ISSN 1989‐8649 Manag. Biolog. Invasions, 2011, 2

Abstract Possible control of introduced giant African land snails (Achatina spp.) by the reintroduced endemic telfairii, Ile aux The giant African land snail (Achatina Aigrettes, Mauritius fulica) is one of the world’s worst invasive , out‐competing Jamie A. COPSEY, Graham SHELBOURNE, Rachael GRICE, Martine GODER, Steeves BUCKLAND, Zayd JHUMKA, Vimul NUNDLAUL, Carl JONES & Nik endemic snails, consuming native COLE vegetation and potentially altering nutrient cycles. Attempts to eradicate Introduction, Hypotheses and consumed by native predators, the snail from islands have only been Problems for Management there is little evidence they can successful with incipient populations. control established populations We present correlative evidence that The giant African land snail Achatina (Raut & Barker 2002). The main native island predators mayt ac as an fulica has now become naturalised objective of the study was to effective control agent for the snail. In on islands throughout the Pacific, analyse the status of an invasive 2000 a population of between 37,300 Caribbean and Indian Oceans Achatina fulica population in and 45,100 African land snails was (Meyer & Picot 2001). Once Mauritius following the estimated on the 26ha nature reserve reintroduction of the omnivorous island of Ile aux Aigrette, Mauritius. established it has had serious Between 2006 and 2007, 260 endemic biological impacts consuming native endemic Telfair’s skink Leiolopisma Telfair’s skink were vegetation, modifying habitats and telfairii. Supportive evidence for the reintroduced to the reserve. Snail out‐competing endemic snails impact of the on reducing the population surveys in 2008 and 2009 (Moore 2005). It has been snail population is provided through showed that the introduced snail implicated in the spread of exotic analysis of skink diet and the population had declined to 5,569 (± plant pathogens and may also alter representation of snails in relation 3,630) and 6,871 (±5,379), respectively. nutrient cycles (Raut & Barker to the availability of other Previous studies showed that the 2002). invertebrate prey items. introduced snails were selective over other invertebrate prey items. We Attempts to eradicate Study Area suggest that predation by the endemic Achatina spp. by physical removal skink has been an important causal have only proved successful with The study was performed on the factor behind the snail population incipient populations (Raut & Barker Open Nature Reserve, Ile aux decline. 2002). Although molluscicides have Aigrettes, a 26 ha coralline island been developed (Raut & Barker with a maximum elevation of 13m Keywords 2002) the financial cost of control and positioned 600 m off the south‐ can be prohibitive (Muniappan eastern coast of Mauritius (Parnell Achatina fulica, Leiolopisma telfairii, 1987; Smith & Fowler 2003). The et al. 1989). Average monthly introduced species, reintroduction use of biological controls (e.g. the rainfall varies from a high of 240 predatory snail Euglandina rosea mm in January to a low of 60 mm in and parasitic worm Platydemus September. The island has been the manokwari) has proved disastrous recipient of an intensive restoration for native gastropods (Civeyrel & programme by the Mauritian Simberloff 1996; Griffiths et al. Wildlife Foundation and now 1993). Although Achatina spp. are supports an almost complete

39 DOI: http://dx.doi.org/10.3391/mbi.2011.2.1.04 J. Copsey et al. Possible control of Achatina spp. by an endemic skink

coverage of native dry coastal forest Ile aux Aigrettes as a source of food Resumen and has been a focal site for the for pigs that were once kept on the reintroduction of endangered island. Despite the occasional El caracol gigante africano (Achatina vertebrate species (Anon 2006; predation of snails by the Indian fulica) es una de las peores invasoras a Cristinnace et al. 2009; Jones & musk shrew Suncus murinus, no nivel mundial debido a que desplaza por competencia a caracoles nativos, consu‐ Hartley 1995; Dulloo et al. 1997; other on the island is known me especies vegetales autóctonas y Newfield et al. 2003). Where the to consume the introduced snail, tiene potencialidad para alterar los ci‐ ebony forest has been restored the which are known to occur at a high clos de nutrientes. soil is rich (40%) in organic matter density on the island (Craze & although it is still relatively shallow Mauremootoo 2002). Los intentos para erradicarlo en islas (10cm depth) (Parnell et al. 1989). solo han tenido éxito en el caso de po‐ Between December 2006 blaciones incipientes. En este trabajo and February 2007, 260 endemic African land snails are presentamos evidencias correlativas de thought to have been introduced to Telfair’s skinks Leiolopisma telfairii que los predadores nativos de una isla han podido actuar como agentes de control efectivos frente al caracol. En el año 2000, dentro de la reserva natural Ile aux Aigrette, en la Costa de Mauricio, la población de Achatina fulica se esti‐ maba entre 37.300 y 45100 ejemplares. Entre 2006 y 2007 se introdujeron 260 ejemplares de Leiolopisma telfairii (un reptil endémico) en la reserva. Los cen‐ sos de Achatina fulica realizados en 2008 y 2009 mostraron un descenso hasta los 5.569 (± 3,630) y 6,871 (±5,379) individuos. El cruce de esta información con estudios previos sobre la dieta de Leiolopisma telfairii permite sugerir que la predación por el eslizón endémico ha podido ser un factor cau‐ sal del descenso en la población invaso‐ ra.

Palabras clave

Achatina fulica, Leiolopisma telfairii, especies introducidas, reintroducción

Figure 1. Telfair’s slink Leiolopisma telfairii and Achatina fulica shell.

40 ISSN 1989‐8649 Manag. Biolog. Invasions, 2011, 2

relative abundance, volume and occurrence the ith prey category, where relative occurrence was the proportion of skinks that had consumed the ith prey category was calculated to determine an importance value (IV) of each prey category (Gifford et al. 2000). The relative abundance of invertebrate prey items within the diet of the skinks was also compared to the relative abundance of invertebrate prey items on the island using Vanderploeg and Scavia's relativised electivity index (EI, Vanderploeg & Scavia 1979; Lechowicz 1982), where values range from + 1 to ‐ 1 Figure 2. Map of the 12.5x12.5m grid system on Ile aux Aigrettes showing 17 sample squares. Inset showing location of study site in relation to Mauritius for the most and least selected prey and Africa (adapted from Craze & Mauremootoo 2002). items respectively, and values near zero represent neutral/random were translocated to Ile aux 2000 were surveyed in 2008 and selectivity. Aigrettes from Round Island, 20km 2009. These grid squares were laid NE of Mauritius (Cole et al. 2009). out in three lines in order to cover Climatic data for the In 2000, prior to the reintroduction all vegetation types on the island southeastern region, including Ile of the skinks, there was a (Fig. 2). Surveys were conducted aux Aigrettes were obtained directly population of 37,300 to 45,100 giant between 8 am and 4 pm, at the end from (Mauritius Meteorological African land snails on the island of the wet season as in 2000. From Services) for the survey periods to (Craze & Mauremootoo 2002). April 2007 to December 2008 prior examine whether climatic factors to and during the repeated snail may have been responsible for Methods population surveys, 131 faecal changes in snail abundance samples were obtained from recorded during this time. Mean In April 2008 and 2009 the individual skinks on Ile aux Aigrettes. temperature and humidity ranges introduced African land snail Invertebrate remains within the for the year 2000, 2008 and 2009 population on Ile aux Aigrettes was faeces were separated, identified during the three month period resurveyed using the same and measured to obtain the volume (March‐May) encompassing the methodology as in 2000 (Craze & of each category. To account for a study periods (April/May) were 25‐ Mauremootoo 2002). A permanent bias arising from numerous small 26 °C and 80‐82%. Rainfall during the grid of 1689, 12.5 m x 12.5 m items being consumed by numerous same period was higher in 2008 quadrats was marked out with individuals in comparison to a few (201 mm) and 2009 (197 mm) than metal pegs prior to the 2000 survey. very large items being consumed by in 2000 (145 mm). This inverse The same 17 grid squares used in a few individuals, the mean of the relationship between snail

41 J. Copsey et al. Possible control of Achatina spp. by an endemic skink

abundance and rainfall could not be groups consumed by skinks 37,300 and 45,100 snails on the examined statistically, although a consisted of Blattodea (IV=44.3%), island (Craze & Mauremootoo relationship was evident. African land snail (21.3%), 2002). The most recent surveys Coleoptera (17.5%), Hymenoptera conducted in 2008 and 2009 Results (8.8%), Lepidoptera (6.4%) and showed that the population of the other (1.7%). In comparison to prey introduced African land snail on Ile In 2008, there were 3.3 snails per availability electivity values of items aux Aigrettes was reduced to 13% grid square, producing a mean found within skink diet showed that (2008) and 17% (2009) of its island population of 5,569 with only African land snails (EI=+0.68) population size in 2000. The ±95% CL (confidence limits) of 3,630 were selected for with a slight significant drop in snail abundance snails. In 2009, an initial estimate of avoidance of, but mostly random followed the reintroduction of the 9.3 snails per grid square was selection of Blattodea (EI=‐0.25), endemic skink, L. telfairii. The skink calculated, although 55% of the moderate avoidance of Coleoptera is a generalist and whilst snails encountered were found in (EI=‐0.69) and almost complete only invertebrate data are just one of the 17 grid squares avoidance of all other categories presented here 60% of skink diet (AN03) sampled. Removing this (EI<‐0.98). consists of fruits, plant material and unusually high count for one grid vertebrates and selection of square produced an estimate of 3.8 Discussion preferred food categories varies snails per grid square and an island seasonally (N. C. unpublished data‐ mean of 6,871 with ± 95% CL of In 2000 the average number of contact author for related data). 5,379 (Fig. 3). snails was calculated at 24.4 per grid However, there is clear evidence square on Ile aux Aigrettes that skinks show a strong selection The main invertebrate producing an estimate between for African land snail predation in the studied area during the period studied , whilst other invertebrate 50000 groups are eaten at random or are 45000 avoided. These findings suggest that 40000 the skink has played a critical role in 35000 reducing the invasive snail 30000 25000 population through direct 20000 predation. 15000 10000 Predation by native species Achatina snail population estimate 5000 on the exotic African giant land 0 snails has been recorded before. 2000 Skink 2008 2009- 2009+ For example, predation by native Release hermit crabs on some Pacific atolls has been suggested as one reason Figure 3. Estimated total population size (±95% CL) of the African giant land for the low abundance of the snail on Ile aux Aigrettes prior to (2000) and after (2008 and 2009) the rein‐ introduced African land snails on troduction of L. telfairii. 2009+ figure represents population estimate includ‐ ing disproportionate abundance of snails in grid square AN03. these islands (Schotman 1989).

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However, no similar studies could humidity over three month period the fact that the skink is positively be found that document such a (March‐May), encompassing the selecting the snail in its diet adds significant impact on these study periods (April/May), for the important weight to this introduced gastropods by a years 2000, 2008 and 2009 were not interpretation conclusion. Further reintroduced species. substantially different. Rainfall annual studies are required to during the same period was higher ensure that the crash in snail Alternative explanations for in 2008 (201mm) and 2009 (197mm) population documented here was the snail population decline include than in 2000 (145mm). Higher not related to some alternative predation by other species, such as rainfall should have benefited the factor. However, as alternative the native land crab, Cardisoma land snail population, at least in hypothesis have been considered carnifex and the introduced musk terms of their observed abundance within the current study we feel shrew. Although no survey has yet during the study period, although confident in making a causative link been performed to determine the the reverse relationship was between skink predation and snail impact of the crabs on the observed. Climatic conditions could population decline. The introduced snails, the crabs are not therefore adequately explain reintroduction of more Telfair’s rarely encountered either during the the decline in snail abundance. skinks to Ile aux Aigrettes is day or night. The shrew population currently being considered which it was considerably lower in 2008 and The disproportionate is hoped will lead to a further 2009 than before skinks were abundance of snails (55% of the decline in snail abundance across released. Chemical pesticides are total) within one grid square (AN03) the island. While it is unlikely the not used on Ile aux Aigrettes and are during the 2009 survey may be skink will eradicate the invasive snail therefore not responsible for snail explained by the relatively deep‐soil from the island, based on the data decline. Introduced populations of and substantial grass coverage presented here it is predicted that it Achatina spp. can experience found in this square, atypical to the will maintain snail densities at a low population crashes after rest of the island. Additionally level. establishment (Eldredge 1988). The building work was being carried out reasons for this decline are not well adjacent to the grid square AN03 Acknowledgements understood although disease has during the 2009 survey and may been suggested (Mead 1979; Cowie have discouraged skinks from The authors are grateful for the 1992). However, the species was foraging in this area. efforts of staff and students from introduced to Mauritius over 200 Nottingham Trent University who years ago (Griffiths & Florens 2006; Conclusions conducted the snail population Cheke & Hume 2008). It would surveys in 2008 and 2009. We also seem surprising for the population The findings of the current study thank the Mauritian Wildlife to decline so dramatically for this suggest that the reintroduced skink Foundation and National Parks and reason, but coincidentally at the L. telfairii may have played a Conservation Service, Mauritius. same time that an endemic predator significant role in reducing the Rouben Mootoocurpen and Heather was returned to the island. population of the invasive snail A. Richards assisted with diet and fulica on Ile aux Aigrettes, Mauritius. invertebrate collection and analyses. Climatic data showed that While recognising the correlative N.C. was supported through the mean values of temperature and nature of the data presented here, Darwin Initiative project ref 15‐038.

43 J. Copsey et al. Possible control of Achatina spp. by an endemic skink

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Bio­sketch Authors

Jamie Copsey has over 15 years training experience in the field of biodiversity COPSEY, Jamieson A (1) conservation. His research interests include natural resource use and invasive species (Corresponding author] (1) management. [email protected]

Graham Shelbourne is principal lecturer at Nottingham Trent University with SHELBOURNE, Graham (2) responsibility for learning & teaching who leads annual undergraduate biology field trips [email protected] to Mauritius. GRICE, Rachael (2)

[email protected] Rachel Grice is a biology graduate from Nottingham Trent University. (3) GODER, Martine Martine Goder works for the Mauritian Wildlife Foundation as a conservation biologist. [email protected]

Her main focus is restoration of small islands and propagation of critically endangered BUCKLAND, Steeves (3) plants. [email protected]

JHUMKA, Zayd (3) Steeves Buckland is a Ph.D. student with nine years of extensive field experience in [email protected] applied conservation, directing, volunteering and assisting conservation related projects locally and internationally. NUNDLAUL, Vimul (4) [email protected]

Zayd Jhumka has worked on several conservation projects for the Mauritian Wildlife JONES, Carl (3) Foundation since 2003. He is currently assigned to the Mauritian Recovery [email protected] Project. (1) COLE, Nik [email protected] Vimul Nundlaul is a Research and Development officer for the National Parks and Conservation Service, Mauritius and is responsible for biodiversity management on the (1) Durrell Wildlife Conservation offshore islands. Trust, Les Augrès Manor, Trinity, Jersey, British Channel Islands,

JE3 5BP Carl Jones is the Scientific Director for the Mauritius Wildlife Foundation and has worked (2) for the restoration of species and systems on Mauritius for more than 30 years. Nottingham Trent University, Burton Street, Nottingham, UK

Nik Cole is a conservation biologist whose applied research over the past decade has (3) Mauritian Wildlife involved rebuilding endangered reptile communities, invasive species management and Foundation, Grannum Road, Vacoas, Mauritius, Indian Ocean island restoration.

(4) National Parks & Conservation Service, Reduit, Mauritius.

Copyrights 2011owned by The Authors

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