Euastacus gumar (a freshwater crayfish)
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
Euastacus gumar (a freshwater crayfish)
2. National Context
Euastacus gumar was first described in 1997, after being collected at two sites on Gorge Creek (a tributary of Peacock Creek) on the Richmond Range, north-eastern New South Wales. In 2000, a limited study of the area surrounding the original collection site found the species in small headwater streams in the Peacock, Tunglebung and northern Culmaran Creek catchments, and suggested that this crayfish was restricted to these catchments. All sites where the species is known to occur are above 320 m. Four of the of the five subpopulations recorded are in the Richmond River National Park. The fifth subpopulation occurs in state forest.
The species is not listed under the EPBC Act, nor is it listed as threatened under New South Wales legislation.
3. How judged by TSSC in relation to the EPBC Act criteria
TSSC judges the species not to be eligible for listing under the EPBC Act. The justification against the criteria is as follows:
Criterion 1 - Decline in numbers
There is no quantitative data available against this criterion. Therefore, the species is not eligible for listing as threatened under this criterion.
Criterion 2 - Geographic distribution
From what is currently known, Euastacus gumar appears to have a restricted distribution that is fragmented. Since formal description there has been only one study on the species, which is unpublished.
Surveys to date have focussed on habitat in streams, or near the edges of streams, in a limited number of areas. Surveys have found this crayfish in five fragmented subpopulations in small headwater streams in the Peacock, Tunglebung and northern Culmaran Creek catchments at elevations above 320 m. Four of the five subpopulations are afforded some protection through national park reservation. Few surveys have been done to the north and east of areas where this species is known to occur, and none have been done to the south. It has been suggested that there are few suitable places for the species to the south and east, and that it is displaced by another crayfish, Euastacus sulcatus, to the north. However more data is required to support this suggestion. Surveys to date have also concentrated on habitat in watercourses. This crayfish builds elaborate burrows on banks of streams. Studies on two other small Euastacus species show these species use extensive burrow systems away from permanent watercourses with very limited movement from these burrows, and with significant numbers of adults occurring only briefly in watercourses. Further surveying is needed to ascertain whether Euastacus gumar uses habitat away from watercourses in a similar way. Sampling to date has been carried out during the daytime. As this crayfish is only active at night, daytime sampling may have overlooked the presence of the species at some sites. At this stage, more surveys and research are needed on distribution and habitat before there is adequate information to evaluate the complete distribution of this crayfish.
The estimated extent of occurrence, based on the known localities of the subpopulations, is 28.72 km2. The extent of occurrence, based on potential habitat within the three catchments where the species is known to occur, could be as high as 106.32 km2. The area of occupancy may undergo extreme fluctuations during the dry season when the habitat available to the species is greatly reduced compared to that available at other times. But further data is needed to test this possibility. No threatening processes affecting the species have been clearly identified. There is an unsupported claim that the introduced crayfish Cherax destructor, found in Richmond Range National Park in the lower reaches on one stream inhabited by Euastacus gumar, may pose a threat.
The TSSC considers that, from the information collected so far, Euastacus gumar appears to have a fragmented and restricted distribution, but more surveys and research are needed before a reasonable assessment can be made of its distribution. There is no evidence that there has been any change in range in the past, and none is predicted in the future. There are no known threatening processes. Therefore, the species is not eligible for listing under this criterion.
Criterion 3 - Population size and decline in numbers or distribution
Although there is some quantitative data available for population size for Euastacus gumar, see Criterion 4, there is no evidence of decline in numbers or distribution. No threatening processes affecting the species have been clearly identified. There is an unsupported claim that the introduced crayfish Cherax destructor, found in Richmond Range National Park in the lower reaches on one stream inhabited by Euastacus gumar, may be a threat.
Therefore, the species is not eligible for listing as threatened under this criterion.
Criterion 4 - Population size
It has been estimated that the total number of mature adults of Euastacus gumar is 455, occurring in five fragmented subpopulations. However since formal description there has been only one study on the species, which is unpublished.
Population details to date are based on sampling once for 4 hours along a 200 m section of stream and finding one female with eggs. The results were then extended to estimate the population over the known distribution. There are a number of problems with the method used, in particular it is not clear how representative this site is of the habitat over the known distribution, and extrapolating from the finding of one female with eggs to produce an estimate of mature adults may not provide a true picture. With regard to the latter problem, the annual cycle of breeding and behaviour of this crayfish does not seem to be known. If sampling was done at a time when few females had eggs, then the total number of mature adults could be greatly underestimated. In addition, the population estimate is based only on the known distribution. As discussed above, further research is needed before a reasonable assessment of distribution is made.
Therefore, the species is not eligible for listing under this criterion.
Criterion 5 - Probability of extinction in the wild
There is no quantitative data available against this criterion.
Since formal description there has been only one study on this species of crayfish, which is unpublished. This study indicates that the species may have a restricted distribution. However, four of the five populations occur in national parks, and no threatening processes have been clearly identified at this stage. There is no indication that the species has undergone any past fluctuations or declines in range. Additional information would be required to support any claims against the criteria.
TSSC recommends that the species Euastacus gumar (a freshwater crayfish) is not eligible for inclusion in the list referred to in section 178 of the EPBC Act.