Friday, 22 September 2017

Manta rays at Denis Island

What are those big sea animals that looks like underwater war planes? They are pelagic fish and one of the most intriguing species; in fact this spectacular animal is highly tolerant towards humans.

Mantas are here again this year, actively feeding in the shallow waters of Denis Island. From late August a few mantas have been sighted, either by diving hotel guests or by the Denis Island diving and fishing team. An encounter with these amazing creatures is purely fortuitous and never fails to amaze those lucky enough to experience it.

The arrivals of mantas at Denis Island correspond to the abundance of food availability. More recently, all along the northwest beach line of Denis island, washed-up zooplankton has been encountered suggesting its abundance in the region.
Mantas are warm water creatures that swim with their large pectoral fins. They have no venom or spine so they are relatively harmless. There are two species of manta rays. The giant manta (Manta birostris) commonly has a wing span of 4.5m (15 feet) but individuals of 9.1 m (29 feet) have been recorded, and it can weigh up to 3 tons (6,600 pounds. The reef manta (Manta alfredi) is smaller (max disc width recorded: 5 m or 16 feet) and it is commonly found in inshore habitats.
The presence of reef manta rays contributes to eco-tourism in certain areas where divers and snorkelers have the opportunity to dive in close proximity to these majestic fish. However manta rays face a huge number of threats such as fishing (both directed and bycatch), habitat degradation, global warming, pollution, ingestion of micro plastics and poor protection status in most regions of the globe. The IUCN Red List has categorized mantas rays as “vulnerable”.
The Manta Trust investigates movement patterns, feeding ecology and demography of reef manta rays in the Seychelles region. By doing this, we hope to gain a better understanding of the health and size of this manta population, as well as where, how, and why these animals move through the various habitats available to them.
Lauren Peel, a PhD student from the University of Western Australia and associated with the Save Our Seas Foundation/Manta ray project in the Seychelles, is very interested in setting up collaborations with researchers and dive shops across the Seychelles in order to get them to report sightings of  manta rays. This will  be with the aim of obtaining an outlook of their distribution and movement patterns. Individual mantas can be identified through the unique pigmentation patterns on the ventral side of their bodies and it is relatively easy to collect ID photos of them by free-diving down in front of them as they approach and take a photo as they swim overhead.

Recently a video of a manta feeding event occurred in Denis Island was recorded, and allowed us to identify two new manta rays and add them to our database. This is very exciting as we previously did not know that mantas were sighted in this area!

Friday, 1 September 2017

North island myna eradication project as told by Claire and Sarah

What is the Common Indian Myna (Acridotheres tristis)? The myna is a bird native to India and South East Asia which has been introduced to various countries around the world. The myna was introduced to the Seychelles potentially to manage the number of insects damaging crops and other vegetation, however this is not confirmed. Is is an aggressive bird that has been known to injure and kill endemic birds as well as damage the eggs.  This has had a severe impact on breeding success and population numbers of endemic species across the islands.

North Island is working towards restoring the island to how it was before it became a farm for fruit, vegetables and coconuts in 1826. Removal of the myna is a huge step in this process and once completed endemic species can then potentially be reintroduced. The Myna Eradication Programme is a partnership of North Island, Green Island Foundations, Chris Feare of Wildwings Bird Management and endorsed by Ministry of Environment,Energy, and Climate Change.  The current programme commenced May 2016 and has since removed 924 myna from North Island.

Photo: partial view of North island seen spa hill  (CWaters)

Our current volunteers, Claire Waters and Sarah Atkinson took over in April 2017 for the final stages of the eradication. We are now reaching a very exciting part of the project where we are starting to see huge progress and can see we are reaching the end of the eradication process. The eradication of the myna has been successfully completed on two other islands in the Seychelles archipelago (Frégate and Denis); which have shown a notable dramatic increase in the native bird population on those islands. The eradication of the majority of mynas on North Island is already benefiting the native species on the islands and is thus proving its conservation importance.

In order to remove the myna, the methodology has changed since the beginning of the project to adapt to the birds’ changing behaviour. In order to be successful in removing the mynas, efforts need to be invested in understanding the bird behaviours and adapting methodologies accordingly. We are now in the process of carrying out surveys throughout the day to locate the remaining birds, which are thought to be in very low numbers.

So what do we do every day? Each day starts at 5:30am where one of the two Myna Eradication Officers, Claire or Sarah, start with a dawn survey at various locations across the island. This involves listening and looking for a dawn chorus, which is easily distinguishable from other birds around the island. Surveys then continue throughout the day, tracking the remaining birds and covering all areas of the island, from the plateaus to the top of the hills along the hiking trails. The other volunteer will begin work at midday, and will carry out the same survey at dusk to locate the birds as they select a tree to roost in overnight.
Photo: Sarah and Claire observing mynas (ASanders)

Interestingly, a previous Myna Eradication Programme on Denis Island found that the myna would roost in one tree together overnight. This has also been suggested to take place around the world. However, on North Island the myna have all been found to roost in pairs across the island. This is one example of the differing behaviour found in the myna on North Island and has made the project more challenging.

It has been found that as the number of myna on the island has dropped significantly, their behaviour has begun to change as well. Their vocalisations have altered to mimic native birds making it more difficult to locate them. This may be in response to low population numbers or in an attempt to disguise themselves. It is also possible that juveniles are learning from native birds in the absence of many adults to learn from. They have also become less confident and are no longer seen on the ground of the plateau. In the coming months, as we near completion of the eradication, there will then be an observation phase of the project, where the island will continue to be surveyed daily to ensure that we have eradicated all birds, this may take place for up to 6 months.

Since the start of the myna eradication, North Island staff have already noticed a significant increase in the numbers of endemic species. This includes the Seychelles Blue Pigeon (Alectroenas pulcherrima) and the Seychelles Sunbird (Necttarinia dussumieri) and is a huge positive step in restoring the island and conserving the unique wildlife of the Seychelles.

Photo: Seychelles white eye on North island (CWaters)

Saturday, 19 August 2017

Rabbit fish research at Denis island

Rabbitfish are the main targeted fish species of the artisanal fishery of Seychelles, consisting of approximately two-thirds of the total annual catch. They are herbivorous and have been shown to help keep reefs healthy by grazing on invasive algae. With such commercial and environmental importance, Ameer chose to dedicate his PhD research to investigating the role that rabbitfish play in a marine environment, and their contribution to the resilience of tropical coral reefs. His research is crucial to small island states like Seychelles, as these regions rely heavily on tourism and fisheries for sustenance.

Ameer is currently conducting research on Denis Island for the fourth part of his thesis. He is specifically investigating the diurnal home range of rabbitfish around Denis Island and what factors, including tidal phase, habitat type and complexity, influence their movements.

                                    Photo (AEbrahim): Ameer conducting research in lagoon at Denis 

Denis Island has two very distinct habitats: vast corals reefs and lush seagrass meadows. Research from other parts of the world is increasingly demonstrating that coastal habitats, such as coral reefs, do not function in isolation but rather as part of a larger habitat network.  Other habitats such as seagrass meadows lie in close proximity to coral reefs, allowing for reef dwelling organisms and materials to travel among these habitats. Numerous species of commercially important herbivorous reef fish, such as rabbitfish, may frequent these habitats through diurnal and tidal fish migrations.

Accordingly, Ameer has dispersed 34 acoustic receivers encompassing the seagrass meadows and coral reefs in both shallow and deep water environments around Denis Island. Each receiver has a range of approximately 250m, allowing them to track the rabbitfish that Ameer has tagged using internal acoustic tags.

                                   Photo (AEbrahim): Placement of acoustic tags 

In many regions of the world, including Seychelles, connected habitats like seagrass meadows are often forgotten when it comes to conservation management. Therefore, this part of Ameer’s PhD will also assist in determining whether rabbitfish are frequenting different habitats such as seagrass meadows, thereby aiding conservation management efforts. Furthermore, his research will hopefully help cement future marine conservation management for the waters surrounding Denis Island. He is now in the process of collecting his data for this research. 

Friday, 28 July 2017

Training in threatened species identification and data gathering protocol

Yesterday, we hosted a training session on threatened species identification, field survey technique and data gathering protocol in the context the project “The development of a co-management plan, designed by fishers to minimise the impact of the Seychelles artisanal fishery on threatened species” also known as the Threatened species project.
Photo: Participants  at the training with the Green Islands Foundation team (MLeotta)

The objective of the Threatened species project is to reduce the Seychelles artisanal fishery’s impact (catch, by-catch and disturbance) on globally threatened species (IUCN classifications: VU, EN, CR).  The project is developing a baseline of threatened species occurrence in the artisanal fishery through fisher interviews and consultation, literature review and an intensive 12-month survey of artisanal catch. The project will support fishers in the identification and development of pragmatic management measures to reduce artisanal fishing pressure on threatened species - (e.g. catch release, only landing mature individuals, reduce effort on critical habitats, gear modification etc…).

Yesterday’s training was organized for collaborators, these are civil society members who assist Green Islands Foundation in collecting species-specific data on IUCN red listed threatened species and species of local concern. In addition, fisheries technicians from SFA were also invited to attend. Mr. John Nevill, Technical Fisheries Advisor on the project carried out the training. The participants given an introduction to the project, presented the species monitored under the project, the monitoring protocol and were shown some initial results from the first four months of data collection.
There are 20 threatened species of teleosts, sharks and rays that are known to occur in artisanal catch in Seychelles.  In addition, there are a number of species that were identified as of local concern at the start of the project also monitored trough this project.
Photo: Slideshow presentations on fish identification (MLeotta)

Through the presentations, Mr. Nevill showed participants how properly identify species and their distinctive characteristics. Participants were given each an Identification card showing all the threatened species monitored through the project that they can use on the field. They were also shown how to properly take measurements through practical sessions in the laboratory at the Seychelles Fishing Authority.  
Photo: Practical session ; how to record total lenght in sharks (MLeotta)

We expect through this training that the participants will be better equipped to collect species-specific data on the field to inform fisheries management decisions.   

Monday, 24 July 2017

Seychelles magpie robin population census on Denis Island, June 2017

A total of 76 individual Seychelles magpie robins were observed during a population census of the species on Denis Island from13-20 June 2017. Fifty seven of the robins observed were ringed and 19 were unringed.  In addition to censusing the population, 12 of the unringed robins were captured and ringed. A total of seven SMR were still unringed at the end of our time on Denis.

Following cat Felis catus and rat Rattus rattus eradications and rehabilitation of native broadleaved woodland habitat, twenty Seychelles magpie robins Copsychus sechellarum (SMR) were introduced to Denis Island in June 2008 as part of a national recovery programme for the species (Burt et al. 2016). For the first two years post translocation the robins were supplementary fed on a daily basis, but supplementary feeding ceased in 2010. Management currently involves the provision of nest boxes, ringing new recruits to the population, and to clearing relatively small areas of fouzer taba fern Nephrolepis biserrata to improve the foraging habitat for the robins within the forested conservation zone.
The purpose of this work was to (i) estimate the current SMR population size on Denis, (ii) map approximate territory locations and identify territory occupants and (iii) ring unringed SMR with metal ID ring and an individually identifiable colour combination.

Photo: Seychelles Magpie robin (KlartjeePuttemans)

The census was undertaken by Rachel Bristol and Indira Gamatis from 13-20 June 2017. All areas of the island were searched several times for SMR. All robins seen were identified i.e. ring combination recorded, and the number and age (adult/ juvenile-based on plumage) of unringed birds was also noted. The locations of individuals and group composition (i.e. who was hanging out with who) was also recorded.
Unringed robins were caught, ringed, measured and blood sampled. They were captured mostly using a spring trap baited with live termites, but also with a mist net using termites as an attractant.

Population size, trend and age structure
A total of 76 magpie robins were seen on Denis during this census. Two of the original robins translocated from Frégate Island are still present. These two males are a minimum of 10 years old as both were adults at the time of translocation to Denis in June 2008. Nineteen individuals, almost all of which were juveniles, were unringed. These 19 individuals represent productivity over the past year. The population trend is increasing, see Figure 1. We are confident this census is fairly accurate, however it is possible a few individuals were undetected, therefore this population estimate of 76 confirmed individuals can be considered conservative.

Figure 1. Trend in Magpie robin population size on Denis Island from introduction in 2008 till present
(Data sources: Burt et al. 2016; Denis Island magpie robin monitoring records; Bristol & Gamatis 2017)
Twelve robins were ringed during this census. Biometric measurements and blood samples were taken from all individuals ringed. Seven individuals were still unringed at the end of our time on Denis.

Photo: Magpie robin juvenile with new rings (R.Bristol)

Territories (location and number) appear to have changed little since the last accurate monitoring in 2016. There appear to be 18 territories on Denis each occupied by 2-6 robins. However we were not on the island for sufficient time to assign all individuals to territories with certainty, or to confirm possible shifts in territory boundaries.

Thank you as always to Green Islands Foundation (GIF) and Denis Island management for enabling this census and providing transport, accommodation and meals.

Bristol RM and Gamatis I (2017) Seychelles magpie robin population census on Denis Island, June 2017. Unpublished report.

Burt AJ, Gane J, Olivier I, Calabrese L, de Groene, A, Liebrick T, Marx D, Shah N (2016) The history, status and trends of the Endangered Seychelles Magpie-robin Copsychus sechellarum. Bird Conservation International 26, 505-523. doi: 10.1017/S0959270915000404.