The distribution and abundance of two endangered fish species in the NSW Upper Murray Catchment.
Gilligan D, Rodgers M, McGarry T, Asmus M and Pearce L (2010) The distribution and abundance of two endangered fish species in the NSW Upper Murray Catchment. Final report to the Murray Catchment Management Authority and Murray-Darling Basin Authority. Industry & Investment NSW – Fisheries Final Report Series No. 127. Cronulla, NSW, Australia. 34pp.
Although important populations of endangered Macquarie perch and southern pygmy perch are known to exist within the Upper Murray Catchment, no information is available on the current extent or relative abundance of the isolated remnant populations. The Murray Catchment Management Authority (CMA) provided funding to undertake surveys and define the range and relative abundance of these species in the two waterways in the catchment (Mannus Creek and Coppabella Creek). Only a single adult Macquarie perch was captured in Mannus Creek, at the downstream boundary of Bogandyera Nature Reserve, 4.3 km downstream of the only other recent verified record of Macquarie perch in the entire NSW portion of the Upper Murray catchment. Aquatic habitat conditions observed throughout the lower portion of the nature reserve remain relatively undisturbed and it is probable that Macquarie perch are present throughout a 9 km reach between a waterfall and agricultural land. This population of Macquarie perch is in need of urgent conservation action including: habitat rehabilitation activities downstream of Bogandyera Nature Reserve to allow for expansion of the populations distribution; pest fish control; provision of targeted environmental flows to encourage recruitment; and the introduction of individuals from another Murray catchment population to reduce reverse inbreeding depression and maintain genetic variation. In contrast, Southern pygmy perch were abundant and widespread in Coppabella Creek. Under normal climatic conditions, they are likely to occupy up to 73 km of waterways. However, because of the drought, they have been restricted to a 23 km stretch of Coppabella Creek. Two natural and two artificial fish passage barriers on Coppabella Creek exclude common carp, redfin perch and eastern mosquitofish from a large proportion waterway occupied by southern pygmy perch.
Since December 2006, Industry & Investment NSW has been aware that the reaches of Coppabella Creek occupied by Southern pygmy perch have been substantially drought affected, with the creek drying to isolated small and shallow pools. Industry & Investment NSW undertook an emergency fish rescue of southern pygmy perch from Coppabella Creek in January/February 2007, removing 122 individuals from three drying pools. These were released in February 2008. However persistent low rainfall throughout 2008 resulted in even drier conditions by February 2009. Industry & Investment NSW obtained funding from the Murray Darling Basin Authority for a second emergency drought response. Approximately 2,000 southern pygmy perch were removed from drying pools and transferred to the Narrandera Fisheries Centre and a facility at Tumut. Follow-up surveillance determined that these pools dried shortly after the fish were rescued.
To aid in development of a longer-term drought management strategy for the population, the Murray CMA provided funds to map the location and depth of remnant pools within Coppabella Creek. Despite a large number of small shallow (< 0.5 m) pools prone to drought impacts, there were a reasonable number of pools greater than 1 m deep which are sufficient to ensure the persistence of the remnant population during drought. Although many individuals will perish as the number of shallow remnant pools dry out, the population as a whole is not as prone to drought impacts as was perceived. To ensure the long-term persistence of the population, ongoing management should protect the habitat quality of the deepest and therefore most permanent remnant pools and maintain the exclusion of alien pest fish at the natural and artificial barriers in the stream. Conservation actions required to conserve the Coppabella Creek population of southern pygmy perch include: maintaining or enhancing an existing weir to maintain ongoing exclusion of common carp, redfin perch and eastern gambusia and promoting the retention and rehabilitation of aquatic vegetation through the exclusion of cattle; re-planting of aquatic plants in those pools were they are absent; willow removal; and controlled re-growth of native riparian vegetation to limit the amount of shading of the creek.
The southern pygmy perch rescued in February 2009 have bred over the spring/summer period whilst in captivity. It is anticipated that around 5,000 individuals are now available for release. Given that our findings suggest that the Coppabella Creek population is resilient to drought, it is not a necessity that the captive fish be returned to their point of capture when drought conditions ease. We propose that the Murray CMA identify a short list of waterways within the Murray CMA area that have few pest fish and abundant aquatic vegetation. Industry & Investment NSW can then identify the best potential release locations and undertake releases of the captive fish. The creation of additional new Southern pygmy perch populations within the catchment will provide insurance against the catastrophic loss of either of the two remaining populations in the Murray CMA area in Coppabella Creek and Billabong Creek.