Section 3

Assessing the risk of Mimosa pigra identify the inherent risk for each potential vector, spread from current mitigation, residual risk (i.e. risk remaining given present management action) and what options 3.1 Introduction were available to address this residual risk. For this exercise NRW staff were divided into regional This section of the report addresses the question of managers and research scientists. The risk of an how best to allocate finite funds in the management adverse event such as the spread of M. pigra seed of M. pigra at Peter Faust Dam. Regular surveys of the can be considered as its likelihood multiplied by its perimeter of the dam, combined with good access consequences. Some vectors could have different tracks and clearance of Melaleuca for detection of consequences. For example, wildlife might move seed M. pigra, are clearly required to ensure no further higher up the catchment, whereas water flow will move production of M. pigra seed. These are a high priority seed directly down the catchment, where impacts are for management and are not considered here as likely to be greater (see Section 1.5). For the vectors negotiable or optional activities, but were nevertheless examined here, the likelihoods and consequences ranked with other management actions. However, the were not considered separately. long-term persistence and vast amount of the seed in the soil will require monitoring for possibly more than An initial workshop was then held in Proserpine in 20 years. This also means that there is a reasonable September 2005 to enable face-to-face discussion of chance of seed being transported outside the dam each vector and the potential mitigation measures. site. The possible routes of transport were identified A scoring system was used to assess the feasibility and the associated risk was assessed through a series of various management options. Some stakeholders of meetings with stakeholders. Options for managing (i.e. Proserpine Chamber of Commerce and tour these hazards were then considered, along with the operators) were unable to attend the workshop, feasibility of implementation. so their input came through face-to-face meetings with NRW and SunWater staff. The results of this 3.2 Methods workshop were circulated in a draft of this report and a further workshop was conducted in March 2006 Conducting risk assessments by using expert with participants having a greater familiarity with the judgement and involving stakeholders has become risk-assessment process and a longer time to consider common practice in environmental management alternative management options. Risk scores, the (Burgman 2005). The approach taken here draws scoring system to assess feasibility of management on these experiences. The six stages of this risk options, and the resultant scores were reassessed assessment, shown in Figure 14, involved close and alternative management options identified at this interaction with all key stakeholders (see Section 2.5 workshop. and Appendixes 1 and 2). The potential pathways for seed transport away from the dam were first identified At the September 2005 workshop, management by NRW officers and SunWater staff. These are options were given a feasibility score out of 10 using ‘hazards’ in risk-assessment terminology (Burgman part of a system for assessing feasibility of controlling 2005), but are given the more specific term ‘vectors’ pest impacts in (Walton 2005). A here. Vectors are usually considered as carriers of management option is feasible if it has widespread disease, but have been used more broadly to include community and government support, it is relatively weed seed transport (e.g. Walden et al. 2004). Initially inexpensive, it is logistically possible and it is effective these vectors were split into those associated with at reducing pest impact and not simply reducing pest moving seed within the dam and vectors moving seed population size. For each management option, points away from the dam. This dichotomy was subsequently were allocated for each of 12 attributes covering seen as largely unnecessary as the vectors and sociopolitical, technical and financial aspects of the associated management actions were generally the option (Table 1). This latter assessment is consistent same, although the consequences were different. with the national post-border weed risk management protocol developed by the Weeds Cooperative This list of potential vectors was mailed to all Research Centre (Virtue et al. 2005) and weed risk stakeholders prior to a workshop to see if any vectors assessments conducted in other states had been missed, to score the risk of each vector (e.g. Virtue 2004). Higher scores in Table 1 reflect on a scale of 1–10, and to consider the current and greater feasibility of management. Most attributes potential mitigation measures (i.e. management are self-explanatory. The difficulty was modifying actions) for each vector. Participants were asked to

Risk of Mimosa pigra spread in Queensland � 13 the original attributes in order to apply them to Participants at the workshop were broken into management options to reduce risk, rather than groups to work on sets of management options. Each following their original intention to more generally group then reported back to the workshop, enabling control a pest across the entire state. A description of participants to contribute to the assessment of all some attributes is therefore given below. options. The advantage of using a scoring system • Of the sociopolitical attributes, landholder over, for example, subjective judgement is that it is support refers to the extent to which landholders transparent and to some extent repeatable, allowing (i.e. SunWater and the local grazier) would have to a large number of attributes to be examined together change present management practice and whether and easy comparison of management options. An they would consider the change worthwhile. equal weighting was given to sociopolitical, technical and financial attributes, but this could also be • State government commitment refers to all agencies reworked. While the assessment is quantitative, some whose support would be required. attributes will be poorly known for a management • Under technical and financial attributes in the option and attribute scores will vary among assessors. original use of this scoring system (Walton 2005) The source of variation can at least be readily a contrast is made between the technical ability identified and the score reassessed with more to reduce numbers (i.e. a high proportion of the assessors or with better information. If an attribute population) and the ability to reduce the financial for a management option was unknown, it was given impact. For this study the contrast is of the ability a low feasibility score of 1. Thus the assessment was to simply stop seed movement (or remove seed or biased towards better known management options. plants) with the ability to reduce the risk of seed A further benefit of using a scoring system is that it spread. These might differ if the management identifiesthose attributes that need to be addressed if option cannot target a high-risk activity or area. the option is to be more seriously considered. • Only some life stages (e.g. adults versus seeds) Scores for the 12 attributes of feasibility were added, of a pest may be susceptible to or targeted by a and then divided by 30 to give a value out of 10 to management action, and so these management be on the same scale as the risk score (see above). options are less feasible than options affecting all The feasibility score was then multiplied by the risk life stages. For M. pigra there are three relevant score to give a total score out of 100, which can be life stages: a long-lived seed bank, seedlings and used to compare and rank management options. For mature plants. Most of the management options this calculation an average risk score was required for considered in this report attempt to reduce the risk each vector from the range offered by stakeholders. of seed spread through stopping actual transport This average was determined from a separate of seed. However, detection and removal of meeting between NRW officers and SunWater. The seedlings and adult plants are obviously important score represented a weighted average based on each in reducing the risk of further seed production and stakeholder’s expertise. 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.

14 Risk of Mimosa pigra spread in Queensland � 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 High or long Medium Low or short None or unknown

Sociopolitical

Local government support 25 12 2 1

Community and industry support 25 12 2 1

Landholder support 25 16 2 1

State government commitment 25 12 2 1

Technical

25 12 Availability of methods 1 Existing Developing

Ability to stop weed movement 25 12 6 1

25 20 20 Life stage targeted 1 All Some Single stage

Logistics of implementation 2 12 25 1

Financial

Cost of methods 2 12 25 1

Cost of surveillance 2 12 25 1

Required duration of action 2 12 25 1

Ability to reduce risk of weed spread 25 12 2 1

Risk of Mimosa pigra spread in Queensland � 15 Figure 14. A chronology for the risk assessment undertaken for M. pigra at Peter Faust Dam.

Stakeholder meeting, 5 July 2005 Stage 1 Identification of potential vectors for seed movement away from dam

Mail survey of stakeholders, August 2005 Stage 2 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

Stakeholder workshop, 8 September 2005 Face-to-face meeting (see Appendix 1) with further Stage 3 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

Stakeholder interviews, September/October 2005 Stage 4 Interviews with stakeholders unable to attend workshop

Stakeholder meeting, February 2006 Stage 5 A draft of this report is circulated to stakeholders for comment. Alternative management options are discussed

Stakeholder workshop, March 2006 Stage 6 Face-to-face meeting (see Appendix 2) to revise estimates vector risk and feasbility of management options (see Appendix 3)

16 Risk of Mimosa pigra spread in Queensland � 3.3 Vectors of seed spread to check that no seeds are being accidentally carried away from the dam. The signs explain how to identify Ten broadly defined vectors for potential movement of M. pigra and who to contact if it is found. These signs seed within and away from the dam were identified. are located at the boat ramp, toilet facility and Camp The risks assigned to each of these by stakeholders Kanga, close to the entrance of the dam. There are also and the weighted averages are given in Table 2. new signs at the entrance to the dam, the boat ramp, Nearly all vectors were scored highly by at least one the recreation area and on the road past the boat stakeholder group, but there was a considerable ramp, all instructing boat users not to get out variation among stakeholders in the level of risk of their boats. This restriction is also advertised in assigned to each vector. Some stakeholder groups fishing magazines, newspaper articles and other tended to be more pessimistic than others extension material. (e.g. SunWater compared with Faust Dam Fish Stocking Association) across most vectors. Some groups Fishing is particularly popular, with annual (e.g. Faust Dam Fish Stocking Association) assigned competitions bringing a large number of visitors to risk over a greater range of values and so regarded Peter Faust Dam. The dam is stocked with barramundi some vectors as clearly riskier than others. and it is the second most popular fishing spot on the east coast. As fishers travel from infested areas in the A brief description and discussion of each vector, Northern Territory, where barramundi fishing is also based on stakeholder comments, are given below. popular, there is a risk that M. pigra seeds could be 1. � Water flow within the dam and water level transported from one fishing area to another in boats, fluctuations equipment or clothing. These concerns were raised in M. pigra seedpods can be dispersed considerable the weed risk assessment of M. pigra for the Northern distances by water as they can float for extended Territory (Walden et al. 2004). There, outbreaks of periods. To date M. pigra plants have been found in M. pigra in areas hundreds of kilometres from the four of the five sections of the dam (see Section 2, nearest infested area indicate vector-borne Figure 10). (e.g. by people and wildlife) dispersal rather than solely water or wind dispersal. SunWater believed As water levels have receded new areas have been there was little redclaw harvesting now undertaken exposed to the elements, allowing seed germination. at the dam because of past overexploitation, which is Destruction of these seedlings, particularly before why they ranked its risk low. they mature and set seed, has relied on regular surveys of the dam perimeter from the waterline up 3. Camping to the full-capacity waterline. As water levels have Camping was seen as a similar risk to water activities receded, the area with M. pigra potentially emerging as it can bring people, clothing and equipment has increased and must be surveyed. into direct contact with the M. pigra seed or soil 2. Recreational fishing, water sports and redclaw contaminated with seed. Again, seed might also harvesting be trampled deeper into the soil. At present public roads run past the dam, allowing easy access to the Recreational activities at the dam involve by far the foreshore. Several types of sign warn people that greatest number of people using the dam. Boats are camping is not permitted at the dam. This restriction landed on the foreshore, allowing people to come is also advertised in newspaper stories, articles in ashore, where they could pick up contaminated soil. fishing magazines and on signs at the boat ramp. M. pigra seed might by picked up in fishing gear, Areas of the dam are also marked as restricted and clothing and other equipment. People walking through off-limits to campers. mud near the water’s edge could bury seeds deeper into the soil profile, thereby increasing the time taken Many stakeholders commented that people ignore for germination and therefore delaying depletion of signs and continue to camp throughout the dam the soil seed bank. There are signs instructing people area. Fishing competitions are seen as particularly not to land boats on any foreshore, other than the problematic, with a large, concentrated number of designated boat ramp. However, there is still a high campers and increased activity in and around the level of ignorance regarding conditions of entry. In dam. It was unclear how these restrictions could be some cases, signs are simply being ignored and enforced. people continue to come ashore in M. pigra-infested 4. Wildlife areas. Several wildlife species are potential vectors of Present signage at the dam site (see Section 2, Figure M. pigra seed away from the dam. They include feral 13) warns people about the presence of M. pigra at pigs, wild dogs, wallabies and various bird species, the dam, to avoid collecting soil, sand or water, and particularly waterbirds. Mature seed and pods and

Risk of Mimosa pigra spread in Queensland � 17 seed-contaminated soil have the potential to adhere 5. Livestock grazing to fur and feathers. Seed can also be ingested Cattle, camels and horses all graze within the primarily (e.g. by mammalian herbivores known to M. pigra-infested areas (Figure 15) and are able to graze on M. pigra) or secondarily and then passed in transport seeds in much the same way as wildlife. dung at a new location away from the dam, where the Cattle and horses currently range down to the seed might still be viable (Benyasut and Pitt 1992). foreshore, but camels have recently been excluded. Even relatively short-distance movement of seeds Grazed M. pigra plants have been found at the dam. above the high water mark at the dam is a problem, Seed-contaminated dung, particularly that of livestock, as they will then be outside the survey area and seed can also be picked up by vehicles. 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.

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

18 Risk of Mimosa pigra spread in Queensland � 6. Pig hunting 10. Extraction There are currently authorised and unauthorised The risks of M. pigra seeds being extracted with sand pig hunters active at Peter Faust Dam. Authorised and gravel and deposited over a wide area are high. hunters are aware of the location of M. pigra and are As the cost of sand has risen, unauthorised extraction considered to generally be responsible. Unauthorised has become more common, but is difficult to police. pig hunters are particularly problematic as they have Downstream extraction from the Proserpine River has been operating in the M. pigra-infested areas and already been stopped due to environmental impacts, often dump pig viscera throughout the dam site and but contractors have been caught removing sand in beyond. Pig hunters are currently uncontrolled and breach of restriction notices. There is currently poor unmonitored. Pig hunting is also taking place outside awareness in the extraction industry of the threats of normal working hours, making it difficult to enforce posed by M. pigra. Extraction of dam sediment compliance. Hunters and their dogs are accessing has taken place on one known occasion from a areas by four-wheel-drive vehicles and also by boat, M. pigra-infested area within the dam. thus providing a number of ways of picking up seed. 11. Management activities 7. Track use and off-road driving Workers at the dam might inadvertently pick up seeds Two groups of people need to be considered while travelling in M. pigra-infested areas. However, separately. The first group are people accessing the since daily survey work began in 2003, NRW and dam for recreational use, such as fishers, pig hunters SunWater have instigated a comprehensive system and campers, and those wanting to access the of washdown procedures involving four washdown dam (illegally) to extract soil. The second are those facilities. There is also a system of ‘clean’ and ‘dirty’ employed to work at the dam, such as SunWater tracks. Workers at the dam use only the clean tracks staff, road workers, Ergon Energy employees, the unless they are involved in the eradication program. local grazier and staff involved in the eradication of Use of dirty tracks requires use of the washdown M. pigra (see Vector 11). Recreational users of the facilities. A detailed entry and exit procedure has dam were seen as the more difficult to manage. Some been developed. 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.

Risk of Mimosa pigra spread in Queensland � 19 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.

Risk Vector 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

20 Risk of Mimosa pigra spread in Queensland � 3.4 Management options plants. Adequate tracks are also required to allow workers rapid exit in case of emergency (e.g. illness A wide range of management options to address or injury). each potential vector of seed spread was identified in the mail survey and workshop. These options are 2. Recreational fishing, water sports and redclaw described below and are grouped by each potential harvesting vector of spread. Option 2.1 Education Some vectors had virtually all management options Community awareness can be raised further through in common. Therefore these vectors (1a–b and 2a–c the media, particularly those servicing these activities in Table 2) were grouped and a common risk score (e.g. fishing magazines). There have been community- estimated to allow a total score to be calculated. service announcements and the problem has been advertised on stickers, fridge magnets, identification 1. Water flow and fluctuations within dam cards, rulers, posters and warning brochures. There Option 1.1 Continued surveys of the dam are now several warning signs at the dam in strategic Surveying is carried out throughout the year by two locations (see Section 3.3, vector 2). However, control officers in the mainM. pigra-infested area. compliance with restrictions has been poor and More personnel are used on a regular basis. Access to heightened awareness will not necessarily lead to the survey areas is time consuming, usually taking an an improvement. hour or more before survey work can start. This is due Some formal assessment (e.g. visitor surveys) of to the rough terrain and the large number of gates. level of awareness and monitoring of compliance Cattle grids will speed up the operation. Increased (e.g. number of incursions into restricted areas survey intensity (i.e. more thorough inspection) or over time per 100 boats or visitors) would help better search methods (e.g. option 1.5 below) will be evaluate extension activities. Hills (2002) evaluated required to reduce the risk of missing plants. a campaign aimed at making recreational fishers in Survey effort will need to increase to account for the the Northern Territory more aware of serious weeds larger survey area with lower water levels, but such as M. pigra and changing their behaviour to could be reduced as water levels increase. Survey reduce the risk of weed spread. Evaluation involved a effort should be stratified according to probability of mail survey prior to and following information being M. pigra seedling emergence. This happens to some broadcast through a variety of media. Following the extent, with greater effort in two core areas with high campaign, the majority of respondents believed seed density, but this could be optimised by formally they had an improved knowledge and recognition of matching survey effort with probability of emergence weeds, had a better understanding of weed impacts and probability of detection. and how weeds spread, and were more likely to report weeds. Extension methods were ranked according Option 1.2 Additional resources used during periods to cost and visibility. A newsletter to the local when germination is most likely fishermen’s association was the most visible source Effort can be stratified by area (see option 1.1 above) of information, followed by signage at boat ramps, and also over time, providing the most efficient use of posters and television. Apart from the newsletter finite resources. (which was free), cost declined directly with visibility Option 1.3 Contour banks or sediment curtains around rank, although the cost of signage was many times high infestation areas greater than other information sources. Unfortunately, it was not clear from the results reported by Hills Contour banks could be useful following moderate (2002) whether the awareness campaign had actually rainfall events, but would not be useful following changed the behaviour of fishers. cyclonic rain. The Department of Natural Resources and Water is Option 1.4 Sediment curtain to restrict seed movement undertaking a bioeconomic analysis of managing A sediment curtain could also be employed, but it M. pigra at Peter Faust Dam. This will involve would be costly and might not be effective. modelling the potential distribution of M. pigra and its consequent costs (see Section 1.5). The costs and Option 1.5 Ensure continued access to infested areas benefits of alternative management actions will then through track maintenance and clearance of Melaleuca be examined to seek an optimal strategy. Part of this regrowth work has involved questionnaire surveys of people This is a continuation of current practice, providing fishing at the dam. These surveys provide some more efficient surveys (see option 1.1 above) and insight into who to target in an awareness campaign. improving the probability of detection of M. pigra

Risk of Mimosa pigra spread in Queensland � 21 Sixty-nine questionnaires were recently completed 2.1 above). The threat of closure of the whole dam during the low fishing season in February 2005 appears to be encouraging most people to adhere (Tumaneng-Diete 2005). On average, visitors during to the restrictions. However, a system of penalties the low season estimated they made 13 ± 3 fishing might also be required. SunWater and the local trips (range 1–120) to Peter Faust Dam per year grazier have agreed to place a gate at the end of and they made 32 ± 5 trips (range 0–105) to other Crystal Brook Road. fishing destinations. Other fishing destinations Policing restricted access was seen as both necessary included , Lakefield National Park, and problematic. Some staff of SunWater, Whitsunday Cairns, Townsville, , Lake Awoonga and Shire Council and NRW working at the dam have been Hinchinbrook Island. Visitors’ towns of residence were reluctant to confront people disobeying signs. They are an average of 468 ± 88 kilometres (range 1–3000) neither required to perform these duties nor have they from Peter Faust Dam. Forty per cent of visitors had been trained in policing. As landholders, SunWater travelled <100 kilometres from home to the dam. and the local grazier are legally responsible for taking Not surprisingly, there was a negative correlation reasonable steps to keep their land free of M. pigra, a between the number of visits and distance travelled Class 1 pest plant under the Land Protection (Pest and from home. However, the relationship was largely Stock Route Management) Act 2002. This obligation a result of the lack of >10 visits by people travelling does not extend to ensuring no further spread of >600 kilometres from home. Multiple visits per year the pest, which would require restricted access and were still being made by people from interstate, and a enforcement of that restriction. large number of visits per year (three visitors making at least ten visits) were being made by people living Appropriate enforcement involves signs, fences a moderate distance (200–400 kilometres) from the and other markers identifying the restricted zone dam. Eighty-eight percent of visitors used their own and removal or reporting of people not complying. boats to fish, the remainder using a lure or trap from Nevertheless, people disobeying these restrictions the bank or a hired boat. Eight percent of visitors were are committing an offence by trespassing, which is a planning to trap redclaw crayfish, suggesting this matter for state police. They would also be committing activity, while small, is not trivial (see Section 3.3, an offence under the Act by knowingly transporting vector 2). vehicles (including boats) contaminated with M. pigra seed. People must take reasonable steps These statistics highlight the need, at least for to ensure vehicles are free of seed. NRW could serve low-season visitors, for an extension campaign an emergency quarantine notice on part or even beyond the local area. Most visitors (62 per cent) all of the dam (see option 2.4 below), which would made multiple visits to Peter Faust Dam per year and provide stronger legal support for enforcement. no doubt made visits in other years. Therefore, there This is effective for three months and stipulates the is likely to be value in educating visitors at the dam requirements of landowners, areas where access is site, particularly if heightened awareness of M. pigra restricted and enforcement by authorised people. at the dam, its potential impact, and how to avoid its Alternatively, under Local Government Local Law spread comes through word of mouth. The survey also No. 14, Whitsunday Shire Council can develop a ‘local highlights the potential for M. pigra to be spread well law policy’ to restrict access to land encompassing beyond the catchment by recreational users of the Peter Faust Dam, for the purpose of preventing the dam. High-season surveys are also required. spread of M. pigra. This option is currently being Option 2.2 Public washdown facilities pursued. Enforcement would obviously be most important during popular periods such as fishing There is currently no washdown facility at the tournaments. boat ramp, but there would need to be monitoring and policing of its use by trained staff if one were Option 2.4 Quarantining of the entire dam constructed. This option involves denying public access to the Option 2.3 Restricted access dam and surrounds, whether it is for fishing, crayfish trapping, water sports, camping or simply sightseeing. Vehicle access to M. pigra-infested areas can be This option was considered a last resort as most limited through fencing and road closures using gates stakeholders see the dam as a valuable tourist (see option 7.1 below). Boat access to the shoreline is attraction. Continued public use of M. pigra-infested more difficult to restrict and is the management action areas, despite advertised restrictions, has frustrated identified here. Marker buoys just off the western attempts to contain and eventually eradicate shoreline could be used to delimit the high-risk area. M. pigra. In some cases, fences have been cut and Compliance will be difficult to achieve even with there have been aggressive responses from members substantial extension programs (see option

22 Risk of Mimosa pigra spread in Queensland � of the public to requests to leave areas where they are the latter concern being shared with hunting with dogs prohibited. Prohibiting public access to the dam would (Choquenot, McIlroy and Korn 1996, Department of require closure of the main access road. the Environment and Heritage 2005). Prohibiting public access could be undertaken by Option 4.2 Improved understanding of pig movements serving an emergency quarantine notice to relevant A radio telemetry study would help quantify the risk landowners (SunWater and the local grazier) under the of seed spread posed by feral pigs. It would identify Land Protection (Pest and Stock Route Management) the time spent by pigs in the M. pigra-infested Act 2002. However, a range of restrictions are areas and the probability and distance of movement possible under an emergency quarantine notice of downstream. However, at a stakeholder meeting in which prohibiting access to the entire dam is only February 2006 Jim Mitchell (NRW), a pig research one, extreme, option. Alternatively, the notice could scientist, advised the group that pigs were unlikely to regulate what a person can do on the land move outside the catchment, but pigs could still move (e.g. line fishing but no cray trapping) and could seed outside the area being surveyed for M. pigra restrict access to part of an area (see option 2.3 plants. This study is therefore likely to shift emphasis above) or regulate how contaminated material must to surveying creek lines and other shaded areas to be treated (e.g. a holding period for cattle in a locate resting areas for pigs within the dam catchment, M. pigra-free area, see options 5.1 and 5.2 below). where transported seed is most likely to be deposited. Again the Act places an onus on landowners to try to eradicate M. pigra at the site and on the public to not 5. Livestock grazing transport seed, but it does not restrict access unless Option 5.1 Holding period for cattle that is identified in an emergency quarantine notice. Stakeholders generally agreed that cattle that have Option 2.5 Conditions for fishing permits been grazed in potentially M. pigra-infested areas A condition of permit to fish at Peter Faust Dam could should be held for a period (at least seven days is be to complete a course describing any restrictions required in the Northern Territory) before being moved and an understanding of how to minimise weed seed from the dam. A formal agreement on this arrangement spread. A further option is to have a boom-gate entry is needed between the local grazier and NRW that into the boat ramp at the dam. The permit would includes covering the additional direct and indirect include a swipe card to activate the boom. costs (e.g. feeding, transport delay, change in cattle condition) of holding cattle. 3. Camping There was a suggestion that this agreement would Option 3.1 Enforcement of camping ban include use of a Weed Hygiene Declaration Enforcement is required, given the continuing (http://nrm.dnr.qld.gov.au/pests/weeds/weed_ disregard of signs and barriers (see option 2.3 above). spread/legal/weed_hygiene_dec.html), providing This would involve advertised penalties and policing. assurance that cattle have been treated in such a way as to minimise the risk of spreading M. pigra. Option 3.2 Education This declaration (written notice) is a legal Signs and other awareness efforts have not stopped requirement under the Land Protection (Pest and people camping, but they might still have reduced the Stock Route Management) Act 2002, but only refers to number of offenders and thus the risk of M. pigra certain Class 2 declared plants. While the declaration seed spread. is not required in this case, it is nevertheless an offence under the Act to knowingly transport vehicles 4. Wildlife or other things such as stock or fodder contaminated Option 4.1 Baiting program for feral pigs with M. pigra seed, and people must take reasonable Trapping programs for feral pigs have been largely steps to ensure transported items are free of seed. unsuccessful and there is currently no baiting at the Buyers of contaminated stock would also be able to dam. Pig hunting will reduce numbers, but is likely sue for damages. to be less effective than baiting (Choquenot, McIlroy Option 5.2 Cattle excluded from high-risk areas and Korn 1996, Department of the Environment and Fencing high-risk areas (i.e. parts of the western Heritage 2005). Ground shooting has been found to foreshore of the dam) from livestock would be costly be ineffective at reducing feral pig numbers to low initially, but is likely to be cost-effective in the longer densities unless it is intensive. In contrast, baiting can term. It would substantially reduce the risk of stock provide a rapid and substantial reduction. Aside from picking up seed and would reduce the number of cost, the disadvantages of baiting include non-target animals needing to be held before transport (see mortality and the method being considered inhumane, option 5.1 above). There would be an obvious cost to

Risk of Mimosa pigra spread in Queensland � 23 the landholder through lost production related to the the risk of M. pigra seed being extracted. Surface or size and quality of the areas excluded from grazing. benthic extraction is clearly a much higher risk.

6. Pig hunting Option 8.2 Downstream surveys Option 6.1 Policing unauthorised hunting Direct surveys would be difficult in some areas (e.g. beyond Spruce’s Crossing) because of vegetation. As discussed earlier (see Section 3.3), this activity is To be feasible, monitoring would need to be of low difficult to police, but it might become easier if limited intensity, targeting likely establishment sites points of entry to M. pigra-infested areas were through (e.g. open, disturbed, moist areas such as flood fencing and road closures using locked gates (see plains). If this was not feasible, monitoring would have option 7.1 below). to rely on downstream landholders identifying Option 6.2 Washdown procedures for hunters M. pigra (see option 9.2 below) or opportunistic sightings (e.g. by NRW, SunWater or Whitsunday Shire Authorised hunters are instructed to leave Council officers). pig viscera and other carcass off-cuts in designated areas where they can be checked Option 8.3 Water release through offtake rather than periodically for M. pigra seedlings. A further spillway requirement would be to wash down both vehicles At the time of the workshop the feasibility and safety and carcasses, which is a requirement for all workers of this option were unclear. Recent investigations entering the high-risk areas of the dam (see Section indicate that it would not be feasible. 3.3). Chiller boxes also provide an opportunity to inform hunters of the presence of M. pigra at the dam 9. Irrigation and how to minimise the risk of spread. Option 9.1 Sub-artesian retrieval rather than surface Option 6.3. Ban pig hunting pumping This would simplify policing and reduce traffic in the Unfortunately most people do not have access to high-risk areas. Nevertheless, enforcement of the ban underground water, so water would still need to be would be required (see option 6.1 above). The control released from the dam. of pigs through hunting would need to be replaced by Option 9.2 Education of downstream users a baiting program (see option 4.1 above). Notably M. pigra was found at the dam by the local 7. Track use and driving off-road grazier. Downstream landholders and employees Option 7.1 Fence access to the foreshore are the people most likely to encounter M. pigra. Community monitoring is likely to be the only feasible The closure of tracks providing access to the foreshore method, despite its unreliability, because of the cost was seen as a priority by all stakeholders. Again of alternatives such as direct monitoring (see option fencing is costly but would be cost-effective in the long 8.2 above), given the size of the survey area and the term. It is the most effective option for stopping traffic, difficulty of sampling rare objects. including four-wheel-drive vehicles, and access needs to be denied for a long time, given the longevity of Information can be provided to downstream users M. pigra seeds in the soil. Therefore the costs of in a number of ways. The ability to correctly identify fencing will be offset to some extent by the reduced M. pigra is obviously critical. Actual specimens are costs of policing, signage and the overall reduced ideal and preferably shown on site rather than as risk of M. pigra seed spread. A locked gate at the end potted plants. A field day at the dam would provide of the public road heading south-west from the boat the broader context and an opportunity to discuss the ramp would provide a further barrier. issue with a range of people. Option 7.2 Education Option 9.3 Quarantine both dam and water Track closures would need to be supported by an Related to option 2.4, this would be an obvious cost to awareness campaign targeted at key groups such as irrigators (or government through compensation) and fishers and pig hunters. a high surveillance cost. Option 9.4 Screening of irrigation water 8. Water flow from dam Strainers in the Boondoomba and Wivenhoe pipelines Option 8.1 Continued extraction of water through are used to avoid the transfer of exotic fish, such underwater gates as tilapia, and their eggs, between water bodies in Queensland (Tarong Energy 2003). Appropriate Fortuitously this extraction point will also minimise filters would need to be developed forM. pigra seed.

24 Risk of Mimosa pigra spread in Queensland � This option has a very high initial cost, but would be result they cannot be directly compared with other effective at reducing the risk of seed spread through management options. irrigation. It would obviously not stop the spread from Enhancement (i.e. temporal and spatial stratification) water flowing over the spillway. of current surveys was ranked highly by stakeholders. 10. Extraction industry Management of the risk posed by cattle ranked highly, reflecting its importance and feasibility. However, Option 10.1 No extraction permits in area cattle-exclusion areas scored poorly because of The extraction industry is a potential vehicle for perceived low support among government and the spreading not only M. pigra but other declared plants. landholder, and relatively high cost. Education of The increased cost of soil has increased this risk. recreational users had a moderate ranking, as did There needs to be better monitoring of the industry by restricting their access to high-risk areas. Achieving NRW and better awareness of the risk of weed seed compliance was generally considered difficult and spread through transport of soil. This option would ranked below other options. However, options require signage, policing, fines and restricting road involving restricting access and imposing conditions of access (e.g. locked gates) to more effectively deter entry (e.g. washdown facilities, conditions for fishing extraction of soil from the dam and nearby. permits) should not be seen as alternatives as they often required policing to be effective. Many options, 11. Management activities such as restricting access points to the water through Surveys, control and research undertaken at the dam fencing and locked gates, would make policing easier. involve procedures to reduce the risk of seed spread. Pigs are likely to be best managed through a ban These were considered important but sufficient on hunting and implementation of a 1080 baiting and, while these procedures do not eliminate risk, program to control numbers. further options to minimise the residual risk were not An alternative to ranking management options is to considered in this assessment. only consider options above some threshold total score. The combination of relatively low risk and low 3.5 Ranking management options feasibility would dismiss a management option. There Scores for the feasibility of each of the above are breaks in the scores at 45 and 55, providing two management options are presented in Table 3 along tiers for consideration. with the risk score (Table 2) and the product of the A more thorough evaluation of management options two (total score). Options have been ranked by the to minimise the risk of spread of M. pigra involves total score. The scoring system ignores potential building an explicit model, describing the probability interactions among options. For example, the two of seed spread by various means. The effect of options addressing camping scored relatively uncertainties in model parameters (e.g. environmental moderately when viewed in isolation. However, the variation, visitation rates, wildlife density, cattle combined effects of both could be very effective. Not movement) on risk of spread and optimal management surprisingly there was overlap among options between can be explored through simulation. The actual direct vectors such as improved education, policing and and indirect costs of each management option need restricting access. to be calculated and compared, as well as the cost The continuation of the present surveys was ranked of M. pigra spreading beyond the dam. The simpler, only moderately, largely because the vector it faster and cheaper approach described here provides addressed had a low-risk score. If the vector had been the starting point, identifying a range of vectors and persistence or expansion of a M. pigra population at mitigating management options that can now be the dam, then the score for continuation of surveys formally modelled. 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

Risk of Mimosa pigra spread in Queensland � 25 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 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

1.4 Sediment curtain 1.0 6.5 7

26 Risk of Mimosa pigra spread in Queensland � 3.6 Making management decisions 3.7 Monitoring and performance evaluation While the rankings in Table 3 provide some guidance Whatever management is undertaken, there needs to management, it is not obvious how best to to be some monitoring of its effectiveness. The goal allocate resources. Spending the most resources is to reduce the risk of M. pigra spread by specific, on management options targeting vectors with potential vectors. Finding M. pigra outside the dam the highest risk is unlikely to be the most efficient does not necessarily indicate failure of management way of reducing overall risk of weed spread, as has as the risk of spread cannot be eliminated entirely. been argued for endangered species management Therefore, this should not be used as a performance (Possingham et al. 2002). It may be optimal to spend indicator, although the rate of spread would be an most money on action that relatively cheaply reduces a appropriate indicator where M. pigra was already moderate risk to low risk, rather than spending money spreading. Appropriate indicators are likely to be on a more expensive option that can only slightly reductions in the activity (assumed to be correlated reduce a large risk. A hypothetical example of this is with risk of weed spread) of people, pigs and cattle in shown in Figure 16, where cattle exclusion the M. pigra-infested areas, use of washdown facilities (e.g. using fencing) is considered costly and is and survey effort downstream of the dam. 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.

Risk of Mimosa pigra spread in Queensland � 27 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.

28 Risk of Mimosa pigra spread in Queensland � References

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30 Risk of Mimosa pigra spread in Queensland �