The decline of the endemic Fijian crested iguana Brachylophus vitiensis in the Yasawa and Mamanuca archipelagos, western Fiji

Abstract

The endemic Fijian crested iguana Brachylophus vitiensis, categorized as Critically Endangered on the IUCN Red List, has been recorded from several islands in western Fiji. We conducted a survey for the crested iguana on 12 uninhabited and five inhabited islands in the Yasawa and Mamanuca archipelagos of western Fiji in September 2000. Night searches for sleeping iguanas along a total of 11.2 km of forest transects suggest that crested iguanas are either extremely rare or extinct on all of these islands. Although we collectively searched a total of 44 km of transect over 123 person hours, we located crested iguanas on only four islands: three small uninhabited islands (all ,73 ha) and one large inhabited island (22 km). In July 2003 we resurveyed two islands identified as having the best potential for the long-term conservation of crested iguanas, and found that populations were continuing to decline. We suggest that the scarcity of crested iguanas on all islands surveyed is due to the combination of habitat loss and the introduction of exotic predators. All islands surveyed have free ranging goats, forest fires have occurred repeatedly over the last few decades, and feral cats are established on many islands. To reverse the population decline of this species immediate intervention is required on selected islands to halt continuing forest degradation and to clarify the effects of introduced predators.

Critically Endangered Fijian Crested Iguana (Brachylophus vitiensis) Shows Habitat Preference for Globally Threatened Tropical Dry Forest

“…Although we have some knowledge of the habitat and vegetation preferences of B. vitiensis, this work has been largely opportunistic in nature (with the exception of Harlow and Biciloa [2001] and Harlow et al [2007]). A previous study of B. vitiensis on Yadua Taba demonstrated that iguanas were primarily found in forest vegetation, were not found in nonnative forest types including grasslands, and were observed in very low abundance in rocky-cliff or shrubland vegetation (Harlow and Biciloa 2001).…”

“…Previous published estimates of the population size of iguanas on Yadua Taba range from 200 (Gibbons 1981) to over 6,000 (Laurie et al 1987, Harlow andBiciloa 2001) and also report higher abundances in tropical dry forest and coastal tropical dry forest. Few (3%) iguanas were found in Casuarina forest with tropical dry forest un-dergrowth, suggesting that a closed canopy, which Casuarina does not provide, may be important for iguanas to avoid predation by Pacific harriers (Circus approximans) (Harlow et al 2007).…”

“…Currently only Yadua Taba and another small island, Macuata, harbor viable populations. The Macuata population is small, consisting of <80 individuals (Harlow et al 2007), and Yadua Taba is the stronghold for the species, containing >6,000 individuals (Harlow and Biciloa 2001). All other populations are extremely small and likely doomed because of continued tropical dry forest habitat loss due to clearing, grazing by goats, fire, invasive plants, and predation (Harlow et al 2007).…”

“…The Macuata population is small, consisting of <80 individuals (Harlow et al 2007), and Yadua Taba is the stronghold for the species, containing >6,000 individuals (Harlow and Biciloa 2001). All other populations are extremely small and likely doomed because of continued tropical dry forest habitat loss due to clearing, grazing by goats, fire, invasive plants, and predation (Harlow et al 2007).Although the population of B. vitiensis on Yadua Taba is currently thriving and secure, it is still vulnerable to the accidental introduction of exotic predators, disease, wildfire, invasive alien plant species, and natural hazards such as tropical cyclones, which are capable of decimating the population. As such, translocations of iguanas from Yadua Taba to other suitable islands within the former range of B. vitiensis have been proposed as a viable conservation management option for the species (IUCN Species Survival Commission 2008).…”

“…Although we have some knowledge of the habitat and vegetation preferences of B. vitiensis, this work has been largely opportunistic in nature (with the exception of Harlow and Biciloa [2001] and Harlow et al [2007] The overall aims of the project were to determine the major vegetation types present on Yadua Taba and quantify the forest habitat preferences of B. vitiensis to (1) characterize the vegetation types on Yadua Taba for tropical dry forest regeneration monitoring and (2) identify the most suitable forest habitats for future iguana translocation projects. Specifically, the objectives were to (a) identify the major vegetation types on Yadua Taba and map their current distribution, ( b) determine the extent of tropical dry forest regeneration on Yadua Taba, (c) compare the plant species diversity of Yadua Taba tropical dry forest with that on other Fijian islands, and (d) estimate iguana abundance and density in the different forest types and identify their preferred habitat(s).…”