It’s official – there could be snakes in NZ

COPPERHEAD ROAD

 

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 Zealand; where environmental conditions are comparable to those in South-eastern Australia/ Tasmania, and where an abundance of small prey (e.g. mice, rats, birds, Litoria frogs) exists.

If Austrelaps superbus was to establish on the West Coast or elsewhere in New Zealand, it is likely that it would inhabit open grassland or scrubland habitats on the edges of rural and forested areas (c.f. dense native forest), where sun-basking areas are readily available and a hasty retreat into thick vegetation would be possible if threatened. On the West Coast, the species may also favour historic mine tailing sites, where large piles of rocks and debris – largely covered by weedy vegetation – provides suitable refuge and basking sites, as well as an abundance of prey (e.g. mice, lizards and invertebrates). The species is also likely to remain close to water bodies (e.g. lakes, ponds, streams, irrigation channels) given their propensity to swim, hunt and overwinter in burrows close to water.

The potential impact on native fauna, as prey, would be restricted to small-bodied animals, such as invertebrates (e.g. weta, crickets, and possibly beetles), Oligosoma skinks, geckos (Mokopirirakau, Woodworthia and possibly Naultinus spp.), frogs (e.g. Leiopelma frogs), ground-dwelling or foraging birds, and potentially bats. Introduced species (e.g. mammals, Litoria frogs, and small or juvenile birds) would probably feature highly in the diet, given the relatively high abundance of exotic species in New Zealand. However, the extreme potency of Austrelaps superbus venom would cause serious harm or mortality of most living organisms in New Zealand, if a bite were to be delivered.

One other genus of south Australian snake, Notechis spp. (Tiger snake), potentially fits the notifier’s description and would also be capable of surviving on the West Coast. Notechis spp. share a very similar reproductive strategy and behaviours to Austrelaps spp., and also highly venomous. The probability of establishment and potential risks to native fauna by Notechis spp. are considered equivalent to those described for Austrelaps spp.

Likelihood of Establishment

If we consider the location where sighting took place (near Nelson Creek), then we can be fairly confident that the most likely source of incursion would have been via gold mining shipping routes into Charleston, Hokitika, Greymouth and/ or Westport from South Australia in the 1860s and 70s as suggested; given the remoteness of the site.

Considering the notifier’s sighting was made a little over a century later (c. 1990) then we can assume that snakes must have reproduced, given a conservative estimate of the lifespan of wild elapids is 5 – 20 years (i.e. any founder snakes would long since have perished). If we then consider the reproductive rate of an Austrelaps spp., and account for recruitment not occurring every year, a 50% juvenile survival rate, c. 2-3 years to reach sexual maturity, and low predation pressure in the New Zealand environment then theoretically a colony in excess of 100 individuals could readily have established over the period of a century.

Although, shy and unobtrusive, Austrelaps spp. can frequently be observed in their natural habitats in Australia, especially in areas where population densities are moderate to high (D. van Winkel, pers. obs.). That said, it is unlikely that a colony of snakes (of moderate density and potentially representing a highly venomous species) could have remained so poorly reported by the public and herpetological community in an area of the Grey Valley, which although considered remote is still surrounded by large areas of agricultural farmland, small communities, and populated towns.

While it is possible that a lack of reported snake sightings (especially of juvenile snakes) may be attributed to misidentifications on the part of the observer(s) (e.g. if only part of an animal is seen it may be mistakenly identified as a lizard or eel), it seems less likely that an observation(s) of an adult snake (≥ 1 m in length) in a terrestrial setting (c.f. an aquatic setting, where the animal may be confused with an eel) would fail to be reported or spoken of more widely.

Professional Correspondence

Correspondence with several professional (n = 5) and amateur herpetologists (n = 3) throughout New Zealand failed to add further clarity or confirmation of the presence of snakes on New Zealand’s West Coast, let alone an Austrelaps sp. on the West Coast. Dedicated lizard surveys in the lower Grey Valley, during the summer of 2013/14, which included public requests for information on West Coast lizard sightings (published in the West Coast Messenger and The Clarion), did not bring forth any information (historical or current) on snakes in the area (M. Lettink pers. comm. 16 July 2014). Furthermore, sources within amateur herpetological groups (e.g. New Zealand Herpetological Society) offered no verified evidence that venomous snakes have ever been present in captivity in New Ze aland, let alone surviving in the wild. A search of the Department of Conservation Amphibian and Reptile Distribution Scheme database (ARDS; accessed 16 July 2014) and the Ministry of Primary Industries (MPI) Reptile and Amphibian Incursion database (accessed 16 July 2014) did not reveal any historic records of Austrelaps spp. in New Zealand; however, a single Notechis ater has previously been reported (date unknown) as a border interception in New Zealand.

Given the general New Zealand public’s perception of snakes (e.g. fear provoking), and the propensity for ‘out of the ordinary’ observations/ information to diffuse through small communities and the media, the paucity of public and professional knowledge of snakes in the wild offers little confidence that an established colony persisted or continues to persist on the West Coast.

 

References

Cogger H G (2014). Reptiles and Amphibians of Australia. Seventh Edition. Csiro Publishing,

Australia. 1033 pp.

Shine R (1979). Activity patterns in Australian elapid snakes (Squamata: Serpentes: Elapidae).

Herpetologica, 1-11.

Shine R (1987). Ecological ramifications of prey size: food habits and reproductive biology of

Australian copperhead snakes (Austrelaps, Elapidae). Journal of Herpetology, 21-28.

 

EDITOR’S FOOTNOTE: The only part of the report Investigate magazine would question is the assumption that no other snakes have been seen in New Zealand. As we reported last issue (Aug/Sept 2014), a search of old newspaper archives turned up a large number of snake sightings right up to around 1900, and we reprinted those in the article.

Related posts: