Fears for future of rare snails

Press, 1 March 1984, Page 18

Fears for future of rare snails

By

The trouble with snails is that they lack charisma. Snails are yech. They ooze out of the undergrowth at night. They eat cabbages, and get eaten by Frenchmen. They leave trails of slime everywhere they go.

Thus the rare native snails of the Oparara region are no help at all to the conservation groups (including the Wildlife Service) which have been arguing with the Forest Service on their behalf for more than three years since the Forest Service announced and began to implement its controversial management plans for the region, where some unusual ecological communities are found. The plans included clear-felling and burning areas in the Oparara for replanting in pines.

A few hundred, or a few thousand, snails were squashed or burnt. Big deal. Who cares?

Snails do not have what it takes to become one of the big conservation issues — people do not care about snails the way they might care about the kakapo, say, or the whales.

“Save the whales” was a wonderful slogan — it gained worldwide support for Greenpeace International. “Save the snails?” You have got to be joking. All it has is alliteration.

The matter is not funny. The giant land snails of the Oparara region are not ordinary snails. They do not eat cabbages — they do not eat any vegetation at all. They eat worms. They are unique, belonging to a genus called powelliphanta which is found in New Zealand, and nowhere else. Powelliphanta snails occur as far north as Lake Waikaremoana and as far south as Resolution Island at the head of Dusky Sound, but their major populations are in the top end of the South Island. This includes the north-west Nelson biological refuge, which escaped glaciation in the last ice age and consequently has an unusually

DERRICK ROONEY

high percentage of endemic flora and fauna. They are carnivorous, live in the deep litter on the forest floor, and eat worms and slowmoving insects. Powelliphanta annectans, the species behind the present controversy, is found only in an area of probably less than 100 square kilometres in the Oparara region, between the Heaphy and Karamea Rivers in the north and south and the Ugly River in the east. The whole area is part of the northwest Nelson State Forest Park.

While the snail’s preservation is not a major issue in the total Oparara controversy (both sides are agreed on its zoological significance, and its major habitat is to be preserved), the real importance of the argument is that it has highlighted what conservation groups see as a legislative weakness.

All the powelliphanta species are protected under the 1980 Wildlife Amendment Act, to the extent that members of the public are not allowed to pick up and take home empty shells yet, a provision in the legislation enables the Forest Service to continue logging in areas inhabited by the snails. There have been big differences, too, between the Forest Service and conservation groups (again including the Wildlife Service) on the distribution and status of the snails, and on the effects of logging on their habitat. In March, 1982, a Forest Service spokesman was quoted in a Nelson newspaper as saying that the Oparara snail was known to occur in an area of more than 70,000 ha. After the Wildlife Service pointed out that the whole area, including the Karamea plains and estuaries, between the rivers contained only 53,000 ha, the Forest Service estimate was revised to 39,000 ha.

Since a Wildlife Service report later in 1982 on the snail populations in the area revealed that in the northern part of the region, on

the Gunner Downs, Powelliphanta annectans was replaced by another, previously undescribed species, there has been considerable downwards revision of this figure. It is now generally agreed that the maximum area that could be occupied by the Oparara snail is about 11,000 ha. The Wildlife Service says that a more realistic figure, excluding land where snails are either very scarce or absent, is about 7000 ha, of which only about 2700 ha along the Oparara River contains high densities of snails. If this is accepted, the modification of a few hundred hectares of snail habitat by logging or clear felling assumes much greater significance. While the recent announcement by the Minister of Forests (Mr Elworthy) that this season’s burn-

offs in the Oparara would be the last took some of the heat out of the argument, further unresolved differences continue between the Forest Service and conservationists.

An argument of long standing continues over the actual effect of logging on the snail population, and the ability of the Oparara snail to recolonise areas which have been replanted with exotic species of trees. A statement by a Forest Service spokesman, broadcast by the Nelson radio station in February, 1982, that more snails have been found in logged forest than in unlogged forest, drew a sceptical response from conservationists. Partly as a result of this, the Wildlife Service made a detailed survey of snail populations in the Oparara and the adjoining Gunner Downs, early in March, 1982.

A report on the survey, published subsequently by the Wildlife Service, noted that “because neither we nor the Forest Service carried out extensive surveys in comparable logged and unlogged forests, there are no grounds for definitive statements regarding the preferences of snails for logged or unlogged forest. However, both the Forest Service and the Wildlife Service found that the highest densities of snails in the Oparara area were in the unlogged silver beech forests on the limestone flats. Eight years after parts of this forest had been logged, snail numbers in the cut-over area were low.

“In parts of the medium snail density zone, in rimu/hardwood forest, snail numbers appeared to be medium 16 to 17 years after the forest had been logged. In the exotic conversion zones of the upper Oparara Plateau, the drastic land-use change will probably eliminate powelliphanta ...”

The report also noted that shell counts in two adjoining areas in the mid-Oparara, one unlogged and

one logged in 1974, indicated that the population was 12 times larger in the unlogged forest. On the other hand, an unlogged area of “medium snail density” contained only a few more snails than an adjoining area which had been logged 16 years earlier and allowed to regenerate in tree fern, kamahi, and other native species. The Wildlife Service was unable to assess the areas which had been clearfelled, burnt, and planted in pines, because these activities “were too recent and extensive for snails to have reinvaded the area.” However, the report added that the very different habitat provided by a pine plantation, and its shortterm nature, would make this area unsuitable for a permanent population of powelliphanta snails. The Forest Service disagrees with this, maintaining that the snails will recolonise areas planted in pines, and will thrive there. Powelliphanta snails could be found in pine plantations six to eight years after planting, the Westland Conservator of Forests (Mr P. Berg) said in a statement reported in “The Press” in January of this year.

Conservationists are still not convinced of this, but the argument has become largely academic since the Forest Service announced in early February a switch .in its plans for exotic plantations from the controversial Oparara sites.to previously logged areas near Break Creek, where snail numbers are low or nonexistent.

Yet to be resolved is the question of whether the legislative loophole should be plugged — the loophole which enables the Forest Service to continue logging the snail habitat, while the creature enjoys total protection from all other forms of human predation. On a happier note, the future of the undescribed Gunner Downs species of snail seems secure. Its habitat is not threatened by logging.