To translocate western ringtail possums or not
For about a decade Busselton/Dunsborough’s growth and development rate and the associated intensive land clearing in the main areas of occupancy for western ringtail possums dictated translocation as the preferred management option.
However, already in 2002 senior researchers had doubts that it could be the most appropriate course of action in all circumstances as it had not been proven to produce conservation benefits for the species. Its use was recommended only when alternative strategies had been adequately assessed and ruled out and if there was no other viable option. In-situ conservation was clearly regarded as the superior alternative. (De Tores, 2002)
The first and so far only investigation into the viability and appropriateness of translocation of western ringtails was conducted between 2006 and 2008 and only 9 animals out of 68 lived for longer than 200 days after being translocated - a clearly unacceptable result. Modelling on the basis of the results showed that out of every 100 animals translocated only 9-16 could be expected to survive to the end of their first year. After 2 years only 1.6 animals per 100 translocated individuals would still be alive. (Clarke, 2011)
According to the EPBC Act Policy Statement 3.10 “translocation does not reduce the impact of an action, and is not considered to be a mitigation or offset measure as it is unlikely to result in a positive conservation outcome for the species.” (DEWHA, 2009)
However, due to our political reality translocations will remain a management strategy.
Species that are listed because of their limited geographic range and their low numbers are considered most likely to benefit from the establishment of new populations through translocation, which would mean, that it could actually benefit our ringtails.
However, site selection within the limited conservation estate where species can thrive is not only already extremely hard, conditions could also change under human-induced climate change and render benefits short-term (e.g. translocations to the still cooler southern coast of WA).
IUCN reintroduction guidelines (IUCN, 2013) also clearly state that threats at a site of former occupancy must be identified and either removed or be considerably reduced before translocations. As the habitat was clearly inadequate or no local extinction would have ensued, it needs to have recovered naturally (e.g. after fire) or be actively restored. In our changing climate, mere floristic characteristics (e.g. presence of Agonis flexuosa) might not provide enough evidence that a patch is suitable habitat.
Control of predators is probably the most common form of habitat restoration. However, eradication is unrealistic and long-term predator reduction programs are costly and seem only effective when conducted on a landscape scale.
In the case of ringtail translocation 1080-baiting for fox control was expected to result in improved survivorship, as seemed to happen in the initial translocations in the 1990s (Clarke, 2011, de Tores et al, 1998). Increased cat predation when fox density was reduced (mesopredator release) ended this hope and all other causal factors of low survivorship, in particular habitat values such as food quality, could not be manipulated. Animals being weak and malnourished due to unsuitable habitat might have played a major role in the advent of increased predation.
Also, cat predation was not the only increased threat: one endangered species (carpet pythons) was eating the other (ringtail possums).
Dispersal patterns of the translocated ringtails also hinted at fairly low carrying capacity of the release sites (Clarke, 2011), which indicates suboptimal habitat quality. Small populations, particularly when under predation stress, are highly vulnerable to extinction in the long term.
The alternative to translocation would be in-situ conservation. If the scope of a proposed development is small and the ringtail population size is low and there is opportunity for dispersal in the surrounding areas, shepherding the animals away from the affected vegetation during clearing can be achieved through the service of a ‘possum spotter’.
If the scope of the development and/or the population size is large and dispersal opportunities are limited, population density could end up unsustainably high in the retained habitat. Over-browsing of vegetation or forced dispersal of residents into unsuitable habitat could be the consequence. (De Tores, 2009)
The only well documented case for a mix of translocation and in-situ conservation is the Busselton Hospital Redevelopment. 30 animals were translocated into a predator-proof fenced area – but in a non-peppermint region – and survival was very low. A recent survey (anecdotal) indicated that some animals had survived and bred but the figure for current sightings was extremely low (3 sightings).
The retained animals at the development site however have not only bounced back to pre-translocation numbers but the figure in October 15 has been higher than ever.
Anecdotal evidence also suggests that ringtail numbers have stayed high but sustainable at a development (Acacia Caravan Park now Aqua Resort) without any translocations.
Discussion:
There seems to be no doubt whatsoever that good habitat areas can sustain viable population numbers even with development happening. However, the development needs to be sensitively done. A major issue seems to be that measures that are tooted as mitigating – such as the presence of a possum spotter or monitoring for a couple of years – do not truly soften the impact on the ringtail population. A possum spotter can guide animals out of harm’s way on the day of the clearing but if food and shelter resources are too severely reduced, the animals often enough end up as road kill while trying to find new habitat to stay in.
Monitoring would at least provide some insights into the problem and inform management about success rates or otherwise.
The lack of monitoring and reporting is clearly a major weakness of any conservation effort – with or without translocation. It seems completely dependent on funds provided by development proponents and it usually ceases when the obligations of the developer have been met.
The level of monitoring should be set during the planning process and it needs to be adequately resourced with good reporting in place. Only prompt and effective communication and pre-set rules how to interfere if anything goes wrong, can safeguard longer term successes.
The reasons for the sudden and rapid decline of the (translocated) Leschenault Peninsula population and for 2 years even the fact of the crash itself stayed unknown due to lack of regular monitoring (De Tores et al, 2004).
Not a single one of the 5 major translocation sites have retained significant populations – most are down to almost undetectable numbers for various reasons.
