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Is this threatened species in decline? The devil’s in the detail

Data appears to show populations of Tasmanian devils have stabilised. Biologist Allen Greer asks why you’re not hearing that from the state government or advocates of “saving” the devil.

If you’ve heard about the Tasmanian devil, you probably know that a transmissible tumour, devil facial tumour disease (DFTD), threatens the species with extinction. But you probably don’t know that for the last five years the devil population in the wild has stabilised, albeit at levels about 80 to 85% lower than pre-disease times.

The reason you wouldn’t know this is the data is in a graph in a Tasmanian government report, and the result has not been mentioned in any of the government’s public information sites. It is most notably absent from the Save the Tasmanian Devil Program’s website, which describes itself as “your primary source of authoritative, up to date information on Devil Facial Tumour Disease. We will keep you informed of what is being done to save the Tasmanian Devil and how you can help.”

The graph is a plot of the number of devils sighted in the state government’s annual state-wide spotlighting surveys along 172-odd 10-kilometre road sections between 1985 and 2012. Spotlight Summary Report 2012-13 reveals a decline in devils beginning with the appearance of DFTD in 1996 and then a levelling off beginning in 2008 and continuing to the present …

Raw counts of additional mammal species observed during the Annual Statewide Spotlight Surveys, mainland Tasmania (2002-2012)

This survey and the data it gathers represent the longest and geographically broadest continual monitoring of the devil population available. The data is robust and used routinely in other research articles on the devil.

That something is up is also suggested by a single passing comment in the media. A 2013 New Year’s Day newspaper report said in some areas the devil population had “unexpectedly stabilised”. This information could have only come from within the STDP. The apparent stabilisation also now explains why, since early 2010, official statements of the decline in overall devil numbers have remained unchanged at 80-85%.

The STDP maintains at least three “long-term monitoring sites” that might or might not be informative as to the status of the devil populations. The names and locations of the sites are not in the public domain, so it is not clear if they are new sites, in which case they would be relatively uninformative, or old sites for which population estimates were available up until 2007 or 2008, depending on the site, but then stopped. Toward the end, surveys at these old sites were providing the first indications the populations might be stabilising. In fact, the populations at some of the old sites, such as those on Forestier/Tasman and Freycinet peninsulas, are slated for removal and replacement, thus eliminating their value in providing insight into the long-term progression of DFTD.

Despite the recently published spotlight survey results indicating a stabilising of the population as a whole, the STDP wrote on its website as recently as September 2013: “There is no evidence to date of the decline in devils stopping …”

Why have the Tasmanian government, the STDP and devil researchers all been silent on this potentially important development in the progress of the disease? One can only speculate. But the fact that the entire STDP is based on a story of an inexorable decline in the devil population, any news the decline may have stopped could jeopardise the STDP’s funding base. This is especially the case with funding from private donations, solicited nationally through the Save the Tasmanian Devil Appeal and the STDP website, and internationally through the recent initiative of sending “ambassador” devils to overseas zoos.

If the devil can save itself, what need is there for the Save the Devil industry?

*Dr Greer has a PhD in biology, and was formerly a principal research scientist at the Australian Museum. He is unaffiliated with any institution.

  • 1
    Bo Gainsbourg
    Posted Wednesday, 18 December 2013 at 2:00 pm | Permalink

    This article is a bit weak. Assuming a halt, even temporary in what is obviously a catastrophic decline in a species, without data. Which is what the author appears to be doing, is “courageous” in the Jim Hacker meaning of the word to say the least. The ‘industry’ meme thrown at conservation activities from time to time is usually a cheap shot, and without more data appears to be the same here. When Devils are starting to re-expand and occupy old habitat in more normal numbers might be time to relax the caution. But it would be dumb to do so on the face of the data, and lack of it, presented in this article.

  • 2
    Posted Wednesday, 18 December 2013 at 2:27 pm | Permalink

    It appears the author hasn’t been hesitant in speculating despite the acknowledged lack of data. Nothing like a good conspiracy theory to get the fingers tapping. “If the devil can save itself”? Well perhaps it’s not so much the hardiness of the devils that might be stopping the decline, but the continuing support of STDP and others?

  • 3
    Posted Wednesday, 18 December 2013 at 5:30 pm | Permalink

    It must be silly season. Nearly 2000 km of spotlight survey consistently finds a bare handful of devils (<20), and that's somehow good news? That's not the Tasmania I remember.

  • 4
    Posted Wednesday, 18 December 2013 at 9:32 pm | Permalink

    Thanks for the information free article, Crikey - how’d you ever get the reputation as a rumour-rag?

    Have devil populations stabilised? The only information we’re given is a conspiratorial reading of a website (it hasn’t been updated, ergo, Illuminati!), and a low-effort survey of an entire state. Here’s a clue: “There is no evidence to date of the decline in devils stopping” is a statistical statement. It depends on the power and structure of the survey method and the natural variation in the population.

    For example, aggregated statewide results will mask regional variation in trends, particularly if the road network is biased towards certain areas of the state. The disease is predominantly on the east coast, moving west. The “stable” numbers for 5 years might reflect a collapsed eastern population, and a temporarily uninfected western population. This doesn’t mean the devils have “saved themselves”. Alternatively, when populations are small (like the current devil population), chance variation becomes much more influential. Statistically insignificant increases become more likely; real declines are harder to observe. We would expect a population which has declined to 15% of its historical levels to be harder to track. The point is that wildlife surveys are really complicated, particularly for rare species, and Greer needs to offer more - a lot more - than an eye-balling of an Excel spreadsheet. His reading feels a lot like the climate skeptics picking only the last decade of temperature and calling an end to global warming.

    “One can only speculate”. No, I can think of another option.

  • 5
    Blair Rideout
    Posted Thursday, 19 December 2013 at 10:21 am | Permalink

    Dr Greer appears to have been writing these anti-STDP opinion pieces for some time. Rather than take his “research” to reputable journals, he publishes online on his own web site, without peer review. I think it’s safe to say that Crikey has been taken in by someone whose opinion lies outside the scientific establishment on this issue, or perhaps even has a particular axe to grind. “Stablilising” a decimated population at a low level - without any reference to the health of that population - is far from returning said population to a sustainable level. And we also need to consider the additional pressure Devil populations may face due to the recent approval of mining leases in the Tarkine.

  • 6
    Mark Duffett
    Posted Thursday, 19 December 2013 at 11:56 am | Permalink

    These comments have a curious tenor. How is it ‘obvious’ that a catastrophic decline is ongoing? Another perspective comes from the fact that similar (~20) or smaller numbers are also observed for eastern quolls, Forester kangaroos, spotted quolls and feral cats. None of these are considered endangered in Tasmania, indeed they remain common for the most part.

  • 7
    Posted Sunday, 22 December 2013 at 4:45 am | Permalink

    The Devil population has declined by more than 95% in the original locations of Devil Facial Tumour Disease outbreak. Check the federal listing advice (http://www.environment.gov.au/biodiversity/threatened/species/pubs/299-listing-advice.pdf).

    The IUCN Red List also classifies a species as threatened when its population has declines by more than 30% over 10 years or 3 generations (whichever is longer), where the driver of the decline has not ceased (i.e., DFTD).

    Given these enormous observed declines, and given that the driver is still present, the onus of proof about whether the decline is ongoing or not rests on those who would argue that it has ceased. Is it “obvious” that the sun is going to rise tomorrow morning?

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