AN ASSESSMENT OF EXOTIC SPECIES IN THE TONLE SAP BIOSPHERE RESERVE AND ASSOCIATED THREATS TO BIODIVERSITY A RESOURCE DOCUMENT FOR THE MANAGEMENT OF INVASIVE ALIEN SPECIES December 2006 Robert van Zalinge (compiler) This publication is a technical output of the UNDP/GEF-funded Tonle Sap Conservation Project Executive Summary Introduction This report is mainly a literature review. It attempts to put together all the available information from recent biological surveys, and environmental and resource use studies in the Tonle Sap Biosphere Reserve (TSBR) in order to assess the status of exotic species and report any information on their abundance, distribution and impact. For those exotic species found in the TSBR, it is examined whether they can be termed as being an invasive alien species (IAS). IAS are exotic species that pose a threat to native ecosystems, economies and/or human health. It is widely believed that IAS are the second most significant threat to biodiversity worldwide, following habitat destruction. In recognition of the threat posed by IAS the Convention on Biological Diversity puts forward the following strategy to all parties in Article 8h: “each contracting party shall as far as possible and as appropriate: prevent the introduction of, control, or eradicate those alien species which threaten ecosystems, habitats or species”. The National Assembly of Cambodia ratified the Convention on Biological Diversity in 1995. After reviewing the status of exotic species in the Tonle Sap from the literature, as well as the results from a survey based on questionnaires distributed among local communities, the main issues are discussed, possible strategies to combat the spread of alien species that are potentially invasive are examined, and recommendations are made to facilitate the implementation of a strategy towards reducing the impact of these species on the TSBR ecosystem. The TSBR contains the largest continuous areas of natural wetland habitats remaining in the Mekong basin and the largest permanent freshwater body in South-East Asia, the Tonle Sap lake. The TSBR, due to the size of the annual inundation, forms the most important of the flooded areas for fish production in the Mekong river system, and the catch from the Tonle Sap area represents around 60% of Cambodia’s inland fishery production. Besides the importance of the floodplain habitat for fish, it also supports the largest colonies of endangered waterbirds in South-East Asia and currently yields what is probably the world’s largest snake harvest. There are many pressures currently impacting on the lake and floodplain ecosystem, which are only likely to increase further in the short term, including habitat degradation, population growth, fishing pressure and potential hydrological changes. In the past, invasive alien species, being biological organisms themselves, have often been underestimated as a threat to biodiversity. Managers also lacked the knowledge on how to control invasive alien species and a lack of prioritization meant that there was very little funding available for any eradication efforts. The understanding of the threat invasive alien species pose to native ecosystems is increasing however and with it the recognition that due attention needs to be given to their presence and impact, especially in natural ecosystems important for conservation. Therefore, by assessing the current status of exotic species and their impact on their environment, this study hopes to identify key issues that need to be addressed in order to negate the threat of invasive alien species in the TSBR and avoid the huge environmental and economic costs that will occur if such invasions continue to be ignored. i Results Of the 50 or so exotic species considered in this report, there are two mammal, two mollusc, one amphibian, one crustacean, one insect, two reptile (as well as hybridized crocodiles), but 15 plant and 31 fish species. Out of all these species, the majority (which are fish with 28 species) have not been reported yet or remain unconfirmed that they have established populations in the TSBR, but they could potentially occur now or in the future as they are known to be in the Mekong basin, adjacent wetlands or are reared for aquaculture or aquaria within the basin. These species are Siam Weed (Chromolaena odorata), Mission Grass (Pennisetum polystachyon), Peruvian Primrose (Ludwigia peruviana), Apple Snails (Pomacea spp.), North American Bullfrog (Rana catesbiana), Red-eared Slider (Trachemys scripta elegans), Chinese Softshell Turtle (Pelodiscus sinensis), Louisiana Crayfish (Procambarus clarkii), Chinese False Gudgeon (Abottina rivularis), Acheilognathus barbatulus, Chinese Bitterling (Rhodeus sinensis), Arapaima (Arapaima gigas), Goldfish (Carassius auratus), Mrigal (Cirrhinus cirrhosus), African Catfish (Clarias gariepinus), Pacu (Colossoma macropomum), Grass Carp (Ctenopharyngodon idella), Mosquito Fish (Gambusia affinis), Catla (Catla catla), Barbel Steed (Hemibarbus labeo), Spotted Steed (Hemibarbus maculates), Bighead Carp (Hypopthalmichthys nobilis), Suckermouth Catfish (Hypostomus plecostomus), Metzia lineata, Oriental Weatherfish (Misgurnus anguillicaudatus), Blue Tilapia (Oreochromis aureus), Mozambique tilapia (Oreochromis mossambicus), Nile Tilapia (Oreochromis niloticus), Red-bellied Pacu (Piaractus brachypomus), Guppy (Poecilia reticulata), Sailfin Molly (Poecilia velifera), Stone Moroko (Pseudorasbora parva), Puntius semifasciolatus, Redbreast Tilapia (Tilapia rendalli), Green Swordtail (Xiphophorus helleri), and Southern Platyfish (Xiphophorus maculatus). There are also captive populations of hybridized crocodile, due to the mixing of Crocodylus siamensis stock with Crocodylus rhombifer and/or Crocodylus porosus on crocodile farms in or near the TSBR area, especially around the town of Siem Reap. The European Honeybee (Apis mellifera) has also been introduced around Siem Reap in attempts at breeding and harvesting this species. These attempts have largely failed, but there may still be some people with colonies of Apis mellifera. Of the remaining 18 exotic species that have been confirmed as having established populations in the TSBR from various studies, there are two domestic rat species, three species of fish and 12 plant species. The two species of rat, Rattus rattus and Rattus norvegicus, are long established and largely commensal to man, but have also been known to establish populations in natural habitats. Their impact on other fauna in the TSBR is unknown. Three species of fish, Common Carp (Cyprinus carpio), Silver Carp (Hypopthalmichthys molitrix) and Rohu (Labeo rohita) are regularly caught in small quantities from fishing lots on the Tonle Sap lake and river, and along the Mekong. It is likely that populations migrate between the Mekong and Tonle Sap lake, as do the majority of native fish, but this has not been confirmed. Although populations at present seem to be low, it is unknown if they are increasing and if there have been any negative impact to the environment as a result of their establishment. A recent survey (18-19 November) of the Prey Kos area in Kampong Chhnang by a WCS/TSCP team revealed that an exotic species of fish “Trey Chaab” has been turning up regularly in fishermans' catches recently, and has been caught intermittently for around a year now. People from the area also report it as having human-like teeth, a description that fits that of a Pacu. The fish in question may be Red-bellied Pacu (Piaractus brachypomus), which has ii been banned for aquaculture by the FiA, but fishermen report there may be two different yet similar species occurring in the Prey Kos area, also mentioning a similar species with very sharp teeth (which would indicate a Piranha). One man was reported as having been bitten by such a fish while swimming. A positive identification is required. During this study there were a few reports of Apple Snails from individuals in Prek Loung Commune, Battambang (a villager mentioned a Japan Snail) and Sna Ansar and O Sandan Commune, Pursat. These reports need to be investigated further. Most exotic plants seem to be long established already. The most abundant of these seem to be Water Hyacinth, Giant Mimosa (Mimosa pigra), Water Lettuce (Pistia stratiotes), Para Grass (Brachiaria mutica), Hippo Grass (Echinochloa stagnina) and Cutgrass (Leersia hexandra). Unfortunately at the time of preparing the questionnaire, the latter four species were not included due to a lack of a suitable Khmer name, so additional feedback on distribution, abundance and impacts from communities living in the TSBR was not gathered. Water Hyacinth can be considered a problematic species mostly due to the impact it is having on people by clogging up waterways and hindering movement. There is also likely to be an ecological impact due to its abundance, but this has not been documented and still needs to be properly assessed. However, when questioned most people would prefer to have it available for them to use, although they admitted that they would like to see it somewhat reduced in quantity. People collect it in small quantities as food for pigs and caged fish as well as themselves, and for making hammocks and string. It is also used in fisheries as a fish attractant, as it is reported that fish feed off aquatic insects attracted to the plant and use the mats as shelter. Exotic plants are restricted in their distribution by environmental conditions. It was found that some exotic plants, namely Candlebush (Senna alata), Purging