The ‘Conservation translocation handbook for New South Wales threatened freshwater fishes’ (April 2021, PDF) has been released with important recommendations for conservation of nine threatened freshwater fishes in the NSW Murray-Darling Basin catchment. The handbook outlined the threats that freshwater fish face in Australia, such as habitat loss and degradation, invasive species, over-exploitation, pesticides, pollution, water abstraction and flow alteration, and climate change impacts. On top of these threats, the Millenium Drought from 2001 to 2009 and the recent bushfires (2019-2020) have devastated and put immense pressure on native freshwater fish species, mainly due to large flow reductions and habitat destruction. Freshwater fish face an uncertain future in NSW and urgent conservation action is required to protect these species’ survival.
Conservation translocation involves intentional movement and release of fish (or other organisms) for a conservation benefit, and there are two types. Population restoration is one type of translocation, which involves the release of individuals within the species natural range to enhance existing population numbers and diversity, or to reestablish a population where there once was one. Conservation introduction focuses on preventing a species extinction, and involves releasing a species outside its natural range to avoid extinction.
Conservation translocation can improve threatened species persistence and recovery in facing the combined pressures of habitat degradation, changes in water availability and climate change, however it has to be implemented carefully and each species has different requirements.
The handbook is a guide for conservation translocation projects of these freshwater fish species:
- Murray Hardyhead
- Olive Perchlet
- Oxleyan Pygmy Perch
- River Blackfish in the Snowy River
- Round-snout Galaxias
- Short-tail Galaxias
- Southern Purple-spotted Gudgeon
- Southern Pygmy Perch
- Stocky Galaxias
It provides an outline of the current conservation status, threats and what conservation translocation methods should be used for each species based on the latest research. There are several factors that need to be considered in management to ensure the species survival.
- Freshwater habitats are linear, highly connected and dynamic.
- The ecosystems are often impacted by threats (river regulation and uncontrolled introduced species).
- Freshwater species often have many traits that make them vulnerable to extinction and difficult to introduce to a new area (small body size, small home range, limited dispersal, high degree of ecological specialisation).
- Fragmentation of populations has reduced capacity for natural recolonisation.
The Murray Hardyhead is a critically endangered freshwater fish species, endemic to lowland floodplains in the Murray and Murrumbidgee rivers. A combination of river regulation in the 20th century and droughts in recent years has resulted in large declines in population numbers and limited isolated populations. It is predicted that without imminent action, the remaining subpopulations will be lost in the next 10 years. The Murray Hardyhead is restricted to isolated moderately saline wetlands, open water and aquatic vegetation, and primarily feeds on microcrustaceans. Increasing water level and surface area enhances zooplankton abundance, which benefits breeding success, especially during the spawning period from September to March. There is sufficient understanding of the Murray Hardyhead’s life stages to inform appropriate conservation of existing populations. The species can be spawned in ‘ex-situ’ breeding in aquaria, tubs and ponds, however, they do not exhibit reproductive behaviour until water temperature reaches above 24 degrees Celsius.
The Olive Perchlet is recognised as endangered in NSW and critically endangered in South Australia. The species was once widespread all through the north and south catchments of the Murray Darling Basin in NSW, Queensland, South Australia and Victoria, as well as coastal streams in north-eastern NSW and south-eastern Queensland. The impacts of introduced fish, spawning and recruitment restrictions, habitat loss and degradation from cold water pollution and river regulation, have resulted in the species having a patchy, almost absent distribution in the Murray Darling Basin, with populations surviving mainly in coastal Queensland and NSW waterways. Olive Perchlet inhabit shallow, low flow areas of vegetated creeks, wetlands, swamps and rivers. The handbook explains that Olive Perchlet can be successfully maintained and spawned in ponds, however, not in aquaria like other freshwater species.
Oxleyan Pygmy Perch
The Oxleyan Pygmy Perch is recognised as endangered, and is endemic to low-lying coastal plains of southern Queensland and northern NSW, inhabiting slightly acidic, brown stained, well-oxygenated water in slow-flowing pools and backwaters. They can live in a range of waterways, such as coastal streams, river channels, lakes and swamp drainages with sandy-soil. Currently, there are populations spread from Tin Can Bay near Noosa to Richmond River, however, the populations are severely fragmented and in continued decline. The species often can be found in Wallum heath habitats, however, these habitats have been severely impacted by drought conditions and human actions. Conservation and population spawning of this species requires aquaria and cannot be spawned in conservation tubs or ponds.
River Blackfish (population in Snowy River)
The five River Blackfish species are considered endangered in NSW and SA. The handbook had a particular focus on the population of River Blackfish residing in the Snowy River, the only known population in NSW. River Blackfish are non-migratory, have a small home range and mainly undertake nocturnal activity. Research for conservation of the species has found that it can only breed when water temperatures exceed 16 degrees Celsius. The species faces many threats such as habitat degradation, erosion, unseasonal shifts in water temperatures due to river regulation and water releases, increased siltation, introduced species, as well as the impacts of climate change (changes in bushfires, droughts, floods, rising water temperatures). Breeding of the NSW population of River Blackfish in captivity has not been widely researched, so the research into breeding of other Blackfish species has been used to extrapolate findings to hypothesise how the NSW Snowy River population would react in similar conditions. As the NSW population generally lives in higher altitudes and cooler streams than other populations, it is unknown exactly how they will respond, and may require different breeding conditions.
Galaxias species (Round-snout, Short-tail, and Stocky Galaxias)
The Round-snout Galaxias is recognised as internationally endangered, and threatened in Victoria. Its range is limited to dispersed subcatchments of the Snowy, Genoa and Cann Rivers in NSW and Victoria. Similarly, the critically endangered Short-tail Galaxias has a very restricted range, located in three creeks in the upper reaches of the Tuross River catchment in southern NSW. The Stocky Galaxias is also critically endangered, and found only in a three kilometre reach of shallow alpine creek in the upper Murrumbidgee catchment.
These three species face similar threats to their survival, such as declining habitat range from increased sedimentation and reduced riparian vegetation and water quality from agriculture and forestry, climate change impacts (such as bushfire, drought and floods), rising water temperatures, drying waterways, invasive species, and species population fragmentation (which reduces genetic diversity). The handbook explains that mimicking environmental conditions in an aquarium during spawning seasons, cooler temperatures and intensive management to ensure reproductive success are essential to breeding in captivity, however, the studies also found the fish to have a heightened aggressive nature compared to when they are in the wild.
Southern Purple-spotted Gudgeon
The Southern Purple-spotted Gudgeon is critically endangered in SA, endangered in NSW and threatened in Victoria. The population was historically widespread across southern Queensland and northern NSW and reached into Victoria, however its presence in the southern Murray Darling Basin has declined significantly. The species has not been known to be seen in southern NSW or in South Australia since the 1970s or in Victoria since the 1990s. Translocation and releases of the species have had varying successes in the Murray Darling Basin, and more research is required to improve species uptake in a habitat. Overall, the Southern Purple-spotted Gudgeon prefers small streams and wetlands, however the species has been in decline due to intensive flow regulation and diversions and competition with invasive species. The species is responding well to spawning in captivity. Interestingly, the handbook recommends increasing food abundance, instead of temperature variables to stimulate spawning.
Southern Pygmy Perch
The Southern Pygmy Perch is critically endangered in South Australia, endangered in NSW and threatened in Victoria. Where it was once found widely throughout the entire southern end of the Murray Darling Basin, the accumulative consequences of European settlement, such as habitat and wetland degradation, river regulation, cold water pollution, and introduced species, have resulted in a fragmented population. There are now 14 genetically distinct subpopulations of the species as a result of the fragmented populations in south-eastern Australia. Translocation to improve the species survival and increase genetic diversity is now essential, however, it is more complicated as some species are unlikely to breed with others, with reintroduction attempts having mixed successes. The species naturally occurs in still or slow-flowing streams with abundant aquatic vegetation, yet knowledge gaps still exist about its biology and ecology requirements to improve breeding and translocation success. The handbook suggests that a water temperature of 21 degrees Celsius was often the species spawning cue, and they were not reproductively successful in aquariums, compared to a pond.
These freshwater species face a precarious future, however, this handbook is an important step in improving their future survivability. This handbook can guide future translocation and breeding projects for these specific fish, and inspire further studies.
Feature image: Murray River. Photo credit: South Australian Government.