Aquatic ecosystem health

Background

• Background
• The use of CHIP data
• Overall aquatic ecosystem condition
• Macroinvertebrate condition
• Riparian condition
• Native fish
• Native fish abundance and biomass
• Native fish stocking

This indicator focuses on the health of rivers and streams in the ACT. Although some urban wetland and lake sites contribute to the ecosystem health assessments presented, these do not allow comprehensive assessments of Canberra’s urban lakes and wetlands.

There are also no available assessments of wetland condition in the ACT. However, upland bogs and fens are included in the Conservation Effectiveness Monitoring Program being undertaken by the ACT Government (see Indicator B2: Extent and condition of conservation areas).Brawata, R., B. Stevenson and J. Seddon, 2017, Conservation Effectiveness Monitoring Program: An Overview, Environment, Planning and Sustainable Development Directorate, ACT Government, Canberra. This monitoring program will provide data on the condition of these wetlands in the future.

This indicator also includes assessments of native fish and macroinvertebrates. These provide an indication of the health of aquatic ecosystems and demonstrate the biological impacts of degraded habitat, changes to flows and water quality, and the impacts of invasive aquatic species.

Assessing ACT’s aquatic health – the Catchment Health Indicator Program (CHIP)

This is the first ACT State of the Environment report to use data from CHIPUpper Murrumbidgee Waterwatch, 2018, Catchment Health Indicator Program 2018, Waterwatch, Canberra. The program provides a score of catchment health in the ACT region using data collected by Waterwatch volunteers and staff. Assessments include monthly water quality data, macroinvertebrate (water bugs) abundance and diversity collected twice a year from key sites, and riparian vegetation assessments conducted every two years. When combined for an individual stretch of waterway (a reach), these data produce a score that indicates the overall health of that reach. A reach only receives a score if the minimum data requirement is met.

Assessments are accompanied by a report card supplied by the local Waterwatch coordinator to provide expert knowledge on condition results and possible issues. The report cards ensure that vitally important context is provided by the coordinators who know the underlying geology, hydrology, land use and history of the catchments. These considerations must be considered when using and interpreting the CHIP.

In 2018, CHIP produced 96 reach report cards informed by 232 site surveys. These were conducted by over 200 volunteers and included 2,081 water quality surveys, 192 macroinvertebrate surveys and 220 riparian condition surveys.

The total area surveyed by CHIP is more than 11,400 square kilometres and includes 5 catchments: Southern ACT catchment (26 reaches); Molonglo catchment (26 reaches); Ginninderra catchment (15 reaches); Cooma region (23 reaches); and the Yass catchment (6 reaches). Information on these catchments are provided in annual CHIP reports.

Condition and trends

The use of CHIP data in the ACT State of the Environment report

Because this is the first inclusion of CHIP data in state of the environment reporting, the results can be seen as baseline data. Future State of the Environment reports will use this baseline data to assess changes in aquatic ecosystem health in response to changing conditions and management activities; they will also present data on the average CHIP score (condition) for reaches over a 4-year period aligned to the State of the Environment reporting periods. This approach is considered to be more accurate than comparisons of annual data which often represent short-term changes rather than actual trends in condition. This 2019 report uses average scores for the 2015 to 2018 period.

CHIP results for the Cooma region and Yass catchment are not presented in this report because they are situated almost entirely in NSW. However, for catchments in the ACT that include NSW lands (Molonglo and Ginninderra), all reaches in the catchment are included.

It is important to note that the site selection used for CHIP has a significant influence on the overall number of reaches assigned to a particular condition score. For example, having a high proportion of survey sites in urban areas will likely mean a higher total of sites in poorer condition categories. Consequently, although figures on the number of reaches in each condition category may be useful for an overview of CHIP results, they should be viewed with caution. It is more appropriate to compare changes in individual reach condition over time, than to make comparisons between different reaches and catchments.

Information on reaches used for CHIP assessments, including individual condition scores, characteristics and location, and the main pressures affecting condition, can be found in annual CHIP reports.Upper Murrumbidgee Waterwatch, 2018, Catchment Health Indicator Program 2018, Waterwatch, Canberra.

Overall aquatic ecosystem condition – the Catchment Health Indicator Program

Overall condition was assessed for 67 reaches in the Ginninderra, Molonglo and Southern ACT catchments, with scores averaged for the 2015 to 2018 period.

For the total reaches assessed, 38 (57%) were in fair condition across the 3 catchments and 26 (39%) were in good condition (Figures W3 and W4). Only 2 reaches were found to be in excellent condition and 1 was assessed as poor. Aquatic condition is strongly influenced by land use with reaches in fair condition mostly in urban and rural areas, and those in good and excellent condition mostly on conservation and protected lands.

Only 2 of the 15 reaches assessed in the Ginninderra catchment were in good condition, the rest were classed as fair. For the 26 Molonglo catchment reaches, 11 were found to be in good condition and 15 were classed as fair. The Southern ACT catchment had the highest proportion of reaches in good to excellent condition with 15 out of the 26 reaches assessed (58%). It was also the only catchment with excellent condition scores, although this was only achieved for 2 reaches. The higher proportion of good and excellent condition reaches is mainly due to the catchment having large areas of conservation and protected lands with unmodified landscapes. For urban and rural areas in the Southern ACT catchment, 10 reaches were classed as fair and 1 as poor.

These results show that aquatic ecosystem condition is variable across the ACT. Although results are strongly linked to land use, the presence of some reaches in good condition in urban areas shows that healthy aquatic ecosystems can be supported with effective management and water-sensitive design.

Macroinvertebrate condition – Catchment Health Indicator Program

Aquatic macroinvertebrates are a diverse group of insects, crustaceans and molluscs that include dragonflies, stoneflies, snails, yabbies, water boatmen and worms. They are relatively sedentary and spend at least part of their life in aquatic ecosystems. Macroinvertebrates are critical to aquatic ecosystem health because they are an important food source for fish and other species such as platypus, and are critical to ecosystem processes such as nutrient cycling. 

Because macroinvertebrates are widespread, easy to sample and sensitive to a range of pressures, they are routinely used as indicators of the condition of aquatic systems and their surrounding catchments. Land use change, aquatic and riparian habitat modification, water pollution, and river regulation all affect macroinvertebrate community health. 

The CHIP assesses macroinvertebrate community health for each reach using the results of 2 annual surveys from key sites. The assessment methodology can be found in the 2018 CHIP report.Upper Murrumbidgee Waterwatch, 2018, Catchment Health Indicator Program 2018, Waterwatch, Canberra.

Macroinvertebrate condition was assessed for 65 reaches in the Ginninderra, Molonglo and Southern ACT catchments, with scores averaged for the 2015 to 2018 period. For the 65 reaches assessed, 26% were found to be in poor to degraded condition, with 49% classed as fair (Figures W5 and W6). Only 25% of reaches assessed were found to have good to excellent macroinvertebrate condition. The Ginninderra catchment had no reaches with good macroinvertebrate condition, the Molonglo catchment had 8 reaches, and the Southern ACT catchment had 5 reaches classed as good and 3 as excellent.

The CHIP scores for macroinvertebrate condition are strongly linked to land use, with urban and rural areas generally having fair to poor condition. In such areas, high levels of pollution, alteration to natural flows and loss of riparian vegetation are likely to have had a negative effect on macroinvertebrate communities. Macroinvertebrate results are also likely influenced by the mostly dry conditions over the assessment period, with reduced flows affecting the diversity and abundance of macroinvertebrates (see Indicator W2: River flows).

Riparian condition – Catchment Health Indicator Program

The riparian zone is the land and vegetation that fringe aquatic ecosystems. They are vital for aquatic health as these zones provide habitat, stable banks, shade, buffers and filters for incoming run-off, reducing sediments, nutrients and pollutants, and food for aquatic species. The loss and degradation of riparian zones compromises both aquatic and terrestrial biodiversity. Riparian zones are particularly important during drought periods, providing refuge for terrestrial species and helping to reduce the impacts of low flows on aquatic systems. Riparian vegetation is often the only native vegetation remaining in heavily modified landscapes, making them vital wildlife corridors. The health of riparian zones is often dependent on river flows with many riparian species requiring regular flooding for regeneration. Changes to natural flow regimes and the increased occurrence of drought has significantly reduced the flooding of riparian zones, leading to a decline in riparian vegetation health (see riparian connectivity in Indicator B4: Extent and condition of native vegetation.

The CHIP assesses riparian condition for each reach with surveys conducted every 2 years. The assessment methodology can be found in the 2018 CHIP report.Upper Murrumbidgee Waterwatch, 2018, Catchment Health Indicator Program 2018, Waterwatch, Canberra. It should be noted that the current riparian assessment methodology results in poor scores for sites without extensive tree canopy cover. Consequently, riparian condition assessments for naturally treeless ecosystems such as swamps, bogs and fens, are unlikely to reflect their true condition. The riparian condition methodology is being reviewed to improve assessments of naturally treeless ecosystems.

Riparian condition was assessed for 67 reaches in the Ginninderra, Molonglo and Southern ACT catchments. Only 14% of reaches were assessed as having good to excellent riparian condition, 37% were found to be in fair condition and 48% were assessed as poor to degraded (Figures W7 and W8). The Ginninderra catchment had no reaches with good riparian condition, the Molonglo catchment had 5 reaches, and the Southern ACT catchment had 4 reaches classed as good and 1 as excellent. 

As with overall CHIP scores and macroinvertebrates, riparian condition is strongly linked to land use, with urban and rural areas generally having fair to degraded condition due to vegetation clearing. However, there were also fair and poor reaches in conservation and protected areas demonstrating that riparian health can be degraded regardless of land use due to impacts of changed flow regimes and pest plants. However, some of these lower scores also may reflect the methodology used.

The restoration of riparian health is perhaps the most easily achievable of actions required to improve aquatic ecosystem condition. The replanting of native species in cleared riparian zones and the removal of weed species would greatly improve aquatic health and the amenity of aquatic ecosystems for the ACT community.

Native fish

The distribution and abundance of native fish is highly dependent on the condition of aquatic ecosystems. Pressures on native fish include: 

• alteration and reduction of natural flow regimes 
• structures such as dams, road crossing and weirs that create barriers to the movement of fish 
• degraded habitat including loss of riparian vegetation 
• invasive fish species which place pressure on native fish through predation, competition for habitat and resources, disease and habitat modification 
• degraded water quality, and 
• recreational fishing, particularly unregulated (unlicensed) fishing, which impact on species already affected by other pressures.

The ACT Government undertakes fish surveys in Cotter River above Cotter Reservoir, the Murrumbidgee River and selected urban lakes. Main findings for the distribution and abundance of fish species include:

Cotter River

• The data shows a strong population of Two Spined Blackfish in the Namadgi National Park above Cotter Reservoir. 
• The recovery of Two Spined Blackfish following the 2003 bushfires and Millennium Drought. This recovery has been supported by environmental flows from dams. 
• Evidence of an expansion of Macquarie Perch upstream of Cotter Reservoir following the construction of a fishway at Vanities Crossing in 2001. 
• The population of Macquarie Perch has been supported by the translocation of fish from Cataract Reservoir as part of a genetic rescue project.

Murrumbidgee River

• The decline of Trout Cod following the cessation of conservation stocking by the NSW Government in the Upper Murrumbidgee Catchment. 
• Murray Cod have shown an increase above Redrocks Gorge.
• Downstream of Redrocks Gorge, the Murray Cod population shows recovery from a decline after the Millennium Drought. 
• Golden Perch were found to have low population levels in the upper reaches, and populations in the lower reaches were at moderate detection levels showing a small increase after the Millennium Drought. 
• The Golden Perch population is likely to be dependent on connectivity with populations downstream of the ACT. This is dependent on the occurrence of sufficient flows at the right time of year.

Urban lakes

• Murray Cod and Golden Perch are stocked to Canberra’s urban lakes and selected ponds. However, they generally do not breed in these environments and so require ongoing stocking to maintain populations. 
• Successful reproduction of smaller native species, such as Carp Gudgeon, is common in urban lakes and ponds.

Barriers to fish passage in the ACT

Connected waterways are critical for the survival of native fish. Structures such as dams, weirs and road crossings create barriers that can prevent fish passage. Native fish move within and between waterways to breed and to locate critical resources such as food, shelter, nursery sites and spawning grounds. Native fish species can also utilise different parts of river systems for different life cycle stages. For example, the Murray Cod (Maccullochella peelii) and Golden Perch (Macquaria ambigua) usually travel upstream to find suitable breeding areas. Barriers that prevent fish passage can also cause populations to become isolated, which can lead to inbreeding and loss of genetic diversity.Pavlova, A. et al., 2017, Severe Consequences of Habitat Fragmentation on Genetic Diversity of an Endangered Australian Freshwater Fish: A Call for Assisted Gene Flow, Evolutionary Applications 10(6): 531–550.

An assessment of constructed barriers to fish passage in the ACT conservation estate found: 

• A total of 234 potential barriers to fish passage. 
• Seven of these barriers were beneficial barriers that restricted the movement of pest fish species, preventing competition and the spread of disease. 
• Eighteen sites were assessed as significant barriers to fish movement, 6 sites had a medium level of blockage and 70 sites had a low level of blockage and/or were in low quality aquatic habitat. 
• Of the total of 234 potential barriers, 133 were assessed as not preventing the movement of native fish.Unpublished study conducted by the Environment, Planning and Sustainable Development Directorate.

Native fish abundance and biomass

Fish surveys in the Murrumbidgee and Cotter Rivers show that alien species are common in the ACT. For the Murrumbidgee River, native fish typically account for less than 30% of total fish abundance (Figure W9). 

The biomass (a measurement of the relative size of species) of native fish is even lower in the Murrumbidgee River in comparison to exotic species, typically accounting for less than 20% of total fish biomass (Figure W10). The dominance of alien species in the Murrumbidgee River is mainly due to high numbers of carp. It should be noted that biomass is influenced by the size of introduced fish such as carp, rainbow trout and brown trout which are often much larger than native species. Abundance and biomass can also be influenced by the numbers of schooling species or juvenile recruitment as compared to larger-bodied species and adults.

Native abundance and biomass in the Murrumbidgee River have increased in some recent years with the expansion of Murray Cod populations in 2010, and occasional years of high recruitment producing large numbers of juvenile Murray Cod.

The proportion of native fish abundance is higher in the Cotter River, accounting for over 70% of the total abundance between 2014 and 2019 (Figure W11). Biomass is more variable with native species accounting for between 45% and 70% of the total biomass over the same period (Figure W12).

Native fish abundance in the Cotter River has increased since a low in 2005 during the Millennium Drought. This increase is also generally shown for biomass in the Cotter River, although there was a significant decrease in native fish biomass in 2011 and 2012 due to consecutive large flood events that impacted on breeding seasons. These results show that river flow is a significant driver of changes in native and alien fish abundance and biomass in the Cotter River. In addition to flow, recreational fishing pressure is likely to be reducing the population of alien species in the reach between Bendora and Cotter reservoirs. 

Although native fish abundance and biomass is higher in the Cotter River compared to the Murrumbidgee River, results for both rivers demonstrate that alien species are impacting on native fish in the ACT. River modification has created favourable conditions for alien species to thrive. The greater biomass of alien species has significant implications for native fish communities, particularly in relation to competition for food and habitat resources, as well as the spread of disease and habitat availability.

Native fish stocking

The ACT Government stocks juvenile Murray Cod and Golden Perch into Canberra’s lakes and larger ponds including Lake Burley Griffin (funded by the National Capital Authority), Lake Ginninderra, Lake Tuggeranong, the Yerrabi in Gungahlin, Upper Stranger, Point Hut, West Belconnen and Coombs ponds. Stocking is undertaken to provide recreational fishing and to increase the abundance of native species. The lakes and ponds do not provide the required environmental conditions for the successful breeding of Murray Cod and Golden Perch and so populations must be maintained by regular stocking. Stocking of urban lakes and ponds also aims to reduce the angling pressure on natural riverine populations, such as the Murrumbidgee fish population.

Between 2015 and 2019, over 162,000 Golden Perch and 107,000 Murray Cod were stocked to Canberra’s lakes and larger ponds (Figure W13). Canberra’s lakes account for over 80% of the total fish stocked in the ACT with Lake Burley Griffin receiving over half the fish stocked to the lakes. This is because of the size of the lakes which require more fish to meet the target stocking rate of 200 fingerlings per hectare.

Upper Stranger Pond was stocked for the first time in 2017 with Golden Perch and Murray Cod stocked at high densities after carp were removed. Four ponds in the new Coombs suburb area were also stocked in 2017 to complement a research project on the effects of lake drawdown.

The success of stocking is reliant on fish releases at appropriate intervals with sufficient numbers of fingerlings. Inappropriate stocking levels increases the risk of negative changes to fish population structures.