DWARF GALAXIAS around MELBOURNE, GOING, GOING, NEARLY GONE.
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P. J. Unmack & G. J. Paras
Dwarf galaxias (Galaxiella pusilla) is one of the smallest members of the family Galaxiidae. Its distribution includes coastal Victoria from the Mitchell River to the drains in the South-East of South Australia, North-Western Tasmania and Flinders Island in Bass Strait. It is an attractive aquarium fish (at least when it was legal to keep them in Victoria) which featured in the first issue of Fishes of Sahul. Males are quite spectacular in breeding colouration, they have a bright red/orange line down their side and two less prominent black lines either side of it. Females are silver-grey all over. Maximum size is 45 mm T.L. for females and 35 mm T.L. for males.
Why have they declined?
Dwarf galaxias was once widespread throughout southern Victoria in slow flowing creeks, lagoons, swamps and seasonally ephemeral habitats. The decline is thought to be caused by habitat destruction and dambusia (Gambusia holbrooki, otherwise unfortunately known as mosquitofish). Because of its decline dwarf galaxias is listed as a protected taxa under the Fauna and Flora Guarantee Act of Victoria (FFG). Unfortunately, under the FFG the collection and keeping of dwarf galaxias in Victoria is prohibited. Despite this criticism, the FFG is without doubt a landmark of legislation that is years ahead of other conservation law in Australia.
Changes in local distribution
Prior to European settlement dwarf galaxias was probably common in most creeks flowing into Port Phillip Bay. By 1993 only four populations remained, as of June 1994 three exist and by the end of 1995 there may only be two left in the Port Phillip Bay drainage. Of the last four populations, two are found in Dandenong Valley and two on the Mornington Peninsula, one in Devil Bend Creek, the other in Tuerong Creek. [At a few localities dwarf galaxias are occasionally collected amongst large numbers of dambusia. We do not consider these to be viable breeding populations due to their small size and a lack of evidence that permanent populations exist. We also feel these individuals may simply be dispersants from other populations, thus only representing transitory populations].
Status of populations
At Tuerong Creek it was known dambusia occurred in the lower reaches with dwarf galaxias in the upper reaches. During 1993 it was discovered that dambusia had colonised the upper section containing dwarf galaxias. Native Fish Australia (Victorian Branch) (a conservation group dedicated to saving Australia's larger native fish as well as having considerable interest in smaller natives) contacted the local region of the Victorian Department of Conservation and Natural Resources with a proposal to translocate remaining dwarf galaxias to nearby dambusia free constructed wetlands where populations could have established. Unfortunately there was little response in terms of action by the department and they are now extinct in this creek.
Devil Bend Creek
In Devil Bend Creek dambusia occur in the lower reaches and dwarf galaxias occur in the upper reaches. Here, dambusia is slowly but surely moving upstream and eliminating dwarf galaxias. As there are no known physical barriers to stop them expanding their range upstream the gambusia pose a serious threat to this dwarf galaxias population. There is no information on how far upstream dambusia have so far colonised. This population urgently needs investigation. Consideration should be given to the construction of barriers to prevent dambusia progressing further upstream. Refuge populations need to be established.
The most significant Dandenong Valley population of dwarf galaxias occurs in Tirhatuan Swamp is on a reserve managed by Melbourne Water. Tirhatuan Swamp dries out in most summers (although it hasn't done this in the last two years due to wetter summer conditions than usual), when it does, dwarf galaxias presumably aestivate in yabby or crayfish holes, (similar to hibernation but occurring during summer rather than winter). Dambusia first invaded the area in the mid 1980s when a drain (which also contained dwarf galaxias) near Tirhatuan Swamp was colonised during major floods in Dandenong Creek. As part of Melbourne Water's dwarf galaxias enhancement program an additional wetland was constructed between Tirhatuan Swamp and the drain to increase the dwarf galaxias population. By the end of the first winter dambusia had colonised the new wetland (1990). No dambusia were present in Tirhatuan Swamp at least until mid 1993. Presumably they gained access during the wettest December ever recorded in Melbourne as dambusia were detected during January 1994. Melbourne Water had plans to remove dambusia at the beginning of their enhancement works but this was never undertaken. Attempts are currently being made to relocate sufficient numbers of dwarf galaxias from Tirhatuan Swamp to La Trobe University Wildlife Reserve to establish refuge populations. Dambusia must be removed from surrounding habitats and the co-existing population needs to be monitored to determine if dwarf galaxias survive until the swamp next dries out and kills dambusia. If the population disappears before Tirhatuan Swamp dries out then refuge populations, (if successful) can be used to re-establish dwarf galaxias once dambusia have been eliminated.
Another very small population exists in a drain flowing into a tributary of Dandenong Creek. Fortunately, dambusia are not present nearby. A major threat is poor quality runoff from urban areas including a major road and suburb less than a kilometer upstream. The drain is on land owned by Melbourne Water and is at least safe from adverse site development. Hopefully in the near future it will be enhanced and protected to the benefit of dwarf galaxias.
Despite dwarf galaxias being common in a small corner of Tasmania (where dambusia is not present) and South-Eastern South Australia (where there aren't many dambusia yet) they continue to steadily disappear from Victoria. We may be loosing distinct subspecies that are presently unrecognised, (dwarf galaxias was once considered to consist of three subspecies, one on the mainland, Flinders Island and Tasmania). Genetic studies to determine the distinctiveness of various populations are sorely needed. Further populations must not be allowed to knowingly disappear, action must be taken to safeguard and expand them. If nobody does dwarf galaxias will be going, going, gone.