The Regional Catchment Strategy for the Port Phillip & Western Port region
Method (Waterways and Wetlands)

The Healthy Waterways Strategy assesses condition for seven indicators of waterway health.  The descriptions of these assessment methods below are excerpts from the ‘Healthy Waterways Resource Document (draft 2012)’. The seven indicators are:

Platypus

Platypus condition was assessed by looking at the current abundance (size of population) and relative abundance of the populations based on the catch per unit of effort (CPUE). CPUE is based on the number of individual platypus captured and the survey effort (number of traps). Relative abundance is measured by assessing the current abundance against reference condition for each population.

An appropriate reference condition for a system was defined as the maximum three yearly average of the annual maximum CPUEs recorded in the core populations in the system for the period of available record (that is, a rolling three-yearly average of the annual maximum CPUE recorded across populations within a system was calculated, and the maximum value selected). The reference condition provides an indication of a system’s potential to support platypus abundance based on historic capture data. The three year average allows for consideration of the variability in capture rates through time and to minimise the impact of single year potential outliers. The upper reference condition is 1 (based on the highest reported
CPUE within the region being 0.98).  There are two exceptions:

  • The Lower Bunyip, Lang Lang and Bass system does not have three consecutive years of data available and so the maximum two-yearly average annual maximum CPUE is used.
  • The Upper Yarra system has only four years of capture data (2002, 2008-10).   The annual maximum CPUE recorded in the Upper Yarra in 2002 is used as the reference, rather than adopting a value that reflects drought-affected years.

This is based on: in the ten systems with sufficient data, four recorded the maximum three-yearly average annual maximum in 2001 or 2002; and the maximum did not occur in any system after 2005.  Populations were assigned to the HWS systems for the current condition assessment. The current condition ratings per system are based on the scores in the table below.  Not all populations (and systems) have been surveyed every year and so there are variable temporal extents of data to inform the reference condition in each system.  In most systems, adequate data is available to provide confidence in the assessment of condition at the system scale. The confidence in the data to adequately represent the condition and distribution of platypus populations is limited by the strengths and weaknesses of the sampling method. For example, population condition is based on capture data only and is not influenced by sightings. In some systems, there was limited data to assess platypus communities; in these cases expert opinion was used to rate the current condition.

Platypus condition ratings
Rating Score Explanation
Very high 0.81-1 Platypus abundant
High 0.71-0.8 Platypus very common
Moderate 0.61-0.7 Platypus common
Low 0.41-0.6 Platypus present in low numbers
Very low 0-0.4 Platypus present in very low numbers

 

Fish

The condition of fish was assessed by examining freshwater fish populations rather than single species and uses measures of:

  • Species richness – the number and types of species – comparing the numbers of fish species against the fish species expected.
  • Nativeness – the proportion of species that are native

These measures were averaged to produce a score per system. The data used to conduct the assessment came from the Department of Sustainability and Environment (now the Department of Environment and Primary Industries) aquatic fauna database and fish survey reports held by Melbourne Water.

The limited data available for estuarine species prevented their analysis. Estuarine species have been flagged for research throughout the period of the Healthy Waterways Strategy.

The expected species lists were based on all of the native and exotic freshwater species historically recorded. Thirty-six species of freshwater fish (native and introduced) are expected across the region. The expected lists vary from area to area across the system.

The initial analysis was conducted in the five catchments: Werribee, Maribyrnong, Yarra, Dandenong and Western Port; and three altitudinal zones, because altitude is one of the most important factors that determines which fish species are likely to be found in a waterway: lowlands (0-200m), slopes (200-400m), upland (400m+). These zone boundaries were used as part of the development of system boundaries for the HWS. The final assessment to determine the current fish condition for each system re-analysed the data to the HWS system boundaries.

The assessment tool PERCH (Pre European Reference Condition of fish) – a metric established within the Murray Darling Basin Sustainable Rivers Audit – was used to sensitivity-test the results from the expected lists.  The fish condition ratings per system are based on the scores in the table below.  There is adequate data available to provide confidence in the assessment of condition at the system scale.

Fish condition ratings
Rating Score Explanation
Very high 0.801-1.00 Almost all native species that have been recorded in the catchment are present. Native species greatly outnumber exotics
High 0.701-0.80 Most native species that have been recorded in the catchment present.  Native species outnumber exotics
Moderate 0.601-0.70 About half the expected species present.  Significant proportion of the recorded fish exotic
Low 0.401-0.60 A large proportion of the expected species not recorded in the system. Exotic species likely to dominate Poor fish diversity and abundance
Very low 0.0-0.40 Most expected species not recorded.  Exotic species dominate.  Very poor fish diversity and abundance.

Frogs

Frog condition was assessed looking at the diversity of frog species rather than single species using a measure of species richness – comparing the number of frogs species recorded with the number of frog species expected.

Frog data in the Port Phillip and Western Port region has been collected through numerous independent monitoring studies and programs. Significant amounts of frog data were available from Melbourne Water’s Frog Census program, the Department of Sustainability and Environment (now the Department of Environment and Primary Industries) , university assessments and consultants.  The species richness score was calculated for each system. The expected species list for each system was created based on a combination of the species recorded in the system over the entire dataset, and expert opinion as to which species may be recorded.  Eighteen species of frogs (native and introduced) have been regularly found in the rivers, lakes and wetlands in the Port Phillip and Western Port region.

Only species included in the ‘expected’ list for each system are included when calculating the metrics (if a species not on the expected list was observed the record was not used in the calculation of the metric). The current condition ratings are based on the scores in the table below.

There is adequate data available to provide confidence in the condition assessment at the system scale for most systems. An analysis of species richness and the fact that more than 40 surveys have been carried out in 5 years gives confidence that the frog community has been adequately sampled.  Systems with less than 40 surveys are considered to have insufficient data to adequately represent the baseline condition with confidence.  In these systems the data was compared with an assessment based on likely habitat.

Frogs condition ratings
Rating Score Explanation
Very high 0.81-1 Almost all species present
High 0.71-0.8 Most species present
Moderate 0.61-0.7 About half the expected species present
Low 0.41-0.6 A significant proportion of the expected species not recorded,
poor frog diversity
Very low 0-0.4 Few of the expected frog species recorded, very poor frog diversity

Birds

The bird condition assessment examined communities of birds in an area, rather than looking at one or a few selected species.  Native water-dependent bird species were considered in two sub-sets: streamside and wetland birds.  The assessment considered measures of:

  • Species richness – the number of expected bird species observed in an area (the number of different types of species recorded) compared to the number of species expected.
  • Frequency of occurrence – the proportion of surveys in an area in which each species was recorded.

The wetland and streamside bird condition scores are then averaged to generate a single score for an area. The data used in the assessment came from Melbourne Water-commissioned bird surveys and the combined BirdLife Australia dataset. Most of the 11,000 bird surveys at wetlands or along waterways in the Port Phillip and Western Port region came from voluntary bird surveys compiled by BirdLife Australia.  The ‘expected’ species of bird includes only appropriate native species of bird and ignores introduced species, vagrants to the region, pelagic seabirds, coastal birds, species with a limited distribution across the region, and arid zone or open country birds. A list of wide-ranging streamside species was generated from assessment of the entire BirdLife Australia bird atlas database and modified in light of expert opinion. Preliminary analyses show that species richness using this restricted list of bird species does track our understanding of waterway condition.

A second list of wetland-dependent birds is used for the wetland assessment using the same approach.  Some 57 wetland bird species and 113 streamside bird species were expected, having been regularly found at water habitats and occurring widely in the Port Phillip and Western Port region. Nativeness was not included as it is not a significant indicator of condition – of the 300 bird species regularly recorded in the region, only 11 are non-native.  The bird condition ratings are based on the scores in the table below.

The bird data was analysed for each system. In most systems there was sufficient data (over 50 surveys) to provide confidence in the assessment of condition. In systems where there was insufficient data to assess wetland birds, condition ratings are based on streamside birds only.

Birds assessment ratings
Rating Score Explanation
Very high 0.81-1 Almost all expected streamside and wetland species recorded in the
High 0.71-0.8 Most expected streamside and wetland species recorded in the system
Moderate 0.61-0.7 About half the expected streamside and wetland species recorded
Low 0.41-0.6 Poor bird diversity, most expected streamside and wetland species not
recorded, low abundance
Very low 0-0.4 Very poor bird diversity, most expected streamside and wetland species not recorded, low abundance

Vegetation

Vegetation condition was assessed using the Index of Stream Condition (ISC) streamside zone score. The ISC combines information on the width, continuity and diversity of native vegetation, with information on weed cover used to evaluate the health and quantity of streamside vegetation by comparing it with an Ecological Vegetation Class (EVC) benchmark as the reference condition.

In Victoria, plants are grouped into EVCs based on their types and structure. An EVC consists of one or a number of plant communities that seem to be associated with a recognisable environmental niche (such as a wetland), and that can be characterised by several adaptive responses to ecological processes. The Department of Environment and Primary Industries has defined all EVCs within Victoria.

The ISC data was combined for each system, and the average score was used to rate each system. The current vegetation rating per system are based on the scores in the table below.  The ISC was correlated with Melbourne Water’s Healthy Waterways Vision vegetation assessment (Vision assessment) – a more spatially detailed rating of current vegetation quality. Where the ISC score differs by two or more points from the Vision assessment, it is considered that there is limited ISC data coverage to adequately define the result for the system.  In most systems, there is confidence in the ISC assessment of vegetation condition at the system scale.

Vegetation condition ratings
Rating Score Explanation
Very high 8.1-10 Vegetation community largely the same as reference condition
High 6.1-8 Vegetation community largely the same as reference condition although species may be missing and some weed invasion present
Moderate 4.1-6 Vegetation community resembles reference condition although species
may be missing and weeds present
Low 2.1-4 Vegetation may have components of the reference community but has
exotic species and is fragmented
Very low 0-2 Fragmented and degraded vegetation

Macro invertebrates

Macro invertebrate populations have been assessed using SIGNAL – a measure of macro invertebrate families sensitive to water quality sensitive. SIGNAL stands for Stream Invertebrate Grade Number – Average Level.  The SIGNAL index uses these differences in sensitivity of invertebrates to calculate a score or grade indicative of the state of a particular site. Tolerant groups are assigned a lower SIGNAL score and sensitive groups a higher score. By applying the SIGNAL score, which has been assigned for every macro invertebrate family, we can calculate the overall SIGNAL score of a site.  The region is well represented with SIGNAL data. The current condition assessment has been sourced mainly from Index of Stream Condition assessments.

The current condition ratings are based on the scores in the table below.  There is adequate data available to provide confidence in the assessment of condition at the system scale.

Macro invertebrate condition ratings
Rating Score Explanation
Very high 7.01-10 Excellent state of stream water quality
High 6.00-7.00 Healthy state of stream water quality
Moderate 5.00-5.99 Mild pollution
Low 4.00-4.99 Moderate pollution
Very low 0-3.99 Severe pollution

Amenity

A literature review revealed that there is no standard way of monitoring amenity at waterways.  Amenity was assessed using Melbourne Water’s Community Perceptions of Waterways – a tailored social research program which we conduct every two years to assess how the community values/relates to/perceives waterways in the region. The survey collects information on community knowledge, behaviour and attitude across several issues related to waterways. Data from the community perceptions of waterways research on ‘satisfaction with waterways’ and ‘rating waterways as an escape from urban areas’ was used to develop the condition ratings.

Using the postcode of the respondent to link to the relevant geographical system, the average score was generated per system. The current condition rating amenity per system is based on the scores in the table below.  In several systems there is insufficient data to have high confidence in the assessment of current condition.

Amenity condition ratings
Rating Score Explanation
Very high 80.1-100 Very high level of satisfaction with amenity
High 70.1-80 High satisfaction with amenity
Moderate 60.1-70 Moderate satisfaction with amenity
Low 40.1-60 Low satisfaction with amenity
Very low 0-40 Very low satisfaction with amenity