VN April 2023

Vetnews | April 2023 23 (Canlas et al. 2017). Grein and Chen (2018) reported that eBay recently removed 45,000 listings over a 12-month period that were not in compliance with their wildlife trade policies. Exotic pets becoming exotic pests Although most animals transported beyond their native range for sale as exotic pets remain in captivity for the duration of their lives and never establish a non-native population, many individuals are released or escape confinement while in the care of importers, wholesalers, retailers, or consumers (Duggan et al. 2006; Strecker et al. 2011; Vall-llosera and Cassey 2017a). Why owners release exotic pets is not widely documented, but reasons include difficulty in providing care for large, old, aggressive, or sick animals (Duggan et al. 2006; Holmberg et al. 2015; Stringham and Lockwood 2018). Surveys of aquarium owners indicated that 2–10% of consumers deliberately released unwanted fish (Duggan et al. 2006; Chang et al. 2009; Strecker et al. 2011). To the best of our knowledge, there are no published surveys demonstrating the propensity of consumers to release pet amphibians, reptiles, mammals, or birds, but Vall-llosera and Cassey (2017a) suggested that existing data on pet releases or escapes vastly underestimate the number of exotic pets that become free-living, especially highly mobile species like birds. In cases where an animal is purchased explicitly for release as part of a ceremony or competition, or the species is kept for only a brief period (eg as jewelry), the probability of release is quite high (Su et al. 2015). Existing research indicates that past trade in exotic pets has resulted in the successful establishment of non-native species. Krysko et al. (2011) showed that, of the 140 non-native reptiles and amphibians that have been introduced into Florida, nearly 85% arrived via the pet trade. Rosa et al. (2017) determined that 70% of invasions by mammal species in Brazil over the past 30 years were also due to the pet trade. Hulme et al. (2008) reported that exotic pet escapes were the primary source of new non-native species establishments of amphibians, reptiles, mammals, and birds in the EU; Rixon et al. (2005) identified at least 100 species of freshwater fishes in the aquarium trade that had been introduced into North American freshwater bodies, with 40 having established populations; and Rhyne et al. (2012) identified 33 marine fish species imported for the pet trade that had been introduced into US coastal waters. Furthermore, it is broadly suspected that the marked rise in the number of established non-native fishes in marine waters in the EU over the past decade is due to the recent rapid growth of the marine aquarium industry (Katsanevakis et al. 2013). These reports clearly demonstrate that the exotic pet trade has contributed a wide variety of non-native species worldwide. However, evidence from invasion biology suggests that these tallies are only the tip of the iceberg. In a comprehensive evaluation of the link between trade volume and number of non-native species, Essl et al. (2011) showed a decade or more lag between the time when trade activity increases and when populations of non-native species were recorded as introduced. Most of the published statistics reviewed above stem from trade patterns that were manifest several decades ago and therefore do not reflect the current rise in exotic pet ownership worldwide. If current behaviors and policies continue unchanged, many countries will see the establishment of populations of exotic pet species at rates above historical trends over the next several decades. Which exotic pets will establish non-native populations next? A fundamental component of biosecurity policy is predicting which exotic pet species will establish new non-native populations – that is, which traded pet species will escape or be released, find suitable habitat, successfully reproduce, and persist to establish self- sustaining populations? This is a challenging question, given that a variety of factors – including the species characteristics, the nature of the pet market, and environmental conditions – will influence overall establishment success. The ecological “fit” between a species’ life-history requirements and the habitat into which it is introduced plays an important role in the successful establishment of exotic pets,as it does for most non-native species (Hayes and Barry 2008). At a basic level, an introduced exotic pet must be able to physiologically tolerate local environmental conditions; for example, marine fishes released into fresh water are unlikely to survive and establish non-native populations (Weigle et al. 2005), and freshwater fishes predominantly native to tropical or sub- tropical regions are unlikely to establish populations within temperate or boreal habitats (Bradie et al. 2013). Generally, established non- native vertebrate species are characterized by high fecundity and broad environmental tolerance (Springborn et al. 2011, 2015; Capellini et al. 2015; Howeth et al. 2016). Carrete and Tella (2008) also demonstrated that wild-caught bird species traded as exotic pets were more likely to establish non-native populations than captive-bred species. Another key factor affecting establishment success is the number of individuals released and the number of release events, which together are known as “propagule pressure” (Cassey et al. 2018). For most exotic pet species, we simply do not know the magnitude or spatial extent of their introduction and therefore have no direct way of measuring propagule pressure. However, a consistent pattern in the literature is the relationship between the number of individuals imported into a country for sale as pets, howmany years the species was for sale, and establishment success (vanWilgen et al. 2010; Kikillus et al. 2012; Vall-llosera and Cassey 2017a). All else being equal, the larger the number of individuals that are sold in a region, the larger the number that would be accidentally or deliberately introduced, thereby raising propagule pressure and elevating establishment success (eg Bradie et al. 2013). At local scales, most exotic pets are released within urban centers or in nearby aquatic ecosystems (van Ham et al. 2013), which is likely a function of Article >>> 24