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Gongylomorphus bojerii 

Scope: Global
Language: English
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Taxonomy [top]

Kingdom Phylum Class Order Family
Animalia Chordata Reptilia Squamata Scincidae

Scientific Name: Gongylomorphus bojerii (Desjardin, 1831)
Common Name(s):
English Bojer's Skink
Synonym(s):
Scincus bojerii Desjardin, 1831

Assessment Information [top]

Red List Category & Criteria: Critically Endangered A2abce ver 3.1
Year Published: 2015
Date Assessed: 2015-05-11
Assessor(s): Cole, N. & Payne, C.
Reviewer(s): Bowles, P.
Justification:
Listed as Critically Endangered on the basis of a population decline in excess of 80% since 2010, inferred from the apparent complete eradication of the largest subpopulation within two years following the introduction of invasive mammals to Flat Island. Invasion remains a continuing threat to populations on the remaining, much smaller islands where this lizard still occurs. This species is dependent on active conservation management to prevent the establishment of alien invasive species within its remaining range, and the species is therefore considered to be undergoing a continuing decline although the population presently appears to be stable.

Geographic Range [top]

Range Description:

Bojer’s Skink is a Mauritian endemic that was once widespread throughout much of the Mauritian mainland and surrounding islands (Vinson and Vinson 1969). However, the invasion of the Common Wolf Snake Lycodon capucinus and Musk Shrew Suncus murinus have caused severe reductions in the skink’s distribution, and the species now only exists on offshore islands where these species are absent (Tonge 1990, Jones 1993, Freeman 2003). The current distribution of the species consists of: Serpent Island (0.32 km2), Round Island (2.19 km2), Gunner’s Quoin (0.76 km2 limited to 0.67 km2), Gabriel Island (0.42 km2), Pigeon House Rock (0.006 km2, within which the skink is limited to 0.004 km2) and Ilot Vacoas (0.01 km2, within which the skink is limited to 0.006 km2). Two additional subpopulations now exist on Ile de la Passe (0.02 km2, within which the skink is limited to 0.01 km2) and Ile aux Fouquets (0.03 km2, within which the skink is limited to 0.01 km2) as a result of reintroductions (Cole et al. 2009, 2013). The species was also present on Flat Island - representing an estimated 41% of its area of occupancy and 80% of its global population - until the invasion of shrews in 2010. It has not been detected since 2011 despite extensive annual surveys, and is thought to have been lost altogether within two years of the invasion (MRRP 2011, Cole 2011, 2012, Stanbury 2012, Cole et al. 2014).

Countries occurrence:
Native:
Mauritius
Additional data:
Estimated area of occupancy (AOO) - km2:3.63
Number of Locations:8
Upper elevation limit (metres):280
Range Map:Click here to open the map viewer and explore range.

Population [top]

Population:

The Bojer’s Skink population is currently stable following a massive sudden decline beginning in 2010. The total current population has been estimated as 128,996 individuals. The population is considered to be divided into three subpopulations: Serpent Island (700 individuals), northern islands (127,000 individuals) and the southeastern islands (1,296 individuals); although the latter two consist of multiple island populations with little dispersal ability, none of the population sizes are below 100 individuals and are therefore considered viable. As a result the population is not considered to be severely fragmented. The current population estimate was obtained from genetic estimates of effective population size, transects, capture-mark-recapture, and absolute density studies through the Mauritius Reptile Recovery Programme run by the Durrell Wildlife Conservation Trust, Mauritian Wildlife Foundation and National Parks and Conservation Service.

Current Population Trend:Stable
Additional data:
Population severely fragmented:No

Habitat and Ecology [top]

Habitat and Ecology:

This is a diurnal skink that occupies most habitat types on the islands of Mauritius. It is predominantly terrestrial, although is frequently seen climbing vertical rocky features, trees, shrubs and herbaceous plants to bask or in search of food (Cole et al. 2009). Native grasslands dominated by Stenotaphrum dimidiatum support the highest densities of this species, seconded by forested and palm rich habitats, with a mixture of deep leaf litter and rotting logs (Cole et al. 2009, Mauritius Reptile Recovery Programme MRRP 2011). The diet consists mainly of small invertebrates as well as fruits and small vertebrates (Vinson and Vinson 1969, Cole et al. 2009). The species will scavenge carrion and dropped food from island visitors, and are occasionally cannibalistic (Vinson and Vinson 1969, Cole et al. 2009). Animals lay two eggs per clutch, which are buried into the soil or under logs (Vinson and Vinson 1969, Cole et al. 2009). Repeated surveys of individuals identified from their dorsal patterns on the southeast islands have demonstrated that they can reach sexual maturity within a period of ten months and live for approximately three to four years (MRRP unpublished data). Annual apparent survival has been estimated at 54% (Cole et al. 2009); generation time, based on the best available estimate of mean age at reproduction, has been estimated at three years (N. Cole, unpubl. data). It is not known how many clutches individuals produce within a season, but from captive breeding of Gongylomorphus at Durrell Wildlife Conservation Trust it is thought to be at least three clutches per season (M. Goetz pers comm. 2012). The skinks are reproductively active between July and February (MRRP unpublished data). Juveniles hatch between August and April, although low levels of reproductive activity do occur outside of these dates (MRRP unpublished data). Of all the islands where the species currently exists, Round Island has the greatest elevation at 280 m above sea level, and skinks occur at all altitudes. 

Systems:Terrestrial
Generation Length (years):3

Use and Trade [top]

Use and Trade: There is no use of or trade in this species.

Threats [top]

Major Threat(s):

Historically, the Bojer’s Skink population declined considerably since the 19th Century due to the introduction of lizard predators, including the Common Wolf Snake (Lycodon capucinus) and Musk Shrew (Suncus murinus) (Vinson and Vinson 1969, Tonge 1990, Jones 1993, Freeman 2003, MRRP 2011, Cole et al. 2014), and it is now extinct on the main island of Mauritius. Other introduced predators such as rats (Rattus norvegicus and R. rattus), mongooses and feral cats, are also thought to have contributed to these historical declines (Jones 1993).

The recent introduction of the shrew to Flat Island has led to the loss of approximately 80% of the global population since 2010. Gabriel Island, Ile aux Fouquets, Ilot Vacoas and Ile de la Passe are also threatened with the introduction of the shrew, Common Wolf Snake and other invasive predators. The other islands are also threatened with invasion by these species, but to a lesser degree owing to their remoteness and/or inaccessibility. Round Island is further protected by the permanent presence of wardens and established biosecurity protocols. The rate of offshore island invasion events is approximately three non-native fauna species per year (23 invasion events in the past eight years), several of which have posed a significant threat to terrestrial biodiversity. However, in most cases the Durrell Wildlife Conservation Trust, Mauritian Wildlife Foundation and National Parks and Conservation Service have prevented establishment following these incursions (MRRP unpublished data).

Other threats to the skink on the smaller islands include: trampling of habitat; littering that entraps and kills skinks; and fire as a result of human activities on the accessible islands. Severe climatic conditions are also thought to cause fluctuations in skink abundance on some of the islands (Cole et al. 2014). The smaller islands are heavily trespassed despite being closed to public access leading to threats from disturbances and accidental introductions of predators.

Conservation Actions [top]

Conservation Actions:

Bojer’s Skinks are part of a current conservation programme by the Durrell Wildlife Conservation Trust, Mauritian Wildlife Foundation, and National Parks and Conservation Service to restore the reptile communities on the offshore islands of Mauritius.

The extant populations form two main haplogroups that separate the Ilot Vacoas population from those in the northern populations (Austin et al. 2009). The Serpent Island population is genetically similar to the other northern populations but morphologically distinct (Freeman 2003; Austin et al. 2009). Currently, the Ilot Vacoas and Serpent Island populations are treated as separate conservation management units from the other northern populations.

The Serpent Island population is considered to be stable, as it is remote and difficult to access, such that there is little threat from direct anthropogenic disturbances. The Ilot Vacoas population has been the focus of recent conservation action. Shrews were eradicated from Ile de la Passe (Varnham et al. 2002) and the skink was reintroduced to the neighbouring Ile aux Fouquets and Ile de la Passe between 2007 and 2013 where they are now well established (Cole et al 2009, Cole et al. 2013, Michaelides et al 2014).

The eradication of introduced mammalian herbivores and predators from some of the northern islands were significant conservation actions that have led to increases in skink abundance since the 1980s, at least for Gunner’s Quoin and Round Island (Bullock 1986, North et al 1994). Serpent Island, Round Island, Pigeon House Rock, Gunner’s Quoin and Ilot Vacoas have been designated as closed Nature Reserves and National Parks.



Citation: Cole, N. & Payne, C. 2015. Gongylomorphus bojerii. The IUCN Red List of Threatened Species 2015: e.T62251A13482733. . Downloaded on 18 September 2018.
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