New aliens in Australia: 18 years of vertebrate interceptions

Context. Australia has a high diversity of endemic vertebrate fauna. Yet, transnational human activities continue to increase the rate of transportation, introduction, and establishment of new alien vertebrates in Australia, to the detriment of environmental and socio-economic services. Eradication of invasive vertebrates is often costly and without guarantee of success; therefore, methods for detecting, intercepting and preventing the transport of alien species earlier in the invasion pathway provide substantial benefit. Aim. To anticipate emergent threats to Australian biosecurity posed by the transport and introduction of new alien vertebrates over time. Methods. We collated vertebrate interception data from various mainland Australian State, Territory and Commonwealth government reporting agencies, including data from a previously published study, at both pre-border and post-border stages from 1999 to 2016. Using Generalised Linear and Generalised Additive Modelling we predicted trends in interception frequency using predictors such as vertebrate taxa, detection category and alien status. Key results. Interception frequency increased over time for all vertebrate classes, for pre-border stowaways and for post-border captive and at-large interceptions, with no saturation in the accumulation of new species over time. Five species were responsible for almost half of all incidents, of which red-eared sliders (Trachemys scripta elegans), boa constrictors (Boa constrictor) and corn snakes (Pantherophis guttatus) are prominent in Australia’s illegal alien pet trade. Rose-ringed parakeets (Psittacula krameri) are prominent in the legal alien cage-bird trade, which remains poorly regulated. Asian common toads (Duttaphrynus melanostictus) were frequently detected as stowaways, and most stowaway incidents originated from Southeast Asia, particularly Indonesia, via shipping. Data deficiency for pre-border incidents increased rapidly in 2015 and 2016. Conclusions. Australia is subject to a persistent and increasing risk of alien vertebrate introductions and incursions over time, due partly to emergent trends in the alien pet trade as well as increased global trade and tourism. Implications. The future of Australia’s biosecurity remains dependent on stringent border security to prevent the arrival of novel species, but our findings also highlight the importance of ongoing management and control of high-risk species already present, often illegally, within Australia.