Memoirs of" the Museum of Victoria 56(2):43 1-433 (1997) 28 February 1997 https://doi.org/10.24199/j.mmv.1997.56.34 A CONSERVATION PROGRAMME FOR THE PARTULID TREE SNAILS OF THE PACIFIC REGION Paul Pearce-Kelly. Dave Clarke, Craig Walker and Paul Atkin Invertebrate Conservation Centre, Zoological Society of London. Regent's Park. London NW1 4RY, UK Abstract Pearce-Kelly, P., Clarke, D., Walker, C. and Atkin, P., 1 997. A conservation programme for - the partulid tree snails of the Pacific region. Memoirs ofthe Museum of Victoria 56(2): 43 1 433. Throughout the Pacific numerous endemic mollusc species have either become extinct in the wild or are currently facing the threat of extinction as a result of introduction of the predatory snail Euglandina rosea and the New Guinea flatworm Platyclemus manokwari. Without determined conservation efforts, including the establishment of ex situ breeding programmes, much of the region's endemic snail fauna will be lost. Since 1986 a collabor- ative international conservation programme has been in place for partulid tree snails. The participating institutions currently maintain a total of 33 taxa in culture (comprising > 12 000 snails). The conservation status of all 1 17 partulid species has been assessed usingthe Conservation Action Management Plan (CAMP) process. Target ex situ population sizes required to maintain 90% of starting heterozygosity over 100 years have been calculated using the analytical model programme CAPACITY (Pearce-Kelly et al., 1994) The genetic management requirements of the breeding programme have necessitated the development of a colony management computer database enabling demographic management and analy- sis of the populations. The ability of long term captive-bred snails to readapt to natural field conditions was investigated using a trial release and monitoring experiment at Kew Gardens. Field introduction trials via the construction of predator-proof forest reserves, were commenced in 1994. Introduction dae. Euglandina paid scant attention to its intended Achatina target preferring to prey on sur- An ill-conceived attempt at biological control of the smaller endemic snails. Extensive field the African land snail Achatina fulica (using the veys have determined that many partulid through- snail predator Euglandina rosea and the New species have been preyed to extinction Guinea flatworm Platydemus manokwari) has out their natural range (Murray and Clarke, resulted in large numbers of endemic mollusc 1984; Pearce-Kelly et al., 1994). community, in species becoming extinct, or facing the threat of In 1986 the international zoo Breeding extinction, throughout the Pacific region. With- association with IUCN's Captive an international con- out the establishment of ex situ breeding pro- Specialist Group, devised grammes many of these endemic species will servation programme to establish viable ex situ endangered partulid face extinction. populations of as many tree snails of species as possible. The programme is currently The 1 1 7 species of Polynesian culture 33 taxa (totalling the family Partulidae once spread over a wide maintaining in in group of volcanic islands of the west, central and > 12 000 individuals) in 18 collections America. south Pacific. Each island had its own endemic Europe and North in 1994 used the Conservation species, which were often further restricted to A workshop Plan (CAMP) process (Seal individual valleys. The product of extraordinary Action Management to assess the conservation status of selective pressures, Partula (the largest and most et al., 1994) within the Partulidae. This review studied genus of the Partulidae) has provided every species that no species could be considered researchers with an invaluable insight to the determined and identified 53 mechanisms behind speciation (Johnson et al., as being less than endangered species as being in need of urgent captive- 1995). In addition to their scientific importance assistance (Pearce-Kelly et al., 1 994). many species of Partulidae are valued elements breeding Because of the intensive culture requirements of the region's rich cultural heritage. Partulidae, together with the The introduction of Euglandina has had a dis- associated with the large number of species requiring captive- astrous effect on the region's species of Partuli- 431 432 P. PEARCE-KELLY ET AL. breeding assistance, the workshop calculated the Kew Gardens. This 16 month trial suggested target population sizes required to maintain that long term captive-bred Partula populations 90% of starting heterozygosity over 100 years have retained their ability to readapt to a natural using the analytical model programme environment and diet (Pearce-Kelly et al., CAPACITY (Flesness and Mace, 1988; Soule et 1995). The latest development has been the al., 1986) The results of this exercise suggested commencement of reestablishment on the that a minimum of 250 adults, together with French Polynesian island of Moorea (Murray, their associated young, need to be maintained 1995). Because of continued predator threat, for each species in the breeding programme. this aspect of the programme has involved the construction of a predator-proof reserve, 20 m The demographic labyrinth X 20 m, built with cheap locally available materials, and containing three species of Maintaining healthy genetic populations of any cap- tive-bred Partula snails (Murray, species over successive generations requires a 1995). For the foreseeable future, it is not possible management protocol that takes account of the to progress beyond the predator-proof major factors that lead to loss of genetic diver- reserve strategy due to the high numbers of surviving sity. These factors are genetic drift (the random Euglandina in the habitat. These process which results when a limited sample of Euglandina are feeding on native micro-snails in the leaf genes from one generation is transmitted to the litter and will continue next), inbreeding depression (mating between to prevent the full re-establish- ment of Partula into the relatives which can result in reduced characters wild until effective predator control measures are developed. such as fertility and growth rate), artificial selec- To ensure that the captive tion (the disproportionate survival of individ- snails do not become uals adapted to the prevailing environmental diseased, lose their natural resilience to endemic micro-organisms, conditions — in captivity selective pressures or introduce alien microbes when returned to their native may differ from those in the wild) and disease. In habitat, an extensive screening exercise order to balance these considerations the snail is in place to determine the nature and levels cultures are maintained along inbred and out- of enteric gut fauna and flora in both bred lines with genetic drift and inbreeding the wild and captive Partula populations. depression being minimised in the outbred lines while the inbred lines best reduce the risks of selection pressures and disease. Other conservation initiatives The taxa in the Partulidae programme derive Educational material is being produced to help not only from different islands but from differ- raise public awareness of the ecological disaster ent valleys and collection sites within valleys. facing the indigenous snail fauna throughout the Each of the 1 00 collection > sites represents a Pacific and, to illustrate how Polynesians can genetically unique population which needs to be help prevent further extinctions ofendemic mol- maintained as a separate breeding line. The need luscs, legislation is being formulated to prohibit for generation separation and monitoring of the further introduction of alien species into French four developmental stages (defined as new born, Polynesia. These two initiatives are the most juvenile, subadult and adult) are further effective conservation action that can be taken management complications. These considera- to reduce the likelihood of alien predators being tions are compounded by the need to maintain introduced to islands that have thus far escaped populations as colonies of up to 200 snails, of such disastrous importations. mixed age structure. The development of a com- puterized colony database (CERCI) has, for the Conclusion first time, enabled the detailed monitoring and The extinction analysis of demographic trends, and environ- of endemic species of mollusc throughout mental and genealogical data in colony popula- the Pacific is continuing. Without tions. concerted in situ and ex situ action, of the nature outlined above, it can only escalate. The signifi- cance Re-establishment for conservation of such action is high- lighted by the number of species currently The effectiveness of the breeding programme in afforded a second chance of survival through maintaining viable populations was tested in captive-breeding programmes. In addition to 1994 when a group of zoo-bred Partula taeniata benefiting the individual target species, such was released on to Polynesian plants growing at programmes are potential conservation models CONSERVATION OF PARTULID TREE SNAILS OF THE PACIFIC REGION 433 for many of the more than 1000 IUCN-listed Pearce-Kelly, P., Clarke, D. and Mace, G.M., 1994. threatened mollusc species. Partula '94: An action plan for the conservation of the family Partulidae. Zoological Society of Lon- References don: London. Pearce-Kelly, P., Mace, G. and Clarke, D., 1995. The Fleness, N. and Mace, G., 1988. Population databases release of captive bred snails (Partula taeniata)