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Wetlands Australia 33: Keeping pigs out of floodplain wetlands

Author: Nathan Waltham, James Cook University

In November 2016 the Burnett Mary Regional Group constructed an exclusion fence surrounding the Round Hill Reserve, a coastal wetland in the upper reaches of Round Hill creek, in the Baffle catchment (north of Bundaberg, Queensland). The objective was to control feral pig (Sus scrofa) access to the wetland. Round Hill creek is a restoration priority because of its Fish Habitat Area and Directory of Important Wetlands designation.

In collaboration with the Burnett Mary Regional Group and Queensland Parks and Wildlife Services, the desired wetland values and services were established with a focus on waterbirds, native vegetation, water quality and aquatic fauna recovery.

Feral pigs damaging the wetlands. Photo: S Jackson, Queensland Parks and Wildlife Service.

The key results were:

  • Of the 5 wetlands surveyed, the fenced wetland in Eurimbula National Park supported a more diverse floristic community than unfenced wetlands. After the first 12 months, the fence was ineffective at protecting fragile marsh vegetation from cattle trampling (confirmed by drone imagery classification and field observations) because land tenure arrangements with the adjacent landholder includes cattle access inside the fenced section of the park.
  • Water quality measured for physio-chemical (temperature, conductivity, dissolved oxygen and pH) along with nutrients and total suspended sediments varied among wetlands and surveys. Dissolved oxygen was at times critically low, below fish asphyxiation thresholds which might explain the low fish numbers recorded.
  • Twelve fish species were recorded with Gobiidae (goby) and Pseudomugil signifier (Pacific Blue-eye) most abundant. Two exotic species; Oreochromis mossambicus (Mozambique Tilapia) and Gambusia affinis (Eastern Gambusia) were present. Macrobrachium rosenbergii (Giant River Prawn) were also caught, along with the economically important Metapenaeus bennettae (Greasy-back Prawn) and Metapenaeus macleayi (School Prawn).
  • More waterbird species were detected during the post-wet than during the dry season surveys, presumably related to water availability.

Recommendations for future action include:

  • Maintenance of feral animal fences is necessary, well beyond the completion of the project, to ensure the wetland has a chance of successful restoration.
  • More trials like the earth ramp are needed to build a knowledge base towards a design that is most effective for arthropod movement over fences.
  • Despite limited value as fish habitat under current climatic conditions, regardless of fencing being present or not, future sea level rise might render these wetlands more important.
  • Cattle accessing fenced wetlands is counterintuitive and land tenure permitting this should be reviewed.

Further information

See details on the Australian Government’s National Environmental Science Program (Tropical Water Quality Hub) website at: Project 3.3.2 - Science evaluation of coastal wetland systems repair projects across GBR catchments

For more information contact Dr Nathan Waltham (James Cook University) Nathan.waltham@jcu.edu.au.

Surveying wetlands using a fyke net. Photo: Nathan Waltham, James Cook University.