SNAKE SEARCH OFFICIAL REPORT
Last issue Investigate broke the story that New Zealand has an undetected colony of venomous Australian Copperhead snakes in the remote wilderness of abandoned South Island gold mines. This was after a prospector and geologist encountered one on the West Coast. The Ministry for Primary Industry’s official report, just released to Investigate, concludes the land would be ideal for snakes and the South Island could be home to about 100. The only problem? No one else has seen them. This is the full report by herpetologist DYLAN VAN WINKEL of consultancy firm Bioresearches:
In 1990, while prospecting for gold beyond Nelson Creek (42° 24′ 50.59″ S; 171° 33′ 42.11″ E) in the Grey Valley, West Coast, a “greenish brown, 30-inch long” snake was observed coiling up the arm of one of the prospectors. The notifier reportedly flung the snake off his arm and down a sluice face to rocks below.
The notifier subsequently identified the snake as a Victorian copperhead (Austrelaps superbus) from comparative photographs of Australian species. Further correspondence with local West Coast gold miners and a scientist at Landcare Research lead to the suggestion that a colony of snakes could be present in the West Coast gold mining districts. It was also suggested that the snakes may have entered the country during the gold rush period of the 1860s and 70s, when thousands of miners emigrated from the Victorian goldfields to the West Coast. Any snakes that may have stowed away in miner’s crates and equipment on sailing vessels could have freely entered New Zealand, via ports at Charleston, Hokitika, Greymouth and Westport, given the absence of biosecurity inspections.
The following report provides information on the ecology of Austrelaps spp., and assesses both the probability of establishment and potential risks to native fauna if establishment of an Austrelaps sp. were successful in New Zealand.
Aspects of Austrelaps Ecology and Life Cycle
The genus Austrelaps Worrell 1963 (commonly referred to as Australian copperheads) is represented by three species, including the pygmy copperhead (Austrelaps labialis; c. 80 cm, up to 120 cm), highland copperhead (A. ramsayi; c. 1.3 m, up to 1.7 m), and the lowland or southern copperhead (A. superbus; c. 1.3 m, up to 1.7 m). The three species are distinguished from each other based on head scalation, length, and distribution (Cogger 2014).
The genus is confined to south-eastern Australia, including the islands of Bass Strait and Tasmania (approximate latitudinal range from c. 30°S to 43°S), and occurs across a wide altitudinal range (sea-level to c. 1000 m) and wide range of climate regimes (e.g. temperatures range between c. -2°C to 41°C throughout their natural distribution).
Austrelaps spp. inhabit a broad range of habitats, from coastal sand dunes to grasslands to riparian margins, open forest and alpine tussocks; preferentially selecting sites near to water or marshes/ wetlands. Austrelaps spp. are both diurnally and nocturnally active, and have the ability to remain active at temperatures below 10°C. They feed principally on ectothermic vertebrates, especially frogs, lizards and small snakes; however, they are known to prey on invertebrates (e.g. grasshoppers), small mammals and birds.
Austrelaps spp. (particularly A. superbus) are well adapted to cool and temperate climates, and all species employ an ovoviviparous reproductive strategy (i.e. development of embryos inside eggs that are retained within the females’ body until they are ready to hatch. Young are then birthed live). Mating occurs in late summer/ early autumn, and females give birth to litters of 3 – 32 young the following mid- to late-summer; after a winter quiescence period (Shine 1987). Reproduction may not occur each year.
Little information is available on the movement or dispersal rates of Austrelaps spp.; however, Shine (1979) suggested that gravid female A. superbus are generally sedentary, yet males may move more extensively. Austrelaps spp. are mostly terrestrial (ground dwelling) rather than arboreal (tree dwelling), but are known to climb trees occasionally.
Copperheads are notoriously secretive and inoffensive, preferring to avoid encounters with humans where possible. This significantly lowers the probability of close human interactions and as a result, snakebites from this species in Australia are relatively uncommon. Continued provocation will certainly result in defense behaviours such as body flattening, hissing and violent striking, in an attempt to bite. The venom is strongly neurotoxic, but is also powerfully haemolytic [destroys red blood cells] and cytolytic [induces tissue death and gangrene] (Cogger 2014).
Potential Threat to New Zealand
Austrelaps suberbus is a generalist with regard to habitat and prey selection, and is tolerant of cool to cold, wet climates within its natural range. These characteristics suggest that it is certainly possible for this species to survive and reproduce successfully on the West Coast, as well as in many other regions of New ZealandWOULD YOU LIKE TO READ MORE OF THIS STORY?
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