Article Index

Ecological health

Measures of ecological health complement water quality monitoring and reporting and provide more information about the overall health of the waterway.

The Parks and Wildlife Service is also working with project partners at Murdoch University and the DWER to monitor and evaluate the condition of fish and seagrass communities as indicators of waterway condition.

In addition, some iconic species including the bottlenose dolphins and the western school prawn are being investigated in more detail to understand their populations and factors affecting them.

Monitoring and evaluating fish communities

The Parks and Wildlife Service continues to partner with Murdoch University to annually sample and report on fish communities as an indicator of condition in the Swan Canning Riverpark, with contractual arrangements extending until 2018.

Murdoch University developed the Fish Community Index over five years (2007-12) in collaboration with the State Government. The index uses a suite of fish metrics, including diversity and the number of species, to characterise the fish community and its response to estuarine condition. The index does not focus on individual species or measure biological performance or health of any individual fish species.

The primary purpose of the Fish Community Index is to provide an ecological indicator of estuary condition that complements existing water quality monitoring and evaluation. The index is applied annually as part of an on-going monitoring and reporting framework.

Since 2012, fish communities have been monitored in summer and autumn at six nearshore and six offshore sites in the upper, middle and lower Swan, as well as in the lower Canning.

In 2018, the shallow nearshore areas were assessed as being good to fair, and offshore waters of the system were assessed as fair – good. These results indicate slightly better ecological condition of both nearshore and offshore waters during 2018 compared with 2017. This reflects the lack of any widespread or severe hypoxia during the 2018 monitoring period in contrast to the widespread impacts of a flood event that occurred in 2017.

Across the estuary as a whole, the ecological condition based on fish communities has been assessed as generally good to fair in nearshore and offshore waters since 2008 and 2011, respectively.

Seagrass health and distribution

Seagrasses are some of the most productive organisms in the world with productivity rates that can be twice that of forests. They play a role in maintaining oxygen levels at the sediment/water interface, support diverse and productive faunal assemblages and are an important food source for animals such as WA’s iconic black swan.

In the Swan Canning Riverpark there are three main species of seagrass, with paddleweed (Halophila ovalis) the dominant species.

The Parks and Wildlife Service has worked with DWER to develop a robust and easily repeatable method of surveying seagrass species composition and percentage coverage at sites in the lower Swan and Canning estuaries. This is coupled with monitoring of seagrass response to environmental pressures. Insights into seagrass health and distribution provided by this monitoring and evaluation program provide a useful complement to existing water quality reporting and will allow management policies to be specifically targeted at improving the resilience of seagrass in the Swan and Canning estuaries.

Two reports have been released describing the projects and their results to-date.

Dolphin population and health

Bottlenose dolphins (Tursiops aduncus) are a much loved feature of the Swan Canning Riverpark. The Parks and Wildlife Service has a keen interest in the Riverpark’s resident dolphins and works to engage the public in Dolphin Watch, a community-based citizen science dolphin monitoring program, and support research by Murdoch and Curtin universities.

Murdoch University researchers have surveyed the dolphin population in the Swan Canning Riverpark since 2011 and have recorded 52 individual dolphins (including 13 calves) using the waterway during that time. Of those, at least 22 dolphins (excluding calves) are considered resident in the Riverpark.

The dolphins are a natural part of the coastal environment and the Swan Canning Riverpark and are subject to a range of factors that can affect their survival, with an estimated 50% mortality rate in the first five years of life. It is not unusual for at least one dolphin death to occur in the Riverpark in any year. In 2009, six deceased dolphins were collected from the Swan Canning Riverpark over a period of five months, causing serious alarm. A range of factors influenced the mortality event. Morbillivirus was found to be present in the population and is thought to be the underlying factor in the dolphin deaths.

Murdoch University works in partnership with the Parks and Wildlife Service to investigate dolphin deaths in the Riverpark, through necropsy and pathology testing. The university is also researching dolphin health in more detail by taking skin biopsies from live dolphins and evaluating any markers of chronic stress. 

Factors affecting prawn populations

Scientists are using a restocking program to investigate factors that limit the natural recruitment of western school prawns in the Riverpark.

The project, a partnership between Murdoch University and the Parks and Wildlife Service, the Australian Centre for Applied Aquaculture Research (ACAAR) and the Fisheries Research and Development Foundation, is underpinned by a restocking program. The restocking program was made possible by the Recreational Fishing Initiatives Fund and supported by Recfishwest and the Fisheries Division of the WA Department of Primary Industries and Regional Development.

Since the project began in 2012, more than 2400 otter and hand trawl samples have been taken to evaluate stock status and distribution relative to an array of environmental factors. Laboratory and field investigations have examined temperature, salinity and sediment preferences.

This work, along with predation investigations, is complemented by ACAAR's culture and release of 4.5 million prawns and community engagement through the Parks and Wildlife Service's Prawn Watch initiative.

More information on Prawn Watch is available on the River Guardians website.

Foreshore condition

Rivers and estuaries are constantly changing their form in response to natural geomorphic processes, shifts in natural conditions in the surrounding catchment, and human impacts. The foreshore is a dynamic boundary that responds to relative movements in land and water.

Foreshores in the Swan Canning Riverpark comprise two main types:

  • Non-built foreshores: natural shorelines without engineered erosion protection systems, which can be further divided into rocky, vegetated and sedimentary shores. Each of these has different sensitivity to change.
  • Built foreshores: hard-engineering approaches to shore stabilisation that reduce the response of the foreshore to various environmental conditions. These artificial shorelines can be further divided into groyne fields, revetments and walled foreshores.

An assessment of Swan Canning Riverpark foreshores in 2008 reported on the condition of built and natural assets.

The strategy is divided into two parts - the findings of the foreshore assessment describing foreshores, their pressures and condition, and a management strategy summarising foreshore issues, defining management responses and identifying priorities for action.

The assessments, completed in 2008, are currently being reviewed.