Invasive Alien Species

Invasive Alien Species are recognized as one of the leading threats to biodiversity and also impose enormous costs on agriculture, forestry as well as human health. Increase in trade, tourism and travel have enhanced the spread of invasive species. Invasive species can be birds, plants, fish, mammals or microbes.

Introduced Species often consume or prey on native ones, overgrow them, infect them, compete with them, attack them or hybridize with them. However not all non-native species are harmful.  The Vulnerability of island ecosystems, especially threats from IAS is echoing throughout the world. In Seychelles, the issue of IAS is being considered a national priority and therefore appropriate resources allocated to tackle it.

FAUNA

Ring-Necked Parakeet (Psittacula krameri)

This introduced parakeet is also known as the rose-ringed or green parakeet or ‘Kato Ver Kolye Roz’ in Creole. The species was probably introduced as caged pet around the end of the 20th century on Mahé Island. Some birds escaped and established viable populations around the southwest region of Mahé Island. One parakeet is resident on Silhouette since 1995. The first group of individuals was reported in 1997, when a group of seven birds was recorded at Pointe Conan. The species is now established on Mahe and there are concerns that if ever it reaches Praslin where the Black Parrot is confined, there is the possibility that it will be outcompeted by the more aggressive Parakeet. The possibility of transmitting diseases is also high. The agricultural sector of the economy is however experiencing the effects of the parakeet on fruits production as the parakeet feed exclusively on seeds and fruits.

The conservation Section is receiving help from the public who have informed them upon sighting the parakeet and given information about their activities.

Several monitoring and shooting attempts were carried out by the Department of Environment with technical support from the Public Services Support Wing of the Seychelles Police to minimize the population of this bird and bring it to an end. This is simply because if these birds compete and/or breed with the Seychelles black parrot it will cause much severe impact on our environment and also in the act of risking diseases. Monitoring activities are undertaken early morning between 0545 and 0700 hrs and evenings between 1645 and 1900 hrs. During the monitoring, the parakeets have been observed feeding in orchards close to human habitations. When it reaches 3 years, the male acquires a pink collar which extends below the chin, hence the name ring-necked parakeet. The collar is not apparent in the females.  They feed mostly on ripe fruits especially guava: eating a hole in the fruit and then eating the seeds and on seeds of Bwa nwanr

It has been found out that ring-necked parakeets disperse in response to food availability. A yellow form of the parakeet has also been observed on numerous occasions at Jardin Du Roi and Anse La Mouche.

The usual method of using Mist-Nest proved ineffective even though nets were raised above their standard heights. It was hoped the raised nets would overlap with the parakeet flight paths, but unfortunately they proved to be clever birds by flying under and sideways of the nests. That was when internal discussions led to shooting as an option. Due to their short dispersals in response to food availability, continuous sightings at a particular site are not guaranteed. So first it was important to follow these birds to determine their feeding sites.

Traditional feeding sites were determined during sporadic visits and shooting activities were targeted at these particular sites. Observations suggest that they feed throughout the day. The latest population estimate is around 250 individuals on Mahe Island.

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Psittacula krameri

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The Crested Tree Lizard (Calotes versicolor)

The first observation of C. versicolor in Seychelles dates back to the 27th of September 1982 at Barbarons on Mahe Island.

The Ministry became aware of C. vesicolor’s presence in Seychelles when staff from Anse Aux Pins clinic reported the first specimen on the 27th October 2003. The individual was apparently captured on Sainte Anne Island by a local and transported to Mahé to be kept as a pet. The lizard managed to escape and was caught about 500 m away. The good thing is that it was spotted in time by concerned individuals. A survey that was immediately conducted on the island revealed a viable population of 20-25 mature individuals in close proximity to the jetty. According to island staff, the first observed occurrence dates back towards late 2001 when the resort was near completion. Apparently the species was confined to the beachfront area where construction materials were offloaded and could have been accidentally introduced in containers from Mauritius.

The lizard comes from Southern Asia, from India to China and the provenance of Seychelles population is not really known. It is usually tan or grey with brown banded, its long tail is twice its body (length up to 40cm). Prominent crest extending from neck down to the body. Its food habitat is mainly insectivorous including ants, crickets and beetles while it also have an opportunistic omnivorous feeding habit including small vertebrates and some plant materials.

The Crested Tree Lizard can be found from sea level from 600-1000 m in dry, open shrubland and cultivated land. It favors tree trunks, rocks, wasteland, garden, parks and all man-made habitats. It uses a sit and wait hunting strategy often from a high point. It is a territorial animal. Females and juveniles tend to forage on the ground in the grassy and shrubby vegetation while the male adults stay in the open more often. They roost on vegetation (up to 9 m) at the tips of twigs, shoots and inflorescence. It is also known that this lizard is able to swim in fresh and sea water.

The Crested Tree Lizard could have an impact on any kind of birds, it preys on eggs and small birds. All endangered bird on Mahé could be threatened. The worst thing that could happen would be an introduction of this lizard on such predator free island like Aride and Bird Island.

Anecdotal observations on C.versilor behaviours have revealed very interesting information. They climb with great agility, often jumping from branch to branch. The toes are long and pointed to aid with gripping and the long tail is used for balancing. They hide behind stems and coconut palm trunks and upon approach of humans, flatten the body laterally until they are almost invisible. They are able to rotate their eyes independently of each other hence the ability to detect danger from afar. They are most active 2-3 hours after sunrise where most often territorial adults would station themselves on a conspicuous object such as a rock to display. This activity coincides with feeding. They have been observed feeding on a variety of invertebrates and vertebrates. Their diet also comprises of crickets and grasshoppers. Different instinctive methods such as the use of glue, nets and manual removal of individuals have been utilized so far. The most successful has been manual removal whereby individuals, once spotted, are flushed, pursuit until caught. The Saint Anne population is now under control and there has not been any reliable report since 2006.

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Barn Owl (Tyto alba)

The barn owl was introduced in Seychelles from East Africa in 1949 for the control of rats in coco nut plantations. The department of Agriculture introduced three barn owls first to Ile Platte on the 27th April 1949. Later on, 15 were introduced to Union Vale on the 31st December 1951. (Annual Agriculture Report 1949, 51) 6 were introduced at Le Niole on July 29th 1952 and August 9th the same year. Barn Owls were found to be on all granitic islands of Seychelles in 1974 including Cousin & Cousine. The introduction of Barn Owls in Seychelles in 1949 by the Department of Agriculture was an unsuccessful attempt to control rats. Records show that instead of eating rats the barn own turned on the local birds, Particularly the Fairy Tern and cause great damage.

From pellet analyses done on Aride from March- May 1993, it was concluded that the preferred food of Barn owls seems to be Terns, both young & adults, principally taken during the main tern-breeding season. At other times of year, mice & lizards feature prominently in the diet.  Analysis of stomach content of Barn owl by the Conservation Section reveals that they also take frogs and cockroaches.

In order to control the Barn owl which preys on birds, especially the White Tern, a premium of Rs5 per owl was paid by the Seychelles Government for 22 owls in 1969. To encourage the killing of Barn owls, the R5 premium was increased to R30 in 1971 and on Aride since 1973. With the introduction of the R30 bounty by the Department of Agriculture, Barn owls have been killed simultaneously on all areas of Mahe as well as on Praslin.

The Barn Owl is locally known as Ibou. It is by far bigger than the native Scops Owl. Both sexes are similar in size & colour. Barn owls are a golden buff colour with a white heart-shaped face & a small beak. They rely on their hearing to hunt at night using these distinctive facial discs to take in sounds all around. The owl processes these sounds through its ears.

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Indian House Crow (Corvus splendens)

It is widely believed that the Indian House Crow (Corvus splendens) or Korbo, in Creole, was originally introduced to Seychelles via an Indian cargo vessel in 1977. As the name suggests, the species is native to India but has breeding range throughout most Asian countries. They are often assisted by ocean going vessels, where apparently, sailors feed and encourage them to remain on board. They however often abandon ship at the first sight of land and establish viable populations on the nearest land mass. This has resulted in a wider distributional pattern extending towards the east African coast. Being an omnivorous scavenger favoring dumping sites, they are most often successful colonizers of foreign territories; where with their powerful beaks and menacing behaviors often out-compete other avian species and/or prey on smaller native fauna. Thus, they are considered as pests throughout their range.

The Indian House crow is a dark medium-sized bird and in the Seychelles, it has been reported mainly from the granitic islands. In strong sunlight, deep purple gloss can be observed on the wings and appears to glitter giving them a brilliant coloration. The dark color intertwines with grey patch extending from the neck towards the upper back.

Around 1980’s, an estimated number of about 30 individuals were sighted and 9 were subsequently shot. Most sightings were around the northeastern region of Mahe in close proximity to dumping sites. They were observed feeding on discarded waste and in gutters, thus the likelihood of their spreading diseases was not ruled out. Complaints received from members of the public include loss of agricultural crops such as fruits, vegetables and poultry. Impact on biodiversity includes preying on endemic geckos, lizards, spiders and eggs as well as young of small endemic birds.   Collaborative efforts between the Ministry of Environment and the Department of Defense to eradicate the population have prevented further disperse in Seychelles. This mutual agreement was facilitated by the 500 Seychelles rupees bounty placed on the scavenger’s heads. The population was apparently eradicated in 1994. However, single individuals were observed in 1998, 2000 and sightings of 2 birds reported during 2002. In July 2005, another lone individual was spotted and subsequently disposed off.

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Baboon Spider

A lone baboon spider was found in a container during 2005. It was caught as a result of good co-operation between the different stakeholders especially Customs Officers. No other sightings of Baboon spider have been made so far

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Red Eared Slider (Trachemys Scripta elegans)

The fresh water terrapin ‘Red-eared slider’ has been introduced via the aquarium trade. This turtle is very common in the US and is used a lot in live pet trade. Such a terrapin, should it establish itself might displace the endemic ‘soupap’ by competing with them for food and habitat. Until now five of such terrapins have been located at Belombre, Victoria, Ma Constance, N.E Point and Beau Vallon on the main island of Mahe. They are known rapacious predators within their range, and could easily out-compete endemic terrapin species and might have an impact on other aquatic organism, if left to thrive.

The easiest way to identify a Red Eared Slider is by the red or sometimes yellow patch that is found just behind the eye.

Note: The Red Eared Slider is more aggressive than the endemic terrapins and could easily out-compete them for both food and nesting sites.

The Conservation Section is in the process of trying out various methods to assess the wild population of Red Eared Slider. The surveys are now also yielding valuable information about our local terrapins.

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FLORA

Alien plants are common in all habitats of the granitic Seychelles. Lowland forests are mostly composed of alien trees of former plantations. In mid-elevation forests more than half of the trees are alien cinnamon (Cinnamomum verum). Only managed offshore islands, Inselbergs (glacis), and tiny pockets of relatively undisturbed palm, cloud and dry forest are relatively free of alien plants.

Nevertheless, compared to other oceanic islands Seychelles may have been quite lucky. Cinnamon is by far the most common alien tree and it could even be a blessing in disguise. These are mostly woody species, but recently different creepers have expanded in lowland areas and some of these species are starting to invade natural areas. The dominance of most forests by cinnamon since the 19th century may have kept out other invaders. Soils in Seychelles are very poor in nutrient, in particular phosphorous. Thus, invasive plants have to adapt to very particular soils. The low fertility may also reduce the risk that alien plants negatively affect the soils.

Invasive plant management is closely linked to habitat management; especially in the case of common alien plants such as Cinnamon. Past experiences have shown that large-scale removal of Cinnamon is not effective. Rather, Cinnamon should be seen a solution. Cinnamon has several characteristics that may facilitate habitat restoration. It does not form dense thickets in contrast to many other invasive plants and native plants seem to regenerate well under its canopy. Cinnamon also produces very nutritional fruits that are important food source for endemic birds and fruit bats. The nutritional fruits may however produce negative effects on native plants because Cinnamon may distract birds and fruit bats from dispersing native species. On the main Seychelles islands in contrast to small islands such as Cousin or Aride, alien plants will in future always be part of the vegetation of natural areas.

Managing Alien Invasive Species

Invasive species are recognized as a threat to biodiversity worldwide. Most of the habitat in Seychelles is dominated by alien species that have been introduced as timber, crop or horticultural plants. Some of these species hinder regeneration of native species, alter ecosystem processes and threaten to invade the few native habitats that remain. Accidents happen and any new introductions to Seychelles will require early detection and rapid action.

A number of management programmes for invasive species have been carried out, mostly on an experimental basis. For example, a COI project tried different methods of control for invasive species such as Chinese guava (Psidium cattleianum) in high altitude forests. There have been small scale ring-barking of certain invasive trees by the Department of Environment.

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