European Union invasive alien species project
From 2011 to 2015 SIF implemented an extensive four year project funded by the European Union. This ambitious project aimed to address the problem of invasive species in the two World Heritage Sites in Seychelles. Securing this funding was a major achievement for SIF and allowed us to develop, implement and mainstream a strategic programme to assess and reduce the impacts of invasive alien species at the Vallée de Mai and Aldabra Atoll. A range of species were targeted under this project and significant progress was made in many areas.
In 2012 after an intensive period of tracking, the last feral goat was eradicated from Aldabra. This marked the end of the feral goat inhabitation on Aldabra and the completion of an eradication programme that lasted for more than a quarter of a century.
Introduced birds on Assumption
The EU project aimed to research, develop and implement an eradication plan for the two introduced bird species that were present on nearby Assumption Island to protect Aldabra’s native avifauna. This element of the project was started in 2011 and after removing over 5000 red-whiskered bulbuls, the last bird was finally shot in 2014. This impressive accomplishment marked it as the largest scale avian eradication in the world at the time. The introduced Madagascar fodies on the island were also targeted and over 3000 birds were culled. The last Madagascar fody was shot in January 2015 and successful eradication was declared in early 2017.
In 2013 a project to eradicate the ring-necked parakeet from Mahé was launched. This species was largely restricted to Mahé (with a single bird culled on Praslin and on Silhouette) but its presence on the island posed a significant threat to the endemic Seychelles black parrot via food and nest site competition and novel disease transmission, such as Beak and Feather Disease Virus (BFDV). The project is now in the monitoring and follow-up phase and hoping to be able to complete this eradication soon.
Sisal occurred at three locations on Aldabra and control of this invasive plant has been ongoing since the 1970s. In 2013 research was carried out into eradication techniques and, after reviewing mechanical and chemical control methods, a chemical approach was applied which had been shown to be successful in many invasive plant eradications and was the most effective method in the trials. All three sisal stands were treated in 2014 and continue to be checked for re-growth at regular intervals. Aldabra should very soon be sisal-free once more.
Rats and cats
Black rats are thought to have been accidentally introduced to Aldabra by some of the early traders to the islands. This highly invasive species has been identified as the most damaging invasive rodent to island ecosystems and therefore their eradication will be essential for the long-term protection of Aldabra’s biodiversity. Preparations included an extensive feasibility studies of which one was funded under the EU project. Trapping of rats was conducted in 2013 and 2014 to establish the relative abundance, breeding status and diet of the populations on Picard, Malabar and Grande Terre. A mark-recapture method was used to establish the density of the rats. Bait trails were also conducted to investigate any secondary effects of the use of poisonous bait, and also to establish the most effective methods of distribution. More preparation and trials are required before any rat eradication project can be initiated. Feral cats only occur on Grande Terre Island and trapping was undertaken to establish cat diet and breeding status.
Yellow crazy ants
Yellow crazy ants are one of the most notorious invasive species in the world, having been responsible for catastrophic ecosystem ‘meltdowns’ on other islands. They were first recorded in the Vallée de Mai in 2009 and since then an annual survey has been conducted to monitor the population’s abundance and spread.
Introduced plants in the Vallée de Mai
In 2013 a comprehensive plant survey was completed of all of the introduced and native plants in the Vallée de Mai and surrounding area. This survey showed that the palm forest had a lower proportion of introduced plants than the rest of Seychelles. Using this data, combined with literature research and consultation with local experts and members of partner organisations, such as the Seychelles National Parks Authority (SNPA), a management strategy was developed for these invasive plants. The adult reproductive trees of six species were chosen to be controlled first, and a combination of ringbarking and herbicide was used for each tree. The use of herbicide was only decided upon after trials to ensure that there would not be any side effects, either to the surrounding vegetation or water quality. To test the results of the control methods, the team regularly check the treated trees. Control and management of invasive plants have now been ongoing for several years at the Vallée de Mai, and several invasive plant species have already been eliminated from the site, with many others controlled and maintained at lower levels than before the EU project started. This work has continued as part of SIF’s core activities at the site long after the EU project has ended. More details on all of the activities under this project can be found in our annual reports from 2011, please go here to download them.
UNESCO funded eradication of introduced birds on Aldabra
A sobering reminder that invasive species threats require constant vigilance and efforts came in March 2012 when two introduced bird species were confirmed to be present on Aldabra. The two species, the Madagascar fody and the red-whiskered bulbul, were the same species being eradicated by SIF from Assumption, which is where they came from. These bird species posed a threat to Aldabra’s native avifauna via competition for food and breeding territories, disrupted ecological processes and novel pathogen transmission. An additional concern was that the Madagascar fody would hybridise with the Aldabra fody, which was later confirmed in 2015 (see publications). Until this discovery, Aldabra was one of the largest tropical islands in the world with an entirely native avifauna, and swift action was needed to prepare for and initiate an eradication programme to remove these birds rapidly before their increase in numbers and range made it impossible. Thanks to a generous emergency funding grant from UNESCO, the team was able to start a major eradication programme in 2012, which was successfully completed in 2017.
Initially 1-3 bulbuls were thought to be at the same region of Takamaka on Aldabra, but this was later confirmed to be only a single bird. After many months of careful observations and planning, in 2013 the team were successful in capturing and removing this invasive species from Aldabra. Subsequent surveys have confirmed that there are no other red-whiskered bulbuls on Aldabra.
The population of Madagascar fodies was initially estimated at 100-300 birds (in 2012) and the fodies were confirmed to have established breeding territories, with the population already covering a large area of the Takamaka region in eastern Grande Terre. The team conducted a thorough survey of the area to map the boundaries of the invasion and concentrate their efforts within this area. By the end of the first season more than 100 fodies had been culled using a combination of mist-netting and shooting. Although the UNESCO funding ended in 2013, the eradication of the fodies was continued under SIF’s activities. Madagascar fodies have not been seen since early 2015, when the last one was culled, and the eradication was declared a success in March 2017. Following these successful eradications Aldabra is once again the world’s largest tropical island with no introduced birds.
GEF Protected Area project
In 2010 SIF secured funding from the Global Environmental Facility (GEF) under the multi-partnered project ‘Strengthening Seychelles’ protected area system through NGO management modalities’. Under this project SIF aimed to:
- Increase the extent of the Aldabra Marine Protected Area
- Improve surveillance of the area
- Research and develop sustainable financial mechanisms for the atoll
- Develop thresholds and bio-indicators as benchmarks in the management of Aldabra’s ecosystems
To apply for an extension of Aldabra’s MPA further understanding was needed of the outer reef habitats. To this end a habitat map of the outer reefs was compiled under this project. This mapping work identified that the reef extended past the protection zone at the time, justifying the need to extend this area. An application for an extension of the area was made and has been approved by government. Effective protection of the area comes from good enforcement and surveillance, and communications for the atoll were improved in 2012 with the installation of a stronger VHF radio communication system covering the majority of the atoll. Identification of meaningful threshold values of potential concern requires up to date ‘baseline’ information on the state of Aldabra’s biodiversity. To gather this information several surveys were launched in 2011 to assess the abundance and distribution of flagship bird species. These include annual surveys of breeding frigatebirds to establish population trends, a census of Aldabra rails on Picard, and monitoring of landbird nesting success on Picard. A marine monitoring programme was also developed under this project to allow the detection of changes to the marine ecosystem in response to environmental or anthropogenic pressures, and derive indicators of marine ecosystem health. The marine programme now includes SCUBA dive transects to monitor benthic cover and fish assemblages, bleaching surveys, coral recruitment surveys, and Baited Remote Underwater Video systems (BRUVs) and unbaited systems (RUVs) to monitor abundance and distribution of fish populations. The initial data collected has provided a baseline that will allow subsequent changes to be detected and measured, and which can be used to guide management decisions.