Key Threatening Process Nomination Form For adding a threatening process under the Environment Protection and Biodiversity Conservation Act 1999 (epbc act)




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4.Deer abundance


Moriarty (2004) observes that feral deer in Australia have moved, relatively recently, ‘from a minor component of the Australian biota to one that is now widespread’. Others also note recent population increases and range expansions (Jesser 2005; Peel et al. 2005; West and Saunders 2007). Moriarty’s (2004) study was based on a comprehensive survey in 2002, with a very high return rate, of government land management agencies in each state and territory. The reported number of herds was 218. Although the majority of deer were in long-established acclimatisation-derived herds, the vast majority of herds were only recently established, with >90% established since about 1990 due to escapees/releases from deer farms and translocations by hunters.
The recent increase in feral deer populations can be partly attributed to a crash in prices for farmed deer in the early 1990s: ‘Some animals escaped and were not recovered. Others were liberated as the cost of feeding them began to outweigh their value, even for slaughter. Some were purchased from farmers or trappers, to be released by those wishing to create their own populations for hunting or aesthetic reasons’ (Jesser 2005). Moriarty (2007) also attributes the ‘dramatic’ increase in releases to the increased popularity of hunting, and the use of more effective control measures by land managers leading to less game species in some areas.
Almost half the total herds (44%) reported in 2002 were from NSW, a quarter from Victoria (23%), 15% in Queensland, 11% in South Australia and less than 5% each from the other states and territories (Moriarty 2004). Average population sizes were reported to be about 12,000 animals for herds deriving from acclimatisation (having had much longer to breed), about 140 animals per herd from farming releases/escapes and about 120 animals per translocated herd.
Table 1: Population and herd numbers estimated by Moriarty (2004)




Fallow

Red

Sambar

Chital

Rusa

Hog

Total

Population (%)

55,000 (28)

32,500 (17)

70,700 (36)

13,000 (7)

15,000 (8)

9300 (5)

196,000

Herds (%)

85 (39)

65 (30)

8 (3)

28 (13)

23 (11)

9 (4)

218

Moriarty (2004) estimated total feral deer numbers at 200,000. However, this number is a considerable underestimate. In 2008-09 Victorian hunters reported killing 34,000 Sambar (Gormley and Turner 2009) – an impossible feat if the total Australian population size was not much more than the 71,000 reported for 2002 in Moriarty (2004).


However, Moriarty’s 2002 estimate was a considerable increase on that for 1980 by the Standing Committee on Agriculture (1980, cited in Jesser 2005), with the difference between the two estimates suggesting that deer in acclimatisation herds (the longest-established and largest herds) had more than tripled in two decades, climbing from fewer than 50,000 (in 20 herds) in 1980 to about 170,000 in 2002. Jesser (2005) suggests that changes in management ‘enabled some populations to increase beyond the critical threshold below which they previously had been held by hunting and natural predation.’ That more than 90% of Australia’s feral deer populations are only recently established due to farm releases/escapes and translocations implies a worryingly large potential for population expansion in the near future.
Numbers of Sambar, the most successful deer in Australia, have risen dramatically in Victoria. In 1995, they were estimated to number 8000 (Bentley 1995) and Moriarty (2004) estimated nine times that number (70,700) in 2002. In 2004 Victorian hunters were reportedly killing >8500 Sambar annually (Peel et al. citing DSE 2005) but just five years later they reportedly killed four times as many (34,000) (Gormley and Turnbull 2009) suggesting a total population numbering in the hundreds of thousands. The Victorian Government’s website says hunting ‘appears to have little noticeable effect on the success of the species’, that Sambar have steadily extended their range into NSW and the ACT, and that their density is increasing. Modelling by Ray and Burgman (2006) based on analysis of suitable habitat suggests the potential Sambar population in Victoria could climb as high as 1 million.
Surveys of government land managers suggest that deer numbers in NSW are also rising rapidly. Deer presence was reported from 30 new NSW locations between 2002-2005, equivalent to an increase in range by >8000 km2 (West and Saunders 2007). Areas with reported high deer density quadrupled.
Populations from other areas also are reported to be increasing although not as rapidly. Dryden (2009) calculates that the population of feral Red Deer in the Brisbane and Mary River valleys of southeast Queensland size has increased at about 6 percent per year over the past 130 years. The current population, estimated at 16-20,000, has probably been augmented by escapes and releases from deer farms. They have been spreading out of the Brisbane River valley into surrounding areas.
Deer have a large potential for population increase. Hone et al. (2010) calculated maximum annual population growth rates for 5 of the 6 species feral in Australia (Table 2).
Table 2: Population growth rates for feral deer species (Hone et al. 2010)




Female age at first reproduction (years)

Maximum annual population growth rate rm

Maximum annual proportion to be removed to stop population growth

Axis axis

0.92

0.76

0.49

Axis porcinus

0.83

0.85

0.52

Cervus timorensis

1.00

0.70

0.46

Cervus unicolor

1.25

0.55

0.40

Dama dama

1.55

0.45

0.34

Forsyth and Caley (2006) propose that most large herbivores, particularly when introduced to a new environment, exhibit eruptive population dynamics: ‘following introduction to new range or release from harvesting, the herbivore population increases to peak abundance, crashes to a lower abundance, and then increases to a carrying capacity lower than peak abundance’. The post-decline density is lower than the initial peak because the quantity and/or quality of food has been reduced, as preferred and browse-intolerant species decline and are replaced by unpalatable or more browse-tolerant species. Such a population dynamic has the potential to damage ecosystems and result in biodiversity losses, some of which are likely to be irreversible (Coomes et al. 2003). Current reports of rapid increases in deer populations in many areas are thus of considerable concern.


The greatest densities of feral ungulates occur in inland Australia west of the Great Divide. Deer, by contrast, are distributed throughout most of eastern and southern Australia where feral herbivore pest densities have been relatively low. Bioclimatic models show there is vast potential for expansion of all deer species into new areas (Moriarty 2004). For example, Sambar, Rusa and Hog Deer are tropical Asian deer that currently have their main Australian populations outside the tropics. As Moriarty (2009) says, ‘If deer population trends in Australia continue to increase at their current rate, deer species are likely to rival both feral pigs and feral goats in distribution, abundance and impacts in the near future.’

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