BASELINE ASSESSMENT OF FRESHWATER MUSSEL POPULATIONS ... · BASELINE SURVEY OF FRESHWATER MUSSEL...

Report to:

MW Klunzinger, D Strebel, SJ Beatty, DL Morgan & AJ Lymbery

Centre for Fish & Fisheries Research Murdoch University

December 2011

BASELINE ASSESSMENT OF FRESHWATER

MUSSEL POPULATIONS WITHIN THE URBAN

WATERWAYS RENEWAL PROJECT

BASELINE SURVEY OF FRESHWATER MUSSEL POPULATIONS FOR THE URBAN WATERWAYS RENEWAL PROJECT

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Authors: MW Klunzinger, D Strebel, SJ Beatty,

DL Morgan & AJ Lymbery

Centre for Fish & Fisheries Research,

Murdoch University

December 2011

BASELINE ASSESSMENT OF FRESHWATER

MUSSEL POPULATIONS WITHIN THE URBAN

WATERWAYS RENEWAL PROJECT

Report to:

Frontispiece: from top to bottom – Bickley Brook facing downstream towards the confluence with Canning River, near Royal

Street bridge, Gosnells, WA. Carter’s freshwater mussel (Westralunio carteri) photos: Michael Klunzinger.

Acknowledgements: This survey was funded by SERCUL for the

Urban Waterways Renewal Project. We would

like to thank Julie Robert, Dr Judith Fisher, and

Brett Kuhlman for project coordination. We

especially thank Alice Atkinson, Matt Grimbly,

volunteers Sara and Nick for field assistance

and Monica Estrada and Shaun Meredith for

organising water quality data acquisition.

Thanks also to Tim Storer for providing

information on salt-affected marron.


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Summary & Recommendations

No live freshwater mussels (Westralunio carteri) were found in Sites 1BC (Bannister

Creek), 2BBC (Bickley Brook – Canning River Confluence), 8WR (Wungong River) or 9RL

(Wungong River - Riverside Lane) of the Urban Waterways Renewal Project.

Only empty shells of W. carteri were found within the Canning River between Royal

Street Bridge and ~50 m downstream from the Bickley Brook Confluence, which was

probably the result of mass mortality from a salt wedge that moved upstream above the

Kent Street Weir in February 2011.

Salinisation of this normally freshwater section of the Canning River was further

evidenced by the colonization of Fluviolanatus subtorta, a normally estuarine species of

mussel which is usually not found in freshwater habitats. Numerous F. subtorta had

attached to the empty shells of W. carteri, carapaces of Smooth Marron (Cherax cainii)

as well as woody structures within the river.

No W. carteri shells were found within Bannister Creek, Bickley Brook or the Wungong

River sites.

The salt wedge was also probably responsible for 100% mortality of W. carteri within

Yule Brook, near SERCUL.

Live W. carteri within the Canning River were found near Homestead Park, extending

downstream to 300 m above the Royal Street Bridge.

Although live freshwater mussels were found within Yule Brook in October 2009, and

above Nicholson Rd Bridge within the Canning River, this survey indicates that W. carteri

is now likely to have become locally extinct within a ~8.5 km stretch of the Canning.

Shell measurements indicate that most W. carteri within these extinct populations were

aging and lacked new recruits and even where live W. carteri were surveyed, very few

young mussels (<40mm long) were located and a majority were >60mm in length.

Dense root mats of Swamp Paperbark (Melaleuca rhaphiophylla) and Flooded Gum

(Eucalyptus rudis) within the river harbored the largest densities of W. carteri (up to 65

mussels/m2) and appeared to be important habitats for recruitment because these were

the only areas within our surveys that had younger mussels (<40 mm). Furthermore,

mussel densities and abundance decreased as we moved further away from the river

banks and become virtually non-existent within the middle of the river channel.

Westralunio carteri is becoming increasingly rare in the Swan-Canning catchments,

having once extended from the Avon River into the Swan and Canning Rivers and their

major tributaries from the drinking water catchments to within the areas which are now

largely estuarine. A comprehensive assessment of the species within the remaining

populations in the tributaries of the Swan-Canning catchments and the Canning River is

necessary to determine the viability of the species in the near future.


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The loss of this species may have unknown consequences for water quality within these

catchments. Freshwater mussels are generally known to filter large volumes of water

and have been shown to improve eutrophic catchments in Europe, USA and New

Zealand. Thus, a quantified study of filtration rates and algae removal capacity of W.

carteri is necessary to determine their importance, to estimate their potential as a

bioremediator of nutrients and predict how their loss will impact the rivers.

Recolonisation of W. carteri within UWR sites will largely depend on the availability of

freshwater (i.e. <2.0 ppt salinity), suitable habitats for adult and juvenile mussels as well

as the necessary host fishes upon which the parasitic larvae (‘glochidia’) of W. carteri

depend for development, survival and dispersal. Provision of adequate supplies of

freshwater and mitigation of pollutants such as saltwater, industrial/agricultural and

household chemicals, chlorine and fine sediments is necessary to ensure freshwater

ecosystem function and integrity. Stability of freshwater mussel (W. carteri)

populations should be used as appropriate bioindicators of freshwater ecosystem

function throughout the Swan-Canning catchments and in other regions of the south-

west where the species is found.

The Canning River, Perth, WA


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Contents

Summary & Recommendations ............................................................................................. 3

Introduction .......................................................................................................................... 6

Urban Waterways Renewal Project ......................................................................................... 6

Aquatic freshwater biodiversity of south-western Australia ................................................... 6

Aims of the study ..................................................................................................................... 9

Methodology ....................................................................................................................... 10

Sampling sites ........................................................................................................................ 10

Freshwater mussel sampling ................................................................................................. 20

Water quality data ................................................................................................................ 22

Statistical analysis ................................................................................................................. 22

Results and discussion ......................................................................................................... 22

Freshwater mussel distribution and abundance ................................................................... 22

Freshwater mussel population structure ............................................................................... 26

Water quality ......................................................................................................................... 28

Conservation implications and recommendations ................................................................ 30

References .......................................................................................................................... 32

Appendix ............................................................................................................................. 35


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Introduction

Urban Waterways Renewal Project

The Swan and Canning River catchments were identified as a coastal ‘hot spots’ owing to high

nutrient loads in 2006. The Australian Government subsequently funded the Swan River Trust

to develop the Swan-Canning Water Quality Improvement Plan (WQIP) with an aim to reduce

nitrogen and phosphorus inputs within the catchments (SRT 2009). Of the 30 sub-catchments

assessed in the Swan-Canning Catchment, priority areas with high nutrient concentrations were

identified and targeted for local WQIPs. Water Quality Improvement Plans have been

developed for Bickley Brook, Southern River and Bannister Creek to assist State and Local

Governments and communities to prioritise management areas for improvement in water

quality.

Within Metropolitan Perth, the ‘Urban Waterways Renewal’ project (UWR), funded by

the Australian Government through Water for the Future – National Water Security Plan for

Cities and Towns program, the South East Regional Centre for Urban Landcare (SERCUL) has

partnered with the Department of Water, Water Corporation, Swan River Trust as well as local

governments within the cities of Canning, Gosnells and Armadale to implement the WQIPs. The

Australian Government is providing $4 million for implementing actions identified in the Swan-

Canning WQIP.

Aquatic freshwater biodiversity of south-western Australia

South-western Australia is home to a unique array of plants and animals, a large proportion of

which are found nowhere else. The freshwater ecosystems of the south-west harbor a highly

endemic assortment of macrofauna which includes 11 species of freshwater fishes (82%

endemic), 11 species of freshwater crayfishes (100% endemic), 2 species of turtle (100%

endemic), 30 species of frogs (93% endemic; 15 species breed in freshwater), many waterbird

species, snakes, water rats and only one species of freshwater mussel (Morgan et al. 1998,

2011; Davis & Christidis 1999; Allen et al. 2002; Nevill 2005; Tyler & Doughty 2009; Wilson &

Swan 2010). Together with other fauna including aquatic and terrestrial macro- and micro-

invertebrates, macrophytes, riparian and terrestrial vegetation, these fauna interact to form a

complex food web with various trophic levels which are strongly influenced by nutrient

concentrations (nitrogen, potassium and phosphorus are particularly important). This survey is

focused on Carter’s Freshwater Mussel (Westralunio carteri), which is one of several indicator


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organisms which will be used as bioindicators of freshwater biodiversity in the UWR project

areas.

Freshwater mussels

Freshwater mussels filter particulates and plankton from the water column, contributing to

water clarity and quality. As they burrow and move through the sediments, they are thought to

enhance benthic oxygenation. Their shells are home to a multitude of other fauna including

hydra, algae, other molluscs, freshwater shrimp, and empty shells can provide shelter for

juvenile freshwater crayfishes and small benthic fishes such as gobies. They are a favoured

food item by water rats and, historically, were important to indigenous peoples for food, tool

use and trade (e.g. Vaughn and Hakenkamp 2001; Walker et al. 2001; Strayer 2008; Klunzinger

2011). Freshwater mussels are sensitive to environmental changes (Ponder & Walker 2003)

and, like freshwater fish fauna, can be considered important bioindicators of aquatic ecosystem

condition (Lymbery et al. 2008; Beatty & Morgan 2010).

Carter’s Freshwater Mussel is endemic to the south-west and found nowhere else

(McMichael & Hiscock 1958; Walker 2004). This bivalve has a unique life cycle in which its

larvae, known as ‘glochidia’ must attach to a host, which is generally a fish to complete its

development to the juvenile mussel stage. This interaction is thought to serve as a dispersal

mechanism (Bauer & Wächtler 2001; Strayer 2008). Until recently, little was known of the

species biology, reproductive development, ecology and its host fishes (Klunzinger et al. 2011a,

unpublished data). Kendrick (1976) documented the disappearance of W. carteri from the

River Avon, presumably as a result of secondary salinisation. In recent years, the species has

undergone population contractions in parts of its range, also presumed to be linked with

salinisation of waterways within the south-west agricultural zones (Keighery et al. 2004) and

was listed as ‘Vulnerable’ under international conservation criteria in 1994 (IUCN 2011). The

species is categorized as ‘Priority 4’ fauna under an interdepartmental listing by the Western

Australian Department of Environment and Conservation (DEC 2011), meaning that the species

is in need of monitoring. Recent work by Klunzinger et al. (2010) has shown that the species is

intolerant of salinities above 3.0 ppt, dehydration can cause localized population reductions

(Klunzinger et al. 2011b) and field reports have shown that low dissolved oxygen (<20%) also

may cause mortality (Klunzinger et al., unpublished data). Despite localized extinctions in

systems such as the Avon River, Moore River, Blackwood River, Kalgan River and others, the

species remains legislatively unprotected (Klunzinger et al., unpublished data).

Freshwater Mussel declines

Freshwater mussels have undergone major declines in population range due to a combination

of habitat change, such as riparian vegetation degradation and secondary salinisation of inland


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reaches of the major rivers (Kendrick 1976; Beatty et al. 2010a; Klunzinger et al. 2010,

unpublished data); impacts from sedimentation, loss of host fishes, barriers to host fish

migrations, inability of glochidia to successfully transform on feral fishes, predation by feral

animals, contaminants such as heavy metals and chemicals, eutrophication leading to anoxia,

exotic macrophyte blooms (e.g. Salvinia molesta), drought, lack of environmental flows,

destruction from construction projects and livestock trampling (e.g. Walker et al. 2001; Beatty

et al. 2010b; Jones & Byrne 2010; Klunzinger et al. 2011b). Salinisation of inland areas has

resulted in only ~44% of flow in the largest 30 rivers in the south-west of WA remaining fresh

(Mayer et al. 2005).

Examples of threats to freshwater mussels: (A) Drying; (B) Barriers to host fish migrations;

(C) Salinity/drought; (D) Erosion/sedimentation; (E) Livestock trampling; (F) Salvinia

molesta. Photos: A - E - Michael Klunzinger; F – WRC 2002.

(A) (B)

(D) (C)

(E) (F)


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Aims of the study

The aims of this study were to:

Determine whether freshwater mussel populations are present within the study area.

Determine the distribution and population structure of freshwater mussels in Urban

Waterways Renewal sites.

Interpret results of surveys and identify priorities for management.

Carter’s freshwater mussel, an important bioindicator of freshwater ecosystem health in south-western Australia. (photo: M. Klunzinger)


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Methodology

Sampling sites

A total of 4 pre-defined UWR sites (Figure 1) were assessed using qualitative

(presence/absence) and quantitative (abundance and density) methods to provide details of

the freshwater mussels within Bannister Creek (site 1BC; Figure 2), Bickley Brook – Canning

River Confluence (site 2BBC; Figure 3). Additional sites within the Canning River near the Royal

Street Bridge included an area between (32°02.046'S, 115°57.160'E) and (32°02.605'S,

115°57.956'E) (see Figure 4). Other UWR sites were surveyed within the Wungong River (sites

8WR and 9RL; Figures 5 and 6) in the cities of Canning, Gosnells and Armadale, respectively.

The Canning River near Homestead Park between (32°03.138'S, 115°58.262'E) and (32°02.825'S,

115°58.079'E) (see Figure 7) and Yule Brook near SERCUL between (32°02.024'S, 115°57.058'E)

and (32°02.046'S, 115°57.160'E) (see Figure 8) were also surveyed.

In order to provide an overall summary of the previously known distribution of

freshwater mussels in the Canning River catchment, the MusselWatchWA distributional

database was accessed and the distribution of freshwater mussels in this catchment was then

mapped and included for comparison (Figure 9).

UWR sites sampled for freshwater mussels. (A-B) Bannister Creek; (C-D) Bickley Brook –

Canning River Confluence; (E-F) Wungong River.

(A)

(C)

(E) (F)

(B)

(D)


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15


16


17

Quadrats 1-5

Quadrats 6-10

Quadrats 26-30

Quadrats 16-25

Figure 9 Distribution of Westralunio carteri in the Swan-Canning catchment (excluding this study). Data

maintained by the authors in the MusselWatchWA database.


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Freshwater mussel sampling

At each site, a 50 m stretch of stream was visually examined for freshwater mussels from the

water surface using a bathyscope or feeling for mussels by hand when water clarity was poor.

Where mussels were found, relative abundance and density was determined by counting the

number of mussels in 1 m2 quadrats which were randomly placed on the stream bed at each

site as per Strayer & Smith (2003). Quadrats were constructed of 15 mm diameter round PVC

tubing and open elbows. At each site, we recorded substrate type on the river bottom (rock,

gravel, sand, mud, silt and/or detritus, woody debris, etc.). For each mussel collected from the

quadrats, the maximum length (ML), maximum height (MH) and width (W) of the shell was

measured with mechanical callipers to the nearest 0.01 mm (Figure 10). Mussels were

identified to species level as per McMichael & Hiscock (1958) and Walker (2004). All mussels

were released after being measured, but empty shells were retained for future study.

Maximum Height Index (MHI) and Shell Obesity Index (WLI) according to McMichael & Hiscock

(1958) was derived from the following formulas:

and

.

A bathyscope was used to search for freshwater mussels (right) and when found, density was

determined by counting the number of mussels in 1 m2 PVC quadrats (left).


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Figure 10 Morphological measurements of freshwater mussels using mechanical callipers (methods as

per McMichael & Hiscock 1958 and Walker 2004).

Maximum Height

Maximum Length

Width


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Water quality data

Physico-chemical parameters of water quality (temperature (°C), pH, dissolved oxygen (DO as

%), salinity (ppt) and conductivity (µS/cm)) were measured using an Oakton® PCD650

waterproof portable multimeter and data was obtained from the Department of Water (WA),

SERCUL and the Swan River Trust.

Statistical Analysis

Mapping of faunal distributions was undertaken using ArcGIS® and NearMap® software.

Graphical and statistical analysis of mussel densities, and length-frequencies were undertaken

using SigmaPlot®11.0. Statistically significant differences (P < 0.05) in mussel shell

measurements were determined using Analysis of Variance (ANOVA) in Sigma Plot® 11.0.

Results and discussion Freshwater mussel distribution and abundance

Only empty (dead) freshwater mussel shells were found at Yule Brook and the Bickley

Brook Confluence and within a ~160 m2 area of Canning River associated with Bickley Brook; no

freshwater mussels were found at the Wungong or Bannister Creek sites. A freshwater mussel

kill incident had previously been reported in February 2011, 150 m upstream from the Royal St

Bridge. Although no official report was released, the information was documented (Meredith,

pers. comm.). These mussels probably died from an influx of saline water that breached the

Kent St Weir.

During this study, an additional survey ~2.2 km upstream from Royal Street Bridge, near

Homestead Park, revealed the presence of many live W. carteri. The river was then surveyed

downstream from this point to determine the extent of the remaining populations within the

river reach. The extent of live W. carteri extends to ~450 m upstream of Royal Street bridge.

Since 2009, mass extinctions of the species have occurred along a 8.5 km section of the Canning

River above Kent Street Weir, which probably resulted from dehydration in Yule Brook and

possibly other tributaries in October 2009 and the movement of a salt wedge upstream above

the Kent St Weir from 2010 to 2011 (Klunzinger et al., unpublished data; Meredith, pers.

comm.). The distribution of W. carteri within the Upper Canning River and downstream,

including Canning Dam and associated tributaries, to Roley Pool is largely unknown due to the

inaccessibility of areas associated with drinking water supplies and residential properties.

During this study, Fluviolanatus subtorta, an estuarine species of mussel was found

attached to empty shells of W. carteri (Figure 11) in Yule Brook and Canning River below Royal

St Bridge near UWR Site 2BBC, demonstrating observable salinisation in this area of the river.


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Further downstream in the Canning River, near the Kent Street Weir, live Smooth Marron

(Cherax cainii) were also found with many, what appear to be F. subtorta, attached to their

carapace and may even have resulted in the loss of an eye (Figure 11 – Storer, pers. comm.).

Marron are acutely intolerant of salinities above 17 ppt and adults can withstand prolonged

periods of up to 8 ppt, however salinities of <5 ppt are probably required to complete the life

cycle of the species (de Graaf et al. 2010). Elsewhere in the south-west, this estuarine mussel

has been found where habitats have become too salty for the survival of W. carteri (Kendrick

1976; Pen 1999; Klunzinger et al., unpublished data). Several experiments conducted at the

Murdoch University Fish Health Unit revealed that W. carteri is acutely intolerant of salinities

above 3.0 ppt (Klunzinger et al. 2010), which is in agreement with studies of other temperate

Australian freshwater mussels within the same family (Walker 1981; Widarto 1996).

The densities of freshwater mussels surveyed during this study ranged from one to as

many as 65 mussels/m2 within the survey sites (Table 1). Densities were greatest near the river

banks amongst tree roots and woody debris with muddy sand substrates and few, if any

mussels were found in mid-channel runs or in areas that were dominated by extremely soft

organic sludge. A breakdown of the localised distributions of W. carteri within each site are

presented in Figures 6-8. Densities observed within each quadrat are presented in the

Appendix.

Table 1 Density of freshwater mussels (Westralunio carteri) within the study area. Site River Name Density Range

(number of mussels/m2)

Avg. Density (number of mussels/m2)

1BC Bannister Creek Bannister Creek --- 0.0

2BBC Bickley Brook – Confluence Canning River 1-65 8.1 (±1.1) ☠

2BBC Bickley Brook Bickley Brook --- 0.0

8WR Wungong Wungong River --- 0.0

9RL Riverside Lane Wungong River --- 0.0

SERCUL Yule Brook 1-15 2.4 (±0.8) ☠

Homestead Park Canning River 3-48 12.9 (±5.8)

☠Only dead mussels with empty shells were found


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Figure 9 Examples of the estuarine mussel Fluviolanatus subtorta (arrows) attached to the empty shells of

the freshwater mussel Westralunio carteri within the Canning River, near Royal St Bridge


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Figure 11 Examples of clusters of the estuarine mussel Fluviolanatus subtorta (arrows) attached to the

orbital carapace (top and bottom left) and abdominal segments on the underside of the tail of Marron

(Cherax cainii) captured near the Kent Street Weir within the Canning River. Photos: Tim Storer (DoW).


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Freshwater mussel population structure

Mean MHI was 60.3%, which is within the range reported for W. carteri (60-70%; McMichael &

Hiscock 1958). Length-frequency distributions of mussels surveyed in this study are presented

in Figure 12. Mussels in the Yule Brook site were the largest, dominated by individuals in the

70-75 mm shell length range followed by mussels in the Canning River sites, which was

dominated by individuals within the 60-70 mm size range. Average shell length of mussels

within Yule Brook was 71.74 mm, which was significantly larger than those within the Canning

River sites, which were 66.45 and 67.68 mm long at the Bickley Brook Confluence and

Homestead Park sites (F = 9.022, df = 347, P < 0.001). Average shell lengths of mussels within

the Canning sites were not statistically different (t = 1.443, df = 275, P = 0.448).

Very few smaller individuals (<40 mm) were recovered during the surveys, but several

small mussels were found amongst dense root mats of Swamp Paperbark trees (Melaleuca

rhaphiophylla) int the Canning River near Homestead Park, which suggests they may be a

favoured habitat for developing juveniles. Although these few small individuals suggest some

recent recruitment, the length frequency patterns of W. carteri within the study area suggests

that regular recruitment may not have occurred in recent years and the population is aging and

probably in decline, although we are uncertain of the age-at-length of the species within this

system, and would need to validate age with growth rates.

The influx of salt from the estuary appears to have completely annihilated W. carteri in

the Canning River to a point approximately 450 m above Royal Street Bridge. Mussel shells

measured downstream of this point are reflective of now locally extinct populations. Refuges

of freshwater tributaries and pools within this reach could still harbour survivors, but additional

surveys would need to be undertaken to determine whether this is the case.

Because no live mussels were observed in the UWR sites, obviously no investigation of

reproductive status could be initiated. Further upstream behind Fancote Park however, regular

sampling of W. carteri on a monthly basis since 2009 has revealed that roughly half of the

population is composed of females and half is composed of males; spawning occurs in late

winter; embryos are brooded to the glochidia stage and released with the onset of warmer

waters in late spring to early summer (between September and November to around early

December) (Klunzinger et al., unpublished data). This period is the most critical time in the

developing freshwater mussel’s life cycle when glochidia have a brief opportunity to contact

host fish; appearing later, the detached transformed juvenile mussels face the challenge of

finding suitable habitat, avoiding predation by other macroinvertebrates and fishes and

obtaining the necessary food supply and environmental conditions for survival (Walker 1981;

Walker et al. 2001; Strayer 2008). Worldwide, little is known about the juvenile stage of

freshwater mussels in wild populations (e.g. Strayer 2008); the same is true for south-west WA.


27

Yule Brook

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100

0

2

4

6

8

10

12

14

16

18

Canning River - near Homestead Park

Shell length (1 mm size classes)

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100

0

2

4

6

8

10

12

14

16

18

Bickley Brook - Canning River Confluence

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100

Nu

mb

er

of

mu

sse

ls

0

2

4

6

8

10

12

14

16

18

Figure 12 Length-frequency distributions of Westralunio carteri within the Canning River in

November 2011. Green bars represent live mussels and red bars represent dead, empty

mussel shells.


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Water quality

A comprehensive analysis of water quality over time and space is beyond the scope of this

study. Instead we will focus on key sampling points and issues associated with the death of

freshwater mussels within the Canning River catchment. In 2010-2011, an exceptionally low

rainfall in the winter and high tides the following summer caused estuarine waters to breach

the Kent Street Weir, resulting in a salt wedge which travelled upstream from the Canning

Estuary to at least the Royal Street Bridge (Meredith, pers. comm.). A mussel kill was reported

to the Swan River Trust by a number of river management staff from various agencies within

the locality on 22 February 2011 which was followed by water quality sampling by the Swan

River Trust and Department of Water. A sample of dead mussels was collected and delivered to

the Department of Fisheries by Swan River Trust staff for post-mortem examination. Results

showed that the specimens were autolytic, but no parasites were found. Although the species

was reported as ‘blue mussel’, this was apparently made in error and noted later, but no official

change to the reporting document was made (Meredith, pers. comm.). The correct

identification of the species was confirmed as Westralunio carteri (Klunzinger pers. comm. with

Meredith). Water quality measurements taken during this incident are presented in Table 2.

During this survey, all mussels near the Royal Street Bridge were dead, even though

some were previously alive in November 2010 and 24 February 2011 (Lymbery and Klunzinger

et al., unpublished data). The few freshwater mussels which may have remained alive along

the banks in February 2011, probably became salt affected shortly after sampling, as evidenced

by Swan River Trust water quality measurements the following day and the empty shells found

in this study. The data obtained from the Swan River Trust showed the importance of sampling

throughout the water column and at various depths. The freshwater mussels behind Fancote

Park in Kelmscott remain alive and reproductively fit where water quality is generally fresh

(<0.5 ppt), well oxygenated and probably low in algal concentrations. The low dissolved oxygen

near Royal Street during the late afternoon and supersaturation the following day may very

well have presented physiological stress in W. carteri. In other regions where they have been

studied, freshwater mussels are particularly sensitive to hypoxic and anoxic stress and can

result in death in severe cases (Walker 1981; Humphrey 1984; Sheldon & Walker 1989). The

low DO threshold for W. carteri is currently unknown.

The heavy salt concentrations from the 25 February 2011 sampling (Swan River Trust

data), was probably the leading cause of death in this system. Klunzinger et al. (2010) reported

an LD50 of ~2.0-3.0 ppt and an LD95 of ≥4.0 ppt for W. carteri, so the much higher

concentrations observed in February (≥11 ppt) would certainly have been lethal to the local

population.

From available data, within the Bannister Creek and Wungong River sites,

environmental variables alone do not explain the absence of W. carteri. If, at one time, W.


29

carteri existed within the sites we surveyed, their disappearance could have been caused by

any number of factors, but we cannot speculate without historic data. The presence of

industrial, household and perhaps even agricultural chemicals within the waterways can be

detrimental to freshwater mussel populations (e.g. Strayer 2008). In other regions where they

have been studied, freshwater mussels are know to have been eliminated from a number of

anthropogenic toxins; the major contaminants include anoxia from domestic and industrial

wastes, acid mine drainage (Ortmann 1909; Neves et al. 1997), ammonia (Auspurger et al.

2003), chlorine and chlorination by-products (Goudreau et al. 1993), heavy metals (Naimo

1995), industrial chemical spills (e.g. Crossman & Cairns 1973; Sparks et al. 1999; USFWS 2002),

synthetic pesticides (Conners & Black 2004), polycyclic aromatic hydrocarbons (Weinstein &

Polk 2001) and unionised ammonia (Auspurger et al. 2003; Newton 2003; Mummert et al.

2003) to name a few.

Table 2. Water quality parameters associated with freshwater mussel deaths in the Canning River during February 2011.

Date Freshwater mussel status

Time Site GPS Temp. (°C)

Salinity (ppt)

pH DO (%)

Microalgae (No. cells/mL)

25 Oct 2010

Alive 1:00 PM Behind Fancote Park, Kelmscott

32°06'42"S 116°01'00"E

18.8 0.454 7.11 95.6 n/a

Nov 2010 Alive DATA NOT AVAILABLE

Royal St Bridge, 0.5 m from river bank

32°02'39"S 115°57'57"E

DATA NOT AVAILABLE n/a

24 Feb 2011


32°06'42"S 116°01'00"E

25.6 0.117 7.66 63.9 n/a

Alive 3:00 PM Royal St Bridge, 0.5 m from river bank

32°02'39"S 115°57'57"E

28.8 0.097 7.12 30.9 n/a

25 Feb 2011

Dead 10:58 AM 50 m upstream Royal St Bridge

32°02'39"S 115°57'57"E

29.1 11.51 6.64 198.5 4,040,000

Dead 11:04 AM 100 m upstream Royal St Bridge

32°02'40"S 115°57'58"E

30.2 15.2 6.76 223.2 3,555,200

15 Oct 2011


32°06'42"S 116°01'00"E

18.7 0.101 8.08 73.5 n/a

11 Nov 2011

Dead DATA NOT AVAILABLE

50 m upstream Royal St Bridge

32°02'39"S 115°57'57"E

DATA NOT AVAILABLE n/a


30

Conservation significance and recommendations

The number of dead freshwater mussels (W. carteri) found within the Canning River and lack of

live W. carteri within any of the UWR sites is cause for concern, particularly in light of the fact

that historic records show that the species’ was once present within these systems. Salinity is

probably the leading cause of death of freshwater bivalves in the Swan-Canning Catchments,

which has resulted in large range contractions since European settlement (Kendrick 1976;

Keighery et al. 2004; Klunzinger et al., unpublished data).

Many of the remaining populations of W. carteri are maintained by freshwater flows

and within dams along the Darling Scarp, which includes the Canning and Helena Rivers.

Smaller tributaries of the Swan River, including Bennet Brook, Jane and Susannah Brooks and

tributaries of Ellen Brook, such as Yalyal, Boorara and Lennard Brooks are maintained by

groundwater (Beatty et al. 2010b). As such, maintaining dam water levels, groundwater

reserves and discharge and environmental flow releases will become increasingly important

and more challenging as the climate becomes hotter and drier (e.g. Beatty et al. 2010a,b). In

heavily populated areas of south-east Asia such as Singapore, for example, freshwater flows

from rivers have been reduced to drinking water dams and are essentially the last remaining

native arks for populations of freshwater fauna (Clements et al. 2006), thus outlining the

importance of maintaining water quality and levels in dams. The use of chlorine in drinking

water supplies is a common treatment to prevent human ailments, but chlorination within

open water dams can have detrimental effects on wildlife, particularly sensitive fauna such as

freshwater mussels (Valenti et al. 2006). The effect of chlorine on W. carteri has never been

tested.

Dehydration has been shown to negatively impact W. carteri and some populations are

being lost from drought and de-watering (Klunzinger et al. 2011b). Sedimentation from

construction projects and erosion is another killer, which swallows populations of freshwater

mussels, clogging their siphons and leading to death in some areas (Jones & Byrne 2010;

Klunzinger et al., unpublished data). In some streams, for example, W. carteri is restricted to

thin edges (~20 cm wide) along stream banks while the stream channels are filling with coarse,

mobile sand (Beatty et al. 2010b). In rural areas, trampling from livestock has devastating

consequences for W. carteri (Jones & Byrne 2010; Beatty et al. 2010b).

The main issues concerning potential re-introduction of W. carteri into UWR sites are

salinity and sedimentation. If, at some stage, there may be an initiative to re-introduce the

species, sedimentation will need to be minimized and adequate habitat with sediments soft

enough for mussels to burrow, but stable enough so they stay in place will need to be secured.


31

Maintaining riparian vegetation, in-stream macrophytes and woody debris in the rivers will

enhance native freshwater fish habitats which are necessary for the recruitment of W. carteri

and will provide structure and biodiversity necessary for a functioning ecosystem. An

investigation into the habitats necessary for juvenile W. carteri settlement and survival is also

necessary. Some decisions will need to be made on whether the Canning River and its

tributaries above Kent Street Weir will be managed as a freshwater river or as an extension of

the estuary. Indeed, the massive amounts of W. carteri which have been lost from summer-

time salt wedges will take many years to recover, if at all and captive rearing to boost numbers

may become necessary in the future.

In other UWR sites, pollutants such as industrial, agricultural and household chemicals

need to be prevented from entering the waterways and persistent contaminants, such as heavy

metals, will need to be monitored and mitigated. Toxicology on W. carteri to various chemicals

may initially be necessary to determine tolerances, but protocols for testing surrogate

organisms (i.e. those which closely match W. carteri in terms of physiological and

environmental tolerances) that have a shorter generation time and are more readily available

will need to be developed. More funding to answer basic questions about the life cycle,

population viability and abundance will be necessary to ensure the survival of the only endemic

freshwater mussel in south-western Australia. This mollusc may prove useful in the removal of

undesirable algae and nutrients within UWR sites in the future and is a vital component of a

functioning freshwater ecosystem. For the reasons outlined above, abatement of threats such

as sedimentation, salinity and contaminants will need to be addressed before considering re-

introduction and existing viable populations of W. carteri will require protection. A system-

wide assessment of the existing W. carteri populations within the Swan-Canning catchments is

necessary to determine the long-term viability of the species.


32

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Appendix

Freshwater mussel (Westralunio carteri) densities observed within the survey quadrats during this study.

River Name Site Quadrat

No.

Density (No.

mussels/m2)

Status River

Name

Site Quadrat

No.

Density (No.

mussels/m2)

Status

Canning River

Near Bickley Brook Confluence

1 1 Dead Yule Brook

Near SERCUL

1 1 Dead

“ “ 2 0 “ “ 2 0

“ “ 3 0 “ “ 3 0

“ “ 4 20 Dead “ “ 4 0

“ “ 5 65 Dead “ “ 5 2 Dead

“ “ 6 16 Dead “ “ 6 4 Dead

“ “ 7 4 Dead “ “ 7 2 Dead

“ “ 8 7 Dead “ “ 8 0

“ “ 9 23 Dead “ “ 9 1 Dead

“ “ 10 4 Dead “ “ 10 0

“ “ 11 5 Dead “ “ 11 0

“ “ 12 14 Dead “ “ 12 0

“ “ 13 0 “ “ 13 0

“ “ 14 1 Dead “ “ 14 0

“ “ 15 1 Dead “ “ 15 0

“ “ 16 2 Dead “ “ 16 15 Dead

“ “ 17 0 “ “ 17 0

“ “ 18 0 “ “ 18 0

“ “ 19 0 “ “ 19 0

“ “ 20 0 “ “ 20 0

Canning River

Near Homestead Park

1 44 (41 Live)

(3 Dead)

“ “ 21 0

“ “ 2 48 Live “ “ 22 0

“ “ 3 8 Live “ “ 23 5 Dead

“ “ 4 0 “ “ 24 1 Dead

“ “ 5 0 “ “ 25 0

“ “ 6 0 “ “ 26 2 Dead

“ “ 7 0 “ “ 27 4 Dead

“ “ 8 3 Live “ “ 28 2 Dead

“ “ 9 7 Live “ “ 29 0

“ “ 10 19 (18 Live)

(1 Dead)

“ “ 30 1 Dead

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