Overview. The Monuriki Island Iguana is genetically and morphologically unique and its population has been determined to be of high risk of extinction due to its single location on Monuriki, a 40-hectare (100 acre) uninhabited island off the west coast of Fiji. For the past decade, there has been increased conservation investment for this island to keep the iguanas from going extinct. Invasive goats and rats were removed and an iguana captive-rearing program started. In the spring of 2015, San Diego Zoo Global helped support a release and short-term telemetry study to see if released iguanas survived on their own in the wild (Chand et al. 2015). This short-term analysis showed some success as iguanas were tracked and surviving two months post-release, but the following year (2016) only a few were detected. The current study supported the closure of the captive-rearing program and the release of the remaining founder stock, plus 32 captive-produced offspring. We followed iguanas for almost five months in this study, to determine longer-term survivorship and search for animals that were part of the 2015 release. The fieldwork component of the project was completed late July 2017, but the analysis and report will be continuing until early 2018 per agreement with the IIF.

Telemetry. We had previously developed a short-term radio attachment protocol, but for this project we needed the transmitters to stay attached for up to five months for continuous telemetry. Through some experimentation, trial, and error, we developed an attachment method to the tail, that although not optimal, worked to allow us to track most of the iguanas through the study period.

We attached transmitters to three study groups: 10 captive-reared and released iguanas, 10 released founder stock (born in the wild and captive for a few years), and 10 wild-captured iguanas (never captive). This study design allowed comparison of behavior and survivorship between these three groups. We presumed that the last group of wild animals would be the control group for how iguanas normally behave on Monuriki. We were able to track most iguanas in the three groups, although there was attrition over time through transmitter loss and some mortality within the first two study groups.

Field Surveys. We conducted night surveys across five months to try to relocate PIT-tagged iguanas from the May 2015 release of 32 captive-bred iguanas. We were able to find and capture only six of these iguanas and they appeared to be doing well, some of which were found paired with wild iguanas that had persisted on the island. During these surveys, we captured 39 wild iguanas. All that were large enough were photographed and PIT-tagged. This total count indicates the success of the rat and goat eradication was very positive for iguanas, with noticeable recruitment on island. Prior to 2016, no hatchling or young iguanas were detected on Monuriki Island. We are concerned that despite all the field effort during 2017 we only detected six of the 32 released iguanas from 2015, which, if correct is only an 18.7% survival rate over two years. Future captive-breeding projects might need to include soft releases, or other cage modifications if survivorship really is this low among captive-produced animals. But, we are encouraged that we did get some long-term survivorship and will consider using this tool in the future, possibly with these modifications.

We had some issues with rechargeable batteries, making some surveys less successful then they could have been and resulted in a little data loss. We will use only non-rechargeable batteries in the future.

This will be an ongoing project; we are still working on analyzing the movement data. All data points have been moved into GIS and we will be conducting spatial analysis soon to determine if the three study groups have different movement patterns and home-range sizes.

Training and Outreach. We trained and mentored a student from the University of Oklahoma on project management, radio-telemetry, and iguana biology specific to Monuriki. We also trained a local team on the project skills, especially telemetry. Unfortunately, we were not able to find a student from University of the South Pacific to participate in this project as intended. The local community greatly appreciated our weekly presence on the island during the five months and spent a lot of time learning from our student in the field.

As part of relating the success of the Monuriki Island Iguana story, we are continuing to put out information about the program. In 2016, we published a short paper on the repatriation of iguanas to Monuriki (Chand et al. 2016). In 2017, we presented a poster at the IUCN Island Invasives Conference in Scotland highlighting the overall program and including some early study results (Fisher et al. 2019). We will present this same poster at the Iguana Specialist Group meeting in Cuba, November 2017.

Impact. This program shows that we can recover Fijian Crested Iguanas on an island with critically low numbers of individuals remaining. The population estimate was in the low tens when the program started less than 10 years ago. Through captive rearing and invasive species removal, we now have a population of wild iguanas in excess of 100. This next reproductive season should really boost the population as it will be the first year some of the captive-produced and younger wild iguanas will breed, as they mostly hatched after 2012 when rats were removed. Seeing how rapidly the remaining native population recovered after rat eradication may help us better evaluate the need for captive breeding in the future. A cost-benefit analysis will always be needed, and this study will help with decisions for other critically at-risk populations around Fiji. For the first time, we’ve shown we can repatriate founder animals and obtain a 2-year survivorship among captive-bred iguanas in the wild. Our outreach and training goals were met and the program stands as a great example of a community conservation approach with technical support from our team.

This program has clearly been initially successful but raises some additional questions, especially about the role of captive breeding in recovering iguanas. In this case, where invasive species were removed and captive breeding conducted, the value of captive breeding might be much less than in scenarios where invasives cannot be removed, such as for the Grand Cayman Blue Iguana program. Since the small group of iguanas left on the island were so successful reproducing after rat eradication, we might have hindered recruitment by removing 10 pairs of animals to the captive facility where their reproductive output might have been less than if we had left them in the wild. This question may become more important if we find little reproductive contribution from the captive-bred iguanas in future genetic analyses. In contrast, if we had not been able to remove rats, we feel captive breeding would have been essential for recovery since no juveniles were previously observed since surveys began in 1998. This will be a consideration as we work to complete the recovery plan and assess other similarly at-risk iguana populations. The Monuriki project was an objective in the 2008 Crested Iguana Recovery Plan, and its success gives us hope for future projects included in the new revised recovery plan.

Future. In the future, we plan to continue monitoring population growth of the island’s iguanas. We will continue to collect genetic samples, such that in five or so years we can attempt to analyze the relatedness and genealogy of new iguanas on Monuriki Island. This will allow us to determine whether the captive-bred iguanas are contributing to current and possible future offspring on the island, or if they were not reproducing. We do have some guarded concerns about wild survivorship for captive iguanas, and we might recommend modifications to cage designs or suggest soft releases to ensure higher long-term success if we engage in these type of programs in the future. We will continue to analyze and publish this data so it can serve as an example in our recovery plan revision for this species.

Lastly, we are extremely grateful to the IIF for funding our research and restoration program for these critically endangered species. We are continuing basic research on systematics and this year described another new species from Fiji, the Gau Iguana (Brachylophus gau), increasing the diversity of living Fijian iguanas by 25% and are currently working on additional species descriptions (Fisher et al. 2017).

References:

Chand, R., Niukula, J., Vadada, J., Fisher, R., Lovich, K., Pasachnik, S., Rasalato, S., Thaman, B., Seniloli, E., Tuamoto, T., Yanuya, T. and Harlow, P. 2016. Captive breeding and re-introduction of the Monuriki Island Crested Iguana in Fiji. Pp. 76–81 In: Global Re-introduction Perspectives: 2016. Case Studies from around the Globe. Soorae, P.S., ed. Re-introduction Specialist Group and Abu Dhabi, UAE: Environment Agency-Abu Dhabi. Gland, Switzerland.

Fisher, R.N., Niukula, J., Harlow, P.S., Rasalato, S., Chand, R., Thaman, B., Seniloli, E., Vadada, J., Cranwell, S., Brown, J., Lovich, K. and Thomas-Moko, N. 2019. Community-based conservation and recovery of native species on Monuriki Island, Fiji. Poster. Pp. 552–557 In: Veitch, C.R., M.N. Clout, A.R. Martin, J.C. Russell and C.J. West (eds.), Island Invasives: Scaling up to Meet the Challenge. Proceedings of the International Conference on Island Invasives. IUCN, Gland, Switzerland.

Fisher, R.N., Niukula, J., Watling, D. and Harlow, P.S. 2017. A new species of endangered iguana Brachylophus Cuvier 1829 (Sauria: Iguania: Iguanidae) from Gau Island, Fiji Islands. Zootaxa 4273(3): 407–422.