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Management program for the Brushtail possum Trichosurus vulpecula (Kerr) in Tasmania - Review of background information

Prepared by Tasmanian Parks and Wildlife Service, October 1996


Crop protection

  1. Crop protection permit applications contain information on the type and area of the crop requiring protection, the locality of the property, the pest species and the method of control. The following uses this information to determine the magnitude of the crop protection problem in Tasmania and identify which areas crop damage by possums is most prevalent.

Crop Protection Permit Trends

  1. As mentioned previously, the fall in skin prices since 1980 has led to a decline in the number of commercial permits issued. As commercial hunting has decreased the demand for crop protection permits has increased. This is illustrated in Figure 3 which contrasts the number of crop protection permits and commercial permits issued since 1983. The rise in demand for crop protection permits was accompanied by a significant increase in brushtail possum abundance (see Figure 8).

Regional Trends in Crop Protection

  1. Table 2 shows that 68% of crop protection permits are issued to landholders in the midlands and southeast which together comprise less than 25% of the area of Tasmania. Indeed, the highest numbers of both commercial and crop protection permits were issued for the midlands region with the southeast of Tasmania also figuring highly for both types of permit.
Table 2: Percentage of all crop protection permits issued per region 1989-1994
Region % of all Permits
1. North West 0.8
2. North 8.1
3. North East 8.5
4. West 0.3
5. Central 6.9
6. Midlands 44.5
7. East 2.8
8. South East 23.6
9. South West 4.6
Tasmania 100.0
  1. The increase in the number of crop protection permits issued in recent years is examined by region in Figure 4. This shows that most regions have undergone a significant increase in the number of permits issued. Regions 6 and 8, the midlands and southeast of Tasmania respectively, show the greatest increase of all nine regions. Both of these regions have undergone massive increases in possum numbers since 1985 Figure 9.

Type of Crop and Method of Crop Protection

  1. Permits to control possum damage specify the method of control allowed. These methods include live trapping, spotlight shooting or in exceptional circumstances in which alternatives are not feasible, poisoning with 1080 baits. Figure 5 shows the percentage of permits issued during the period 1990-96 for each of the methods of control. The majority were issued specifying spotlight shooting, while only 1% allowed 1080 poison to be used.
  2. A total of 48% of crop protection permits issued in 1993/94 were for the protection of pasture and fodder crops. Vegetable, grain and fruit crops between them accounted for 35% of permits and tree plantations 13% of permits (see Figure 6). Pasture/fodder also comprised the greatest area of land that required protection at 173,800 hectares or 88.6% of the total area of all crops needing protection. The method used in the protection of crops varied and often depended on the type of crop. For example, in 1993/94 all permits to live trap and release were issued to reduce or prevent damage to suburban gardens and/or buildings. In contrast, 96% of crop protection permits that used spotlight shooting issued were for the protection of cereal crops, vegetable crops, pasture, and tree plantations. Poisoning with 1080 was only used to protect tree plantations.

SURVEY AND MONITORING

  1. In order to fulfil the three objectives of brushtail possum management in Tasmania a knowledge of the status of the population is essential. This is achieved by direct monitoring of the population.

Monitoring the Population

  1. Brushtail possums are timid, cryptic animals, more readily seen at night than during the day and often occur in densely vegetated country. Thus, many of the traditional methods of censusing wildlife, such as transect counts and aerial surveys, are inappropriate to possums. A method using spotlight surveys has been adopted and subsequently found to be a reliable method of monitoring possum numbers (Johnson, 1977; Southwell & Fletcher, 1993; Driessen & Hocking, 1992).
  2. Commencing in 1975, spotlight surveys have been conducted each November/January along a series of fixed transects randomly located throughout those parts of Tasmania subject to brushtail possum harvesting (see Figure 7). Each transect comprises 10 km of roadway which is surveyed along both sides from a vehicle travelling at approximately 20 km/h. Counts of all non-domestic animals are made.
  3. An attempt is made to standardise the survey method with respect to a number of potential sources of variation (Southwell and Fletcher, 1993). Surveys are therefore held on nights when visibility is reasonable, while individual transects are generally surveyed at the same time of night, using the same observer.
  4. Initially, a series of 51 transects was used, but in 1985 as a result of research done on the spotlight survey technique (Southwell and Fletcher, 1985) this was expanded to include a total of 141 transects. A further 23 transects have been introduced since 1985 bringing the total number to 171 on mainland Tasmania and seven on Flinders Island.
  5. Recent analysis of data gathered since 1985 has established that the precision of the method is now around 6%, thereby enabling population changes of at least 20% to be detected (Driessen and Hocking, 1992). This is considered to be satisfactory for management purposes.

Population Trends

  1. Between 1975 and 1995 brushtail possum numbers have undergone an overall increase in abundance in Tasmania (Figure 8). This increase did not however, occur uniformly across the state, being largely restricted to the central and southeastern parts of Tasmania (Figure 9). Possum numbers remained largely unchanged in the northeast and northwest.
  2. The overall increase in possum numbers is attributed to a number of factors including a decline in hunting pressure and continued clearing of land for forestry and agriculture (Driessen and Hocking, 1992). Rainfall also influenced brushtail possum abundance, with periods of low rainfall resulting in low possum numbers. These factors are discussed below:

Effect of Rainfall on Possum Abundance

  1. The pattern of rainfall in Tasmania is characterised by low variability, with variations in annual rainfall of greater than 40% being virtually unknown (Australian Bureau of Statistics, 1991). This contrasts with the situation over much of mainland Australia where annual rainfall can regularly vary by over 50%. As a consequence of this low variability in rainfall, Tasmanian brushtail possum populations do not show the extreme fluctuations in abundance (Driessen and Hocking, 1992) that characterise mammal populations in the drier parts of mainland Australia (Caughley et al. 1985, Bayliss 1985). Nevertheless, rainfall has been found to have an influence on the abundance of brushtail possums in Tasmania (Driessen and Hocking, 1992).
  2. Driessen and Hocking (1992) found marked reductions in brushtail possum abundance across Tasmania following several droughts in which rainfall was reduced by approximately 25% below average. In each case, increased reproduction and survival of young resulted in a rapid recovery of possum populations following a return to pre-drought conditions.

Effect of Land-use Practices on Possum Abundance

  1. Although broad-scale land clearance is detrimental to many native mammal species, it is well known that brushtail possums benefit from clearing practices that produce a mosaic of pasture and native forest (Green, 1973; Johnson, 1977; Driessen and Hocking, 1992). This mosaic vegetation provides the possum with den and/or refuge sites and a ready food supply.
  2. Fire is frequently used in the process of regenerating forests felled for sawlogs or pulp wood. This practice initially produces unsuitable habitat for brushtail possums and displaces animals. However, as regrowth occurs possum density increases rapidly from a minimum during the first six months following a fire to reach a maximum four to six years later. Brushtail possum density was found to stabilise after about six years and then decline to a minimum between 40 to 60 years after the fire (Hocking, 1981). In forest habitats that had been burnt two to six years previously Hocking (1981) also found a reduced age of first reproduction, increased survival of the 12 to 24 month age-class, and larger body size in brushtail possums.
  3. The rate of land clearing is now much reduced: 6000 ha/year between 1980 and 1990 as compared to 15000 ha/year between 1972 and 1980 (Kirkpatrick and Brown, 1991). However, the combined effect of increasing areas of regenerating forest (via forestry practices), intensive cropping, land clearing for agriculture amongst native forest, and a reduction in skin prices have led to increased population levels of brushtail possum. This situation is expected to continue.

Effect of Hunting on Brushtail Possum Abundance

  1. Between 1976 and 1980, commercial brushtail possum hunting reached historically high levels with over 250,000 possums being taken each year for 6 years. Since that time, poor skin prices have resulted in a decline in the size of the commercial possum harvest to fewer than 10,000 in 1995. Over this period, possum abundance has undergone a corresponding increase and is now at record levels (Figure 10). The inverse correlation between harvest level and abundance seen in Figure 10 provides strong evidence that hunting pressure can have a major impact on possum abundance.

LEGISLATIVE BASIS FOR MANAGEMENT

  1. The harvest of brushtail possums is regulated by the PWS under the Wildlife Regulations,1971 of the National Parks and Wildlife Act,1970. Under the Act, brushtail possums are partly protected wildlife throughout Tasmania and may only be taken in accordance with the authority conferred by the appropriate permit or licence.

Taking of Brushtail Possum

  1. As partly protected wildlife, brushtail possum may be taken only under licence during a proclaimed open season (Reg. 2). There is no requirement, however, for the Director to issue a licence (Reg. 4). It should be noted that an open season for brushtail possum has not been proclaimed since 1973.
  2. Except with the permission of the Director, the holder of a licence may not take brushtail possum during the period from one hour after sunset to one hour before sunrise (Reg. 21(4)). Similarly shooting from within 10 metres of a vehicle is prohibited without permission of Director as is use of a spotlight, steel jawed traps, snares, poisons, or other chemical compounds (Reg. 21(10, 11 & 5).
  3. The Director may issue special permits allowing brushtail possum to be taken for special purposes including the protection of crops and pasture (Regs. 6 & 7).
  4. Permits may specify conditions including the duration of the permit, the manner in which its authority may be exercised, precautions to be observed, disposal or sale of products and the keeping of records (Reg. 8).

Trading of Brushtail Possum Skins

  1. A licence is required to deal in untreated or unmarked skins (Reg. 13(1)).
  2. A fauna dealers licence (skins) authorises its holder to buy untreated, unmarked skins and to sell marked skins during a period of 12 months. (Third Schedule, Part 1).
  3. Buyers of unmarked skins must produce them for royalty payment within 28 days of purchase. Skins on which a royalty has been paid must be stamped by a Service officer (Reg. 14(2)).
  4. Holders of a fauna dealers licence (skins) must maintain records of all sales, purchases and other dealings in skins. The records must show:
    1. the date of dealing;
    2. the number of skins involved; and,
    3. the name and address of the person to whom the skins were sold, or from whom they were purchased.
  5. Copies of these records must be returned each month to the Director (Reg. 15 (3, 4, 5)).

QUOTAS AND THEIR DERIVATION

  1. Various means are available to managers to exercise control over the size or extent of a harvest. Direct methods include the use of quotas and the specification of regions to be harvested, while indirect measures such as limiting the number of harvesters or the period over which harvesting can occur, can also be used.

Quotas

  1. Quotas are set using information (where available) on:
    • current population trends;
    • the need for crop protection;
    • review of previous harvests;
    • significance of mortality outside the quota;
    • seasonal conditions;
    • proportion of population (and habitat) not subject to culling; and
    • current land-use practice and trends in land-use.
  2. The quota is defined as the maximum number of individuals of the designated species which may be taken by shooters during a specified period in accordance with an approved State management program. Between 1983 (when quotas were first introduced) and 1993 the possum quota was defined as the number of animals entering the commercial trade whether used on the domestic market or exported. This was based on the number of skins sold or royalties. From 1995 onwards the quota will be defined as the maximum number of brushtail possums to be taken under commercial and crop protection permits.
  3. The commercial quota is proposed by the Tasmanian Minister responsible for the National Parks and Wildlife Act in consultation with Environment Australia. This document as well as the proposed quota for brushtail possums will be forwarded for consideration by the Commonwealth Minister responsible for the Wildlife Protection (Regulation of Exports and Imports) Act,1982.

REGULATORY CONTROL AND LAW ENFORCEMENT

  1. The protection and management of the brushtail possum is provided by the Wildlife Regulations,1971 made under the National Parks and Wildlife Act, 1970.
  2. The PWS has a staff of 7 Enforcement Officers whose primary responsibility is the enforcement of the wildlife regulations. These officers are assisted in their work by park rangers stationed in various field centres throughout the State who protect brushtail possums on reserved land and help with enforcement on other lands. A strong liaison is maintained with officers from other statutory authorities such as police and fisheries, who have ex officio powers under the Act and provide assistance on a regular basis.
  3. Wildlife Enforcement Officers are responsible for the inspection and branding of brushtail possum skins and the collection of Government royalties. All premises licensed to deal in brushtail possum skins are regularly inspected and records are checked to ensure that all skins available for the commercial trade have been taken pursuant to the regulations and in accordance with the approved management program. Wildlife Enforcement Officers enforce the Wildlife Regulations in the following ways:
    • undertaking regular and frequent patrols throughout Tasmania in an effort to detect any illegal taking of possums;
    • carrying out inspections of crop damage caused by wildlife, including possums, and issuing permits to control that damage;
    • inspecting all premises licensed to deal in possum products and checking records to ensure that all skins and meat are taken legally; and,
    • branding all possum skins that enter the commercial trade and collecting Government royalties payable on them.
  4. Successful prosecutions of brushtail possum related offences occur on a regular basis in Tasmania as evidenced by Table 3. The decline in commercial possum hunting has led to the fall in the number of offences committed and hence the number of charges laid. This is also reflected by the percentage of the total fines that were possum related. This percentage is an indication of the constant effort put into the enforcement of the regulations with regards the taking of brushtail possums.
Table 3: Summary of prosecutions of possum related offences 1981-1994
Note: the percentage in the last column is the proportion of the total fines paid for wildlife offences that were brushtail possum orientated.
Year Charges Convictions Dismissals Fines ($)
1981/82 66 54 12 1,596 (19.5%)
1982/83 61 53 8 2,332 (11.6%)
1984/85 31 28 3 1,261 (4.8%)
1985/86 23 19 4 1,026 (3.9%)
1986/87 39 24 3 1,070 (4.4%)
1987/88 7 0 0 -
1988/89 36 17 15 787 (3.2%)
1989/90 5 5 - 420 (1.6%)
1990/91 19 11 6 506 (2.1%)
1991/92 12 7 1 514 (2.0%)
1992/93 2 - - -
1993/94 26 23 3 1,140 (4.7%)
1994/95 15 15 - 1,870 (5.8%)
1995/96 3 3 - 75

ANIMAL WELFARE

  1. Under the National Parks and Wildlife Act, 1970 the primary concern of the PWS is the conservation of wildlife species. Nevertheless, the Service encourages high standards by shooters in order to ensure that brushtail possum are killed humanely.
  2. Any acts of cruelty can be prosecuted under the Animal Welfare Act, 1993 which is primarily policed by inspectors of the RSPCA. and the Tasmanian Police Force. In addition sections of the Wildlife Regulations, 1971 of the National Parks and Wildlife Act, 1970 specifically prohibit certain methods of taking brushtail possum which are considered to be cruel such as the use of snares and steel-jawed traps.
  3. The commercial harvesting of brushtail possum is restricted to shooters using a rifle and spotlight. Special permission may be given to particular permit holders to take possums by live-trapping using cage-traps. Live trapping must be conducted in accordance with the relevant code of practice approved under the Animal Welfare Act