Threatened Species and threatened ecological communities
Minister for the Environment and Heritage decision on advice 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)
Notopala sublineata (Murray-Darling Basin population consisting of N.s. sublineata and N.s. hanleyi) (River Snail)
Notopala sublineata is a medium-sized (20-25mm) freshwater snail with a round shell that ends in a conical spire. Its outer shell is generally dark green but may also be greenish brown to dark brown, with or without bands. The body of the animal is similar to other snails but possesses a prominent snout and short eye stalks on the outside of the tentacles.
The ecology of the River Snail is not well known. This snail is a herbivore that grazes on organic matter found on hard surfaces in free-flowing bodies of water. It is a member of the family Viviparidae so named because they give birth to small young snails rather than laying eggs. In this family, the female broods the young until they are able to crawl away, so species within this family have limited dispersal abilities.
The taxonomy of the genus Notopala in Australia is currently under review. Winston Ponder of the Australian Museum, the expert undertaking the review of the genus, currently recognises that, on the basis of morphology, the species Notopala sublineata is made up of three subspecies: Notopala sublineata hanleyi, Notopala sublineata sublineata and Notopala sublineata alisoni. (Essentially, Winston Ponder has combined two taxa that were originally considered to be separate species, Notopala sublineata and Notopala hanleyi, into the one species.) The subspecies sublineata is restricted to the Darling River and its related tributaries; the subspecies hanleyi is restricted to the Murray River and Murrumbidgee River drainages; and the subspecies alisoni is found in rivers draining into the Eyre Basin, such as the Cooper and Diamantina Rivers and a few coastal rivers, notably the Dawson River in Queensland. The subspecies sublineata and hanleyi, while being quite distinct in parts of their range, tend to merge around the lower parts of the Darling River. Within the species Notopala sublineata, it is the population that occurs only within the Murray-Darling Basin, which comprises the subspecies sublineata and hanleyi, that is considered to be threatened. The subspecies alisoni does not occur in the Murray-Darling Basin, is still extant over much of its range and is not considered to be threatened.
The extent of occurrence of the Murray-Darling Basin population of Notopala sublineata is believed to have reduced dramatically since the 1950s-1970s. It is believed that the population is extinct within the natural environment, with subspecies hanleyi currently known to occur in one irrigation pipeline, and possibly occurring in a second pipeline, in the South Australian Riverland, and the subspecies sublineata being thought to occur in only one irrigation pipeline in the Darling River catchment, NSW. There is a small-scale community project, organised by the South Australian Field and Game Association, that is breeding the subspecies hanleyi in captivity at Loveday Wetlands in South Australia. Captive-bred River Snails from this project have been moved to at least two other wetlands. At one of these sites, the snails are being held in captivity and have successfully bred. Little information is available on the second translocation site.
Notopala sublineata (Murray-Darling Basin population consisting of N.s. sublineata and N.s. hanleyi) is not listed under the EPBC Act. The species Notopala sublineata has been listed as endangered, which is the highest available category of endangerment, under the NSW Fisheries Management Act 1994, and as threatened under the Victorian Flora and Fauna Guarantee Act 1988. The advice from the scientific committee of each state suggests that the species which has been listed in New South Wales and Victoria followed that proposed by Winston Ponder, that is Notopala sublineata incorporates all subspecies - Notopala sublineata sublineata, Notopala sublineata alisoni and Notopala sublineata hanleyi. Notopala sublineata hanleyi is also listed as one of the native species that characterises the endangered ecological community 'Aquatic Ecological Community in the Natural Drainage System of the Lower Murray River Catchment' which is listed under the NSW Fisheries Management Act 1994.
The Minister for the Environment and Heritage, the Hon. Dr David Kemp MP, noted that the taxonomy of the genus Notopala in Australia is currently under expert review, the Committee's advice that the two taxa that were originally thought to be separate species, Notopala sublineata and Notopala hanleyi, are proposed to be combined into the one species Notopala sublineata and that the species Notopala sublineata is actually made up of three subspecies: subspecies hanleyi, subspecies sublineata and subspecies alisoni. The Minister also noted that the new form of the species Notopala sublineata and its subspecies have not been formally published in scientific literature.
The Minister concluded there is uncertainty about the precise taxonomy of the River Snail.
TSSC judges the species to be eligible for listing as critically endangered under the EPBC Act. The justification against the criteria is as follows:
There is no evidence available against this criterion.
Therefore, the species is not eligible for listing under this criterion.
Historically, the Murray-Darling Basin population of Notopala sublineata was found on the sediments and hard substrates (rocks, logs etc) in shallow areas of freshwater rivers. Based on information from museum records and the literature, the species was widely distributed and quite common in the Murray-Darling Basin. For example, in 1935, Cotton noted that the subspecies hanleyi was 'of fairly common occurrence on Murray native camp sites'. In the 1940s, Johnston and Beckwith reported a collection of 4677 specimens of the subspecies hanleyi from the lower Murray River region.
Within the Murray-Darling River system, the River Snail rapidly declined in area of occupancy from about the 1950s-1970s, and the species now appears to be extinct within its natural habitat. There is little information on rates of change of numbers over this time.
The last report of the subspecies hanleyi in its natural habitat was from the Murray River at Wood's Point in the early 1980's. It is not clear when subspecies sublineata was last reported in its natural habitat, but some of the last records of live snails appear to be around the mid to late 1970s. The natural habitat of the River Snail in the Murray-Darling Basin has been surveyed for molluscs in recent times, particularly in the lower Murray River region (e.g. Suter et al. 1995; Sheldon & Walker 1998), but the surveys have failed to locate living specimens of the River Snail of either subspecies. It is considered most likely that both subspecies are extinct in their natural habitats.
The Minister noted the Committee's advice that both subspecies are likely to be extinct in their natural habitats. He also noted that knowledge of the current distribution of the species appears to be based on general surveys for molluscs in the lower Murray-Darling, with very limited survey effort outside this region and few targeted surveys for this species anywhere within its range. The Minister concluded that the distribution and abundance of this species is not well known.
In the lower Murray River region, the decline in the area of occupancy of the River Snail coincided with increased flow regulation in the river system in the 1950s, and studies in the region suggest that the decline is possibly a result of increased regulation, particularly by dams and weirs. Before regulation, the River Snail most likely fed on bacteria present in the biofilm (coating of algae, bacteria and fungi) on submerged rocks and wood of the littoral region of the river. With the regulation of water, the patterns of water-level fluctuations and underwater light regimes have changed resulting in changes in the littoral biofilms in the river system. The biofilms are now much lower in bacterial content than was previously the case, having been replaced with a filamentous algae that is less nutritious for these Snails (Sheldon & Walker 1997). Although these studies referred to the lower Murray River region, it is thought that flow regulation and changes to food supply are likely to similarly have affected River Snails, and caused their decline, throughout the Murray-Darling Basin.
The introduced European Carp Cyprinus carpio may also be a threat to the River Snail. Carp spread throughout the Murray-Darling Basin after they were released into the Murray River near Mildura in 1964. Carp can alter a river environment by destroying aquatic vegetation and increasing the turbidity of water. The Warrego and Paroo Rivers have low levels of water regulation, but Carp appear to have spread into these rivers in the 1970s. Therefore, a factor in the decline of River Snails in these river systems may be changes to the systems caused by the presence of Carp.
Though the Murray-Darling Basin population of the River Snail has not been found recently in its natural environment, it is occasionally found in irrigation pipes. In 1992 scientists became aware of new populations of the subspecies hanleyi existing in an irrigation pipeline near Barmera, South Australia. The River Snails were subsequently identified at one other pipeline in the same area. The pipelines are more than 50 years' old, fully enclosed and more than 2 m below the ground. It is likely that the Snails colonised the pipes after being sucked into the pipes with water intake from the river. The wetted inner surfaces of the pipes provide extensive areas for microbial production and organic accumulations that are a ready food supply for snails. Microbial biomass tends to have a high nutritive value and is known to enhance the growth and fecundity of aquatic snails.
Sheldon & Walker (1993a) and Walker (1996) reported that populations of a number of species of aquatic freshwater molluscs occur in irrigation pipes in the Riverina areas of South Australia. At times, some of these species, including River Snails, occurred in such large numbers that they blocked pipes, pumps and sprinklers and fouled the water when they died from lack of oxygen when the pumps were stopped. In these areas, managers and irrigators have used chemicals, such as chlorine, in an attempt to remove mollusc species from the pipes. There are, however, limits to chemical control, as the pipe water in this region is often used for domestic purposes. Use of chemicals can kill a large number of River Snails, though some survive in areas of pipes that are not flushed and that act as refuges. The Snails can then recolonise the pipes from these refuge areas. Snails can also protect themselves to some degree by sealing themselves within their shells when conditions are harsh. Other measures, like back-flushing (flushing water through the pipes in the opposite direction) are sometimes used, but back-flushing is not effective when the Snails occur in very large numbers.
The Minister noted the Committee's advice that the snail appears to only live within human created structures (pipes, whether irrigation or artificially created habitat). The populations that exist within irrigation systems depend on adequate water flow, ironically, itself dependent on periodic flushing of the pipes.
The Minister concluded that should listing occur, there would be considerable uncertainty about the conservation outcome of such a listing and that it was not at all clear that listing would contribute to the survival of the River Snail.
The current status and the extent of occurrence of the River Snail in irrigation pipelines in the Murray-Darling Basin is not clear as surveys have been limited. In pipelines, usually the innermost pipes are inaccessible and sampling for the Snail can only occur at the outlets.
Currently, subspecies hanleyi appears to be reduced to only one irrigation pipeline in South Australia, from where it nearly disappeared in 1998-1999, and it possibly occurs in a second pipeline. In the future, it is likely to build up in large numbers within the pipelines and may need to be removed by chemicals again. Researchers at the University of Adelaide have sampled throughout other suitable areas in the lower Murray River region of South Australia, including in irrigation pipelines, and have not found the River Snail. In the Remark region of South Australia, there have been limited surveys of irrigation pipes for molluscs, and the River Snail has not been recorded, however, a number of other species of molluscs are known to block irrigation pipes in this area.
Outside South Australia, there appear to have been no surveys for the River Snail in irrigation pipes. Subspecies sublineata has only been recorded from one irrigation pipe in the Darling River catchment over the last 10 years. Its occurrence in the pipe has not been checked recently, and it may no longer occur there.
Overall, there have been sufficient surveys conducted which when considered with the anecdotal reports, support the view that the River Snail is not widespread in irrigation pipes within the Murray-Darling Basin.
The Minister noted the Committee's view that the River Snail is not widespread within the Murray-Darling Basin but also noted that there has been inadequate survey for the species in artificial habitats, such as the irrigation pipes, to determine the extent and abundance of their occupancy.
Currently in South Australia, there are efforts to translocate captive-bred River Snails to the wetlands of the Murray River, but it is not clear if the translocated populations are being kept in captivity or how successful these efforts have been.
From the information currently available, the Murray-Darling Basin population of the River Snail appears to have declined markedly in its geographic distribution, and is believed to be confined to artificial habitat within its original range of occurrence. The snail has recently been recorded in a few irrigation pipelines in the Murray-Darling Basin but population numbers and the full geographical distribution of these subspecies within irrigation pipelines has not yet been determined. However, direct threats to the River Snail in these pipes have been identified. There has been an observed decline in the quality of the species natural habitat and a dramatic decline in the species natural area of occupancy.
Therefore, the species is eligible for listing as critically endangered under this criterion.
The Minister noted the Committee's advice that the species is eligible for listing under this criterion. However, the Minister considered there was sufficient uncertainty about its distribution and abundance and the conservation outcome of such a listing that he was not satisfied it was eligible for listing under the EPBC Act.
There is no evidence available against this criterion.
Therefore, the species is not eligible for listing under this criterion.
There is no evidence available against this criterion.
Therefore, the species is not eligible for listing under this criterion.
There is no evidence available against this criterion.
Therefore, the species is not eligible for listing under this criterion.
The Murray-Darling Basin population of Notopala sublineata (River Snail) was previously believed to have been common in the Murray-Darling Basin but has experienced a decline in range since the 1950s-1970s, and is now considered extinct in its natural habitat. The decline has most likely resulted from a decrease in the quality of suitable habitat, as a result of water regulation and the introduction of the European Carp. It appears that this species has found a substitute habitat in the Murray-Darling Basin in irrigation pipelines. While the River Snail has been reported in a few irrigation pipelines within the Murray-Darling Basin, their extent of occurrence in irrigation pipes is not clear. However, evidence currently available suggests the snail is not widespread within these irrigation pipes. In addition, the geographic distribution of the species is both restricted to a few locations and precarious for the survival of the species. The species is therefore eligible for listing under the EPBC Act.
The Minister noted the Committee's advice that the species is eligible for listing under the EPBC Act. For the reasons noted above, the Minister considered that there was sufficient uncertainty about the nomination that he was not satisfied it was eligible for listing under the EPBC Act.
TSSC recommends that the list referred to in section 178 of the EPBC Act be amended by including in the list of critically endangered category:
Notopala sublineata (Murray-Darling Basin population consisting of N.s. sublineata and N.s. hanleyi)
The Minister has carefully considered the advice of the Threatened Species Scientific Committee and has decided to reject the advice to list the Notopala sublineata (River Snail) as a threatened species under the Environment Protection and Biodiversity Conservation Act 1999 (the Act).