Emerging invasive threats: the alpine newt
There is a growing appreciation globally of the occurrence and ecological impacts of herpetological invasive species. New Zealand has historically suffered relatively few such incursions or establishments due to its relative isolation, yet as cross-border freight volume grows so too have the rates of interception of reptiles and amphibians. The Biosecurity Act 1993 provides effective justification for border management and controls on importation, yet incursions have still occurred. One such incursion is the alpine newt.
The alpine newt ranges from the French Atlantic coastline north to Denmark and eastwards to the Ukrainian Carpathians, Romania, and Bulgaria. It is widely distributed in the Balkans. Isolated populations are also present in southern Italy and northern Spain. It has established as an invasive species in the United Kingdom, where it was intentionally introduced, and in the Sierra de Guadarrama, central Spain. The species occurs from sea level to around 2,500 m a.s.l. in the Swiss and French Alps. One population naturally occurs in isolation in the Carpathian Mountains of NW Spain. Across this range the newts are described as consisting of six phenotypically and geographically distinct subspecies.
Alpine newts annually migrate to and breed in freshwater, and exhibit a high fidelity to natal waterbodies which may be permanent or ephemeral. They become sexually mature at 2 to 4 years of age. Like many Urodela (newts and salamanders), alpine newts engage in complex aquatic courtship dances that culminate in spermatophore transfer from male to female for internal fertilisation. Males develop flexible cutaneous crests on the tail and dorsal surface during the breeding/aquatic phase (see picture below). Females can produce up to 200 eggs per breeding season, which are laid individually or in small numbers on vegetation low in the water column. These eggs hatch in 10 to 30 days and can develop to metamorphosis in 75 days. Development may also be delayed, and neoteny (sexual maturity with aquatic larval characteristics retained) has been observed in high-altitude populations of some sub-species. Alpine newts grow to a maximum total length of 11 cm, can live beyond 20 years in the wild, and feed on invertebrates. It is an adaptable species able to occur in modified environments as well as those that are ecologically intact.
The invasion history of this species in New Zealand is limited to a single known event associated with aquaculture and the pet trade. This event was investigated by the Ministry for Primary Industries (MPI) and is the focus of an eradication effort being led by MPI and the Department of Conservation (DOC). The location of the release in the central North Island is in close proximity to native Leiopelma spp. frogs, and as such the newts are regarded as a serious threat for transmitting the chytrid fungus and other pathogens they are known to vector in their native range. First detected by a member of the public in May 2013 and reported to MPI, the specimen was identified as a sub-species that originates in the Tuscany region of Italy. An intensive survey of the immediate area quickly identified many high-density populations consisting of all life-history stages and confirmed that a population had established within an approximate 300 m radius. Investigations suggest that the initial release probably occurred somewhere around the turn of the 21st century.
A commitment to contain and eradicate the newt was made by MPI, and towards the end of 2013 a workshop was held to develop an operational strategy. This strategy has gone through a number of iterations. It is currently dominated by an investment in fencing to delimit the incursion and function of newts that includes the deployment of pitfall traps to intercept them and divide the operational area into multiple discrete cells. Waterbodies are intensively trapped with fyke nets and Ortmann traps. Where possible, breeding waterbodies have been drained and capped, while vegetation known to be occupied by newts has been cleared and disposed of on-site through burying. Waterbodies have, in some instances, been replaced by sentinel ponds. These are designed to serve as an attractant for newts searching for their natal ponds, and to ensure that the newts are exposed to capture in pitfall traps or detection through a simplification of refuges available to them. Supporting these core tools is regular searching by detector dogs.
All efforts sit within an operation plan overseen by a technical advisory group (TAG) and supported by a proactive communication plan for all landowners affected by the eradication programme. Capture efforts have seen a marked increase between 2015 and 2017, and newt captures have declined dramatically over the course of the eradication effort (Figure 1).
The eradication effort is a world first for Urodela and as such has been highly adaptive in its approach. This has involved research into the development of several tools and techniques. James Reardon has tested the efficacy of a number of aquatic lures in an attempt to optimise aquatic trap captures. Trials suggested that female newts provide a modest level of attraction to male newts but none of the lure treatments had a significant impact on the proportion of newts captured. Time to capture corroborated the pattern of female newt attractiveness to males, but again the effects were not significant (Figure 2). We also tested the lure effect of glowsticks and meat (spam) on newts as both are reportedly used in the capture of newts but no literature was available that tested their efficacy. Our tests suggest they have no positive effect as a lure for alpine newts. More recently, research is underway to measure trap retention rates and to test alternative pitfall trap designs that improve capture and retention rates. Skeletochronology has also been investigated by Morgan Coleman (Manaaki Whenua - Landcare Research), as ageing of newts captured will be a critical variable in determining the progress of the eradication.
As with all eradications, the operational and TAG teams acknowledge that the greatest test lies ahead as the eradication progresses into the mop-up phase targeting the last individuals, and finally the confirmation of absence. Considering the cryptic nature of the species and its relative longevity, these final stages of the eradication will require considerable commitment from all stakeholders. However, as this eradication effort is a global first, it will hopefully stand as a notable contribution to global biosecurity practice.
This work was funded by the Ministry of Primary Industries and the Department of Conservation.
James T. Reardon (Science Advisor, DOC Threats Group)