of invasive plants on the island and trial control techniques. This project also involved the training of community members in control techniques and an education and awareness program in Denimanu Village on the impact of invasive plants.
Goats have been eradicated from a number of islands where the Fijian crested iguana lives, namely Yadua Taba, Monuriki and Macuata. After Yadua Taba was proclaimed a sanctuary in 1980 most goats were removed. Despite occasional goat captures since then small numbers of goats continued to survive. In 2001 the Zoological Parks Board funded the round-up of some of the last feral goats on the island, a project that involved all the men and boys in the village on the nearby island of Yadua (Taronga Foundation 2008a). Most goats were captured in this round up and by 2004 the last goat had been removed (Taylor Harlow & Niukula 2005). In 2012 both goats and Pacific rats (a href=http://www.issg.org/database/species/ecology.asp?si=170&fr=1&sts=&lang=EN>Rattus exulans) were eradicated from Monuriki island. A small number of crested iguanas were temporarily removed for the eradication campaign and held in captivity for future re-introduction to the island following forest regeneration (Harlow, Fisher & Grant 2012). Lastly, goats were removed from Macuata in 1994 (an island with little natural vegetation left and a small population of crested iguanas at the time of the eradication).
A team of volunteers, staff and students from the University of the South Pacific in Suva assessed the impact of goat grazing, vegetation burning and introduced predators on iguana populations and created an action plan for the conservation of the iguana for use by the National Trust of Fiji (Daltry et al. 2000). The Fijian Crested Iguana Species Recovery Plan 2008-2012 was drawn up by the National Trust for Fiji. It is a detailed five year plan which draws from the knowledge of experts from the University of the South Pacific, NGO institutions, the IUCN Iguana Specialist Group and several Fijian government departments. The plan identified an urgent need to implement captive breeding and undertake field work to determine suitable natural habitats for the crested iguana to use in re-introductions (National Trust for Fiji 2008). It was emphasised in the plan that the captive breeding and translocations be designed to preserve separate island subpopulations of the crested iguana. Production of a management plan for Yadua Taba Crested Iguana Sanctuary and implementation of strategies to further promote native iguana conservation were recommended. For further information on these strategies please see the Fijian Crested Iguana Species Recovery Plan 2008-2012.
Other than the ongoing work which has been done on feral goats and invasive plants preliminary work is being conducted on yellow crazy ants. The Fijian Crested Iguana Project team planned to collect base-line data on crazy ants on Yadua Taba in 2008 which may give scientists a reference point from which to determine if ant numbers are growing and predict the formation of super colonies in the future.
While the ranges of the Fijian crested iguana and the introduced American iguana (Iguana iguana) do not currently overlap in Fiji deliberate or accidental movement of the iguana onto the island is a possibility and it is therefore pertinent to talk about the work which has been done on the American Iguana in Fiji. Awareness campaigns (initiated by the American Iguana Eradication Task Force and the Critical Ecosystems Partnership Fund) were carried out in the region in 2010. An American Iguana Eradication Workshop was also held that year which covered biosecurity measures, inclusion of billboards at landing docks and formation of an iguana eradication team (CI 2013). An eradication strategy also formulated that year evaluated iguana capture methods and concluded that the best chance of success would be through implementing a community-based approach involving the removal of gravid and hatchling iguanas from nesting sites across three to five years (CI 2013). Telemetry studies and other research based on American iguana establishment, dispersal, habitat/food selection, population estimates and control was also conducted to remedy the paucity of information available for this invasive iguana. Further information on this research is available by referring to Status Report: The American iguana (Iguana iguana) in Fiji- May-August 2011.
The remnant grassland and patches of invasive plants on the ridges of Yadua Taba are reverting to native forest since burning stopped in 1980. A vegetation survey of Yadua Taba and comparison with aerial photographs from the 1980s suggest that 10 to 20% of the dry forest had regenerated within the subsequent two decades – corresponding to the initiation of goat control (Olson et al. 2002). In response iguana numbers have grown from an estimated 6 000 animals to more than 10 000 in 2007 and approximately 12 000 in 2012 (Harlow and Biciloa 2001; Morrison et al. 2007; Morrison et al. 2009, in Harlow, Fisher & Grant 2012).
While only one iguana was located on this goat-ravaged island when very little forest habitat remained in 1988 (D. Watling pers. comm., in Harlow, Fisher & Grant 2012) a small population of 80 Fiji Crested Iguanas was estimated for Macuata in 2004 and more recently the population is estimated to have grown to almost 700 individuals (Olson & Keppel 2004; P. Harlow unpublished data 2011, in Harlow, Fisher & Grant 2012). Following goat removal in 1994 forest regeneration has been rapid with 60 to 70% of the island covered in regenerated forest that includes six of the important iguana food tree species (Harlow, Fisher & Grant 2012). The iguana population is expected to continue to grow on Macuata as the forest recovers (Harlow, Fisher & Grant 2012). Projects
1. Goat eradication Yadua Taba island
2. Weed control on Yadua Taba (National Trust of Fiji Islands)
3. Fijian Crested Iguana Project (crazy ant surveys) on Yadu Taba
- IUCN 2014. The IUCN Red List of Threatened Species. Version 2014.2.
- Invasive Species Specialist Group, 2013. Species profile Felis catus in Global Invasive Species Database (GISD)
- Invasive Species Specialist Group, 2013. Species profile Rattus exulans in Global Invasive Species Database (GISD)
- Invasive Species Specialist Group, 2013. Species profile Iguana iguana in Global Invasive Species Database (GISD)
- Invasive Species Specialist Group ISSG 2014. Global Invasive Species Database
- Harlow, P., Fisher, R. & Grant, T. 2012. Brachylophus vitiensis. In: IUCN 2013. IUCN Red List of Threatened Species. Version 2013.2.
- Harlow, Peter S.; Biciloa, Pita N. 2001. Abundance of the Fijian crested iguana (Brachylophus vitiensis) on two islands. Biological Conservation. 98(2). April, 2001. 223-231.
- Pregill, Gregory K.; Steadman, David W. 2004. South Pacific iguanas: Human impacts and a new species. Journal of Herpetology. 38(1). March 2004. 15-21.
- Harlow, Peter S.; Fisher, Martin; Tuiwawa, Marika; Biciloa, Pita N.; Palmeirim, Jorge M.; Mersai, Charlene; Naidu, Shivanjani; Naikatini, Alifereti; Thaman, Baravi; Niukula, Jone; Strand, Erica. 2007. The decline of the endemic Fijian crested iguana Brach
- Morrison, Clare; Osborne, Tamara; Harlow, Peter S.; Thomas, Nunia; Biciloa, Pita; Niukula, Jone. 2007. Diet and habitat preferences of the Fijian crested iguana (Brachylophus vitiensis) on Yadua Taba, Fiji: implications for conservation. Australian Journ
- Keogh, J. Scott; Edwards, Danielle L.; Fisher, Robert N.; Harlow, Peter S. 2008. Molecular and morphological analysis of the critically endangered Fijian iguanas reveals cryptic diversity and a complex biogeographic history. Philosophical Transactions of
- Morrison, Clare; Keppel, Gunnar; Thomas, Nunia; Rounds, Isaac; Harlow, Peter S. 2009. Critically Endangered Fijian Crested Iguana (Brachylophus vitiensis) Shows Habitat Preference for Globally Threatened Tropical Dry Forest. Pacific Science. 63(2). APR 20
- Morrison, Suzanne F.; Harlow, Peter S.; Keogh, J. Scott. 2009. Nesting ecology of the critically endangered Fijian Crested Iguana Brachylophus vitiensis in a Pacific tropical dry forest. Pacific Conservation Biology. 15(2). WIN 2009. 135-147.
- Secretariat of the Pacific Region Environment Programme (SPREP) 1999. Proceedings of the Polynesian Avifauna Conservation Workshop held in Rarotonga, 26-30 April 1999.