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MSc Conservation and Biodiversity 3
ASSIGNMENT COVER SHEET – Research Project 4
Student Name: Rhon Connor ....Uni. No: ………... 5
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Project Title: Distribution, Habitat Association, Species Abundance and Perceptions of Residents 7
towards Achatina fulica in Anguilla 8
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Supervisor: Dr Tom Tregenza 10
Date Submitted: 12th September 2006 Date Received ASU: 12
th September 2006 11
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Feedback: 13
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Marker‟s signature 18
Mark: 19
Moderator‟s signature: 20
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DECLARATION 22
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I certify that this assignment is my own work. I confirm that I have not allowed anyone else to copy this work. 24
Any material quoted or paraphrased from references books, journals, www etc. has been identified and duly 25
acknowledged or references as such. I have read the University‟s policy on plagiarism. 26
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Signed………………………………………………………………………………… 28
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Cover page 30
Title: Distribution, Habitat Association, Species Abundance and Perceptions of Residents towards 31
Achatina fulica in Anguilla 32
Rhon A. Connor 33
Postal address: Rendezvous Bay, Anguilla, British West Indies. 34
Corresponding author e:mail: [email protected] 35
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Abstract 41
Invasive species affect biodiversity and have been associated with high economic costs and other 42
implications for society. One invasive mollusc, which is currently causing considerable damage to the 43
livelihood of people in the Caribbean, is the Giant African Snail (Achatina fulica). The invasion of this 44
mollusc in the Caribbean Island of Anguilla has posed a major challenge to the authorities and 45
residents alike. Here, I investigated the overall distribution of A. fulica, examined the association of A. 46
fulica with three different habitats (grasslands, woodlands and shrubs), recorded its microhabitats, and 47
probe the perception of residents towards the introduced mollusc. I found that there were significant 48
differences in the snails‟ abundance among geographic areas, habitat types and microhabitats. The 49
results indicated that A. fulica was widely distributed in all major habitat types, thereby suggesting that 50
any eradication programme will be extremely costly. The study also revealed that residents 51
considered the snail to be a pest and were supportive of assisting the authorities in managing the 52
destructive mollusc. 53
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Key Words 56
Giant African snail, invasive species, microhabitat, mollusc, biodiversity, Anguilla, pest. 57
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Introduction 62
Biological invasions (invasive or alien species) are harmful non-native animals, plants and 63
microorganisms that have the potential to affect terrestrial and marine biodiversity (Perring et al., 64
2002; Mooney, 2005). In recent times, they have been viewed as a global threat to biodiversity and 65
conservation managers (Simberloof, 2002). These alien species, once established outside of their 66
native range, have the potential to severely alter native ecosystems (Gabriel et al., 2001). 67
Additionally, research has shown that oceanic islands are not only more vulnerable, but suffer greater 68
damage as a result of invasive species (Donlan et al., 2003; Dowd et al 2003). Scientists attribute this 69
theory to many factors, one being that these agents/vectors are away from their natural enemies 70
(predator, parasites, and pathogens), and therefore they have the freedom to adapt and spread rapidly 71
in their new environment (Dowd et al 2003, Molongoy et al 2006). Additionally, studies have 72
associated invasive species with the cause of extinctions in some islands (Donlan et al 2003; Gurevitch 73
and Padilla, 2004). 74
75
The island of Anguilla and the rest of the Caribbean Region are no strangers to invasive 76
species. According to Kairo and Ali (2003), the Caribbean region has a total of 552 invasive species 77
(of which Anguilla have 9). These include various species of snakes, insects, noxious weeds and other 78
micro-organisms which have altered the region‟s ecosystems, affected its economies and posed a 79
serious threat to the health and well being of the residents. One particular invasive which is currently 80
seen as a major threat to the Caribbean Region is the Giant African snail (Achatina fulica), whose 81
origin is Eastern Africa. 82
83
Achatina fulica is recognized by the Global Invasive Species Programme (GISP), as one of the 84
100 most destructive biological invasions in the world. This herbivore has a voracious appetite and is 85
known to feed on over 500 species of plants (Simberloof, 2003). Apart from this, A. fulica poses a 86
potential health risk to humans, as some of its specimens are associated with an intermediate host of a 87
nematode parasite Angiostrongylus Cantonensis, which is commonly known as the rat lung worm 88
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(Civeyrel and Simberloff , 1996; Carvalho et al 2003). This vector has the potential to cause 89
eosinophilic meningoencephalitis and brain damage in humans (Upatham et al 1988). 90
91
The first known record of A. fulica in the Caribbean Region was documented in the French 92
island of Guadeloupe in 1984 (Mead and Palcy, 1992; Civeyrel and Simberloff, 1996; Raut and 93
Barker, 2002). Subsequently, specimens of A.fulica have dispersed and successfully established 94
populations in other islands of the Caribbean archipelago including Martinique (1988), Barbados 95
(2000), St. Lucia (2000), St. Maarten/St. Martin (2000?) and Anguilla (2000). 96
97
As in many other nations, the authorities and the residents throughout Anguilla are concerned 98
about the potential threat of the Giant African Snail. This concern has propelled the authorities to 99
launch an organized campaign towards the eradication of this invasive mollusc. However, due to 100
concerns voiced by a few concerned citizens (over the possible side effects of the molluscicide bait 101
being use), the campaign was prematurely stopped after three months. 102
103
It is important to note that although several scientific studies have been conducted on Achatina 104
fulica throughout the Pacific region, most of them have focused on its potential as a disease carrier, its 105
agricultural impact and/or various biological and natural attempts to control the mollusc. A review of 106
other literature simply provided an overview of the snails‟ biology and its potential use as a food 107
source. However, this is the first study to assess Achatina fulica in various parameters within its 108
physical environs, while at the same time evaluating it socio-economic impact on society. Therefore, 109
this study was designed to investigate a) the distribution of A. fulica in Anguilla, b) the topographical 110
habit of A. fulica, c) the physical location/micro-habitat associated with A. fulica and c) the perception 111
of residents towards A. fulica. In addition, as there are no preliminary data on endemic or introduced 112
snails on Anguilla, baseline data was also collected on specimens of the island‟s terrestrial 113
malacofauna. 114
115
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The main predictions tested in this study are that there will be significant differences in the distribution 116
of A. fulica among villages, habitat types, microhabitats, and that the perception of residents in relation 117
to the mollusc will be dependent on the level of impact they have experienced as a result of the 118
invasive snails. 119
120
Materials and Methods 121
This study was conducted on the island of Anguilla (18.2 N, 63.1W ) from March to July 122
2006. The approach for this research took the form of two components, namely, extensive fieldwork 123
whereby data was collected from several sampling sites, and the distribution of a questionnaire, which 124
sought to ascertain the perception of residents towards the invasive A. fulica. 125
126
Rapid survey of the islands for Achatina fulica 127
Prior to the commencement of sampling study sites, I gathered information from the 128
Department of Agriculture in order to ascertain the distribution of A. fulica on the island. I then 129
conducted a rapid assessment throughout all of the villages (including those not listed by Department 130
of Agriculture) to ascertain the presence or absence of A. fulica on the island. This approach involved 131
having brief informal discussions with 5-10 residents (selected at random) from villages throughout 132
the island to determine whether they have seen or heard of the mollusc in their community. Once the 133
residents identified areas in their community where A. fulica was known to inhabit the area was 134
searched for a fixed period of 20 minutes for evidence (live snails or shells) of the introduced mollusc. 135
Those villages that provided evidence of a positive infestation of the mollusc were recorded and a GPS 136
unit was used to determine the exact location of the specimen(s). Upon completion of the research, 137
villages that were not infested with A. fulica during the initial rapid assessment survey were re-visited 138
to determine whether infestation of the snails had occurred in the area. 139
140
Study Sites 141
For the purpose of this research, the study sites were selected from the list of those villages 142
that were positively infested with specimens of A. fulica during the initial rapid assessment survey of 143
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villages. Five of these villages were randomly chosen for sampling the distribution of the introduced 144
snail. These villages were Upper South Hill, Little Harbour, Stoney Ground, George Hill and Cauls 145
Bottom (see Fig. 1). It is important to note that for each study site, I examined three fairly 146
homogenous distinct topographic structures (habitats). These habitats were categorized as grasslands 147
(5-10 cm tall), shrublands (35-75 cm tall) and woodlands. The vegetation on the island does not have a 148
distinct woodland habitat. Therefore, in keeping with the range established by Walker et. al (2005), 149
areas with trees between 305-915 cm were classified as woodlands type habitats. 150
151
Criteria for site selection 152
I examined each of the five villages in the study to allocate areas that were suitable to be 153
classified as grasslands, shrublands and woodlands. Areas with dense vegetation are extremely 154
difficult to conduct sampling of poorly mobile organisms (Craze and Mauremootoo, 2002). Therefore 155
areas with semi-scattered and accessible vegetation were selected for sampling A. fulica‟s abundance 156
in shrubland and woodland type habitats. However, the final criterion for the site selection of the 157
mollusc was that the areas under investigation must have had at least two dead (shells) and live 158
specimens of the species Achatina fulica. 159
160
Sampling of sites 161
Achatina fulica is mainly nocturnal, therefore sampling only took place during the early 162
morning (at the break of dawn) when the snails were still very active. In order to ascertain the density 163
of A. fulica in each habitat, I randomly established a ten (10) metre transect- with 2 x 2 m quadrats - 164
on alternate sides for the grassland study sites (each transect had 5 quadrats). Subsequent transects 165
were established every 10 metres. This process was repeated 8 times, giving the sampled area a total 166
of 40 quadrats (N=40) for each grassland habitat. Again, due to the level of difficulty associated with 167
constructing quadrats in dense vegetation, the sampling technique for shrublands and woodlands were 168
slightly altered. Sampled areas were selected based on accessibility. However, the same number and 169
size of quadrats for these sites was constructed. Using the protocol established for other studies on 170
mollusc (see Cowie, 1999), timed sampling (5 minutes) was used to sample each quadrat. For each 171
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quadrat, I scoured for A. fulica in various physical locations/microhabitats such as in the leaf litter, on 172
vegetation, under rocks/fallen wood, on tree trucks and on rocks/stony ground. For grassland habitats, 173
snails embedded in the grass were recorded as being in the leaf litter. A total of 600 quadrats were 174
sampled for this study (N=600). 175
176
All individuals of A. fulica that were in each quadrat were then counted, and its physical 177
location/microhabitat association (live specimens) was documented on a data sheet. Additionally, all 178
other species of gastropods that were found in the quadrats were recorded with reference to their 179
morphology. A hand held Garmin Foretrea 201 GPS (Garmin, Kansas, USA) unit was utilized for 180
acquiring the coordinates of all quadrats on the study site. Since wet weather is usually associated 181
with A. fulica being more active, the weather condition was also recorded on the data sheet. Wet days 182
were defined as overnight rain or the presence of dew in the habitat during the sampling, while dry 183
days were defined as the lack of precipitation in the habitat under study. 184
185
Interviews/Survey 186
The perception and participation of the public is an integral component when addressing the 187
issue of invasive species (Simberloof, 2003; Maguire, 2004; Gewin, 2005). Therefore, I conducted a 188
survey to ascertain the views of the public with reference to A. fulica. I designed a questionnaire and 189
randomly interviewed 140 residents (N=140) on the island. The survey was distributed to households 190
of infested villages (not necessarily those villages of the study sites). One individual (18 years or 191
older) from each household was asked a range of questions including (but not limited to), time of 192
introduction, methods of control and impact of snails (see appendix 1). It was hoped that by acquiring 193
such vital feedback from the respondents, the practitioners, residents and environmental managers 194
would have a better understanding of the impact of invasive species in relation to socio-economic 195
factors. 196
197
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Results 198
Distribution of A. fulica 199
The survey indicated that 20 villages were infested with specimens of A. fulica. All of the 200
infested areas were adjoining villages. There were a total of 17 villages that were infested prior to the 201
commencement of the study, while 3 villages became infested during or after that period. At the 202
completion of the survey, only one village to the west (Long Bay) and the most eastern villages of the 203
island were free of the introduced snail (Fig. 1). 204
205
Abundance and Microhabitat/physical location 206
The survey yielded a total of 2,544 snails (876 live and 1668 dead) belonging to the species 207
Achatina fulica that were collected from the sampled sites. I performed a Kruskal-Wallis test 208
(adjusted for ties) to determine whether there were significant differences in the number of snails 209
among villages. The results (H=49.6, d.f=4, P < 0.001) indicated that there were significant 210
differences in the number of snails among villages. This test was also performed to determine whether 211
there was a significant difference in the number of snails among the 3 vegetation types. According to 212
the result (H=63.16, d.f =2, P < 0.001), it indicates that there were significant differences among the 213
snails in different habitat types. 214
215
The data further showed that the village of Stoney Ground had the highest density of A. fulica, 216
while George Hill had the least amount of these snails. However, the study indicated that the village 217
of South Hill had the highest density of live A. fulica, while Caul‟s Bottom had the least amount of 218
live snails (fig. 2). In terms of the dead A. fulica, Stoney Ground recorded the highest density of the 219
species per square metre, whereas George Hill had the least amount of snails. Additionally, the data 220
indicated that there were similar numbers of live and dead A. fulica in George Hill and South Hill (Fig. 221
2). 222
223
Further, with reference to habitat association, the survey indicated that shrublands recorded 224
the highest mean number of A. fulica per quadrat from the sampled population, while the woodland 225
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habitats had the least number of this invasive mollusc (Fig.3). A higher biomass of A. fulica was 226
recorded in the shrubs at Stoney Ground, while Caul‟s Bottom had the least in this habitat. The data 227
also indicated that A.fulica was more prevalent in the woodland habitats of Caul‟s Bottom and George 228
Hill, whereas Little Harbour recorded the least amount of snails in this habitat. The results revealed 229
that there were a fairly even distribution of A. fulica among the woodland and grassland habitats of 230
South Hill and Stoney Ground (Fig.3). 231
232
The survey also indicated that among the three topographical structures under investigation, 233
grasslands were associated with a higher proportion of dead snails when compared to shrublands and 234
woodlands habitat. Alternatively, shrublands were associated with a higher proportion of live snails, 235
while woodland habitats recorded the lowest number of A. fulica snails for this study (see Figs.8 236
a,b,c). 237
238
This study also evaluated the physical location/microhabitat of Achatina fulica. Most of the 239
snails were located on the vegetation during the sampling of habitats (Fig.4). With the exception of 240
Stoney Ground, the data showed that there were very few snails located under the rocks or fallen 241
wood. Meanwhile, there were inconsistencies in terms of the amount of snails located in the leaf litter 242
and on rocks/stony ground for each of the sampled villages. However, the results indicated that the 243
amount of snails found on the tree trunks of the sampled villages were more evenly distributed when 244
compared to the other microhabitats (Fig.4). Additionally, the results also indicated that more live 245
specimens of A. fulica were recorded on wet days compared to dry (Fig. 8 d). 246
247
Other Species of Snails 248
The survey yielded a total of 5, 358 specimens of other mollusc species on Anguilla. These 249
terrestrial molluscs are further classified into six species, namely: Species 1) Drymaeus species- D. 250
virgulatus (family Bulimulidae); species 2) Bulimulus guadalupensis (family Bulimulida); species 3) 251
Chondropoma (Chondropomorus) (family Annulariidae/Licinidae); species 4) Macroceramus (family 252
Urocoptidae; species 5) Drymaeus species- (family Bulimulidi)striped; species 6) Subulinidae species 253
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(see Fig. 5). Species 1 and 3 were found in all sampled villages. Species 2 was recorded in all villages 254
except Stoney Ground. The data also indicated that specimens of species 4 were only found in George 255
Hill and Little Harbour. Species 5 and 6 were only found in little harbour- and were exclusively 256
associated with the woodland habitats (table 1). The data also indicated that the density of A.fulica was 257
relatively close to the most common snail found in the island (table 2). 258
259
Although not recorded in the quadrat sampling, 2 other species of invasive molluscs- 260
Zachrysia Species Z. provisoria or Z. auricoma havenensis (family Pleurodontidae), (Fig.6) and a 261
number of veronicellid slugs were found in some villages during the period when the initial rapid 262
assessment survey for the presence/absence of A. fulica was conducted. 263
264
Perception of the Public 265
Results from the residential survey indicate that 42% of the respondents considered the Giant 266
African Snail to be a major/significant problem while 37% of them viewed it as a pest. (Fig. 7a). I 267
performed a regression test to ascertain whether there was a relationship between the amount of snails 268
in the respondents‟ yard and their perception of the molluscs. The results (r square=0.026, F=3.27, d.f 269
=1,121, P=0.07) indicated that there were no significant relationship with the amount of snails and the 270
perception of residents toward A. fulica. Again this test was performed to ascertain whether the 271
financial loss they experienced as a result of the snails had any bearing on their perception of the 272
mollusc. The results, r square =0.710, F=223.45, d.f =1, 90, p < 0.05, indicated that there is significant 273
relationship between financial losses and perception of snails. Similarly, a regression test suggested 274
that there is significant relationship ( r square=0.787, F = 497.91, d.f = 1, 35, p < 0.05) with reference 275
to the respondents age and their perception of the introduced snail. 276
277
Further, most respondents (44%) stated that the snails have also caused significant damage to 278
their plants/crops (Fig. 7b). In terms of mitigation methods, the majority of the respondents (50%) 279
utilized household salt as a mean of controlling A. fulica while 15% used metaldehyde bait to combat 280
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these herbivorous snails (Fig. 7l). With reference to the geographic origin of A. fulica, 90% of the 281
respondents indicated that they were unaware of the area from which this species originated. (Fig 7d). 282
283
Only 2% of the sampled population indicated that they had seen the snail on the island from as 284
early as 1999, while 52% became aware of the snail‟s existence in 2005 (Fig 7e). The results also 285
indicated that most residents (44%) shared a view that the snail was introduced through the 286
importation of plants (Fig. 7c). In terms of eradication of the mollusc, 50% of the respondents stated 287
that the Government of Anguilla should take measures to eradicate A. fulica, while 37% believed that 288
the authorities should resort to using chemicals as a means of controlling them (Fig.7f). Only 2% of 289
the respondents were supportive of the idea of using the snail as a source of food. 290
291
Data from the questionnaire also indicated that 50% of the respondents believed that a special 292
task force should be created to combat A. fulica, while 35% were of the opinion that it is the 293
responsibility of the Department of Agriculture (Fig.7g). In relation to the question about the A . fulica 294
as a potential disease carrier, 46% of the respondents stated that they were aware that the mollusc may 295
be a risk to their health (Fig. 7h). 296
297
Interestingly, the questionnaire also revealed that most of the respondents (78%) were not only 298
willing to actively participate in an eradication programme, but were also willing to make a financial 299
contribution (83%) towards the eradication of A. fulica (Figs. 7i and 7j). To examine this further, I 300
performed a 2x2 chi square test to ascertain whether the respondents‟ willingness to physically 301
participate in an eradication programme were influenced by them having snails in their yard. The 302
results, square = -0.03, p=1 shows that there is no significant relationship between respondents 303
willingness to participate in an eradication programme and having/not having A. fulica in their yards. 304
Again, this same test was performed to evaluate whether the respondents willingness to pay a 305
contribution towards eradication of the mollusc were related to them having/not having the snail in 306
their yard. The results, square = -0.02, p = 1, shows that there is no difference between persons 307
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willingness to pay and the presence or absence of snails in their yard. As to the issue of who held the 308
ultimate responsibility for eradication of the snails, the results indicated that the prevailing view was 309
that it was the responsibility of all stakeholders (Fig. 7k). 310
311
Discussion 312
This study has indicated that Achitina fulica has successfully manifested and established itself 313
within Anguilla‟s ecological community. With the exception of the villages to the eastern end of the 314
island (Fig. 1), this introduced mollusc has invaded all other communities throughout the island. It 315
must be noted, however, that during the search for study sites the distribution of A.fulica seems 316
somewhat sporadic within the villages. The landscape that was modified had a tendency to be 317
affiliated with an abundance of the snails, while the more undisturbed areas were free of the 318
introduced mollusc. This suggests that A.fulica has a high affinity towards modified habitats. Although 319
With (2002) states that satellite population of newly invasive species is common, this observation has 320
been documented in several other studies on the invasive mollusc, which showed that A. fulica was 321
more prevalent in anthropogenic and disturbed habitats such as gardens, roadsides, wastelands ( 322
Cowie, 1998; Meyers and Picot 2001; Raut and Barker, 2002). 323
324
The trend and rapid dispersal of A. fulica on Anguilla is of great interest. Tomiyama and 325
Nikane (1993) in their radio transmitter experiment to monitor the movement of the species observed 326
that the snails moved in a straight line and that their movement is within limited areas. Perhaps this is 327
the reason why the adjoining villages in the island are gradually being infested with these invasive 328
snails. Singh (1980) also observed a similar pattern of movement in his study of A. fulica in the Bihar 329
States. Another striking point about the migration of these snails is that they seem to be following a 330
westward movement throughout the island. This pattern of movement is quite interesting as most of 331
the tourism related facilities, which employ a significant amount of Anguilla‟s labour force, are 332
located on the western end of the island. This movement may suggest humans are aiding in the 333
dispersal of A. fulica (most likely attached to their vehicles). Kierans et al (2005) observed a similar 334
pattern of dispersal with their study on another invasive mollusc. 335
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336
The abundance of A. fulica on the study sites, although not surprising, is also of great concern 337
to conservation managers and residents on Anguilla, as it indicates the high level of fecundity and easy 338
dispersal that is often associated with these pestiferous snails (Raut and Barker, 2002). Meyers and 339
Picot (2001) states that the snails have reached extremely high densities and biomass (up to 770kg/ha) 340
in New Caledonia. Similarly, the Caribbean island of Martinique has experienced the rapid spread of 341
A. fulica, as its infested area grew from 90 to 310 hectares within one year (Civeyrell and Simberloff, 342
1996). By contrast, the sampled village of South Hill recorded the highest density of live snails 343
(0.66m2). Therefore, with the average weight of A. fulica listed by the GISP at 32g, this suggests that 344
Anguilla‟s A.fulica population is likely to be 221 kg/ha. 345
346
This study also revealed that there were variations in the number of A. fulica among the 347
sampled villages, habitat types, and microhabitats (Fig. 2; Fig. 8a,b,c). As illustrated in the results, I 348
expected Stoney Ground to have a higher biomass of the mollusc. My rationale for this statement is 349
based on reports from the Department of Agriculture that the first known specimens of A fulica were 350
documented in that village (Christopher, 2006 as per. Comm.). This suggests that A.fulica’s biomass in 351
each of the sampled villages may be related to the time of its initial invasion. In terms of A. fulica‟s 352
microhabitat, the abundance of snails on the vegetation suggests that most of the mollusc were 353
foraging during the time the study was conducted; therefore, this study suggests that assessing 354
A.fulica’s microhabitat may be dependent on time of sampling. 355
356
With reference to habitat association of A. fulica, I expected to see higher density within the 357
woodland habitats, as the snails have a preference for dense vegetation (Thangavelu and Singh, 1983; 358
Craze and Mauremotoo, 2002). That the results showed higher densities were associated with 359
shublands and grasslands (Fig. 8b,c) suggests that the low biomass in woodland may be due to A. 360
fulica‟s recent colonisation of this type of habitat. Alternatively, the study revealed that apart from 361
physically being on the vegetation, most specimens of the mollusc were located in the leaf litter, which 362
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is another common microhabitat of this species (Craze and Mauremotoo, 2002; Prasad, 2004). This 363
indicates that A. fulica may have a preference for this type of environment. 364
365
The data also revealed that there are a high percentage of dead A. fulica (66%) in Anguilla‟s 366
sampled population. Most literature states the A. fulica‟s population reaches high densities and then 367
the population drastically declines (Civeyrell and Simberloff, 1996; Meyers and Picot, 2001; Craze 368
and Mauremooto, 2002; Gervin, 2005). As mentioned by Cowie (1998) and Gerlach (2001), this 369
phenomenon (mortality rate) seems to be a common trend on islands that A. fulica had invaded. Other 370
sources have suggested that this drastic decline may be associated with epizootic diseases and lesions 371
(Mead, 1961; Mead and Palcy, 1992), lack of genetic diversity (Civeyell and Simberloff 1996) and the 372
species reaching its carrying capacity (Simberloff and Gibbons 2004). Certainly, the death of the snails 373
at the study sites is not associated with the metaldehyde-baiting programme that was initiated by the 374
Agriculture Department, as those areas were not treated. 375
376
Interestingly, Mead (1961) argues that the radiation from the sun also plays a role in 377
dehydrating and subsequently killing A. fulica. In this study, I observed that the highest density of 378
empty shells of this mollusc was mainly distributed throughout the grassland habitats that were 379
sampled. Therefore, I postulate that with reference to the three topographical structures under 380
investigation, the sun was better able to penetrate the thin grasslands, thereby causing a higher 381
percentage of snails to die in this habitat. Apart from this, I observed that a high density of dead A. 382
fulica was recorded in the grasslands in George Hill (Fig. 8c). Coincidentally, the said area is low 383
lying and was observed flooded on two occasions during the study. Since it takes less that 12 hours for 384
mollusc to drown, I postulate that the high number of snails found dead in this grassland habitat may 385
have been influenced by flooding. It is interesting to note that one beneficiary of the invasive snail is 386
the Caribbean Hermit Crab (Coenobita clypeatus), as it has been observed utilizing the shells of 387
A.fulica on several occasions during the study (see appendix 2). Sant‟Anna et al. (2005) have 388
reported a similar pattern of behaviour in A. fulica infested Brazil. 389
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With regards to the other species of mollusc found in Anguilla, I observed that it was very rare 390
to find live specimens in the sampled quadrats. Some invasive organisms are known to have 391
deleterious effects on endemic species (Gurevitch and Padilla, 2004). For example, the mud snail 392
(Ilyanassa obsoleta) has been known to cause niche displacement on other species of snails (Mooney 393
2001) while the rosy wolf snail (Euglandina rosea) has been associated with the extinction of 394
Hawaii‟s endemic snails (Cowie, 1998; Gerlarch, 2001; Simberloof, 2003). Although A. fulica is not 395
associated with carnivorous activities, its vigorous and aggressive behaviour is associated with 396
competition and even replacement of native snail species (Craze and Mauremootoo, 2002; Mead and 397
Palcy, 2002). This suggests that the invasive A. fulica has potential implications for Anguilla‟s native 398
malacofauna. However, since the population data of the island‟s snails are not available this warrants 399
further research. 400
401
Results from the household survey indicate that the invasion of A. fulica in Anguilla is posing 402
a major challenge to residents and authorities. On several occasions during the study residents were 403
observed removing, baiting, and in some instances burning shrubs from their surroundings to destroy 404
these pestiferous snails (see appendix 3). Most residents resort to salt as a means of controlling the 405
invasive mollusc, but they also believe that the snail bait would be the most effective method of 406
management. Thangavelu and Singh (1993) states that a combination of both methods was most 407
effective in the management of the polyphagous snails. However, the residents and the authorities 408
must be cautioned that most molluscicides are not host specific, (Panigrahi and Raut, 2002; Prasad et 409
al., 2004; Gervin, 2005) and therefore have the potential to implicate other molluscs or non- target 410
species. 411
412
The survey also indicated that most residents did not view hand picking and destroying the 413
snails as a viable and practical method of control. Gerlach (2001) argues that manual collection of A. 414
fulica in the Seychelles (a particular area) was followed by a 98.3% decline of the said species. 415
Similarly, other sources (Mead, 1961; Raut and Barker, 2002) also reported that some populations of 416
A.fulica almost reached to the point of local extinction when this practice was initiated. Although 417
Page 17
Rhon Connor – MSc paper 17
manual collection is quite a tedious and laborious task, and may be more effective with small and 418
incipient populations of A. fulica, authorities in Anguilla may want to consider this option as a means 419
of managing and controlling the spread of the invasive mollusc. 420
421
Further, the study also revealed that residents on the island of Anguilla are eager to launch a 422
collaborative effort to combat, and subsequently eradicate A. fulica. However, it is well known that 423
the longevity of such willingness and enthusiasm expressed by volunteers is short lived. Mead (1961) 424
states that in Southern China, residents were given free bait by the authorities to help control the 425
prolific dispersal of A.fulica, but the authorities had to subsequently halt the programme after some 426
residents expressed their views that it was the government‟s responsibility for controlling the snails. 427
Interestingly, although the respondents indicated a strong sense of willingness for collaboration with 428
the authorities, similar attitudes and sentiments have been expressed throughout the Anguillian 429
community. This suggests that the authorities should be cautious when distributing mollusc bait, and 430
soliciting the help of the wider community. 431
432
It is well established that A. fulica is an agricultural and horticultural pest (Thaguvelu and 433
Singh, 1983; Prasad, 2004; Gervin, 2005). Therefore, it is not surprising to note that most respondents 434
have suffered significant damage to their crops/plants. However, a potential concern for conservation 435
managers is the likely impact A. fulica will have on Anguilla‟s only endemic plant (Rondeletia 436
anguillensis). Sharp spines and small leaves characterize this small stiff shrub-like plant, which is 437
mainly distributed in the northern and eastern end of the island (Walker et al.2005). It is interesting to 438
note that the molluscs are already present in one of the villages (North Side) where this plant is found. 439
Although the snails have not spread to R. anguillensis habitat (limestone holes) in the said village, the 440
mollusc has been sampled in the woodlands of South Hill, which is a similar habitat of this plant, and 441
has been observed foraging on similar plant with thorns. This suggests that A. fulica has the potential 442
to invade and possibly threaten R. anguillensis’ ecological community. Perhaps conservation 443
managers in Anguilla may want to know that the authorities in La Reunion Island and Ile Aux 444
Aigrettes have already taken protective and eradicative measures to safeguard their rare and endemic 445
Page 18
Rhon Connor – MSc paper 18
plants from A. fulica (Meyers and Picot, 2001; Craze and Mauremootoo, 2002). However, the likely 446
impact of A. fulica on Anguilla‟s endemic plant remains speculative, and therefore warrants further 447
research. 448
449
This survey indicates that invasive species can have serious implications for both biological 450
ecosystems and its inhabitants. It also indicates that Achatina fulica has spread throughout the various 451
topographical features within Anguilla. Additionally, with its high rate of recruitment, compounded by 452
the absence of its usual competitors, predators and other associates, A. fulica‟s population is not only 453
capable of sustaining itself, but it is also destined to manifest itself throughout the entire island within 454
a relatively short period. The study also demonstrated that feedback from the public is an integral 455
“tool” when addressing ways of managing and controlling invasive species, and also indicated that the 456
residents throughout the island are not only concerned, but are willing to collaborate with the 457
authorities and play their role in controlling the introduced mollusc. Additionally, since this is the first 458
known malacofauna study to be conducted on the island, the information gathered in this study will be 459
beneficial to any individual who wants to investigate invasive species and other studies on the 460
terrestrial snails of Anguilla and the Caribbean Region. Most importantly, however, this study 461
provides decision makers on the island with empirical data to help them facilitate strategic plans when 462
addressing the issue of the invasive Achatina fulica. 463
464
Conclusion and Recommendations 465
This study has shown that A. fulica has rapidly dispersed throughout the Caribbean island of 466
Anguilla, and is likely to have serious implications for the island's environmental managers. It is 467
obvious that A. fulica‟s population is well established throughout the island, and the initial phase of its 468
containment has been greatly missed. Therefore any thoughts of eradicating this invasive mollusc are 469
most likely to be futile. This is based on reports that although Florida (USA) and Queensland 470
(Australia) have successfully eradicated Achatina fulica, all others attempts throughout the Pacific 471
have completely failed. Thus, the authorities on the island should focus on public awareness and 472
education, and devise strategies to manage and control A. fulica‟s population. This in itself is quite a 473
Page 19
Rhon Connor – MSc paper 19
major task, but proactive, practical and effective strategies must be implemented urgently. It‟s 474
important to note that both mechanical and chemical means of controlling this species have been 475
effective in the past, but they are associated with high costs. Certainly, whatever means of control the 476
authorities initiate, they must be cautioned against the introduction of biological controls or predatory 477
snails. This method has been associated with the extinction of many endemic snails in Hawaii and The 478
Society Islands. It should be noted however that the authorities in the island of Anguilla must now 479
review and upgrade existing legislation on the importation of goods entering the territory. The 480
introduction of strict quarantine measures must also be implemented and enforced to prevent other 481
forms of invasive species from entering the island. 482
483
484
485
Page 20
Rhon Connor – MSc paper 20
Acknowledgements 486
I wish to thank my supervisor Dr. Tom Tregenza for his feedback and guidance with this project; to 487
my mentor Dr. Floyd Homer (Conservation Biodiversity Inc.) who provided valuable suggestions for 488
the manuscript. Special appreciation also goes to Farah Mukhida of the Anguilla National Trust who 489
willingly assisted with the data entry and offered suggestions for the study. Also thank you to Antonio 490
Christopher and William Vanterpool of the Department of Agriculture, Karim Hodge of the 491
Department of the Environment, Oliver Hodge of the Environmental Health Unit, and Guy Mathurin 492
(St. Lucia Ministry of Agriculture) for their resources and valuable information towards this project. 493
My appreciation is also extended to my wife Jackie Connor, Doyle Hughes, Asif Niles, and Alan Mills 494
for their contributions. I am particularly thankful to Dr. David Robinson (USDA APHIS) who 495
identified the snail species found in the study. A special thank you to all the respondents who willingly 496
took part in the survey, and most importantly my gratitude is extended to the Overseas Territories 497
Environmental Programme (OTEP) and the Government of Anguilla for their funding of my 498
studentship…for without them this project would not have been possible. 499
500
501
502
503
504
505
506
507
508
Page 21
Rhon Connor – MSc paper 21
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Mead, A.R. and Palcy, L. (1992) Two giant African land snail species spread to Martinique, French 561
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fulica Bowdich from nursery beds. Current Science 87 (12) 1657-1659 580
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Raut, S. K. and Baker, G.M. (2002). Achatina Fulica Bowdich and other Achatinidae as pests in 582
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species? Conservation Biology 17 (1) 83-92 587
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Simberloff, D. (1996). Impacts of introduced species of the United States. Consequences. 2:2 589
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Simberloff D. and Gibbons L. (2004) Now you see them, now you don‟t!-population crashes of 591
established introduced species. Biological Invasions 6: 161-172 592
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Singh, M.N. (1980) Occurrence of the giant African snail (Achatina fulica) in Bihar State. Journal of 594
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by long-distance jump dispersal: Insights from Argentine ants. Proceedings of National Academy of 598
Science. 98 (3) 1095-1100 599
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Thangavelu K and Singh K (1983) Giant African Snail Achatina Fulica Bowdich (Pulmonata: 601
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(Ferussac) (Stylommatophora: Achatinidae), Equipped with a Radio-Transmitter. Journal of 606
Molluscan Studies. 59:315-322 607
608
Upatham, E.S., Kruatrachue, M., and Baidikul, V.(1998) Cultivation of the Giant African Snail, 609
Achatina fulica. Scientific Society Journal of Thailand. 14:25-40 610
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Vieiral, T. et al. (2004) Acharan Sulfate, the new glycosaminoglycan from Achatina Fulica Bowdich 612
1822 structural heterogeneity, metabolic labeling and localization in the body, mucus and the organic 613
shell matrix. European Journal of Biochemistry. 271, 845-854 614
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Walker, M. M., Hodge, O., Homer, F., and Johnson, W. (2005) A Guide to Common Plants of 616
Anguilla. Anguilla National Trust. 617
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Rhon Connor – MSc paper 25
With, K. (2002) The Landscape Ecology of invasive spread. Conservation Biology vol. 16 no.5 1192-619
1203 620
621
622
623
624
625
626
627
628
629
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Rhon Connor – MSc paper 26
Figure legends 630
Figure 1: Map showing the distribution of the Giant African Snails in Anguilla before and after 631
March 2006. 632
633
Figure 2: Density (per m2) of Live and Dead A. fulica at each survey site. 634
635
Figure 3: Mean Number (se) of live/dead snails per quadrat according to habitat type (N=40 636
quadrats per habitat type) 637
638
Figure 4: The number of live A.fulica according to micro habitat/physical location 639
640
Figure 5: Specimens of Anguillas terrestrial malacofauna. 641
642
Figure 6: Specimen of another invasive species of snail found in Anguilla. 643
644
Figure 7: Graphs showing respondents views in relation to A. fulica (Figures a-l) 645
646
Figure 8: Graphs showing the mean density (snails m-2
) of dead snails from 40 (4m2 647
quadrats/habitats) in relation to its habitats within each village; and the mean density 648
of snails on wet and dry days. 649
650
Table 1: Table showing the villages and number of species of other snails from sampled sites. 651
652
Table 2: Density of Giant African Snails (based on all survey sites) compared to densities of 653
other snail species (also found within the survey sites). 654
Appendix 1 Giant African Snail Questionnaire 655 2 Hermit Crab using A. fulica shell 656 3 A. fulica shells collected by a resident 657
658
Page 27
Rhon Connor – MSc paper 27
Figure 1 659
660
661
662 663
664
Page 28
Rhon Connor – MSc paper 28
Figure 2 665 666
Density of Live and Dead GAS at each Survey Site
0
0.2
0.4
0.6
0.8
1
1.2
1.4
Cau
ls B
otto
m
Sto
ney Gro
und
Geo
rge
Hill
Little
Har
bour
Sou
th H
ill
Survey Site
GA
S D
en
sity m
2
Live
Dead
667 668
669
Page 29
Rhon Connor – MSc paper 29
Figure 3 670
671
# of snails(live/dead)
0
2
4
6
8
10
12
14
Little H. South H. Caul's B. George H. Stoney G.Mean
(se)
no
. o
f sn
ail
s p
er
qu
ad
rat
Grass
shrubs
Woods
672 673
674
Page 30
Rhon Connor – MSc paper 30
Figure 4 675 676 a) On vegetation b) Under rocks and/or fallen wood 677
678
Live Snails on Vegetation
0
20
40
60
80
100
120
140
160
Cau
ls B
otto
m
Sto
ney Gro
und
Geo
rge
Hill
Little
Har
bour
Sou
th H
ill
Village
No.
of
Liv
e G
AS
Live Snails Under Rocks and/or
Fallen Wood
0
5
10
15
20
25
30
35
40
Cau
ls B
otto
m
Stone
y Gro
und
Geo
rge
Hill
Little
Har
bour
South
Hill
Village
No. of Liv
e G
AS
679 c) In leaf litter d) on tree trunks 680 681 682
Live Snails in Leaf Litter
0
10
20
30
40
50
60
70
80
Cau
ls B
otto
m
Sto
ney Gro
und
Geo
rge
Hill
Little
Har
bour
Sou
th H
ill
Village
No.
of
Liv
e G
AS
Live Snails on Tree Trunks
0
5
10
15
20
25
30
35
40
45
Cau
ls B
otto
m
Stone
y Gro
und
Geo
rge
Hill
Little
Har
bour
South
Hill
Village
No. of Liv
e G
AS
683 684 e) On rocks and/or stony ground. 685 686
Live Snails on Rocks and/or Stony
Ground
0
5
10
15
20
25
30
35
40
Cau
ls B
otto
m
Sto
ney Gro
und
Geo
rge
Hill
Little
Har
bour
Sou
th H
ill
Village
No.
of
Liv
e G
AS
687 688
Page 31
Rhon Connor – MSc paper 31
Figure 5: 689 690 a); Drymaeus species- D. virgulatus b)Bulimulus guadalupensis (family Bulimulidae) 691 (family Bulimulidae) 692 693
694 695
696 c) Chondropoma (Chondropomorus) d) Macroceramus (family Urocoptidae) 697 (family Annulariidae/Licinidae; 698
699 700
701 e) Drymaeus Species- (family Bulimulidae) f) Species Subulinidae 702 703
704 705
706
Page 32
Rhon Connor – MSc paper 32
707
Figure 6 708
709 Z. auricoma havenensis (family Pleurodontidae) 710 711
712 713
714
Page 33
Rhon Connor – MSc paper 33
Figure 7 715 716
a b 717
Opinion of GAS
37%
16%
42%
3%
2%
pest
nuisance
major/significant
problem
not a problem
no answer
Damage to Crops and/or Plants by
GAS
44%
42%
1%
12%1%
Yes
No
Don't know
Not applicable
No answer
718 719
c d 720
GAS method of arrival
16%
1%
44%1%
2%
32%
1%
3%
vehicles/containers
on blocks/cement
imported plants
lumber
other
not applicable
don’t know
no answer
Knowledge of Geographic Origin of
the GAS
6%
90%
4%
Yes
No
No answser
721 722
e f 723
Year Learned About the GAS
0
10
20
30
40
50
60
70
80
90
100
1999
2001
2003
2005
No
answ
er
Year
%
Respondents
Measures to Deal with the
GAS
2%
56%
37%
1%
2%
1%
1%
nothing
eradicate
use chemicals to
control
export to countries for
foood
use locally as food
other
no answer
724 725
726
727
728
729
730
731
732
733
Page 34
Rhon Connor – MSc paper 34
g h 734
Agencies Responsible for Baiting the
GAS
4%
35%
50%
10%
1%
individualsaffected
Departmentof Agriculture
special taskforce
other
no answer
Recognition of the GAS as a
Disease Carrier
46%
47%
7%
yes
no
don't know
735 736
i j 737
Willingness to Participate in an
Eradication Programme
78%
16%
6%
yes
no
don't know
Willing to Pay for
Eradiction of the GAS
83%
14%3%
yes
no
don't know
738 k l 739
Agency responsible for eradicating GAS
14%
1%
11%
72%
2%
Agricultural
Department
Residents/community
Government
All stakeholders
No answer
Respondent GAS control measures
50%
15%
15%
0%
6% 1%
13% Household bait
Snail bait
Crush
Hotwater
Other
Not applicable
No answer
740 741
Page 35
Rhon Connor – MSc paper 35
Figure 8 742 743 a) b) 744
Mean Density (se) snails in Woodland Habitat
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
Caul's
Bottom
Stoney
Ground
George
Hill
Little
Harbour
South
Hill
Village
mean
den
sit
y (
se)#
sn
ails p
er
qu
ad
rat
(N=40)
Live
Dead
Mean (se) Density of Snails in Shrubland Habitat
00.5
11.5
22.5
33.5
44.5
55.5
66.5
7
Caul's
Bottom
Stoney
Ground
George
Hill
Little
Harbour
South
Hill
Village
Mean
Den
sit
y (
se)
of
sn
ails p
er
qu
ad
rat
(N=40)
Live
Dead
745 c) d) 746
Mean (se) Density of Snails in Grassland
habitats
0123456789
10
Cauls
bottom
Stoney
Ground
George
Hill
Little
Harbour
South Hill
Village
Mean
Den
sit
y (
se)
of
sn
ails p
er
qu
ad
rat
(N=40)
Live
Dead
Mean (se) # of snails found on wet and dry days in
each village
0
0.5
1
1.5
2
2.5
3
3.5
4
Caul's
Bottom
Stoney
ground
George
Hill
Little
Harbour
South Hill
Village
Mean
(se)
# s
nails
WET
Dry
747
Page 36
Rhon Connor – MSc paper 36
Table 1: 748 749
Species Cauls
Bottom
Stoney
Ground George Hill
Little
Harbour South Hill
Drymaeus species- D. virgulatus (family Bulimulidae)
304 1284 1204 1097 209
Bulimulus guadalupensis (family Bulimulidae)
2 0 55 54 3
Chondropoma
(Chondropomorus) Family annulariidae/Licinidae
107 67 264 400 67
Macroceramus (family Urocoptidae)
0 0 47 171 0
Drymaeus Species- (family Bulimulidae) (striped)
0 0 0 11 0
Species Subulinidae 0 0 0 3 0
Total individuals 413 1351 1570 1736 288
Total species 3 2 4 6 3
750
751
Page 37
Rhon Connor – MSc paper 37
Table 2 752
Snail Species Density
Drymaeus species- D. virgulatus (family
Bulimulidae)
1.708
Bulimulus guadalupensis (family Bulimulidae)
0.0475
Chondropoma (Chondropomorus) Family
annulariidae/Licinidae
0.381
Macroceramus (family Urocoptidae) 0.091
Drymaeus Species- (family Bulimulidae)
(striped)
0.00458
Species Subulinidae 0.00125
Giant African Snail 1.0575
753
754
Page 38
Rhon Connor – MSc paper 38
Appendix 1 755
Giant African Snail Questionnaire 756
757 Village ________________ 758
759
Gender: Male ___ Female ___ 760
761
Age group: 18-25; 26-40: 41-55: 56-70: 70+ 762
763
How long have you lived in this area? 764
Less than one year, 1-2 years 3-4 years Over 4 years 765
766
Are there Giant African Snails (GAS) within 100 m of this area? Y / N (if no Q 4) 767
768
Do you find GAS in your yard? Yes / No (if yes Q 5 ) 769
770
Are you worried that the GAS will invade your premises? Yes / No (skip 5 go to 6) 771
772
Approx. how many do you find in your yard at any given time (with dew / rain)? 773
Less than 50 50 – 100 100-150 150-200 over 200 774
775
Do you think that the population of GAS is Increasing or decreasing? 776
777
Which of the following best describes your opinion of the GAS? 778
A pest a nuisance a major/significant problem its not a problem 779
780
Page 39
Rhon Connor – MSc paper 39
If the GAS has caused you financial losses, which of the following estimates (USD)best describes 781
your loss within the past year? 782
under $50 50-100 100-150 150-200 over 200 783
784
What measures do you take to control it? 785
Household salt snail bait crush them use of hot water other 786
787
Does the GAS cause significant damage to your crops/plants? Yes / No / Don‟t know 788
789
What type of plants are mostly affected? Horticultural / Agricultural /Both 790
791
Do you know the geographic origin of the snails? Yes / No 792
793
How did you first learn of the invasion of the GAS? 794
Agricultural Dept. Anguilla Nat‟t Trust Family/friend other 795
796
Around what year you first heard of these snails in Anguilla? 797
‟99 ‟01 ‟02 ‟03 ‟04 ‟05 06 798
799
Do you think that they (GAS) were intentionally brought to Anguilla? Yes / No / don‟t know (don‟t 800
know Q17) 801
If yes, for what purpose? Food, Pets, Attractions, other 802
If no, which of these methods mostly assist in their arrival? 803
attached to vehicles/containers; on blocks/cement; imported plants, lumber, other 804
805
What measures do you think should be taken to deal with the GAS? 806
Nothing (allow them to remain in isle): eradicate them; use chemicals to control them: export them to 807
countries (food): use them as source of food (locally). 808
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Rhon Connor – MSc paper 40
809
Have you seen them in other neighbouring islands? Yes / No 810
811
Have your area been treated (baited) by the Agriculture department? Yes / No / Don‟t know 812
813
Do you believe that the chemical is effective? Yes No Don‟t Know 814
815
Do you believe that the authorities are doing enough to educate the public about the GAS? Yes / No / 816
Don‟t know 817
818
Do you believe that the authorities are doing enough to educate the public about the GAS? Yes / No / 819
Don‟t know 820
821
Were you given clear guidelines about how to handle the GAS ? Yes / No 822
823
Who do you believe is responsible for the baiting of snails? 824
Individuals affected; Agri. Department; Special task force other 825
826
Who is responsible for the eradication of these snails? 827
Agri. Dept. Residents/Community Government All Stakeholders 828
829
Which of these measures do you believe is the most effective in controlling the GAS? 830
Handpicking and destroying using cooking salt use of snail bait other methods 831
832
Which of the following agencies have you reported sightings of the GAS? 833
Agri. Dept. Env. Dept. Anguilla National Trust None (did not report it) 834
835
Do you know the GAS can carry a potentially serious human disease? 836
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Rhon Connor – MSc paper 41
Yes / No / Don‟t Know 837
838
Will you be willing to participate in an eradication programme? Yes / No / Don‟t Know 839
840
Will you be willing to pay a fee towards the eradiction of the GAS? Yes/No/Don‟t Know 841
842