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         General Impact

    For a detailed account of the environmental impacts of T. scripta elegans please read: Trachemys scripta elegans (red-eared slider) Impacts Information. The information in this document is summarised below. Trachemys scripta elegans has been the most popular turtle in the pet trade with more than 52 million individuals exported from the United States between 1989 and 1997 (Telecky 2001, in Bunnell 2005). Slider turtles became very popular because of their small size, their simple husbandry requirements and their reasonably low price (Teillac-Deschamps et al. 2008). Unsuspecting turtle owners were rarely prepared to maintain large adults (up to 30 cm carapace length) for a significant length of time (up to 50 years) in captivity (Teillac-Deschamps et al. 2008). Larger adult turtles were released by their owners to ponds in many places and because of this, red-eared sliders now occur in freshwater ecosystems in many developed countries with high densities in urban wetlands (de Roa & Roig 1997, Luiselli et al. 1997, Arvy & Servan 1998, Chen & Lue 1998, Lever 2003, Martinez-Silvestre et al. 2003, in Teillac-Deschamps et al. 2008).

    Competition: The competitive advantages of the slider may include lower age at maturity, higher fecundity, and larger adult body size (Arvy & Servan 1998, in Cadi & Joly 2003). Turtles may compete for food, egg-laying sites, or basking places (Bury & Wolfheim 1973, Bury et al. 1979, Rovero et al. 1999, Lindeman 1999, in Cadi & Joly 2003). In a study by Cadi and Joly (2003), Emys were shown to shift their basking activity toward places considered to be of lower quality, while the dominant Trachemys occupied the better basking sites. Other studies have also shown red-eared sliders to compete with indigenous species for food and basking sites (Frank & McCoy 1995, Williams 1999, Salzberg 2000, in Somma & Fuller 2009). The red-eared slider has also been considered occasionally aggressive towards other individuals (Cadi & Joly 2003).

    Threat to Endangered Species: Competitive interactions between T. scripta elegans and the European pond turtle (Emys orbicularis) are of particular interest, as the latter is registered as an endangered species (Appendix II of the Bern Convention, Corbett 1989, Luiselli et al. 1997, Martinez-Silvestre et al. 1997, in Cadi & Joly 2003, see Competition).

    In Washington (USA) they are a potential threat to the Pacific pond turtle (Clemmys marmorata) a declining species endemic to the Pacific states (Brown et al. 1995, Williams 1999, in Somma & Fuller 2009).

    Disease Transmission: Continuous releasing of exotic pet turtles in natural ecosystems increases the risk of parasite transmission to native species, and highlights the impending need for regulation of pet turtle trade in Europe (Hidalgo-Vila et al. 2008); the red-eared slider is known to carry nematodes (Hidalgo-Vila et al. 2008).

    Predation: Turtles introduced near Paris were revealed to have consumed aquatic plants and animals (mostly arthropods and molluscs, Prévot-Julliard et al. 2007, in Teillac-Deschamps et al. 2008).

    Human Health: Reptiles, including turtles, are well-recognised reservoirs for Salmonella, and are a source of human salmonellosis (Nagano et al. 2006).

    Ecosystem Change: The impacts of T. scripta on natural habitats and ecosystems are unknown; should the red-eared slider be released in natural habitats with high ecological value, it would be relevant to monitor any consequences on native fauna and flora, typically invertebrates, amphibians, native turtles and nesting birds (Bringsøe 2006).




         Location Specific Impacts:
    Asia English 
    Competition: The CITES (2003, in Ramsay et al. 2007) report on the trade in chelonians noted that if there is competition with other terrapins, it is more likely to be in temperate regions where basking becomes more important.
    Australia English 
    Ecosystem change: Overseas, red-eared sliders have had major impacts (eg. Levell 2000) and could present a similar hazard in Australia (Burgin 2006).
    New South Wales (Australia) English 
    Competition: Competition from this exotic species could have a detrimental impact on local species such as the common snake-neck turtle (Chelodina longicollis) and the Sydney Basin Turtle (Emydura macquararii dharuk) (Burgin 2006).
    Queensland (Australia) English 
    Competition: Red-eared sliders have the potential to multiply rapidly and spread through Queensland's waterways, becoming the most common turtle in creeks and rivers and replacing native turtles (NRM&W).

    Disease transmission: Red-eared sliders have the potential to carry new diseases and pathogens to native turtles and other aquatic wildlife (NRM&W).
    Sydney (Australia) English 
    Competition: Competition from this exotic species could have a detrimental impact on the local species, the common snake-neck turtle (Chelodino longicollis) and the Sydney basin turtle Emydura macquarii dhoruk (Shelley 2007).
    Bermuda English 
    Ecosystem change: The full extent of its impact on freshwater ecosystems in Bermuda has not been extensively studied (Bacon Gray & Kitson 2006).

    Reduction in native biodiversity: T. scripta elegans may be a threat to endemic fish species in brackish ponds (De Silva 2003, in Varnham 2006), for example the the endemic and endangered killifish (Fundulus bermudae) on which the red-eared slider may prey on in sympatric ponds.

    T. scripta elegans also inhabits some of the only habitat for the diamondback terrapin (M. terrapin); a highly localised native species. The ecological impact of the red-eared slider on native chelonians in other regions has been documented, however, the impact on the Bermudian diamondback is currently unknown (Outerbridge 2008). Local conservationists fear that the feral sliders are competing with the diamondbacks for nesting sites; all known nesting sites for the diamondback in Bermuda are limited to six small sand bunkers on a golf course, of which three are also being used by sliders; further studies are needed to determine the extent to which diamondbacks are being negatively affected by sliders (Outbridge 2008).

    Brazil English 
    Competition: P. Geoffroanus feeds mainly on Chironomidae larvae (Souza & Abe 2000, in Ferronato et al. 2009), which could possibly also be a prey for red-eared sliders.

    T. scripta elegans has a large dispersal and dispersion capacity (Gibbons 1990, Bodie & Semlitsch 2000, in Ferronato et al. 2009). It also seems to be more aggressive than other freshwater turtles (Bels et al. 2008, in Ferronato et al. 2009).

    P. geoffroanus nests in the anthropogenic forest of the Piracicamirim stream. This area could be suitable as nesting habitat for T. scripta elegans as well. Predation of P. geoffroanus nests occurs, however, T. scripta elegans nests can be located at great distances from the water (Mount 1975, in Ferronato et al. 2009) and their eggs can be laid 140 cm deep (Packard et al. 1997, in Ferronato et al. 2009). These characteristics could act defensively against local predators (Ferronato et al. 2009).

    While Cadi & Joly (2003 2004) noted competition for basking sites between native turtles (Emys orbicularis) and introduced red-eared sliders Ferronato and colleagues (2009) have no evidence of competition with native species (Hydromedusa tectifera and P. geoffroanus) as water temperature is considerably milder than in Europe, reducing the need for basking.
    Human health: Red-eared sliders may pose a potential risk to human health as they carry salmonella (de Sa and Solari 2001).

    British Virgin Islands English 
    Other: Ecological impacts remain unstudied, but are likely to be small because of the localised nature of the invasion and the artificial nature of the habitat (Perry et al. 2007).
    Canada English 
    Competition: In Ontario, Red-eared Sliders that have been released into Grenadier Pond have established a local population that apparently competes directly with the natural turtle population (Dog Legislation Council of Canada 1998, in Bunnell 2005).

    Disease transmission: The western painted turtle has been observed at the pond in the Richmond Nature Centre in the past (Griffith 2000, in Bunnell 2005). Sanders and colleagues (2004, in Bunnell 2005) noted attempted nest-building by sliders at the pond, indicating that the species is present and potentially capable of sharing pathogens with native turtles.
    Cayman Islands English 
    Hybridisation: The red eared slider Trachemys scripta has the potential to hybridise with native Taco River slider (Trachemys decussata angusta) (Cottam, 2004 in Varnham, 2006).
    Dominican Republic English 
    Hybridisation: T. scripta competes and hybridises with native turtles (Powell et al. 2000), possibly diluting unique gene pools (Powell & Incháustegui 2009).
    France English 
    Competition: Red-eared slider reproduction has been recorded in three places where the European pond turtle (Emys orbicularis) is living. There is a wide overlap in their ecological niches.

    Threat to endangered species: The IUCN Red List Near Threatened European pond turtle Emys orbicularis, in particular the subspecies Emys orbicularis galloitalica, face competitive pressure from introduced red-eared sliders.
    Germany English 
    Ecosystem change: The concern for the natural environment became obvious from the 1980s (especially in Germany), because increasing numbers of red-eared sliders were released (Bringsøe 2006).
    Israel English 
    Competition: In Israel, T. scripta is believed to compete with Mauremys caspica (Bouskila 1986, in Ramsay et al. 2007).
    Ryukyu Islands (Japan) English 
    Other: Various types of impacts on the indigenous biodiversity have been shown for feral populations of T. scripta elegans outside Japan (Lever 2003, Cadi & Joly 2004, in Ota et al. 2004). However, no pertinent data are available yet for the Ryukyu population.
    Latvia English 
    Threat to endangered species: Spread of invasion of T. scripta elegans in Latvia, besides the influence of this species on the habitat, can result in a direct competition of the species with the extremely rare Latvian species of turtle Emys orbicularis (Pupins 2005, Pupins & Pupina 2005, in Pupins 2007).
    Poland English 
    Competition: On the market, the substitute for the red-eared terrapin has presently become Troost’s terrapin Trachemys scripta troostii, since other turtles are too expensive. Troost’s terrapin may also pose a threat for the native European pond turtle Emys orbicularis.
    Boqueron State Wildlife Refuge (Puerto Rico) English 
    Disease transmission: The red-eared slider (Trachemys scripta elegans) is a known potential vector of diseases that can be transmitted to humans (e.g. Salmonella) (Felix Grana., pers.comm., November 2007).

    Reduction in native biodiversity: The red-eared slider (Trachemys scripta elegans) is reported to compete with the endemic Puerto Rican slider, Trachemys stejnegeri stejnegeri (see Trachemys stejnegeri in IUCN Red List of Threatened Species) (Felix Grana., pers.comm., November 2007).
    Caño Tiburones Natural Reserve (Puerto Rico) English 
    Disease transmission: The red-eared slider (Trachemys scripta elegans) is a known potential vector of diseases that can be transmitted to humans (e.g. Salmonella) (Felix Grana., pers.comm., November 2007).

    Reduction in native biodiversity: The red-eared slider (Trachemys scripta elegans) is reported to compete with the endemic Puerto Rican slider, Trachemys stejnegeri stejnegeri (see Trachemys stejnegeri in IUCN Red List of Threatened Species) (Felix Grana., pers.comm., November 2007).
    Culebra (Puerto Rico) English 
    Disease transmission: The red-eared slider (Trachemys scripta elegans) is a known potential vector of diseases that can be transmitted to humans (e.g. Salmonella) (Felix Grana., pers.comm., November 2007).
    Humacao Nature Reserve (Puerto Rico) English 
    Disease transmission: The red-eared slider (Trachemys scripta elegans) is a known potential vector of diseases that can be transmitted to humans (e.g. Salmonella) (Felix Grana., pers.comm., November 2007).

    Reduction in native biodiversity: The red-eared slider (Trachemys scripta elegans) is reported to compete with the endemic Puerto Rican slider, Trachemys stejnegeri stejnegeri (see Trachemys stejnegeri in IUCN Red List of Threatened Species) (Felix Grana., pers.comm., November 2007).
    Singapore English 
    Competition: Sulaiman (2002, in Ramsay et al. 2007) noted that a major concern for conservationists in Singapore was that sliders may outcompete local species, such as the spiny terrapin and the Malayan box terrapin (Cuora amboinensis). Sulaiman (2002) noted that a female slider can produce up to a dozen eggs twice a year and may out-breed the Malayan box terrapin that lays two eggs each time.

    Other: The large numbers of T. scripta elegans imported into Singapore for sale as pets every year, some of which may be released, is a cause for concern (Sulaiman 2002, in Goh & O’Riordan 2007) because they are present in many freshwater bodies. Some localities, such as the Botanic Gardens, Bedok Reservoir and Bukit Batok Town Park, have high population densities (Goh 2004, in Goh & O’Riordan 2007). It is unknown what adverse effects, if any, T. scripta elegans as an alien species may have.
    South Africa English 
    Competition: In South Africa it is suspected that T. scripta has displaced the native Pelomedusa subrufa through competition (Ramsay et al. 2007).
    Spain English 
    Competition: Although chelonians might never be considered explosive breeders, the number of T. scripta elegans individuals could surpass that of native aquatic chelonians in southern Spain, where T. scripta elegans reach maturity earlier, are more fecund and their eggs are more fertile (Perez-Santigosa Diaz-Paniagua & Hidalgo-Vila 2008). Also, the absence of Spanish terrapins in areas with high predation risk occupied by T. scripta (Pleguezuelos 2002, in Polo-Cavia, Lopez & Martin 2007) suggests that native species are more sensitive to predation pressure. Although these freshwater turtles are predominately aquatic, they have to come to land for basking, where they are potential prey of birds and mammals (Greene 1988, Martin & Lopez 1990, in Polo-Cavia, Lopez & Martin 2007). Behavioral asymmetries could contribute to the greater competitive ability of introduced T. scripta within anthropogenically disturbed environments (Polo-Cavia, Lopez & Martin 2007).

    Polo-Cavia Lopez & Martin (2009a) hypothesised that interspecific differences in morphology, and thus, in heating and cooling rates, might confer competitive advantages to introduced T. scripta. T. scripta showed a more rounded shape than M. leprosa, a lower surface-to-volume ratio and a greater thermal inertia, which facilitates body heat retention and favors the performance of activities and physiological functions such as foraging or digestion, thus aggravating the competition process with native turtles in Mediterranean habitats.
    Ecosystem change: In studies by Polo-Cavia Lopez & Martin (2009b) M. leprosa preferred water with chemical stimuli of conspecifics and avoided water with chemical cues of T. scripta (while T. scripta showed no preference) which suggests that chemical cues could be used by native M. leprosa to avoid water pools occupied by introduced T. scripta. The authors suggest that this avoidance behavior of native M. leprosa may be one of the causes that contributes to the observed displacement of their populations by the invasive T. scripta.

    Threat to endangered species: In the Iberian Peninsula, the introduced red-eared slider is an invasive species that is competing and displacing the endangered native Spanish terrapin (Mauremys leprosa) (Polo-Cavia, Lopez & Martin 2007). The introduction of exotic turtles is considered to threaten the status of the two native species of aquatic turtles (European pond turtle (Emys orbicularis) and M. leprosa), which are at present listed as vulnerable, with declining populations (Pleguezuelos et al. 2004, in Perez-Santigosa Diaz-Paniagua & Hidalgo-Vila 2008).

    Taiwan English 
    Herbivory: In the Taipei Botanical Garden, released individuals of the sliders have almost eradicated the vegetation (water lilies) in a pond (Ramsay et al. 2007).

    Reduction in native biodiversity: Lue and Chen (1996, in Ramsay et al. 2007) suggested that the wide ecological tolerance and dietary habits of sliders may cause impacts on indigenous chelonians in Taiwan.
    Thailand English 
    Competition: The red-eared slider has the potential to disrupt native turtle populations (Thirakhupt & van Dijk 1994).
    United States (USA) English 
    Human health: The red-eared slider may carry diseases harmful to humans and many other species. For example, it is considered a potential vector of Salmonella (Scalera 2006).
    Arizona (United States (USA)) English 
    Other: Potential negative consequences of the widespread introduction of sliders are little-studied, and in some cases may be benign, including in Arizona (Stitt 2005). Stitt (2005) writes "In completely urban settings, where wetlands have been created where once there were none, sliders may provide a glimpse of nature to people otherwise removed from wilderness. There, they join park ducks, swans, and squirrels and provide enjoyment to a sedentary society that appreciates nature, any nature, regardless of origin. In these urban aquatic islands, perhaps red-eared sliders have their place, feeding on koi and grass carp, and being chased into the water by little kids and dogs."
    California (United States (USA)) English 
    Competition: Red-eared sliders (Trachemys scripta elegans) out-compete native turtles, such as the western pond turtle (see Clemmys marmorata in IUCN Red List of Threatened Species), for food and basking spots.

    Disease transmission: Red-eared sliders (Trachemys scripta elegans) may introduce new diseases to native turtle populations.



ISSG Landcare Research NBII IUCN University of Auckland