Minimising the risk of spread of mimosa pigra from Peter ... · Fortunately the outbreak at Peter...

Queensland Primary Industries and Fisheries

Minimising the risk of spread of Mimosa pigra from Peter Faust Dam, Proserpine

Edward Attard, Cassandra Chopping, Peter Austin, Jason Williams and Tony Pople�

Final report to the Department of Agriculture Forestry and Fisheries and the Department of Environment and Heritage

May 2006

Edward Attard and Tony Pople Land Protection, Department of Natural Resources and Water GPO Box 2454, Brisbane Qld 4001

Cassandra Chopping and Peter Austin Land Protection, Department of Natural Resources and Water PO Box 63, Mackay Qld 4740

Jason Williams SunWater, 126 Giddy Road PMB 5013, Ayr Qld 4807

Published by:�

©State of Queensland (Department of Natural Resources and Water) 2006�

ii Risk of Mimosa pigra spread in Queensland�

Contents

Summary and recommendations v�

Section 1–Overview of Mimosa pigra ecology, distribution, impacts and management 1�

1.1 General introduction 1�

1.2 Global distribution and history of introduction to Australia 2�

1.3 M. pigra life history 2�

1.4 Potential distribution in Australia 4�

1.5 Current and potential impacts in Australia and overseas 4�

1.6 Control options and cost 4�

Section 2–Management of Mimosa pigra in Queensland 5�

2.1 Introduction 5�

2.2 State wide strategy 6�

2.3 Management of M. pigra at Peter Faust Dam 6�

2.4 Research on M. pigra in Queensland 11�

2.5 Key stakeholders and their responsibilites 11�

Section 3–Assessing the risk of Mimosa pigra spread from Peter Faust Dam 13�

3.1 Introduction 13�

3.2 Methods 13�

3.3 Vectors of seed spread 17�

3.4 Management options 21�

3.5 Ranking management options 25�

3.6 Making management decisions 27�

3.7 Monitoring and performance evaluation 27�

Acknowledgments 28�

References 29�

Appendixes 31�

iiiRisk of Mimosa pigra spread in Queensland�

iv Risk of Mimosa pigra spread in Queensland�

Summary and recommendations In February 2001 the first infestation (~100 plants) of Mimosa pigra in Australia outside the Northern Territory was found at Peter Faust Dam, near Proserpine, in central coastal Queensland. This shrub continues to have major environmental, economic and social impacts on the coastal floodplains of the Top End of the Northern Territory, where it forms dense, almost monospecific stands. At risk of invasion by M. pigra in central Queensland are canefields, cattle-grazing areas and wetlands of conservation significance.

In 2001 a stakeholder group was assembled, comprising the local cattle grazier, SunWater (which is responsible for management of the dam), the Queensland Cane Growers Organisation Ltd (Canegrowers), Whitsunday Shire Council and the Queensland Department of Natural Resources and Water (NRW). Over the next five years the group oversaw a range of on-ground activities to eliminate M. pigra from the site. This work included describing aspects of the biology of M. pigra at the site, investigating control measures and regular monitoring of the site and removal of plants. However, the presence of vast numbers of M. pigra seed in the soil at the dam and their likely persistence for more than 20 years means that the potential ways that this seed could move from the dam (‘vectors’ of seed spread) need to be identified and managed. These vectors include fluctuating water levels, wildlife, cattle and recreational users of the dam, particularly fishers. In mid-2005 a risk assessment involving the major stakeholders was therefore conducted to identify and evaluate these vectors and then to canvass a number of management options to minimise the risk of M. pigra seed spread. These options were then ranked according to the risk (likelihood × consequence) of seed spread from a particular vector and the feasibility of managing the vector. The latter considered the sociopolitical, economic and technical feasibility of implementing each management action.

A further meeting among stakeholders is required to review the risks of potential vectors, the management options, their scores and resultant ranks. To be efficient, limited funds should be allocated to management options that generate the greatest reduction in overall risk of weed spread. Stakeholders, experts and managers therefore need to compare the cost of options and their ability to reduce risk.

A number of preliminary recommendations can be drawn from this risk assessment:

Monitoring and control

1. Current monitoring and control of M. pigra must be continued, including washdown of vehicles and identifying tracks as ‘clean’ and ‘dirty’. However, monitoring could be more strategic. Greater effort can be directed to periods when germination is most likely and in higher density areas (i.e. temporal and spatial stratification). Access to areas with M. pigra seed and the high detection probability of M. pigra seedlings needs to be maintained by clearing Melaleuca regrowth.

2. Although considered a low priority, monitoring of downstream areas is needed if new incursions are to be identified before their eradication is no longer feasible. Such delimitation is an important criterion for eradication. This is likely to be best achieved through a combination of direct monitoring using trained surveyors and educating landholders in identifying M. pigra and the risks associated with its spread.

Livestock management

3. As a high priority, cattle that have been grazed in M. pigra-infested areas should be held in M. pigra-free paddocks for at least seven days before transport, as practised in the Northern Territory. A formal agreement is required between the local grazier and government to cover additional costs.

4. The highest risk (i.e. high M. pigra seed density) area. on the south-western shoreline, should ideally be fenced to exclude cattle, but was considered a lower priority than other management options.

Restricting access

5. Currently recreational users have physical access to most areas of the dam. The difficulties of policing necessitate restricting road access to the higher risk areas through fencing and locked gates as a high priority. Access to the western shoreline by boats is more problematic, requiring good signage and identification of the prohibited area perhaps using marker buoys.

Education

6. Recreational users of the dam need to be made better aware of M. pigra, its impacts and how it can be spread. There are now several warning signs around the dam, but there needs to be greater exposure of the problem in the media.

vRisk of Mimosa pigra spread in Queensland�

Pig control

7. As a high priority, pig hunting (other than by authorised hunters) should be banned and 1080 baiting used to control numbers.

Compliance

8. An awareness campaign, restricting access and banning pig hunting will all fail unless they are supported by policing the movement of people within the dam area. Enforcing these restrictions is difficult and could require an emergency quarantine notice that stipulates how the dam can be used and allows authorised officers to police use of the dam and issue fines.

Performance evaluation

9. Monitoring is required to determine the effectiveness of management action. Appropriate indicators to monitor are likely to be reductions in the activity of people, pigs and cattle in the M. pigra-infested areas, use of washdown facilities and the survey effort downstream of the dam.

vi Risk of Mimosa pigra spread in Queensland�

Section 1

Overview of Mimosa pigra ecology, distribution, impacts and management

1.1 General introduction

An infestation of Mimosa pigra was discovered at Peter Faust Dam (see Section 2) near Proserpine in central coastal Queensland (Figure 1) in 2001. This

is the first known Australian infestation of this weed outside the Northern Territory, where it has major environmental, social and economic impacts. Similar impacts are possible in Queensland where it might invade canefields, cattle-grazing areas and wetlands of conservation importance.

Fortunately the outbreak at Peter Faust Dam appears to have been contained in the immediate area around the dam, thus providing a good chance of eradication. Over the five years since 2001 managers undertook monitoring, removal and research of M. pigra at Peter Faust Dam in an attempt to eradicate the weed. The program is costly, but is offset by the cost of potential impact and ongoing control if the weed

spreads into its potential distribution area, which includes wetlands throughout northern Australia. Working against this effort is the vast number of M. pigra seed in the soil, some of which may remain viable for more than 20 years (Lonsdale 1992). This long timeframe increases the risk of seed being transported outside the site. This report describes an assessment of this risk and how it can be best managed.

Section 1 of this report provides an overview of the problem, including relevant aspects of the ecology of M. pigra. Section 2 describes the current management of M. pigra at Peter Faust Dam. Section 3 presents the risk assessment, which uses stakeholders to identify various hazards, their risks and potential management options.

Figure 1. Location of Peter Faust Dam in central coastal Queensland

1Risk of Mimosa pigra spread in Queensland�

1.2 Global distribution and history of introduction to Australia

The native range of M. pigra is central and southern America, spanning the tropics from northern Mexico (~25oN) to central Brazil (~23oS) (Walden et al. 2004). It has spread throughout the tropics, including Australia (Figure 2). It was probably introduced to Australia in the 1870s, either accidentally in seed samples for the Darwin Botanical Gardens, as seed in cattle intestines or deliberately as an ornamental, although the exact source is unknown (Miller and Lonsdale 1987). It was confined to Darwin until the 1950s, but by the 1980s M. pigra had spread extensively in the Top End of the Northern Territory. Today more than 80 000 hectares of native vegetation in the Northern Territory has been replaced by M. pigra (Walden et al. 2004).

Where it has been introduced M. pigra invades a wide range of habitats that have been disturbed either naturally or anthropogenically and are moist and open (Walden et al. 2004). Typical habitat includes floodplains and riverbanks. In the Northern Territory M. pigra similarly colonises areas that have been heavily disturbed by feral or domestic livestock (Walden et al. 2004).

Figure 2. Global distribution of M. pigra (after Beckmann 1990). The native range is in dark shading. Locations where it has been introduced are shown as solid circles.

There are a number of ways M. pigra could have reached Central Queensland. The most likely source is the Northern Territory, more than 1500 kilometres away, with a wide range of potential vectors. While the cause is unknown, its spread to Peter Faust Dam in Queensland highlights the risk of establishment of M. pigra across large areas of Australia.

1.3 M. pigra life history

M. pigra has many features that have enabled it to spread rapidly across tropical regions. These are summarised into seven key attributes below (Walden et al. 2004). Unpublished data for M. pigra growing at Peter Faust Dam are also presented for comparison with values for these attributes recorded elsewhere.

1. M. pigra can withstand the anaerobic conditions of inundation and flooded soils by having roots near the surface to take up oxygenated water (Miller, Nemestothy and Pickering 1981). At Peter Faust Dam M. pigra was originally found growing in more than five metres of water (Figure 3) and later in areas of Melalaeuca with large mats of aerial roots where water levels had receded (Figure 4) (Chopping 2004).

2. If cut down, M. pigra can easily resprout from the stump (Wanichanantakul and Chinawong 1979). Following burning, up to 90 per cent of mature M. pigra plants and up to 50 per cent of M. pigra seedlings can regrow (Miller 1988). At Peter Faust Dam 75 per cent of M. pigra plants were reshooting 21 days after burning (Vitelli and Madigan 2005).

3. Maturity is reached quickly, with seed set in the first year (Lonsdale et al. 1985). At Peter Faust Dam plants can mature and produce seed pods in a little as 120 days, with flowering (Figure 5) and pod production occurring year round (Vitelli and Madigan 2004). The seedpods are covered with bristles (Figure 6), enabling attachment to animals and clothing, and flotation on water for extended periods (Miller, Nemestothy and Pickering 1981). The seeds are also dispersed in soil and mud, adhering to vehicles, other machinery and animals (Lonsdale, Harley and Miller 1985). Livestock and native animals sometimes graze M. pigra (Miller 1988) and pass the seeds in their faeces (Miller and Lonsdale 1987).

4. Seed life span varies with soil depth and soil type, and there are suggestions that it might be up to 23 years in sandy soils (Lonsdale 1992). At Peter Faust Dam an average of more than 5000 seedlings per square metre was observed within the core infestation area in 2002 (Figure 7), although seedbanks are being depleted (Vitelli and Madigan 2005).

5. Average seed production has varied between 9000 and 12 000 per square metre per year in the Northern Territory (Lonsdale, Harley and Gillett 1988), with up to 220 000 seeds per year for an individual plant (Lonsdale 1992). At Peter Faust Dam average monthly seed production per plant ranged from 100 to 100 000 per month in 2004. More than 560 000 seeds were recorded for one year from an individual plant (Vitelli and Madigan 2005).

6. M. pigra can grow quickly, at a rate of one centimetre per day, and infestations can double in area in one year. It can also withstand droughts (Lonsdale 1993). At Peter Faust Dam growth rates have ranged from 0.8 to 1.5 centimetres per day (Vitelli and Madigan 2004).

2 Risk of Mimosa pigra spread in Queensland�

7. In the Northern Territory M. pigra is found on a wide range of soil types, including nutrient-poor sandy soils (Miller 1983). However, seed production, seedling density and plant longevity is higher on heavier soils (Lonsdale 1992), whereas seed longevity is greater in sandier soils (Lonsdale, Harley and Gillett 1988). M. pigra can also tolerate at least moderate levels (~50 per cent) of salinity (Miller 1983).

Figure 3. The original infestation of M. pigra at Peter Faust Dam, Central Queensland, in five metres of water.

Photo by C.Chopping.�

Figure 5. The distinctive pink flower and sensitive leaves of

M. pigra. Photo by A. Doak.

Figure 4. M. pigra growing among Melaleuca shrubs. Photo by C.Chopping.

Figure 6. The seed pods of M. pigraº which are covered with bristles. Photo by A. Doak.

Figure 7. Thousands of M. pigra seedlings emerged as the dam water receded. Photo by P. Austin.


1.4 Potential distribution in Australia

The potential distribution of M. pigra in Australia has been modelled by matching the climate of its overseas distribution with the climate across Australia (Figure 8; Lonsdale 1992; Kriticos 2000; Walden et al. 2004). This suggests that approximately 4.2–4.6 million hectares of wetlands in northern Australia is potentially at risk of invasion by M. pigra (Walden et al. 2004).

Figure 8. The potential distribution of M. pigra in Australia (Kriticos 2000).

Given this potential distribution, most (~105) of the 165 nationally important wetlands in Queensland are at risk of invasion by M. pigra, with the largest areas in the Cape York Peninsula and Gulf Plains bioregions (Blackman et al. 2000). There are also four Ramsar sites (i.e., wetlands of international importance covered by the Ramsar intergovernmental treaty for their conservation) that lie within the potential range of M. pigra (Blackman et al. 2000).

1.5 Current and potential impacts in Australia and overseas

Walden et al. (2004) have discussed the potential impacts of M. pigra in northern Australia, emphasising its damaging effects to wetlands. Although M. pigra shows a preference for disturbed areas, even largely intact landscapes can be transformed into dense, monospecific stands of M. pigra, thus altering both the floristics and structure of the vegetation. The further ramifications can be wide ranging, including:

• loss of habitat for native fauna • provision of shelter for feral pigs, and also some native fauna

• altered hydrological regimes • loss of agricultural productivity and increased control costs

• reduced aesthetics of the landscapes.

Similar impacts have been reported overseas, even in its native range, where it has expanded its distribution in cultivated areas (Walden et al. 2004).

1.6 Control options and cost

Once established, the costs of managing M. pigra are high (Storrs 1998). Control options include mechanical clearing, spraying with herbicide and burning. The long-term success of control will also depend on subsequent land management to minimise reinvasion (Walden et al. 2004). A number of biological control agents (seven insects and a fungal pathogen) have been released with some impact on M. pigra infestations, and releases of other agents are proposed. Further assessment is required before their full impact will be known (Walden et al. 2004).

As outlined in the strategic plan for M. pigra (ARMCANZ 2000), the costs of management have been high. The management and subsequent reduction of an infestation of more than 8000 hectares of M. pigra at Gunbalana, close to Kakadu National Park, has cost $7 million over a five-year period. Kakadu remains free from serious infestation through systematic surveys and destruction of new outbreaks. This has required four full-time staff and an annual cost of approximately $500 000. The current cost of the management of M. pigra in the Northern Territory is more than $2.5 million per annum, including research, on-ground control activities and landholder assistance for herbicides. Given this high cost of ongoing control, eradication of this species from Queensland, at a predicted cost of just over $3 million (Queensland Government 2004), is likely to be well worth the investment in the long term.


Section 2

Management of Mimosa pigra in Queensland

2.1 Introduction

Peter Faust Dam (20°41’S, 148°33’E) is located 25 kilometres west of Proserpine at the headwaters of the Proserpine River. The discovery of M. pigra at the dam was made by the local grazier and later confirmed

by the Queensland Herbarium. A combination of wind and water dispersal could see M. pigra invade large areas along the Proserpine River over a relatively short time period (Figure 9). This section outlines the ensuing management of M. pigra at Peter Faust Dam and provides a context for the risk assessment described in Section 3.

Figure 9. Potential area of infestation of M. pigra assuming omnidirectional wind dispersal at a rate of 76 metres per year from the Proserpine River. Colour bands indicate area of spread after 5, 10, 20 and 50 years (Bryant 2005).


As outlined by Austin and Csurhes (2004), M. pigra is a declared pest in all states except the Australian Capital Territory. In Queensland it is declared as a ‘Class 1’ pest under the Land Protection (Pest and Stock Route Management) Act 2002. By law, all landholders must take reasonable steps to keep their land free of M. pigra. Introduction, possession and sale of M. pigra are offences under the Act with maximum penalties of $60 000.

2.2 Statewide strategy

To protect vulnerable areas in Queensland, a state strategy was developed to plan an ongoing program of surveillance and eradication extending across the state (Austin and Csurhes 2004). This strategy outlines five management programs to prevent M. pigra from becoming a significant pest in Queensland:

1. Coordination: Plan, implement, manage, evaluate and revise a statewide, coordinated response to the threat posed by M. pigra.

2. Prevention: Prevent transport of M. pigra seeds into Queensland from the Northern Territory.

3. Surveillance and early detection: Detect new infestations of M. pigra as early as possible.

4. Eradication: Eradicate any M. pigra infestations in Queensland.

5. Research: Develop a capacity to control M. pigra, including an understanding of the plant’s ecology.

2.3 Management of M. pigra at Peter Faust Dam

Peter Faust Dam (Figure 10) is a large water body (74-kilometre perimeter at full supply) that provides flood mitigation primarily for canefields downstream, along the Proserpine River. The dam also provides irrigation water for cane farms and supplies domestic water to a number of towns. The dam was constructed in 1990, reaching almost full capacity the following year. A number of recreational activities are popular at the dam, including water sports, camping and pig hunting. However, the dam is particularly renowned as a site for barramundi fishing.

The current problem is that, while mature plants have been destroyed, seedlings continue to germinate, particularly as waters recede. The enormous seed bank could contain viable seeds for more than 20 years, so any eradication attempt must continue to monitor for at least this long. The location of M. pigra plants at Peter Faust Dam suggests it has been present since 1996, when the water level was at 32 per cent (Vitelli and Madigan 2005). Since then the water supply increased to about 80 per cent capacity, when M. pigra was discovered, and it has since receded. Masses of seedlings (see Section 1.3) emerged as the water fell from 80 per cent to 32 per cent capacity, but only isolated plants emerged as water receded further to 22 per cent in October 2005.


Figure 10. Peter Faust Dam, showing the water level at full supply and location of the main infestations. Also shown are boundaries of the five sections to aid monitoring and control.

7

Figure 11. High density of M. pigra seedlings in the core infestation area. This small plot is monitored and managed by NRW researchers. Photo by P. Austin.

A chronology of management actions, as summarised by Chopping (2004), is given below:

management plan requiring biannual surveys in February and September.

Initial management Control program April 2002 �After discovery of M. pigra in February 2001 at the south-eastern edge of the dam (Figure 10) a series of management actions were implemented, including:

• an immediate small-scale inspection of the south-eastern edge of the dam, which located approximately 100 M. pigra plants

• ground and water surveys around the entire perimeter of the dam to identify, map and control any M. pigra present; this involved the local cattle grazier, SunWater, Whitsunday Shire Council and NRW

• a helicopter survey within the dam and surrounding Proserpine River catchment, which recorded no large (and therefore visible) infestations

• a follow-up survey in September 2001, which recorded 150 recently germinated plants

• establishment of the Peter Faust Dam Mimosa Management Group, now Mimosa pigra Stakeholder Group (Austin and Csurhes 2004), comprising key stakeholders (see below), which drafted a five-year

In April 2002 a second control program was initiated, beginning with further surveys of the dam.

• M. pigra was found to be germinating both in the zone of the receding water level and within the thick Melaleuca band.

• Plant density (400 M. pigra plants per 25 square metres within heavy infestations; see Figure 11) and soil seed-bank levels were determined.

• The management group re-evaluated control options and a decision was made to clear an access track just off the foreshore within the south-western area.

• Additional Melaleuca zones with thick M. pigra present were bulldozed, piled and then burned. This provided access to infested sites and improved detection probabilities of M. pigra plants. Approximately 17 kilometres of track was bulldozed. Washdown sites were established and guidelines developed to minimise the risk of vehicles and other machinery moving seed off-site (Figure 12).

8 Risk of Mimosa pigra spread in Queensland

Figure 12. Washdown facilities, to clean vehicles potentially contaminated with M. pigra seed, have been placed at a number of locations around Peter Faust Dam.�Photos by A. Pople and P. Austin.�

Control program September 2002 Control at the site was again re-evaluated and recommendations were made to:

• undertake monthly inspections of the M. pigra-infested, south-western area of the dam and do random checks of the remaining perimeter

• undertake triannual surveys of the entire dam perimeter in September, February and May

• develop an extension program for minimising the risk of M. pigra spread from the dam (e.g. Figure 13) and highlighting the risk M. pigra poses to the state

• undertake feral pig control regularly • hold cattle for at least five days prior to movement off-site by the local grazier

• clear Melaleuca throughout the south-western area of the dam where most M. pigra plants were found and the majority of seed is likely to be present

• utilise fire management where appropriate.


Figure 13. Signs used to warn visitors to the dam of the presence of M. pigra, how to identify it and avoid transporting it away from the dam. Photos by E. Attard and P. Austin.

Risk of Mimosa pigra spread in Queensland 10

Management 2002–05� SunWater�

• Two full-time control officers were employed in October 2003 and are able to complete a survey of the dam foreshore and control of any emerging M. pigra plants every two months. Control involves a combination of chemical spray using Brush-Off®, physical removal of seedlings near and in water and burning areas, with Atarus® to kill surface seeds.

• The foreshore of the dam area was divided into five operational sections (Figure 10).

• Clearing of Melaleuca has been completed by bulldozer and chain in thicker areas and cleared by blade plough along the foreshore. Areas of regrowth will also require clearing in the future.

• Seed-bank counts have been undertaken within M. pigra-infested areas to assist in future management planning.�

2.4 Research on M. pigra in Queensland

Research has focused on the ecology of M. pigra and its control at Peter Faust Dam as aspects of these might well be unique to the site. In particular, there has been work on (see Section 1.3):

• quantification of the M. pigra seed-bank depletion rates and plant growth rates

• determination of age at maturity (4–6 months) for M. pigra at Peter Faust Dam

• evaluation of the efficacy of mechanical, fire and chemical control

• chemical registrations for both M. pigra and Melaleuca control.

2.5 Key stakeholders and their responsibilities

The Mimosa pigra Stakeholder Group (formerly Peter Faust Dam Mimosa Management Group) was formed to direct management activities. The group comprises the following key stakeholders, with respective responsibilities (Austin and Csurhes 2004).

The department of Natural Resources and Water initiates and coordinates the overall response to the threat posed by M. pigra. In particular:

• continues to research efficient and effective control techniques

• provides education services • maintains human resource capacity to eradicate M. pigra

• provides financial and administrative support to the Mimosa pigra Stakeholder Group

• develops appropriate legislation.

SunWater is responsible for the management of Peter Faust Dam. It’s role is to:

• help eradicate M. pigra where it grows on SunWater land

• maintain human resource capacity to eradicate M. pigra and recognise the need for allocating contingency funding�

• implement property hygiene practices to avoid seed movement by machinery, people and grazing animals.

Local governments

Local governments have a range of respoinsibilities. They:

• provide advice and assistance with respect to the strategic plan including strategic control activities

• ensure that eradication is undertaken on any lands under a council’s control including stock routes, roadsides and town commons

• liaise with relevant stakeholders and community to undertake eradication and awareness

• administer and enforce provisions of the Land Protection (Pest and Stock Route Management) Act 2002

• recognise the need for resource allocation to implement the statewide strategy.

Other Queensland Government departments Other departments such as Department of Main Roads, Environmental Protection Agency, Department of Primary Industries and Fisheries

• ensure awareness and early-detection programs are put in place

• ensure departmental staff cooperate to prevent spread of seeds

• ensure eradication is undertaken on all state-managed lands, including national parks and reserves, state road reserves, rail reserves (state rail authorities) and state forests and forestry reserves.

SunFish and Faust Dam Fish Stocking Association

These organisations:

• help raise awareness of the potential for seeds of M. pigra to be spread in nets and other fishing and boating equipment

• encourage members to take action to help prevent spread and to report any suspected plants.


Primary producer lobby groups Groups such as Queensland Cane Growers Organisation, AgForce and Queensland Farmers Federation:

• help raise awareness of the potential for seeds of M. pigra to be spread by cattle and machinery

• encourage members to take action to help prevent seed and plant spread and to report any suspected plants.

Proserpine Chamber of Commerce and Whitsunday Tourism

These organisations:

• help raise awareness of the potential for seeds of M. pigra to be spread by visitors to the dam

• encourage visitors to take action to help prevent seed and plant spread and to report any suspected plants.


Section 3

Assessing the risk of Mimosa pigra spread from Peter Faust Dam

3.1 Introduction

This section of the report addresses the question of how best to allocate finite funds in the management of M. pigra at Peter Faust Dam. Regular surveys of the perimeter of the dam, combined with good access tracks and clearance of Melaleuca for detection of M. pigra, are clearly required to ensure no further production of M. pigra seed. These are a high priority for management and are not considered here as negotiable or optional activities, but were nevertheless ranked with other management actions. However, the long-term persistence and vast amount of the seed in the soil will require monitoring for possibly more than 20 years. This also means that there is a reasonable chance of seed being transported outside the dam site. The possible routes of transport were identified and the associated risk was assessed through a series of meetings with stakeholders. Options for managing these hazards were then considered, along with the feasibility of implementation.

3.2 Methods

Conducting risk assessments by using expert judgement and involving stakeholders has become common practice in environmental management (Burgman 2005). The approach taken here draws on these experiences. The six stages of this risk assessment, shown in Figure 14, involved close interaction with all key stakeholders (see Section 2.5 and Appendixes 1 and 2). The potential pathways for seed transport away from the dam were first identified by NRW officers and SunWater staff. These are ‘hazards’ in risk-assessment terminology (Burgman 2005), but are given the more specific term ‘vectors’ here. Vectors are usually considered as carriers of disease, but have been used more broadly to include weed seed transport (e.g. Walden et al. 2004). Initially these vectors were split into those associated with moving seed within the dam and vectors moving seed away from the dam. This dichotomy was subsequently seen as largely unnecessary as the vectors and associated management actions were generally the same, although the consequences were different.

This list of potential vectors was mailed to all stakeholders prior to a workshop to see if any vectors had been missed, to score the risk of each vector on a scale of 1–10, and to consider the current and potential mitigation measures (i.e. management actions) for each vector. Participants were asked to

identify the inherent risk for each potential vector, current mitigation, residual risk (i.e. risk remaining given present management action) and what options were available to address this residual risk. For this exercise NRW staff were divided into regional managers and research scientists. The risk of an adverse event such as the spread of M. pigra seed can be considered as its likelihood multiplied by its consequences. Some vectors could have different consequences. For example, wildlife might move seed higher up the catchment, whereas water flow will move seed directly down the catchment, where impacts are likely to be greater (see Section 1.5). For the vectors examined here, the likelihoods and consequences were not considered separately.

An initial workshop was then held in Proserpine in September 2005 to enable face-to-face discussion of each vector and the potential mitigation measures. A scoring system was used to assess the feasibility of various management options. Some stakeholders (i.e. Proserpine Chamber of Commerce and tour operators) were unable to attend the workshop, so their input came through face-to-face meetings with NRW and SunWater staff. The results of this workshop were circulated in a draft of this report and a further workshop was conducted in March 2006 with participants having a greater familiarity with the risk-assessment process and a longer time to consider alternative management options. Risk scores, the scoring system to assess feasibility of management options, and the resultant scores were reassessed and alternative management options identified at this workshop.

At the September 2005 workshop, management options were given a feasibility score out of 10 using part of a system for assessing feasibility of controlling pest impacts in Queensland (Walton 2005). A management option is feasible if it has widespread community and government support, it is relatively inexpensive, it is logistically possible and it is effective at reducing pest impact and not simply reducing pest population size. For each management option, points were allocated for each of 12 attributes covering sociopolitical, technical and financial aspects of the option (Table 1). This latter assessment is consistent with the national post-border weed risk management protocol developed by the Weeds Cooperative Research Centre (Virtue et al. 2005) and weed risk assessments conducted in other states (e.g. Virtue 2004). Higher scores in Table 1 reflect greater feasibility of management. Most attributes are self-explanatory. The difficulty was modifying


the original attributes in order to apply them to management options to reduce risk, rather than following their original intention to more generally control a pest across the entire state. A description of some attributes is therefore given below.

• Of the sociopolitical attributes, landholder support refers to the extent to which landholders (i.e. SunWater and the local grazier) would have to change present management practice and whether they would consider the change worthwhile.

• State government commitment refers to all agencies whose support would be required.

• Under technical and financial attributes in the original use of this scoring system (Walton 2005) a contrast is made between the technical ability to reduce numbers (i.e. a high proportion of the population) and the ability to reduce the financial impact. For this study the contrast is of the ability to simply stop seed movement (or remove seed or plants) with the ability to reduce the risk of seed spread. These might differ if the management option cannot target a high-risk activity or area.

• Only some life stages (e.g. adults versus seeds) of a pest may be susceptible to or targeted by a management action, and so these management options are less feasible than options affecting all life stages. For M. pigra there are three relevant life stages: a long-lived seed bank, seedlings and mature plants. Most of the management options considered in this report attempt to reduce the risk of seed spread through stopping actual transport of seed. However, detection and removal of seedlings and adult plants are obviously important in reducing the risk of further seed production and therefore seed spread.

• Logistics of implementation refers to the influence of such things as access (e.g. remoteness, terrain), number of personnel required and equipment on the ability to carry out the option.

• Surveillance refers to monitoring compliance with and the effectiveness of the management option (e.g. change in the number of illegal campers as a proportion of all visitors).

• Duration of the action refers to whether the management option requires ongoing input (e.g. policing use of the dam at all times), periodic input (e.g. policing only during peak visitation periods) or is a single event (e.g. erection of a sign or fence). Assessing this attribute can be problematic because management options are not mutually exclusive and it is difficult to assess options such as signs, fencing and policing in isolation. Interactions between options should therefore also be considered.

Participants at the workshop were broken into groups to work on sets of management options. Each group then reported back to the workshop, enabling participants to contribute to the assessment of all options. The advantage of using a scoring system over, for example, subjective judgement is that it is transparent and to some extent repeatable, allowing a large number of attributes to be examined together and easy comparison of management options. An equal weighting was given to sociopolitical, technical and financial attributes, but this could also be reworked. While the assessment is quantitative, some attributes will be poorly known for a management option and attribute scores will vary among assessors. The source of variation can at least be readily identified and the score reassessed with more assessors or with better information. If an attribute for a management option was unknown, it was given a low feasibility score of 1. Thus the assessment was biased towards better known management options. A further benefit of using a scoring system is that it identifies those attributes that need to be addressed if the option is to be more seriously considered.

Scores for the 12 attributes of feasibility were added, and then divided by 30 to give a value out of 10 to be on the same scale as the risk score (see above). The feasibility score was then multiplied by the risk score to give a total score out of 100, which can be used to compare and rank management options. For this calculation an average risk score was required for each vector from the range offered by stakeholders. This average was determined from a separate meeting between NRW officers and SunWater. The score represented a weighted average based on each stakeholder’s expertise.


Table 1. Attributes and associated scores (out of 25) used to assess feasibility of management options. For each management option, scores were then added (for a maximum total of 300) and divided by 30 to give a value out of 10 to be on the same scale as the risk score (Table 2) and provide a convenient total score from their product out of 100. Actual scores are shown in Appendix 3.

Attributes

Sociopolitical

Local government support

Community and industry support

Landholder support

State government commitment

Technical

Availability of methods

Ability to stop weed movement

Life stage targeted

Logistics of implementation

Financial

Cost of methods

Cost of surveillance

Required duration of action

Ability to reduce risk of weed spread

High or long

25

25

25

25

25

Existing

25

25

All

2

2

2

2

25

Medium

12

12

16

12

12

Developing

12

20

Some

12

12

12

12

12

Low or short

2

2

2

2

6

20

Single stage

25

25

25

25

2

None or unknown

1

1

1

1

1

1

1

1

1

1

1

1


Figure 14. A chronology for the risk assessment undertaken for M. pigra at Peter Faust Dam.

Stage 1 Stakeholder meeting, 5 July 2005

Identification of potential vectors for seed movement away from dam

Stage 2

Mail survey of stakeholders, August 2005

Each person was asked to identify risk of seed movement for each vector, current and potental mitigation measures and remaining risk (i.e. residual risk). See Table 2

Stage 3

Stakeholder workshop, 8 September 2005

Face-to-face meeting (see Appendix 1) with further discussions on vector risk and options for management of vectors. Management actions ranked according to vector risk x feasibility of management. See Tables 2 and 3

Stage 4 Stakeholder interviews, September/October 2005

Interviews with stakeholders unable to attend workshop

Stage 5 Stakeholder meeting, February 2006

A draft of this report is circulated to stakeholders for comment. Alternative management options are discussed

Stage 6

Stakeholder workshop, March 2006

Face-to-face meeting (see Appendix 2) to revise estimates vector risk and feasbility of management options (see Appendix 3)


3.3 Vectors of seed spread

Ten broadly defined vectors for potential movement of seed within and away from the dam were identified. The risks assigned to each of these by stakeholders and the weighted averages are given in Table 2. Nearly all vectors were scored highly by at least one stakeholder group, but there was a considerable variation among stakeholders in the level of risk assigned to each vector. Some stakeholder groups tended to be more pessimistic than others (e.g. SunWater compared with Faust Dam Fish Stocking Association) across most vectors. Some groups (e.g. Faust Dam Fish Stocking Association) assigned risk over a greater range of values and so regarded some vectors as clearly riskier than others.

A brief description and discussion of each vector, based on stakeholder comments, are given below.

1. �Water flow within the dam and water level fluctuations

M. pigra seedpods can be dispersed considerable distances by water as they can float for extended periods. To date M. pigra plants have been found in four of the five sections of the dam (see Section 2, Figure 10).

As water levels have receded new areas have been exposed to the elements, allowing seed germination. Destruction of these seedlings, particularly before they mature and set seed, has relied on regular surveys of the dam perimeter from the waterline up to the full-capacity waterline. As water levels have receded, the area with M. pigra potentially emerging has increased and must be surveyed.

2. Recreational fishing, water sports and redclaw harvesting

Recreational activities at the dam involve by far the greatest number of people using the dam. Boats are landed on the foreshore, allowing people to come ashore, where they could pick up contaminated soil. M. pigra seed might by picked up in fishing gear, clothing and other equipment. People walking through mud near the water’s edge could bury seeds deeper into the soil profile, thereby increasing the time taken for germination and therefore delaying depletion of the soil seed bank. There are signs instructing people not to land boats on any foreshore, other than the designated boat ramp. However, there is still a high level of ignorance regarding conditions of entry. In some cases, signs are simply being ignored and people continue to come ashore in M. pigra-infested areas.

Present signage at the dam site (see Section 2, Figure 13) warns people about the presence of M. pigra at the dam, to avoid collecting soil, sand or water, and

to check that no seeds are being accidentally carried away from the dam. The signs explain how to identify M. pigra and who to contact if it is found. These signs are located at the boat ramp, toilet facility and Camp Kanga, close to the entrance of the dam. There are also new signs at the entrance to the dam, the boat ramp, the recreation area and on the road past the boat ramp, all instructing boat users not to get out of their boats. This restriction is also advertised in fishing magazines, newspaper articles and other extension material.

Fishing is particularly popular, with annual competitions bringing a large number of visitors to Peter Faust Dam. The dam is stocked with barramundi and it is the second most popular fishing spot on the east coast. As fishers travel from infested areas in the Northern Territory, where barramundi fishing is also popular, there is a risk that M. pigra seeds could be transported from one fishing area to another in boats, equipment or clothing. These concerns were raised in the weed risk assessment of M. pigra for the Northern Territory (Walden et al. 2004). There, outbreaks of M. pigra in areas hundreds of kilometres from the nearest infested area indicate vector-borne (e.g. by people and wildlife) dispersal rather than solely water or wind dispersal. SunWater believed there was little redclaw harvesting now undertaken at the dam because of past overexploitation, which is why they ranked its risk low.

3. Camping

Camping was seen as a similar risk to water activities as it can bring people, clothing and equipment into direct contact with the M. pigra seed or soil contaminated with seed. Again, seed might also be trampled deeper into the soil. At present public roads run past the dam, allowing easy access to the foreshore. Several types of sign warn people that camping is not permitted at the dam. This restriction is also advertised in newspaper stories, articles in fishing magazines and on signs at the boat ramp. Areas of the dam are also marked as restricted and off-limits to campers.

Many stakeholders commented that people ignore signs and continue to camp throughout the dam area. Fishing competitions are seen as particularly problematic, with a large, concentrated number of campers and increased activity in and around the dam. It was unclear how these restrictions could be enforced.

4. Wildlife

Several wildlife species are potential vectors of M. pigra seed away from the dam. They include feral pigs, wild dogs, wallabies and various bird species, particularly waterbirds. Mature seed and pods and


seed-contaminated soil have the potential to adhere to fur and feathers. Seed can also be ingested primarily (e.g. by mammalian herbivores known to graze on M. pigra) or secondarily and then passed in dung at a new location away from the dam, where the seed might still be viable (Benyasut and Pitt 1992). Even relatively short-distance movement of seeds above the high water mark at the dam is a problem, as they will then be outside the survey area and seed germination might then go undetected.

Feral pigs pose a particular threat as large numbers have been recorded at Peter Faust Dam, where they feed in the muddy margins of the dam. As well as being vectors of seeds, they create an environment for seed germination (Wingrave 2005). Fencing at the dam does not restrict pigs, so they are able to potentially cover larger distances than cattle and distribute seed into more inaccessible areas. Pig activity is greatest in the wet season and they are thought to migrate between downstream areas and the dam, although their movement patterns have not been documented here. Risk of seed spread by wildlife declines if adult plants are located and removed before seedpods mature, although transport of soil-borne seed, particularly mud, still poses a threat.

5. Livestock grazing

Cattle, camels and horses all graze within the M. pigra-infested areas (Figure 15) and are able to transport seeds in much the same way as wildlife. Cattle and horses currently range down to the foreshore, but camels have recently been excluded. Grazed M. pigra plants have been found at the dam. Seed-contaminated dung, particularly that of livestock, can also be picked up by vehicles.

Figure 15. Cattle in section 3 (Figure 10), near the heavily infested area. Photo by A. Pople.


6. Pig hunting

There are currently authorised and unauthorised pig hunters active at Peter Faust Dam. Authorised hunters are aware of the location of M. pigra and are considered to generally be responsible. Unauthorised pig hunters are particularly problematic as they have been operating in the M. pigra-infested areas and often dump pig viscera throughout the dam site and beyond. Pig hunters are currently uncontrolled and unmonitored. Pig hunting is also taking place outside of normal working hours, making it difficult to enforce compliance. Hunters and their dogs are accessing areas by four-wheel-drive vehicles and also by boat, thus providing a number of ways of picking up seed.

7. Track use and off-road driving

Two groups of people need to be considered separately. The first group are people accessing the dam for recreational use, such as fishers, pig hunters and campers, and those wanting to access the dam (illegally) to extract soil. The second are those employed to work at the dam, such as SunWater staff, road workers, Ergon Energy employees, the local grazier and staff involved in the eradication of M. pigra (see Vector 11). Recreational users of the dam were seen as the more difficult to manage. Some members of the public were considered as ‘indifferent’ and ‘oblivious’ to the risks of spreading M. pigra outlined on signs and other public notices. Currently the local grazier is intercepting at least three vehicles a week within restricted areas (Faust 2005).

8. Water flow from the dam

All stakeholders at the workshop considered water flow from the dam as a high risk in spreading M. pigra to the wetlands and canefields downstream. Seeds could travel through the intake valves when water is released and pass over the dam wall during a cyclonic rain event that fills the dam to capacity. The dam has filled to 85–98 per cent of capacity on two occasions since 1991. Water is extracted for irrigation and domestic supply from 5 to 7 metres below the surface using a multilevel offtake tower. Baulk gates close to exclude water at all depths outside the desired level.

9. Irrigation

Irrigation is a subset of the previous vector, but has a substantially lower risk (Table 2), more specific endpoints and a unique set of management options compared with water flow over the spillway. SunWater is responsible for water management at the dam, carrying out maintenance and safety provisions related to water storage and use.

10. Extraction

The risks of M. pigra seeds being extracted with sand and gravel and deposited over a wide area are high. As the cost of sand has risen, unauthorised extraction has become more common, but is difficult to police. Downstream extraction from the Proserpine River has already been stopped due to environmental impacts, but contractors have been caught removing sand in breach of restriction notices. There is currently poor awareness in the extraction industry of the threats posed by M. pigra. Extraction of dam sediment has taken place on one known occasion from a M. pigra-infested area within the dam.

11. Management activities

Workers at the dam might inadvertently pick up seeds while travelling in M. pigra-infested areas. However, since daily survey work began in 2003, NRW and SunWater have instigated a comprehensive system of washdown procedures involving four washdown facilities. There is also a system of ‘clean’ and ‘dirty’ tracks. Workers at the dam use only the clean tracks unless they are involved in the eradication program. Use of dirty tracks requires use of the washdown facilities. A detailed entry and exit procedure has been developed.


Vector Risk

1 2 3 4 5 6 7 8 9 10

1a. Water flow within dam R C F MW S

1b. Water level fluctuations F MWRC S

2a. Recreational fishing F C M W SR

2b. Water sports MF RC W S

2c. Redclaw harvesting S M F C WR

3. Camping MWF SRC

4. Wildlife M WF SRC

5. Livestock grazing F MC WR S

6. Pig hunting MW SMRCF

7. Track use and driving off-road RCF MW S

8. Water flow from dam F C MW SR

9. Irrigation S MRF C W

10. Extraction C F M WR S

11. Management activities R CF MW

S = SunWater; M = NRW regional managers; R = NRW weed researchers; W = Whitsunday Shire Council; C = Proserpine Chamber of Commerce; F = Faust Dam Fish Stocking Association

Table 2. Risk of M. pigra seed spread for 11 vectors, with existing controls in place, assigned by six stakeholder groups. Risk scores range from a low of 1 to a high of 10. An agreed final score (grey cell) was determined by consensus at a stakeholder meeting in March 2006. Vectors 1a–b and 2a–c were grouped because they had common management options and so a common risk score was assigned.


3.4 Management options

A wide range of management options to address each potential vector of seed spread was identified in the mail survey and workshop. These options are described below and are grouped by each potential vector of spread.

Some vectors had virtually all management options in common. Therefore these vectors (1a–b and 2a–c in Table 2) were grouped and a common risk score estimated to allow a total score to be calculated.

1. Water flow and fluctuations within dam

Option 1.1 Continued surveys of the dam

Surveying is carried out throughout the year by two control officers in the main M. pigra-infested area. More personnel are used on a regular basis. Access to the survey areas is time consuming, usually taking an hour or more before survey work can start. This is due to the rough terrain and the large number of gates. Cattle grids will speed up the operation. Increased survey intensity (i.e. more thorough inspection) or better search methods (e.g. option 1.5 below) will be required to reduce the risk of missing plants.

Survey effort will need to increase to account for the larger survey area with lower water levels, but could be reduced as water levels increase. Survey effort should be stratified according to probability of M. pigra seedling emergence. This happens to some extent, with greater effort in two core areas with high seed density, but this could be optimised by formally matching survey effort with probability of emergence and probability of detection.

Option 1.2 Additional resources used during periods when germination is most likely

Effort can be stratified by area (see option 1.1 above) and also over time, providing the most efficient use of finite resources.

Option 1.3 Contour banks or sediment curtains around high infestation areas

Contour banks could be useful following moderate rainfall events, but would not be useful following cyclonic rain.

Option 1.4 Sediment curtain to restrict seed movement

A sediment curtain could also be employed, but it would be costly and might not be effective.

Option 1.5 Ensure continued access to infested areas through track maintenance and clearance of Melaleuca regrowth

This is a continuation of current practice, providing more efficient surveys (see option 1.1 above) and improving the probability of detection of M. pigra

plants. Adequate tracks are also required to allow workers rapid exit in case of emergency (e.g. illness or injury).

2. Recreational fishing, water sports and redclaw harvesting

Option 2.1 Education

Community awareness can be raised further through the media, particularly those servicing these activities (e.g. fishing magazines). There have been community-service announcements and the problem has been advertised on stickers, fridge magnets, identification cards, rulers, posters and warning brochures. There are now several warning signs at the dam in strategic locations (see Section 3.3, vector 2). However, compliance with restrictions has been poor and heightened awareness will not necessarily lead to an improvement.

Some formal assessment (e.g. visitor surveys) of level of awareness and monitoring of compliance (e.g. number of incursions into restricted areas over time per 100 boats or visitors) would help evaluate extension activities. Hills (2002) evaluated a campaign aimed at making recreational fishers in the Northern Territory more aware of serious weeds such as M. pigra and changing their behaviour to reduce the risk of weed spread. Evaluation involved a mail survey prior to and following information being broadcast through a variety of media. Following the campaign, the majority of respondents believed they had an improved knowledge and recognition of weeds, had a better understanding of weed impacts and how weeds spread, and were more likely to report weeds. Extension methods were ranked according to cost and visibility. A newsletter to the local fishermen’s association was the most visible source of information, followed by signage at boat ramps, posters and television. Apart from the newsletter (which was free), cost declined directly with visibility rank, although the cost of signage was many times greater than other information sources. Unfortunately, it was not clear from the results reported by Hills (2002) whether the awareness campaign had actually changed the behaviour of fishers.

The Department of Natural Resources and Water is undertaking a bioeconomic analysis of managing M. pigra at Peter Faust Dam. This will involve modelling the potential distribution of M. pigra and its consequent costs (see Section 1.5). The costs and benefits of alternative management actions will then be examined to seek an optimal strategy. Part of this work has involved questionnaire surveys of people fishing at the dam. These surveys provide some insight into who to target in an awareness campaign.


Sixty-nine questionnaires were recently completed during the low fishing season in February 2005 (Tumaneng-Diete 2005). On average, visitors during the low season estimated they made 13 ± 3 fishing trips (range 1–120) to Peter Faust Dam per year and they made 32 ± 5 trips (range 0–105) to other fishing destinations. Other fishing destinations included Tinaroo Dam, Lakefield National Park, Cairns, Townsville, Borumba Dam, Lake Awoonga and Hinchinbrook Island. Visitors’ towns of residence were an average of 468 ± 88 kilometres (range 1–3000) from Peter Faust Dam. Forty per cent of visitors had travelled <100 kilometres from home to the dam. Not surprisingly, there was a negative correlation between the number of visits and distance travelled from home. However, the relationship was largely a result of the lack of >10 visits by people travelling >600 kilometres from home. Multiple visits per year were still being made by people from interstate, and a large number of visits per year (three visitors making at least ten visits) were being made by people living a moderate distance (200–400 kilometres) from the dam. Eighty-eight percent of visitors used their own boats to fish, the remainder using a lure or trap from the bank or a hired boat. Eight percent of visitors were planning to trap redclaw crayfish, suggesting this activity, while small, is not trivial (see Section 3.3, vector 2).

These statistics highlight the need, at least for low-season visitors, for an extension campaign beyond the local area. Most visitors (62 per cent) made multiple visits to Peter Faust Dam per year and no doubt made visits in other years. Therefore, there is likely to be value in educating visitors at the dam site, particularly if heightened awareness of M. pigra at the dam, its potential impact, and how to avoid its spread comes through word of mouth. The survey also highlights the potential for M. pigra to be spread well beyond the catchment by recreational users of the dam. High-season surveys are also required.

Option 2.2 Public washdown facilities

There is currently no washdown facility at the boat ramp, but there would need to be monitoring and policing of its use by trained staff if one were constructed.

Option 2.3 Restricted access

Vehicle access to M. pigra-infested areas can be limited through fencing and road closures using gates (see option 7.1 below). Boat access to the shoreline is more difficult to restrict and is the management action identified here. Marker buoys just off the western shoreline could be used to delimit the high-risk area. Compliance will be difficult to achieve even with substantial extension programs (see option

2.1 above). The threat of closure of the whole dam appears to be encouraging most people to adhere to the restrictions. However, a system of penalties might also be required. SunWater and the local grazier have agreed to place a gate at the end of Crystal Brook Road.

Policing restricted access was seen as both necessary and problematic. Some staff of SunWater, Whitsunday Shire Council and NRW working at the dam have been reluctant to confront people disobeying signs. They are neither required to perform these duties nor have they been trained in policing. As landholders, SunWater and the local grazier are legally responsible for taking reasonable steps to keep their land free of M. pigra, a Class 1 pest plant under the Land Protection (Pest and Stock Route Management) Act 2002. This obligation does not extend to ensuring no further spread of the pest, which would require restricted access and enforcement of that restriction.

Appropriate enforcement involves signs, fences and other markers identifying the restricted zone and removal or reporting of people not complying. Nevertheless, people disobeying these restrictions are committing an offence by trespassing, which is a matter for state police. They would also be committing an offence under the Act by knowingly transporting vehicles (including boats) contaminated with M. pigra seed. People must take reasonable steps to ensure vehicles are free of seed. NRW could serve an emergency quarantine notice on part or even all of the dam (see option 2.4 below), which would provide stronger legal support for enforcement. This is effective for three months and stipulates the requirements of landowners, areas where access is restricted and enforcement by authorised people. Alternatively, under Local Government Local Law No. 14, Whitsunday Shire Council can develop a ‘local law policy’ to restrict access to land encompassing Peter Faust Dam, for the purpose of preventing the spread of M. pigra. This option is currently being pursued. Enforcement would obviously be most important during popular periods such as fishing tournaments.

Option 2.4 Quarantining of the entire dam

This option involves denying public access to the dam and surrounds, whether it is for fishing, crayfish trapping, water sports, camping or simply sightseeing. This option was considered a last resort as most stakeholders see the dam as a valuable tourist attraction. Continued public use of M. pigra-infested areas, despite advertised restrictions, has frustrated attempts to contain and eventually eradicate M. pigra. In some cases, fences have been cut and there have been aggressive responses from members


of the public to requests to leave areas where they are prohibited. Prohibiting public access to the dam would require closure of the main access road.

Prohibiting public access could be undertaken by serving an emergency quarantine notice to relevant landowners (SunWater and the local grazier) under the Land Protection (Pest and Stock Route Management) Act 2002. However, a range of restrictions are possible under an emergency quarantine notice of which prohibiting access to the entire dam is only one, extreme, option. Alternatively, the notice could regulate what a person can do on the land (e.g. line fishing but no cray trapping) and could restrict access to part of an area (see option 2.3 above) or regulate how contaminated material must be treated (e.g. a holding period for cattle in a M. pigra-free area, see options 5.1 and 5.2 below). Again the Act places an onus on landowners to try to eradicate M. pigra at the site and on the public to not transport seed, but it does not restrict access unless that is identified in an emergency quarantine notice.

Option 2.5 Conditions for fishing permits

A condition of permit to fish at Peter Faust Dam could be to complete a course describing any restrictions and an understanding of how to minimise weed seed spread. A further option is to have a boom-gate entry into the boat ramp at the dam. The permit would include a swipe card to activate the boom.

3. Camping

Option 3.1 Enforcement of camping ban

Enforcement is required, given the continuing disregard of signs and barriers (see option 2.3 above). This would involve advertised penalties and policing.


Signs and other awareness efforts have not stopped people camping, but they might still have reduced the number of offenders and thus the risk of M. pigra seed spread.

4. Wildlife

Option 4.1 Baiting program for feral pigs

Trapping programs for feral pigs have been largely unsuccessful and there is currently no baiting at the dam. Pig hunting will reduce numbers, but is likely to be less effective than baiting (Choquenot, McIlroy and Korn 1996, Department of the Environment and Heritage 2005). Ground shooting has been found to be ineffective at reducing feral pig numbers to low densities unless it is intensive. In contrast, baiting can provide a rapid and substantial reduction. Aside from cost, the disadvantages of baiting include non-target mortality and the method being considered inhumane,

the latter concern being shared with hunting with dogs (Choquenot, McIlroy and Korn 1996, Department of the Environment and Heritage 2005).

Option 4.2 Improved understanding of pig movements

A radio telemetry study would help quantify the risk of seed spread posed by feral pigs. It would identify the time spent by pigs in the M. pigra-infested areas and the probability and distance of movement downstream. However, at a stakeholder meeting in February 2006 Jim Mitchell (NRW), a pig research scientist, advised the group that pigs were unlikely to move outside the catchment, but pigs could still move seed outside the area being surveyed for M. pigra plants. This study is therefore likely to shift emphasis to surveying creek lines and other shaded areas to locate resting areas for pigs within the dam catchment, where transported seed is most likely to be deposited.

5. Livestock grazing

Option 5.1 Holding period for cattle

Stakeholders generally agreed that cattle that have been grazed in potentially M. pigra-infested areas should be held for a period (at least seven days is required in the Northern Territory) before being moved from the dam. A formal agreement on this arrangement is needed between the local grazier and NRW that includes covering the additional direct and indirect costs (e.g. feeding, transport delay, change in cattle condition) of holding cattle.

There was a suggestion that this agreement would include use of a Weed Hygiene Declaration (http://nrm.dnr.qld.gov.au/pests/weeds/weed_ spread/legal/weed_hygiene_dec.html), providing assurance that cattle have been treated in such a way as to minimise the risk of spreading M. pigra. This declaration (written notice) is a legal requirement under the Land Protection (Pest and Stock Route Management) Act 2002, but only refers to certain Class 2 declared plants. While the declaration is not required in this case, it is nevertheless an offence under the Act to knowingly transport vehicles or other things such as stock or fodder contaminated with M. pigra seed, and people must take reasonable steps to ensure transported items are free of seed. Buyers of contaminated stock would also be able to sue for damages.

Option 5.2 Cattle excluded from high-risk areas

Fencing high-risk areas (i.e. parts of the western foreshore of the dam) from livestock would be costly initially, but is likely to be cost-effective in the longer term. It would substantially reduce the risk of stock picking up seed and would reduce the number of animals needing to be held before transport (see option 5.1 above). There would be an obvious cost to


http://nrm.dnr.qld.gov.au/pests/weeds/weed

the landholder through lost production related to the size and quality of the areas excluded from grazing.

6. Pig hunting

Option 6.1 Policing unauthorised hunting

As discussed earlier (see Section 3.3), this activity is difficult to police, but it might become easier if limited points of entry to M. pigra-infested areas were through fencing and road closures using locked gates (see option 7.1 below).

Option 6.2 Washdown procedures for hunters

Authorised hunters are instructed to leave pig viscera and other carcass off-cuts in designated areas where they can be checked periodically for M. pigra seedlings. A further requirement would be to wash down both vehicles and carcasses, which is a requirement for all workers entering the high-risk areas of the dam (see Section 3.3). Chiller boxes also provide an opportunity to inform hunters of the presence of M. pigra at the dam and how to minimise the risk of spread.

Option 6.3. Ban pig hunting

This would simplify policing and reduce traffic in the high-risk areas. Nevertheless, enforcement of the ban would be required (see option 6.1 above). The control of pigs through hunting would need to be replaced by a baiting program (see option 4.1 above).

7. Track use and driving off-road

Option 7.1 Fence access to the foreshore

The closure of tracks providing access to the foreshore was seen as a priority by all stakeholders. Again fencing is costly but would be cost-effective in the long term. It is the most effective option for stopping traffic, including four-wheel-drive vehicles, and access needs to be denied for a long time, given the longevity of M. pigra seeds in the soil. Therefore the costs of fencing will be offset to some extent by the reduced costs of policing, signage and the overall reduced risk of M. pigra seed spread. A locked gate at the end of the public road heading south-west from the boat ramp would provide a further barrier.


Track closures would need to be supported by an awareness campaign targeted at key groups such as fishers and pig hunters.

8. Water flow from dam

Option 8.1 Continued extraction of water through underwater gates

Fortuitously this extraction point will also minimise

the risk of M. pigra seed being extracted. Surface or benthic extraction is clearly a much higher risk.

Option 8.2 Downstream surveys

Direct surveys would be difficult in some areas (e.g. beyond Spruce’s Crossing) because of vegetation. To be feasible, monitoring would need to be of low intensity, targeting likely establishment sites (e.g. open, disturbed, moist areas such as flood plains). If this was not feasible, monitoring would have to rely on downstream landholders identifying M. pigra (see option 9.2 below) or opportunistic sightings (e.g. by NRW, SunWater or Whitsunday Shire Council officers).

Option 8.3 Water release through offtake rather than spillway

At the time of the workshop the feasibility and safety of this option were unclear. Recent investigations indicate that it would not be feasible.

9. Irrigation

Option 9.1 Sub-artesian retrieval rather than surface pumping

Unfortunately most people do not have access to underground water, so water would still need to be released from the dam.

Option 9.2 Education of downstream users

Notably M. pigra was found at the dam by the local grazier. Downstream landholders and employees are the people most likely to encounter M. pigra. Community monitoring is likely to be the only feasible method, despite its unreliability, because of the cost of alternatives such as direct monitoring (see option 8.2 above), given the size of the survey area and the difficulty of sampling rare objects.

Information can be provided to downstream users in a number of ways. The ability to correctly identify M. pigra is obviously critical. Actual specimens are ideal and preferably shown on site rather than as potted plants. A field day at the dam would provide the broader context and an opportunity to discuss the issue with a range of people.

Option 9.3 Quarantine both dam and water

Related to option 2.4, this would be an obvious cost to irrigators (or government through compensation) and a high surveillance cost.

Option 9.4 Screening of irrigation water

Strainers in the Boondoomba and Wivenhoe pipelines are used to avoid the transfer of exotic fish, such as tilapia, and their eggs, between water bodies in Queensland (Tarong Energy 2003). Appropriate filters would need to be developed for M. pigra seed.


This option has a very high initial cost, but would be effective at reducing the risk of seed spread through irrigation. It would obviously not stop the spread from water flowing over the spillway.

10. Extraction industry

Option 10.1 No extraction permits in area

The extraction industry is a potential vehicle for spreading not only M. pigra but other declared plants. The increased cost of soil has increased this risk. There needs to be better monitoring of the industry by NRW and better awareness of the risk of weed seed spread through transport of soil. This option would require signage, policing, fines and restricting road access (e.g. locked gates) to more effectively deter extraction of soil from the dam and nearby.

11. Management activities

Surveys, control and research undertaken at the dam involve procedures to reduce the risk of seed spread. These were considered important but sufficient and, while these procedures do not eliminate risk, further options to minimise the residual risk were not considered in this assessment.

3.5 Ranking management options

Scores for the feasibility of each of the above management options are presented in Table 3 along with the risk score (Table 2) and the product of the two (total score). Options have been ranked by the total score. The scoring system ignores potential interactions among options. For example, the two options addressing camping scored relatively moderately when viewed in isolation. However, the combined effects of both could be very effective. Not surprisingly there was overlap among options between vectors such as improved education, policing and restricting access.

The continuation of the present surveys was ranked only moderately, largely because the vector it addressed had a low-risk score. If the vector had been persistence or expansion of a M. pigra population at the dam, then the score for continuation of surveys would almost certainly have been boosted by a high-risk score. A pig-movement study ranked surprisingly high. Downstream surveys were ranked low, largely because water flow from the dam was considered only a moderate risk. These surveys were nevertheless considered low cost with high sociopolitical support. All three of these activities are not really alternatives to other management actions; rather they can direct management activities. As a

result they cannot be directly compared with other management options.

Enhancement (i.e. temporal and spatial stratification) of current surveys was ranked highly by stakeholders. Management of the risk posed by cattle ranked highly, reflecting its importance and feasibility. However, cattle-exclusion areas scored poorly because of perceived low support among government and the landholder, and relatively high cost. Education of recreational users had a moderate ranking, as did restricting their access to high-risk areas. Achieving compliance was generally considered difficult and ranked below other options. However, options involving restricting access and imposing conditions of entry (e.g. washdown facilities, conditions for fishing permits) should not be seen as alternatives as they often required policing to be effective. Many options, such as restricting access points to the water through fencing and locked gates, would make policing easier. Pigs are likely to be best managed through a ban on hunting and implementation of a 1080 baiting program to control numbers.

An alternative to ranking management options is to only consider options above some threshold total score. The combination of relatively low risk and low feasibility would dismiss a management option. There are breaks in the scores at 45 and 55, providing two tiers for consideration.

A more thorough evaluation of management options to minimise the risk of spread of M. pigra involves building an explicit model, describing the probability of seed spread by various means. The effect of uncertainties in model parameters (e.g. environmental variation, visitation rates, wildlife density, cattle movement) on risk of spread and optimal management can be explored through simulation. The actual direct and indirect costs of each management option need to be calculated and compared, as well as the cost of M. pigra spreading beyond the dam. The simpler, faster and cheaper approach described here provides the starting point, identifying a range of vectors and mitigating management options that can now be formally modelled.


Table 3. Scores for feasibility of management calculated using the criteria in Table 1. The risk score from Table 2 is also shown, along with the product of the scores (total score) on which the management options have been ranked.

Management option Feasibility score Risk score Total score

4.2 Pig-movement study 7.1 10.0 71

7.1 Fence access to the foreshore 7.7 9.0 70

4.1 Pig baiting 6.9 10.0 69

6.3 Ban pig hunting 6.5 10.0 65

5.1 Holding period for cattle 7.4 8.0 59

3.2 Camper education 5.4 10.0 54

7.2 Road-user education 5.8 9.0 52

1.2 Target high germination periods 7.5 6.5 49

1.1 Continue surveys 7.5 6.5 49

2.1 Water-sports education 4.8 10.0 48

3.1 Enforcement of camping ban 4.7 10.0 47

2.3 Restricted water-sports access

1.4

4.6 10.0 46

1.5 Maintain access to infested areas 7.1 6.5 46

8.1 Continue water extraction through underwater gates 9.1 5.0 45

2.5 Conditions for fishing permits 4.5 10.0 45

6.1 Police pig hunting 4.1 10.0 41

5.2 Cattle-exclusion areas 5.0 8.0 40

6.2 Washdown for pig hunters 3.6 10.0 36

8.2 Downstream surveys 7.2 5.0 36

2.4 Quarantining the whole dam 3.1 10.0 31

2.2 Public washdown facilities 3.0 10.0 30

9.2 Surveillance by irrigators 8.4 3.0 25

1.3 Contour bank 3.4 6.5 22

8.3 Water release through offtake only 4.3 5.0 21

9.4 Screening of irrigation water 7.0 3.0 21

10.1 No extraction permits 7.3 2.0 15

9.3 Quarantining water 3.5 3.0 11

9.1 Alternative of sub-artesian water 2.8 3.0 8

Sediment curtain 1.0 6.5 7


3.6 Making management decisions

While the rankings in Table 3 provide some guidance to management, it is not obvious how best to allocate resources. Spending the most resources on management options targeting vectors with the highest risk is unlikely to be the most efficient way of reducing overall risk of weed spread, as has been argued for endangered species management (Possingham et al. 2002). It may be optimal to spend most money on action that relatively cheaply reduces a moderate risk to low risk, rather than spending money on a more expensive option that can only slightly reduce a large risk. A hypothetical example of this is shown in Figure 16, where cattle exclusion (e.g. using fencing) is considered costly and is essentially all or none. The risk of cattle spreading M. pigra is relatively high, but reduction in this risk can only be achieved with a large budget. Therefore limited funds are likely to be best spent on pig baiting, which provides a cheaper reduction in risk. With more funds, expenditure on education of recreational users of the dam (e.g. signage), as well as pig baiting, becomes worthwhile.

The financial cost of methods was considered in the feasibility score, but this was subjectively ranked on a coarse scale (Table 1 and Appendix 3). The actual cost of management options is required, even if it is a rough estimate. The ability of management options to reduce risk (as a function of resources) also needs to be determined. This attribute was also incorporated into the feasibility score, but again it was crude. As part of the next step it would be useful for the stakeholder group, with assistance from experts, to construct the cost–risk relationships for viable management options, as portrayed in Figure 16.

Given the objective is to minimise overall risk of M. pigra spreading from the dam, the risks associated with each vector need to be combined. Assuming these probabilities (pi) are independent, the overall risk is one minus the product of each vector’s probability of not spreading M. pigra (1-pi). For example, three vectors may have probabilities of spreading M. pigra of 0.1, 0.05 and 0.01, respectively. The overall risk is 1 – (0.9 × 0.95 × 0.99) = 0.15. Given the relationship between pi and cost (e.g. Figure 16) for each management option, funds from a fixed budget can be allocated to each option to minimise the overall risk.

3.7 Monitoring and performance evaluation

Whatever management is undertaken, there needs to be some monitoring of its effectiveness. The goal is to reduce the risk of M. pigra spread by specific, potential vectors. Finding M. pigra outside the dam does not necessarily indicate failure of management as the risk of spread cannot be eliminated entirely. Therefore, this should not be used as a performance indicator, although the rate of spread would be an appropriate indicator where M. pigra was already spreading. Appropriate indicators are likely to be reductions in the activity (assumed to be correlated with risk of weed spread) of people, pigs and cattle in the M. pigra-infested areas, use of washdown facilities and survey effort downstream of the dam.


Figure 16. Hypothetical example of how to best allocate resources among three management actions to reduce the risk of spreading M. pigra. With few resources (A), funds are best spent on pig baiting because it will generate the greatest reduction in risk. With a moderate level of resources (B), some funds should be directed to public education. With a large budget (C), funds should be spent mostly on cattle exclusion, followed by pig baiting then education.

Acknowledgments

We greatly appreciate the efforts of workshop participants, who all recognise the importance of minimising the risk of spread of M. pigra. We also thank staff at the Land Protection branch of NRW in Brisbane who provided advice during the project and comments on this report. In particular, we thank Phil Maher, Chris Ryan, Mirranie Baker, Glen Fisher and Marc Bryant. Barbara Madigan and Joe Vitelli also provided valuable comments on an earlier draft. We thank Terrence Chen and Moya Calvert for providing figures 1, 2, 8 and 10, Stephen Potts for comments on the report and Hugh Possingham for suggestions on how best to allocate finite funds to management action.


References

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http://www.tarongenergy.com.au/pdf/community

Name Organisation

Peter Austin Department of Natural Resources and Water

Cassandra Chopping Department of Natural Resources and Water

Lindsey Dobe Faust Dam Fish Stocking Association

Charlie Faust Local cattle grazier

Josh Griffiths Whitsunday Shire Council

Shane Haack Department of Natural Resources and Water

Troy Huckstepp Whitsunday Shire Council

Charlie Large Mackay Whitsunday Natural Resource Management Group

Doug Lee Canegrowers

Barbara Madigan Department of Natural Resources and Water

Stephen Potts Department of Natural Resources and Water

Joe Vitelli Department of Natural Resources and Water

Shane Whitney Proserpine Chamber of Commerce

Jason Williams SunWater

Appendix 1. List of stakeholders involved in the mail survey, attending the September 2005 workshop or interviewed in September/October 2005 for this risk assessment.


Appendix 2. List of stakeholders involved in the March 2006 workshop.

Name Organisation

Rebecca Andrews Tourism Whitsundays

Cassandra Chopping Department of Natural Resources and Water

Charlie Faust Local cattle grazier

Bren Fuller Whitsunday Shire Council

Shane Haack Department of Natural Resources and Water

Doug Lee Canegrowers

Barbara Madigan Department of Natural Resources and Water

Tony Pople Department of Natural Resources and Water

Jason Williams SunWater

Kent Worsley Department of Natural Resources and Water

Belinda Yep Department of Natural Resources and Water


Appendix 3. Scores (out of a possible 25, Table 1) for each attribute of feasibility of management actions. Attributes are described in Section 3.2. Scores were added then divided by 30 to give a total out of 10. Totals were multiplied by the risk score (Table 2) to give a value out of 100 that could then be used to rank management options (Table 3).

Management option

Sociopolitical Technical Financial

TotalLocal government support


Landholder support




Life stage targeted


Cost of methods


Duration of action


1.1 Continue surveys 25 12 25 25 25 12 25 12 25 12 2 25 7.5

1.2 Target high germination periods

1.3 Contour bank

1.4 Sediment curtain

1.5 Maintain access to infested areas

2.1 Water sports education

2.2 Public washdown facilities

2.3 Restricted water sports access

2.4 Quarantining the whole dam

2.5 Conditions for fishing permits

3.1 Enforcement of camping ban

3.2 Camper education

4.1 Pig baiting

4.2 Pig movement study

5.1 Holding period for cattle

5.2 Cattle exclusion area

25

1

1

25

25

12

1

1

25

12

25

25

25

25

2

12 25 25 25 12 25 12 25 12 2 25 7.5

1 12 1 1 1 6 25 25 25 2 1 3.4

1 2 1 1 1 6 1 2 12 1 1 1.0

25 25 25 12 25 25 12 2 12 12 12 7.1

12 12 12 12 6 25 12 12 2 2 12 4.8

12 16 2 1 12 6 12 2 2 2 12 3.0

1 25 25 12 12 20 25 2 2 2 12 4.6

1 2 1 25 1 20 25 12 2 2 1 3.1

25 2 12 1 12 20 1 12 12 2 12 4.5

2 25 25 25 12 20 2 2 2 2 12 4.7

1 25 25 25 6 25 2 12 2 2 12 5.4

12 25 25 25 12 20 12 25 12 2 12 6.9

25 25 25 25 12 25 12 12 12 12 2 7.1

25 25 25 25 12 20 12 2 25 2 25 7.4

25 2 2 25 12 20 12 2 25 12 12 5.0


Appendix 3 continued

Management option

Sociopolitical Technical Financial

TotalLocal government support


Landholder support




Life stage targeted


Cost of methods


Duration of action


6.1 Police pig hunting 12 12 16 12 25 6 20 2 2 2 2 12 4.1

6.2 Washdown for pig hunters

12 12 16 2 25 12 20 2 2 2 2 1 3.6

6.3 Ban pig hunting 25 12 25 25 25 12 20 12 12 12 2 12 6.5

7.1 Fence access to the foreshore

25 1 25 25 25 25 20 12 12 25 25 12 7.7

7.2 Road-user education 25 12 2 2 25 6 25 25 12 12 25 2 5.8

8.1 Continue water extraction through underwater gates

25 25 25 25 25 25 20 25 25 25 25 2 9.1

8.2 Downstream surveys 25 25 25 25 12 12 25 2 25 25 2 12 7.2

8.3 Water release through offtake only

1 1 1 1 1 25 20 2 25 25 25 1 4.3

9.1 Alternative sub artesian water

1 2 1 2 1 25 20 1 2 25 2 2 2.8

9.2 Surveillance by irrigators

25 25 25 25 25 12 25 12 25 25 2 25 8.4

9.3 Quarantining water 2 2 2 2 1 12 20 1 2 25 25 12 3.5

9.4 Screening of irrigation water

25 25 25 25 12 12 20 2 2 25 25 12 7.0

10.1 No extraction permits 25 12 25 25 25 12 20 25 25 12 2 12 7.3


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