case studies

The Australian mountain pygmy possum (Burramys parvus) is a threatened marsupial whose range is limited to the alpine regions of Australia – a very small range indeed!  One population at Mt. Buller, discovered in 1996, is critically endangered. It has experienced a decline similar to a population collapse, caused by feral predators and habitat destruction. What’s more, in by the early 2000s, the genetic diversity of this population had reached a very low ebb. This due to its fragmentation...

The Australian mountain pygmy possum (Burramys parvus) is a threatened marsupial whose range is limited to the alpine regions of Australia – a very small range indeed!  One population at Mt. Buller, discovered in 1996, is critically endangered. It has experienced a decline similar to a population collapse, caused by feral predators and habitat destruction. What’s more, in by the early 2000s, the genetic diversity of this population had reached a very low ebb. This due to its fragmentation from other pygmy possum populations in the alpine region over 20,000 years ago. Research from cesar has shown that genetic rescue has helped increase this endangered species population and its genetic diversity.

Why use genetic translocations?

There is a growing interest in using genetic translocations to recover small populations of threatened species. This has the potential to increase gene flow in a population, resulting in higher adaptability, greater genetic diversity and an overall increase in population size.

What did cesar do?

In the spring of 2011 scientists at cesar translocated 6 healthy and genetically diverse pygmy possum males from a central alpine population to the endangered population at Mt. Buller. Annual live trappings, using Elliot type A live capture traps were used to assess changes in the Mt. Buller population size. 

Were the translocations a success?

Trapping data collected in the years after the translocations found that hybrid males were larger than resident males and hybrid females had 4 pouch young compared to less in resident females. Furthermore, overall fitness and longevity in hybrids was greater than it was in non-hybrids.

In 2015, 4 years after the translocations, the Mt. Buller population had increased by ~100 individuals. In 2011 the pygmy possum population at Mt. Buller was only ~55 individuals. However, it must be noted that prior to the translocations, from 2008 to 2011, the Mt. Buller population had increased by ~40 individuals. This is likely as a result of an environmental improvement programme that that had been implemented in the Mt. Buller region, involving habitat restoration, predator control and environmental protection.

While environmental improvements likely lead to a small initial increase in population size at Mt. Buller, the further rapid increase in size is likely to have occurred as a result of genetic improvements from the translocations. Especially when similar environmental improvement programmes in the central alpine region have not resulted in the population increases seen in the Mt. Buller region.

Genetic rescue could save other threatened species

A diverse gene pool is crucial for population adaptation in the face of adverse conditions, such as changing habitats, and disease. cesar is a pioneer in use of genetic rescue techniques to build resilience in threatened populations. Our Mt. Buller Mountain Pygmy Possum work has shown that applying genetic rescue methodology further increased the population of mountain pygmy possum in the Mt. Buller region after threatening processes such as habitat loss, predation and anthropogenic activity had been mitigated. The genetic diversity of mountain pygmy possum ­has increased along with population size as a result of the introductions. A large number of other species could potentially benefit from genetic rescue because many threatened species exist as small isolated populations lacking genetic variation alongside larger populations with higher levels of genetic variation.

The eastern barred bandicoot (Perameles gunnii) is a small marsupial found in south eastern Australia. It is a highly prolific animal, producing up to 5 litters a year with up to 3 young per litter – busy bandicoots! Despite this, the species is listed as vulnerable. The species once had a range from Melbourne, across western Victoria all the way to south eastern South Australia. However, the introduction of the red fox to Australia has caused the species’...

The eastern barred bandicoot (Perameles gunnii) is a small marsupial found in south eastern Australia. It is a highly prolific animal, producing up to 5 litters a year with up to 3 young per litter – busy bandicoots! Despite this, the species is listed as vulnerable. The species once had a range from Melbourne, across western Victoria all the way to south eastern South Australia. However, the introduction of the red fox to Australia has caused the species’ decline. It has been maintained through captive breeding programmes and reintroductions since 1988. Today in Victoria, there are three Eastern Barred Bandicoot populations protected by fox-proof fences, and two Tasmanian island populations. However, research from cesar has shown that the genetic fitness of the Victorian eastern barred bandicoot is in a progressive state of erosion.

Genetic diversity in captive rearing programmes

Understanding the impacts of captive rearing on genetic diversity are crucial to the success of reintroduction programmes. If genetic diversity is lost in a captive breeding programme, it can lead to reintroduced populations that are less adaptable to the changing environment.

cesar conducted an assessment of the genetic diversity within the eastern barred bandicoot captive breeding programme. The genetic variation of multiple populations of eastern barred bandicoot were assessed, including two contemporary populations from reintroduction sites in Victoria, two Tasmanian populations from both North and South of the Island and contemporary and historic populations from the captive breeding sites at Zoos Victoria.  Hair and tissue samples of were analysed to determine the allelic richness of these populations.

What was discovered?

It was discovered that although the founder population of the 1988 captive breeding programme was 40 individuals it is likely that the actual number of bandicoots that contributed to breeding was less than 19. The effective population has also remained below 20 individuals per generation for the duration of the programme. This is an inadequate number of individuals to prevent the loss of genetic diversity. Small populations are known to be prone to the accumulation of deleterious alleles that can become fixed through inbreeding and genetic drift which can limit their capacity to survive.

What does this mean for the future of the eastern barred bandicoot?

Victorian eastern barred bandicoots are losing genetic diversity due to a small effective population size in the captive breeding programme. When a population is very small, then expands through breeding, the genetic makeup of that population remains limited. Unless this decline is mediated it will have consequences for the success of future captive breeding, reintroduction translocations, and could see the extinction of the Victorian eastern barred bandicoot.

What can be done?

Consideration needs to be given to crossing the Tasmanian barred bandicoots with the Victorian populations. We have discovered that the Tasmanian bandicoots are more genetically diverse than those in Victoria and have successfully translocated some Tasmanian male bandicoots to Mt Rothwell in Victoria. In 2019 Eastern Barred Bandicoots from this Mount Rothwell population, which is the largest in Victoria with over 600 bandicoots, will be released at a new fox-free property in Tiverton, Western Victoria. To ensure the success of the release, it will be important for these bandicoots to be as genetically diverse as possible. For this purpose, Dr Weeks and his team are crowdfunding to bring 15 male Tasmanian Eastern Barred Bandicoots to Mount Rothwell. You can read about this here. This genetic translocation could increase gene flow in Victorian eastern barred bandicoot populations, resulting in higher adaptability, greater genetic diversity and an overall increase in population size.

Melbourne Water have developed an environmental management programme for Dandenong Valley and have enlisted the help of *cesar *to assist with the biodiversity component of this programme. A reintroduction program for the small fish species, dwarf galaxias, into sites in Dandenong Valley has been implemented by Melbourne Water with *cesar’s* help. Another small fish that is locally extinct in the Dandenong valley, the Yarra pygmy perch (Nannoperca obscura), has also been identified for reintroduction to rehabilitated sites in the...

Melbourne Water have developed an environmental management programme for Dandenong Valley and have enlisted the help of cesar to assist with the biodiversity component of this programme. A reintroduction program for the small fish species, dwarf galaxias, into sites in Dandenong Valley has been implemented by Melbourne Water with cesar’s help. Another small fish that is locally extinct in the Dandenong valley, the Yarra pygmy perch (Nannoperca obscura), has also been identified for reintroduction to rehabilitated sites in the valley.

A small fish with a small, threatened population

The Yarra pygmy perch is a small freshwater fish <75mm in length. It is found in streams, rivers and lakes that are slow flowing and is often found near aquatic plants. European settlement has resulted in a large decline in Yarra pygmy perch populations as a result of habitat loss and interactions with invasive species. The fish is now listed as a vulnerable. Climate change has also furthered this population decline with recent drought across south eastern Australia causing the local extinction of the fish in the lower Murray river and in parts of Victoria and South Australia.

Genetic analysis to the rescue

Melbourne Water plans to implement a reintroduction strategy for the Yarra pygmy perch, similar to the programme created for Dwarf galaxias. The Yarra pygmy perch reintroduction programme aims to establish populations in a network of interconnected habitats and rehabilitated sites along the Dandenong flood plain. In order for this reintroduction programme to be successful, cesar conducted genetic analyses of existing pygmy perch populations and developed a fish stocking strategy for the Dandenong Valley that maximizes genetic diversity, adaptability and resilience within the region.

Yarra pygmy perch fin clips were taken over the course of a week by the Arthur Rylah Institute of Environmental Research in June 2014. The sampling focused on previously known sites of the fish in the Maribyrnong and the Barwon catchment. A variety of sampling methods were used, including electrofishing, bait traps and dip netting. 152 samples were taken and 148 of these samples were successfully genotyped.

What was discovered?

It was found that there are large differences in genetic diversity between the sampled populations from each catchment. A genetically diverse founder population would have to be bred in order for the pygmy perch reintroductions to the Dandenong valley to be successful. cesar has recommended to Melbourne Water that translocations of genetically diverse populations of Yarra pygmy perch from sites in the Maribyrnong and Barwon catchments to a suitable site in the Dandenong Valley would ensure the creation of a genetically diverse founder population. This is important if the reintroductions are going to be a success as it would increase the populations overall genetic diversity and adaptability.

Breeding a founder population

An ideal scenario would be to collect and breed a founder population made up of 200 - 400 Yarra pygmy perches from 4 sites in both the Maribyrnong and Barwon catchments. This population, under ideal circumstances, would have the potential to grow in excess of 4000 individuals in one season. This would allow for the reintroduction of Yarra pygmy perch to multiple sites in Dandenong valley. The Yarra pygmy perch should be reintroduced to 3 or 4 sites in 4 core locations in the Dandenong valley. This would ensure the short-term persistence of the species at each site and the long-term persistence of the species in the Valley.

Monitoring the progress

Following the reintroduction of pygmy perch populations to the various sites, a continuous monitoring process to determine the populations size and genetic diversity and to help mitigate any threats to the populations viability will be a crucial factor in the populations survival.

Through the use of genetic analysis cesar has helped generate a Yarra pygmy perch stocking strategy that could be vital in aiding the recovery of the small fish’s population.