Adclarkia dawsonensis (Boggomoss Snail, Dawson Valley Snail)

Advice to the Minister for the Environment and Heritage from the Threatened Species Scientific Committee (TSSC) on Amendments to the list of Threatened Species under the Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act)

1. Scientific name, common name (where appropriate), major taxon group

Adclarkia dawsonensis (Boggomoss Snail, Dawson Valley Snail).

2. National Context

The Boggomoss Snail is known to occur in only two populations in the Dawson Valley, northeast of Taroom, on the Dawson River, eastern Queensland. The larger population is in a small patch of riparian habitat at Isla-Delusion. The smaller population is in Boggomoss habitat on the Dawson River near Taroom.

Boggomosses are a series of small, elevated peat bogs or swamps scattered among dry woodland communities, which form part of the Springsure Group of Great Artesian Basin springs in the Dawson River valley, near the town of Taroom in south-eastern Queensland. They are rich in invertebrates and form a vital chain of permanently moist oases in an otherwise dry environment.

The species is not listed as threatened under the Queensland Nature Conservation Act.

3. How judged by TSSC in relation to the EPBC Act criteria.

TSSC judges the species to be eligible for listing as critically endangered under the EPBC Act. The justification against the criteria is as follows:

Criterion 1 - Decline in numbers

Currently, the size of the population of Boggomoss Snails is unknown, but it is suggested there may be only up to 1100 mature individuals remaining, at the two sites where it occurs on the Dawson River in south-eastern Queensland. One site, a small patch of riparian habitat at Isla-Delusion, contains the larger population, with a suggested estimate of 1000 mature individuals, while the second population, in Boggomass habitat on the Dawson River near Taroom is smaller, with a suggested estimate of 100 mature individuals. The likelihood of Boggomoss Snails occurring elsewhere is low, as most of the suitable habitat in the area has been surveyed, and none have been found.

It has been suggested that the Boggomoss Snail has undergone a severe reduction in numbers. One figure given is a loss of at least 80-90% of the population over the last 10 years due to a decline in suitable habitat. There is no quantitative field evidence for this as the Boggomoss Snail was only described in 1996 and little is known of it before then. The reduction in numbers is an inference based on the almost total destruction of its preferred habitat - riparian on alluvial flats in the Dawson River Valley. It the past, it is suspected that the Boggomoss Snail was much more widely spread on these flats, but the flats have been largely cleared for farming.

It has been suggested that the numbers of Boggomoss Snails will continue to decline, with estimates of 5% decline over the next 3 years, with a probability of extinction in the wild of 50% in the next 20 years. It is claimed that if the proposed construction of a dam on the Dawson River goes ahead, that this, together with the current threats, would result in a possibility of extinction within the next three generations. If the proposal to develop a dam on the Dawson River (the Nathan or Dawson River dam) goes ahead, it will impound the site of the smaller population, causing the loss of this population. With the construction of the dam, changes in river flow will possibly change the habitat at the Isla-Delusion site, making it drier. Boggomoss Snails have frail shells that suggest they may be particularly sensitive to habitat modification which exacerbates dryness. Other threats to the Boggomoss Snail that are currently recognised include: at the site of the smaller population, clearing of surrounding vegetation makes the Boggomosses vulnerable to drying out. Fire is also a problem in Boggomoss areas. The Isla-Delusion site is a stock and water reserve that is not protected and is threatened by grazing (which compacts the soil, destroys vegetation and causes the habitat to dry out), introduced weeds, timber collection and quarrying.

It is reasonable to suspect that the Boggomoss Snail has undergone a substantial decline in numbers as a result of clearing of its preferred habitat, the alluvial flats of the Dawson River, for farming activities. Its is now known from only two sites, both unprotected and both subject to the impact of a range of potential, on-going threats. One site will be lost if the proposed dam on the Dawson River goes ahead.

Therefore, the species is eligible for listing as critically endangered under this criterion.

Criterion 2 - Geographic distribution

The Boggomoss Snail's geographic distribution is precarious for the survival of the species and is very restricted. The species is only known from two sites on the Dawson River in south-eastern Queensland. One is on Boggomoss habitat on the Dawson River near Taroom (private property) and the other in a stock and water reserve at the Isla-Delusion crossing. The likelihood of Boggomoss Snails occurring elsewhere is low, as most of the suitable habitat in the area has been surveyed without any other evidence of occurrence of the snail being located. The two known populations are found within 45 ha (0.45 km2) of the Dawson River, c. 44.5 ha at Isla Delusion and 0.5 ha on a private property near Taroom. The area of occupancy is less than 10 km2.

The smaller population is considered to be the result of opportunistic colonisation: the Snail having survived in suitable habitat after floods have transported it from another site. Given the small size of the habitat block (< 1 km2) at this site and the threats to which is subjected, the long term survival prospects of this population appear limited. If the proposal to develop a dam on the Dawson River (the Nathan or Dawson River dam) goes ahead, this population will be lost. Also, the proposed dam may alter the habitat at the Isla-Delusion site through changes in river flow, making this site drier. Boggomoss Snails have frail shells that suggest they may be particularly sensitive to habitat modification which exacerbates dryness. From what is presently known, the proposed dam could cause the extinction of this species in the near future.

Neither of the sites where the Boggomoss Snail is found are managed for the species. The species is subject to a number of ongoing threats - changes to water flows in the Dawson River, drying out of Boggomoss habitat, fire, grazing, introduced weeds, timber collection and quarrying. The current level of threats could lead to a projected decline in the area of occupancy, extent and quality of habitat, number of locations and number of mature individuals.

Therefore, the species is eligible for listing as critically endangered under this criterion.

Criterion 3 - Population size and decline in numbers or distribution

Though the size of the Boggomoss Snail population is not known, it has been suggested that there may be only up to 1100 mature individuals in total at two known sites on the Dawson River, south-eastern Queensland. Neither site is managed for the species. The species is subject to a number of ongoing threats - changes to water flows in the Dawson River, drying out of Boggomoss habitat, fire, grazing, introduced weeds, timber collection and quarrying. If a proposal to develop the dam on the Dawson River (the Nathan or Dawson River dam) goes ahead, the population at one site will be lost through impoundment. The population at the second site, Isla-Delusion, may become drier because of changes in river flow caused by the dam. Boggomoss Snails have frail shells suggesting they may be particularly sensitive to habitat modification which exacerbates dryness.

The numbers of Boggomoss Snails are apparently continuing to decline. There are claims that it will: decline by 5% over the next 3 years; has a 50% probability of becoming extinct in the wild in the next 20 years; and, if the Dawson River dam goes ahead, could become extinct within the next 3 generations.

The Boggomoss Snail, with its estimated population of up to 1100 mature individuals and small, fragmented geographic distribution, could be expected to decline in numbers if impacted upon by the currently unmanaged threats.

Therefore, the species is eligible for listing as Vulnerable under this criterion.

Criterion 4 - Population size

There is no evidence available against this criterion.

Therefore, the species is not eligible for listing under this criterion.

Criterion 5 - Probability of extinction in the wild

There is no evidence available against this criterion

Therefore, the species is not eligible for listing under this criterion.

4. Conclusion

There is little quantitative data available on Boggomoss Snail populations numbers, though there have been surveys of suitable habitat in areas where it is thought likely to occur that indicate the species has a very restricted distribution. The species is likely to have undergone a large reduction in numbers and range because of the almost total loss of its preferred habitat - riparian habitat on alluvial soils on the Dawson River. The remaining two populations are in areas that are not managed for the species, and that continue to be subject to a range of threatening land uses. A key potential threat is a proposal to develop a dam on the Dawson River which will impound one site, causing the loss of this population, and possibly alter the habitat at the other site, making it less suitable for Boggomoss Snails.

The species is eligible for listing as critically endangered under criteria 1 and 2.

5. Recommendation

TSSC recommends that the list referred to in section 178 of the EPBC Act be amended by
including in the list in the critically endangered category:

Adclarkia dawsonensis (Boggomoss Snail, Dawson Valley Snail)