Kath Walker :: Department of Conservation
1. My full name is Kathleen Joy Walker. I hold a BSc degree, and am currently employed as scientist by the Department of Conservation, based in Nelson. I was employed by Ecology Division of DSIR (the pre-curser to Landcare Research) between 1976 and 1980, during which time I began a long working association with the largest genus of endemic giant land snails, Powelliphanta. Between 1981 and 1987 I was employed by the Research Section of the New Zealand Wildlife Service, surveying and preparing reports for the Fauna Survey Unit and continuing specialist work on Powelliphanta distribution, taxonomy and conservation. I transferred into the Science and Research Unit of the Department of Conservation when it took over the duties of the Wildlife Service in 1987, and have been employed there till the present. I spent 8 years as an advisory scientist to the Nelson/Marlborough Conservancy, organizing and carrying out research on various endangered species (including Powelliphanta) and on pest control issues related to threatened species conservation. Since 1998 I have worked full-time on research into Powelliphanta conservation for the Department, have recently published a comprehensive account of the status of the genus (Walker 2003) and am currently Powelliphanta Recovery Group leader, having spent over 24 years studying the genus.
2. The evidence I present today will describe the value of the proposed Cypress mine site to Powelliphanta land snails, the potential adverse effects the proposed mine would have on these values, and whether these effects can be avoided, remedied or mitigated. I visited the Cypress mine site on 18 October 2003 and have made seven other visits to the wider Denniston Plateau, Mt Frederick, Mount William, Millerton and mid-Waimangaroa areas since 1981.
Value of the Proposed Mine Site to Powelliphanta snails
3. Much of New Zealand’s biodiversity is contained within its land snail fauna, and the giant Powelliphanta land snails of North Westland and North-West Nelson are of major significance, not just nationally but internationally.
4. The Powelliphanta land snails of New Zealand (Figure 1) are of very ancient lineage. They originated in the late Paleozoic or early Mesozoic on Gondwanaland, along with the ancestors of native frog and tuatara (Stevens et al 1995). They pre-date by at least 40 million years the rise and fall of the forests and swamps whose decay and subsidence eventually created the coal reserves of the Waimangaroa.
5. Inundation of the New Zealand land mass in the Oligocene and Miocene (20 mya), and glaciation in the Pleistocene led to isolation and speciation in the large land snails (Stevens et al 1995). Like the moa and weta, Powelliphanta land snails developed gigantism, and became jewels in the strange New Zealand world where large flightless invertebrates took the niche occupied elsewhere by small mammals.
6. Today there are about 24 species of Powelliphanta, and most are naturally confined to small localized areas, presumably through a combination of a long and complicated biogeographical history, the snails’ restricted mobility, and habitat specific adaptation.
7. Though they vary greatly between species, most have very glossy shells, delicately marked with numerous bands, in a myriad shades of red, brown, yellow and black (Figure 2). Some species are impressively large, like the fist-sized, golden shelled Powelliphanta superba prouseorum, which weighs as much as a tui.
8. Like other notable New Zealand pre-historic species such as kiwi and tuatara, Powelliphanta are slow-growing, long-lived (averaging about 12-15 years), and have low productivity. They do not reach breeding age until their 5th or 6th year, and lay only 4-10 hard limy eggs annually, with the survival of hatchlings likely to be low. They have few defences against the new predators humans brought to New Zealand. The alpine Powelliphanta have fared better than lowland species as most of the new snail predators are scarce above the bushline. Their small, patchy and localized distribution make Powelliphanta very vulnerable to habitat loss. Not surprisingly, many Powelliphanta are now considered highly threatened species.
9. One such species, Powelliphanta “patrickensis” (Figure 3), is confined to the upper Waimangaroa and Upper Whareatea Rivers on the Stockton-Denniston plateaux. Like all alpine Powelliphanta, it is relatively small - about 3.5 cm. in diameter. It was first discovered in 1949, in the area destined to be smothered in over-burden if the Cypress Mine proceeds. At the time it was described as Powelliphanta rossiana patrickensis, but as more information became available during the 1970’s and 1980’s, it became apparent it was a species in its own right. In the early 1990’s gel electrophoresis confirmed its genetic divergence from Powelliphanta rossiana, and it was tagged with a new name Powelliphanta “patrickensis’ (sometimes Powelliphanta “Denniston”) until it could be formally re-described. This has not yet been done. In its efforts to protect biodiversity, the Department of Conservation has deliberately focussed on the correct identification of taxonomic units and meeting their immediate conservation needs, with the slow and detailed description and naming taking second place.
10. Powelliphanta “patrickensis” is listed as a “Nationally Endangered” species in the Department of Conservation’s threatened species summary (Hitchmough 2002). It was given this rank because it meets all three of the following criteria (Molloy et al 2002): A: Small population and moderate to high recent or predicted decline. A taxon is Nationally Endangered when available scientific evidence indicates that it fits at least one status criterion and one Trend criterion as follows: Status Criteria 1. The total population size is 250-1000 mature individuals. Trend Criteria 1. There has been a decline of ≥ 30% in the total population or habitat area in the last 100 years. 2. There is a predicted decline of ≥ 30% in the total population in the next 10 years due to existing threats.
11. Powelliphanta “patrickensis” was considered to meet the criterion of ‘at best 1000 mature individuals’ as specific searches for live snails found low live snail numbers in almost all sites. The key phrase is “mature individuals”; those snails too small to contribute to the breeding population (and Powelliphanta don’t breed till about age 5, so many live snails seen are juveniles) are not included in this definition.
12. Even if there were more than 1000 mature individuals alive today, Powelliphanta “patrickensis” would still have the same rank as they also fit Nationally Endangered category B: Small-moderate population and high recent or predicted decline; where they would fit at least one status criterion (“The total population size is 1,000-5,000 mature individuals”) and one trend criterion (“There has been a decline of ≥60% in the total population or habitat area in the last 100 years).
13. The cause of this substantial decline has largely been extensive habitat loss due to mining activities and associated fires on Denniston Plateau and open cast mining around Mt Frederick on the Stockton Plateau. The arrival of exotic predators has added additional pressures, but is not the main problem for Powelliphanta “patrickensis”.
14. Unfortunately for its long-term survival, the preferred habitat of Powelliphanta “patrickensis” is low manuka shrubland and bogland on coal measures (Figures 4, 5 & 6) and its distribution closely follows that of the coal resources on the Stockton-Denniston plateaux.
15. They are rare or absent in the taller forest areas of the Mount William range, and on the rock-pavement areas of eastern Mt Frederick, where there is only low vegetation (Figure 7). They are concentrated on the margins of shrubland, particularly in low manuka and mountain beech forest, and in this appear well adapted to the coal plateaux where the geology and drainage created an abundance of edges (Figure 8). The distribution and density of Powelliphanta “patrickensis” is shown in Map 1..
16. To reliably determine the areas of most importance to Powelliphanta “patrickensis” and produce this map, over the last 8 years standard snail surveys have been carried out over all of the Denniston and much of the Stockton plateau. The method involved spending one person-hour searching widely for shells in each 500 m topographical-map sub-square (ie. a 25 ha area). Wildlife surveyor Rhys Buckingham carried out much of the survey while contracted to two coal-mining interests, Solid Energy and Restpine Ltd, with Department of Conservation staff surveying those squares not previously surveyed, and re-doing others as a check that methods and results were consistent between observers and years.
17. The black dots indicating snail density on this map have been placed in the centre of each 25 ha sub-square surveyed, to represent the general distribution pattern. However, this was not the only, and indeed seldom the exact place in the sub-square where shells were found. Snail distribution tended to be clumped along stream and scrub margins, and scarce or absent in poorly vegetated or highly disturbed parts of the sub-square
18. The results of all this survey work show that Powelliphanta “patrickensis” is absent from the Stockton Plateau north of St Patrick Dam, from most of the forested upper slopes of the Mount William Range, from the bare rock pavement areas above the Kiwi Escarpment, and is only patchily and sparsely distributed on parts of the Denniston Plateau. The core habitat for Powelliphanta “patrickensis” is now the mid and upper reaches of the Waimangaroa River, and the Deep Stream catchment.
19. It is tempting to think that this is a snail which thrives on disturbance, and may in fact increase in numbers with mining development, as its distribution pattern so closely follows that of coal resources. However, their very low density near Denniston, and in the Coalbrookdale, Burnetts Face, Cascade and Wharatea coal-mine areas, and abundance in the largely undisturbed upper Waimangaroa Valley and Webb Stream coal resource areas refutes that. Rather, it is likely that this species is one specifically adapted to living in the habitat created by an acidic substrate.
20. Powelliphanta “patrickensis” is highly unusual amongst Powelliphanta in its preference for acidic soils. Within the genus the majority of species show an equally marked preference for alkaline soils where lime for shell growth and egg-shell formation is abundant, and where earthworms are particularly common.
21. The snails are now in very low numbers on Denniston Plateau, probably because of the extensive clearing and burning (Figures 9 & 10) which occurred there during coal mining from the 1880’s to the 1960’s. The remaining snails on the degraded Denniston Plateau are also vulnerable to modern mining methods being used to re-work old coal seams.
22. Powelliphanta snails near Mt Augustus were presumed to be Powelliphanta “patrickensis” but have recently been identified as a separate taxon. Limited survey work to date suggests that open cast coal mining threatens much of the remaining habitat of the Mt Augustus Powelliphanta (Figure 11), which puts this species in immediate danger of extinction themselves. This snail has only recently been brought to the attention of Solid Energy, and further work on this species is planned.
23. The core remaining, and apparently best habitat of Powelliphanta “patrickensis”, coincides with that area identified by Solid Energy as containing coal resources which they wish to extract over the next 50 years (EIA section 1.2 and figure 1.8 ), beginning with the Cypress Mine in the north of the block (Map 2).
Potential Adverse Effects of the Proposed Cypress Mine on these natural values
24. The proposed Cypress Mine pit, overburden pile and associated earthworks would destroy a minimum of 10% of the species remaining habitat and 9.5% of the estimated total snail population. These figures would both rise if there was any habitat loss beyond the edge of the pit and road lines currently drawn, a highly likely scenario.
25. This is higher than the figure calculated by Solid Energy (7%) before the full range of the snail had been surveyed. It was calculated from the proportion of sub-squares with snails affected by the mine (9) in relation to the total number of sub-squares with snails (90). The number of live snails affected was estimated from the proportion of shells found in the surveys of mine-affected sub-squares (100) in relation to all those found outside the mine (1058).
26. Further, if mines planned by Solid Energy for Deep Creek and Cedar Creek eventuate, a further 29% of habitat, and 64% of estimated total population would be lost, giving a cumulative loss of 39% of the snails habitat and almost 74% of the total snail population. Remnant snail habitat will be isolated, decreasing the genetic flow and hence long-term health of the surviving snail populations.
Can the adverse effects of the mine on the Powelliphanta population be avoided, remedied or mitigated?
Remedies: Habitat restoration
27. Solid Energy has proposed land rehabilitation as a major way to remedy the negative impacts of the Cypress Mine on the fauna of the upper Waimangaroa. The AEE (p. 296) states that “the snail can be expected to recolonise the rehabilitated area….. the direct transfer of vegetation will assist with this….recolonisation of the area is likely to be slow…..and the viability of the species is not threatened by the proposed mine”.
28. However, they do not present any data to support their optimistic assertions, and I know of no other sites where Powelliphanta have been able to recolonize after major soil disturbance of this nature and scale. In my view the chances of successful recolonization are slim at Cypress because Powelliphanta “patrickensis” has such specific habitat preferences. Soil moisture, acidity, fertility and depth are apparently important, as is the composition, height and density of the covering vegetation and type and abundance of subsoil and topsoil earthworms. None of these aspects are well enough understood for straightforward replication of suitable snail conditions, even if they had been taken into account in the rehabilitation plan, which they have not been.
29. Solid Energy carried out limited work on invertebrate survival in vegetation transfer trials in 1998 at Stockton. No data were presented on the survival or otherwise of Powelliphanta in the trials. A Powelliphanta shell was found in the piles of direct-transfer vegetation (R. Toft, pers. comm to R. Bartlett; Solid Energy response to questions raised by F. Overmars 30/10/03) so snails are likely to have been present in the area soil and vegetation was stripped from. However, there was no evidence snails survived the process. The Powelliphanta involved was probably not Powelliphanta “patrickensis”, but rather the undescribed Mt Augustus Powelliphanta.
30. Other, more generalist Powelliphanta have survived transfers to natural, unmodified areas similar to their natal areas, However, compared to Powelliphanta “patrickensis”, these species have wide natural ranges and/or undemanding habitat requirements. An analogy would be comparing the ubiquitous fantail, capable of inhabiting all lowland forests of every type, as well as gardens and farmland, with the rock-wren, able to survive only in a specific type of rock-fall on some South Island mountain tops. There are no known cases of Powelliphanta snail transfer to entirely reconstituted substrates, let alone when the snail involved has very specific habitat requirements
31. Powelliphanta depend on native earthworms living in subsoil and topsoil for most of their food, with native slugs a minor component. This earthworm fauna will be lost when the topsoil and subsoil is stripped from the site and stockpiled, as worms cannot survive once the soil has lost its structure and the source of nutrients (growing plants) is no longer available.
32. Worms will only be able to survive in the small areas of directly transplanted material, and such material will make up only a very minor portion of the rehabilitated mine area. According to Solid Energy (Fig 3.16 of the AEE), “intensive direct transplant” of soil and vegetation will largely be confined to the overburden stockpile, small areas of the soil stockpiles, and a small portion of the north pit. For almost the entire north and south pit, intensive direct transfer of soil and vegetation is not practicable.
33. Native worms have specific habitat requirements of their own, most tolerate only a narrow range of environmental conditions, and are not known for surviving or re-invading highly disturbed areas (Lee, 1959). Wherever native vegetation cover has been lost, the earthworm fauna is usually lost too. If conditions in the mined area eventually become favourable, earthworms and then snails may gradually re-invade the area, but the process will be extremely slow.
34. The proposed shape of a rehabilitated Cypress Mine area includes several features which will slow even further re-invasion by earthworms and Powelliphanta land snails; a series of high wall steps with no topsoil and steep angles occurs all along the eastern side of the “restored” pit, while an access road and its associated ditches, runs along the western side of the pit. Steep banks and soil-less strips are large barriers for ground crawling animals.
35. Accordingly, the Cypress Mine would result in the loss of 10% of the habitat of a nationally endangered species for a minimum of 60-100 years and possibly permanent loss, despite proposed remediation efforts.
36. If the lower Waimangaroa mines also eventually go ahead, about 40% of the snail’s total habitat, supporting 74% of the population, is likely to be lost. Because the mid-upper Waimangaroa is prime snail habitat, the loss of it would result in a disproportionate loss of snails. Losing this area, a third of the snails remaining habitat, would destroy two thirds of the population. This level of potential loss needs to be viewed in the context of the habitat loss to mining activities which has already occurred on the Denniston Plateau and around Mt Frederick.
Mitigatation: Predator Control
37. The majority of Powelliphanta shells found on the coal plateau are broken, apparently by predators. Due to the highly acidic nature of the environment, the shell of Powelliphanta “patrickensis” is unusually thin and fragile, without much of an inner limey layer which usually makes the shells hard. This means predators can easily access the snail body without leaving much sign on the shell. The main predators of Powelliphanta “patrickensis” appear to be the native weka and the introduced thrush, possum and rats, but the exact proportions taken by each are unclear. These predators, though widespread, are not abundant in the upper Waimangaroa (Thomas and Toft 1997). Rats are vulnerable to cold conditions and are absent in frost hollows and at higher altitudes, while thrushes and possums are limited by a shortage of forest cover in many areas.
38. To mitigate the effects of the Cypress Mine on Powelliphanta “patrickensis”, Solid Energy has proposed the construction of a fence around a 20 ha area just west of the proposed Cypress Mine pit, and maintenance of the area as snail-predator-free for 30 years. The aim is to create a safe nursery where the snail population can reach high density.
39. However, the proposal has some serious flaws which prevent it providing adequate mitigation for the direct losses the snails will suffer if the mine goes ahead. A fence capable of excluding rats, stoats and possums in the difficult rocky country, dissected by streams, would be very expensive to build. To get maximum conservation value from their investment, during years of high predator numbers (about every 3-5 years) Solid Energy plan to put 18 kiwi chicks (the number anticipated produced annually in the 1000 ha predator-control area) inside the enclosure till they gain sufficient weight to defend themselves from stoats (probably 4-9 months).
40. Unfortunately great spotted kiwi almost certainly eat eggs, juvenile and even adult small and fragile Powelliphanta ‘patrickensis”, as they are known to eat heavier shelled Powelliphanta superba snails (McClennan & McCann 1991). Kiwi probably catch snails at night, when the snails emerge from their shells, and flick the animal out of the shell rather than trying to bash it open. Great spotted kiwi also compete with the snails for food, as earthworms form the major part of the diet for both kiwi (McClennan & McCann 1991) and snails.
41. Though the kiwi chicks would only need to be in the enclosure one year every 3-5, 18 chicks in a 20 ha area, when normal density of an adult pair is 23 ha, constitutes a significant threat to a snail nursery. While the kiwi chicks may benefit from being placed inside a fence stocked with snails, enhanced kiwi densities are likely to undo many of the gains made by excluding exotic snail predators.
42. If kiwi were excluded, would the predator-proof fence be sufficient to mitigate snail losses?
43. Snail numbers are not naturally high in the area identified as a possible site for the enclosure, and it is not clear if the environment can support greatly increased numbers of snails there, even if predator control was successful. Supplementary feeding the snails over a 30 year period to maintain abnormally high snail densities is very unlikely to work: all captive rearing work so far has found Powelliphanta take only live native earthworms, and artificially increasing worm density at the site would be highly problematic.
44. Currently, most shell damage at the site is a result of predation by weka, thrush and possum so excluding rats and stoats won’t make much, if any, difference to the snails. Wekas are a vulnerable native species in their own right, in low numbers on the coal plateaux, and a natural predator of Powelliphanta – they evolved together. Control of weka inside the fence is a moot point. Thrushes will be very difficult to control in any effective manner over a 30 year period. Possum control inside the fence will make a difference to snail numbers but with thrush and possibly weka still there, the increase may not be great.
45. Powelliphanta are long-lived, and 30 years represents the lifespan of only 2-3 generations of snails. In 30 years, when the predator-free area is no longer maintained, the snails will again be exposed to predation.
46. As noted earlier, any rehabilitation of the Cypress Mine to suitable snail habitat will take decades, if it happens at all. Losing, perhaps permanently, 100 ha of good snail habitat while gaining 30 years of predator control in a small area is doing the snails no favours. If the remaining coal resources of the Waimangaroa are also exploited over the next 50 years, and the same approach is taken, then we could end up losing 74% of the snail population during the mining operations, highly modifying or rendering unusable the best snail habitat, and having snails survive in good numbers only in three fenced fragments until the money runs out and predator control is abandoned.
47. There is a real difficulty in designing effective mitigation for the anticipated snail losses of a mine at Cypress. The only substantial snail habitat away from the short–medium term coal mining-threatened Upper Waimangaroa Mining Permit Area is that on Denniston Plateau. Here, predators are not the major problem (there are relatively few on the rocky open tops), rather it is the degraded nature of the snail habitat, something time alone can restore. Money and effort here can unfortunately do little to recompense snail losses elsewhere.
48. As noted by Solid Energy, it will be at least 50 years before substantial native vegetation cover is present on a rehabilitated Cypress Mine, and longer again, if at all, for snails to recolonise the area. This means we won’t know whether mining at Cypress was a sustainable thing to do, as far as the threatened snails are concerned, for at least 60-80 years. Within the next 10-15 years we will presumably want to know whether mines lower down the Waimangaroa are acceptable. Unfortunately approving the Cypress Mine won’t provide information for the latter decision within a usable timeframe. If we continue in a ‘taste it and see’ manner, the costs to endangered snails will only be apparent when all the best habitat and populations are gone and we no longer have the opportunity to correct the situation.
Summary
1. The large land snail Powelliphanta “patrickensis” lives only on the Denniston-Stockton coal plateau.
2. Its preferred habitat is the margins of low forest amidst boggy clearings on coal measures, and its distribution closely follows that of the coal resources on the plateau.
3. The Denniston Plateau has been badly affected by fires and mining and snail numbers there are now very low.
4. There are three remaining core snail areas; Deep Stream, Cedar Creek-Waimangaroa River, and Cypress, and there are plans for coal mines in each of these areas.
5. Powelliphanta “patrickensis” is a “Nationally Endangered” species.
6. Possums, thrushes and in a few places rats, are reducing snail numbers, but the greatest concern is the potential further loss of habitat.
7. Cypress Mine would destroy 10% of the remaining habitat and 9.5% of the remaining snail population.
8. There is no evidence the snails could recolonise a rehabilitated Cypress mine site;
9. Maintenance for 30 years of a proposed predator-proof enclosure to enhance snail density would not solve the real issues of long-term habitat loss and fragmentation.
References
Hitchmough, R. (comp.) 2002: New Zealand threat classification system lists-2002. Threatened Species Occasional Publication 23. Department of Conservation Wellington.
Lee, K.E. 1959: The Earthworm fauna of New Zealand. New Zealand Dept Sci Industr. Res. Bull. 130. Govt Printer Wellington. 486 pp, 371 figs., 25 tables.
McLennan, J.A. & McCann, A.J. 1991: Ecology of the great spotted kiwi Apteryx haastii. Unpublished DSIR Land Resources Contract Report No. 91/48
Molloy, J.; Bell, B.; Clout, M.; de Lange, P.; Gibbs, G.; Given, D.; Norton, D.; Smith, N.;Stephens, T.2002: Classifying species according to threat of extinction: a system for New Zealand. Threatened Species Occasional Publication 22, Department of Conservation, Wellington.
Stevens, G.; McGlone, M.; McCulloch, B. 1995: Prehistoric New Zealand. Reed publishing, Auckland.
Thomas, B. & Toft, R. 1997: Surveys for Fauna in the upper Waimangaroa Valley. Landcare Research Contract Report; LC9697/101 prepared for Kingett Mitchell & Associates Ltd, Auckland.
Walker, K.J. 2003: Recovery plans for Powelliphanta land snails 2003-2013. Threatened Species Recovery Plan 49. Department of Conservation, Wellington, x + 208 p. + 64 plates.
