Natural distribution range of asp viper (source: IUCN Red List 2009a). 

Context in source publication

Context 1

... the most important conclusions and recommendations are presented in chapter 6. Research on the following components was conducted in order to cover the complete risk analysis: risk assessment and risk management. The probability of introduction was determined by the possible introduction pathways of the species into the Netherlands, both present and future. The probability of establishment was determined by the current dispersal range of the species and presence of potential habitat in the Netherlands related to (a)biotic requirements of the species. The probability of spreading was determined with regard to the dispersal capacity of the species by natural means and by human action. Areas or habitats in the Netherlands that are at risk of invasion were selected and possible effects of the presence of asp vipers within these areas were discussed. Based on the results of the three probabilities mentioned above, the impact of the species was determined and the effects and risks were scientifically characterised, using the Invasive Species Environmental Impact Assessement (ISEIA) protocol. Subsequently, the (possible) ecological, economic, and social impacts as a result of the presence of the species were discussed. Based on the results of the risk assessment, measures were identified and proposed to counteract the introduction, establishment, and spreading of and damage caused by the species. The risk management dealt with measures for: The (dis)advantages of each measure were investigated in terms of effectiveness, feasibility, and costs. Finally, a concise protocol was developed, which can be used to act adequately if the species occurs somewhere in the Netherlands in the future. The risk analysis was based on existing data. Several databases and other sources of information were used. These are discussed in further detail below. National (e.g., reports and species distribution atlases) and international literature (e.g., scientific articles via ISI web of knowledge, Google Scholar, Wiley Interscience, and Zoological Records) was investigated in order to get a clear view of existing knowledge regarding the subject. Additionally, several websites, e.g., Global Invasive Species Database and IUCN Red List, were used. Data on the present distribution of asp viper in the Netherlands was obtained using several databases. The extensive database of Natuurbalans-Limes Divergens BV on Dutch fauna was consulted, together with several general websites, e.g., www.waarneming.nl and www.telmee.nl. Also several organisations, e.g., reptile zoo SERPO and local herpetological societies and nature groups, were consulted. The risk analysis was conducted in collaboration with an expert team in order to guarantee a sound scientific basis and justification. The expert team was formed by dr. H.J.R. (Rob) Lenders, assistant professor at the Department of Environmental Science of the Radboud University Nijmegen, W. (Walter) Getreuer, director of reptile zoo SERPO, and ir. B.H.J.M. (Ben) Crombaghs, managing director of Natuurbalans- Limes Divergens BV. Dr. H.J.R. Lenders en ir. B.H.J.M. Crombaghs are authorities regarding research on reptiles and amphibians in the Netherlands. Mr. W. Getreuer delivered a major contribution to the risk analysis regarding knowledge about the present dispersal range of the species and determining possible vulnerable areas in the Netherlands. Furthermore, he has an extensive field experience in removing non-native reptile populations, including the asp vipers near Poortugaal. Therefore, he provided an important input regarding possible measures in prevention, eradication, and control of the asp viper. This chapter presents a short species description of the asp viper. Aspects that are of importance for the risk analysis are considered, mainly distribution, habitat, reproduction, and diet of the species. Table 1 presents an overview of several general characteristics of the species description. The asp viper is a member of the family Viperidae. The species is also known as asp, European asp, and aspic viper. The overall length of the species is about 50-60 cm (Günther & Lehnert 1996; Fritz & Lehnert 2007). In exceptional cases, the snakes can grow up to maximally 85 cm (Fritz & Lehnert 2007). The weight of adults ranges from 60 g to 235 g, and up to 250 g for gravid females (Fritz & Lehnert 2007). Basic colour of asp vipers is pale gray-brown, dark brown, or dark reddish brown. Females have a distinct bright dark pattern on their back. This pattern is less distinct in males. Only slight differences in appearance exist between common European adder and asp viper. The latter has a clear tapering point of the nose, slightly wider back of the head, and two rows of small shields between eye and supra labials (Ameling 1978; Günther & Lehnert 1996). The asp viper’s natural distribution range is located in large parts of France, Italy, and Switzerland, northern Spain, southern Germany, and western Slovenia (figure 1) (Ameling 1978; Fritz & Lehnert 2007). The species prefers hilly landscapes and mountainous areas, mainly at elevations ranging from 800 to 1600 meters. It can even be found up to 3000 meters. Asp viper occurs mainly in dry rocky areas, screes, quarries, open scrubland, and in or near open to half-open forests. The species is cold-blooded and therefore prefers sun exposed slopes. Especially gravid females and juveniles seem to be highly dependant on these structures. Dry and sunny areas with an alternation of rocks and bushes form the optimal habitat (photograph 1) (Günther & Lehnert 1996; Flatt et al. 1997; Fritz & Lehnert 2007). Only one record of more than one free-living asp viper outside its natural distribution area has been recorded worldwide. Eight specimens were found in the wooded area Bos Valckesteyn near Poortugaal, southwest of Rotterdam (the Netherlands). Most likely the animals were introduced deliberately from captivity (SERPO 2006). However, the exact source of this introduction remains unknown. After removing six of the eight animals in October 2006, no sightings of the species at the locality have been recorded since (table 2). Additionally, one melanistic asp viper was sighted in the Zomerlandse Tunnelbos in the Hoekschewaard near the village of Heinenoord, the Netherlands, in July 2006. No additional information of this sighting has been recorded. The species has not been sighted in the surroundings more recently. Reproduction of asp vipers is highly influenced by climatic factors, see also §4.3. Within the northern part of their range, asp vipers reach sexual maturity at the age of five or six years (Fritz & Lehnert 2007). Overall, males are able to mate annually. The reproductive cycle of females is on average every two to four years. It is highly energy and climate dependent and decreases up to once in a lifetime in populations at the northern limits of their distribution range (Flatt et al . 1997; Naulleau et al. 1999; Aubret et al. 2002). Also the length of gestation depends on climatic conditions and ranges from two to four months within the natural distribution range. In cooler climates, e.g., the Netherlands, gestation is probably longer than four months. Asp vipers are ovoviviparous and on average produce an offspring of five to nine individuals (Günther & Lehnert 1996; Fritz & Lehnert 2007). Vipers are generally considered opportunistic feeders (Luiselli 2006). The main diet of asp vipers consists of small mammals, like mice, shrews, and voles, and lizards. Infrequently also little birds and frogs are predated by asp vipers (Fritz & Lehnert 2007). Research in central Italy showed that about 80% of adult asp viper’s diet consists of small mammals. Juveniles (up to 35 cm) mainly consume reptiles (81% of the diet) and to a lesser extent (19%) nestling mice (Luiselli & Agrimi 1991). The main predators of asp vipers are birds, for example members of the families Falconidae and Corvidae. Moreover, hedgehogs, badgers, foxes, martens, weasels, and polecats are considered as incidental predators of the species. Also snake species (e.g., smooth snake, Coronella austriaca ) are potential predators of asp vipers, mainly of juveniles (Fritz & Lehnert 2007). The risk assessment examines the situation in which no measures for prevention, eradication, or control are taken. It focuses on the potential risks of the presence and invasiveness of asp viper in the Netherlands. Therefore the probability of introduction, establishment, and spreading are discussed, resulting in an overview of vulnerable areas and an evaluation of the potential impact of the species. Distribution of asp viper by natural means from its natural range into the Netherlands is very unlikely. The northern limit of its natural distribution range is situated at least 160 km from the Dutch border. Climatic conditions are expected to prevent the species from extending its range northwards (Lourdais et al. 2004). Even with ongoing climatic change, the distance from its natural distribution range is substantial and several unsuitable areas would have to be crossed. Natural colonisation is therefore not considered to be a possible pathway. Introduction pathways caused by humans, both accidentally and deliberately, can result in introduction of asp vipers into the Netherlands. Asp vipers that are kept as pet by snake keepers can escape from captivity. If snakes manage to escape, they will generally be found (an recaptured) within a short distance from the source of introduction, often near urban areas, where most snakes are kept. Hence, the risk of accidental introduction from captivity into natural areas is estimated to be very low. In contrast to accidental introductions, deliberate releases of asp vipers can more easily result in introduction into natural areas. Deliberate releases occur most likely on some distance from urban areas, as releasing non-native species is illegal in the Netherlands. However, asp viper is ...