The Burdekin River is located in far north Queensland. It rises on the northern slopes of Boulder Mountain in the Seaview Range which is part of the Great Dividing Range, west of Ingham. For 886km the Burdekin River meanders towards the coast. Along the way it is joined by a number of tributaries until it discharges into the Coral Sea through the Burdekin River Delta. The river’s catchment area is approximately 130,000 square kilometres and it is Australia’s largest river by (peak) discharge volume.

Along with the Murray River, the Burdekin River is economically important. Below the Burdekin Dam, in the lower catchment, lies northern Australia’s largest irrigation area with approximately 80,000 hectares serviced.

The main user of the irrigated water is sugarcane production. Construction of irrigation infrastructure began in the early 1950s to support cropping on the lower Burdekin flood plain. Irrigation water came from both storages and groundwater. Irrigation infrastructure and cropping activities have changed the natural state of the river and wetlands within.

The freshwater wetlands of the Townsville-Burdekin flood plain now consist of a mix of natural and artificial areas which are inundated permanently or intermittently. Most river systems in this region have strong connectivity with wetland systems that cater for a distinct seasonal flow regime and irregular flooding, allowing inundation of freshwater wetlands during the wet season.

The extensive modifications to the natural state of the flood plain through the construction of dams and weirs, water supply schemes and intensive sugarcane production, has resulted in altered natural regimes. This includes the changes in seasonal flows and tidal influence creating areas of perennial and constant water levels that carry high nutrient loads.

Although the flood plain has been modified due to rural and urban land use, all these wetlands are still of environmental significance. Included in these wetlands is a coastal wetland aggregation that is of both national and internationally importance, Bowling Green Bay.

This coastal wetland aggregation occurs within a large area of low-gradient coastal flood plain rising from shallow marine waters in the coastal zone, to permanent and seasonal freshwater lakes inland of the adjoining coastal plain. The area supports a large and mostly intact mosaic of coastal wetlands containing mangrove communities, highly saline salt pans and freshwater and brackish wetlands on the low-lying coastal plain. It is an important zone that supports the migration of shorebirds and terns, marine turtles and several threatened species.

There are a number of wetlands in this flood plain area consisting of riverine (rivers and deep-water habitats in a channel), lacustrine (lakes and dams) and palustrine (marsh or swamp) systems. Each helps to support a rich diversity of plant and animal life. These areas have high cultural and spiritual significance to Traditional Owners. They have provided an important food, medicine and fibre source for thousands of years. Wetland plants are strongly seasonal and are important to the overall function and critical processes of marshlands. These functions and processes include maintenance of water quality, wildlife habitat, removing sediment, nutrients and toxins from the water, and stabilising loose sediment and preventing erosion.

Although native plants are crucial to the health and processes within a wetland, invasive species can have a catastrophic impact. They can alter hydrological regimes, displace native plants and animals, degrade water quality, alter soil properties, change fire regimes and degrade fishing grounds. Disturbance to riverside vegetation due to water regime changes has contributed to the expansion of weed infestations that can prevent tidal influence which would naturally suppress weed growth. Another factor that has compounded this impact on wetland processes is high nutrient levels in the water.

Over time there has been a number of projects focusing on minimising nutrient flows from irrigated land and sediment transport from eroded grazing lands and stream banks into the system. Fine sediment makes the water turbid and reduces the amount of light that seagrass and offshore corals require to grow and thrive.

Activities to reduce these issues include targeted removal of aquatic and riparian weeds, removing sediment, improving flow regulation, revegetating creek banks and supporting landholders to improve farm management. These works are also seen to be important in protecting the Great Barrier Reef from the detrimental impacts of nutrients and sediments. The state government, local councils, community groups and landholders are all involved in protecting and enhancing the environment in both the upstream and lower reaches of the Burdekin River.

One factor that increases sediment loads is the impact of feral animals, in particularly feral pigs. Feral pigs have an impact on both the environment and agriculture production where their digging activities cause uprooting and removal of plants leading to soil disturbance. As a result, they are a targeted species during coordinated pest control programs.

The Sporting Shooters’ Association of Australia’s (SSAA) Conservation and Wildlife Management (CWM) Queensland is one of the community groups involved in conservation work throughout these wetland areas. Members from Townsville and Cairns have been actively involved in conservation activities through a dedicated Burdekin River Wetland project since 2013.

The coordinated pest control strategy for this project involves trapping and aerial shooting as complementary actions to CWM’s ground shooting activities. CWM’s activities occur both during the day and the night. The project objective is to place sustained mortality pressure on populations of focal species (in this case feral pigs) and thereby significantly reduce their impact on the high conservation values of the wetlands associated with the Burdekin River. The emphasis is on removing as many feral pigs as possible, so hunting activities are pest management focused (maximum reduction) instead of trophy or meat gathering activities.

CWM environmental volunteers record data on the number of feral pigs they despatch and locations sighted. Other information noted includes the time of day, prevailing weather conditions, feral pig movements and habits. Activities are mainly focused in specific high value control areas that contain in order of 30 individual wetlands.

An environmental consultant has been measuring feral pig damage in these areas for a number of years using ground surveys. It has been determined that to suppress the feral pig populations in any area, an annual reduction rate of 70 per cent is required. The current holding capacity of the area has been calculated to be approximately three feral pigs per square kilometre. So 155 feral pigs need to be despatched as a minimum annually to keep numbers and impacts down in the area.

In 2019, the number of feral pigs removed from the area through coordinated pest management totalled 188. Of that tally, CWM environmental volunteers accounted for 124 feral pigs. This included 54 that were taken from the special control areas. Ongoing pressure on the feral pig population was maintained for a total of 158 days that year.

During that time the project was suspended for two months due to flooding, which potentially reduced the total number of days on the ground. CWM members were involved on average 16 days a month, undertaking feral pig control to protect and enhance the environment. Up until March 2021, 233 CWM members contributed a total of 3076 volunteer days to the project.

The CWM’s coordinator believes: “The project’s success is underpinned by two factors. The first is that the coordinated approach of some 233 volunteers working to a set number of parameters, specific data collection requirements and ground shooting techniques is probably the reason behind the project’s successes. The data of pigs removed means nothing until it is compared to the reduction in environmental damage.

“The second is the close cooperation and partnership with the property management who have on numerous occasions credited the measurable success to the dedication and commitment of the volunteers.”

Since 2014, retired zoologist Dr Jim Mitchell has been measuring the success of coordinated control efforts within the Burdekin River Wetlands area. The method to attain this was not to focus on the numbers of feral pigs removed from the area but to monitor ongoing impacts. This was achieved by observing the number of diggings found around the edge of wetlands.

Diggings are an indication of direct negative impacts to soil and the water quality of nearby wetlands. Dr Mitchell set up numerous transect lines (survey points) one metre from the waterline that would be regularly checked to record any observed feral pig activity. A higher activity level would correlate with higher impacts and potential higher feral pig abundances.

Over the years, Dr Mitchell recorded a steady decline in feral pig impacts in the area. Transect surveys indicated a drop from 61 per cent in observed diggings within transect lines areas in 2014 to a low of only 9 per cent in 2019. This shows evidence of a significant fall in feral pig impacts due to the success of the coordinated pest control program. This decline, along with the continued removal of feral pigs at the required 70 per cent reduction rate, is a testament to the efforts of all involved.

The successful environmental outcomes of volunteers’ efforts to the Burdekin River Wetlands shows that environmental input by community groups can go a long way to solve certain issues that our wetland systems face.

With the knowledge that feral pigs are a continual problem, these volunteers will continue to be needed to help suppress the feral pig population in the area to minimise environmental damage.