population assessment of freshwater ......within the study area, live freshwater mussels were...

Report to:

MW Klunzinger & AJ Lymbery Centre for Fish & Fisheries Research

Murdoch University March 2012

POPULATION ASSESSMENT OF FRESHWATER MUSSELS WITHIN YULE BROOK BETWEEN KENWICK LINK & ALBANY HIGHWAY

POPULATION ASSESSMENT OF FRESHWATER MUSSEL WITHIN YULE BROOK BETWEEN KENWICK LINK & ALBANY HIGHWAY

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Authors: ©MW Klunzinger & AJ Lymbery Centre for Fish & Fisheries Research, Murdoch University March 2012

POPULATION ASSESSMENT OF FRESHWATER MUSSELS WITHIN YULE BROOK BETWEEN KENWICK LINK & ALBANY HIGHWAY

Report to:

Frontispiece: from top to bottom – Yule Brook facing downstream, Beckenham, WA. Carter’s freshwater mussel (Westralunio carteri: photo – Rose Udayaniweerasinghe).

Acknowledgements: This survey was funded by SERCUL. We would like to thank Julie Robert and Brett Kuhlman for project coordination. We especially thank Ditte Strebel and Rose Udayaniweerasinghe for field assistance and GIS mapping.


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Background Westralunio carteri Iredale, 1934 is the only freshwater mussel in south-western Australia. Like other freshwater species, it is likely to be responsible for providing valuable ecosystem services including water filtration, sediment oxygenation, structure to stream banks and sediment support, food for other animals including waterbirds, water rats, marron, and shells provide refuge for other small aquatic animals. At one time, the mussel was an important food source for the Noongar people. Since land clearing began in the late 1800s, dryland salinity has caused the species to disappear from much of its former range. It is intolerant of salinities above 3.0 ppt. A recent survey of the lower Canning River (downstream from a point above Royal Street Bridge) and lower Yule Brook (between the confluence with Canning River and just downstream from Kenwick Link) revealed that the species had undergone 100% mortality in these areas, which probably resulted from the upstream movement of a salt wedge in these systems, although water loss and drought-like conditions in 2009 and 2010 in lower Yule Brook may have also caused deaths from dehydration. To determine whether living W. carteri populations remain in Yule Brook above Kenwick Link, and to determine their population structure, an ecological survey was conducted during March, 2012.

Activities • Survey four stretches of Yule Brook between Kenwick Link and Albany Highway for

freshwater mussels

• Determine whether living mussels exist and establish population densities within habitat types

• Determine population structure of living W. carteri

• Use information to provide recommendations for actions required to mitigate impacts and provide advice to assist in species conservation

Methods


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Freshwater mussel presence was determined by searching 50 m2 sections of stream in an upstream oriented search pattern. Where freshwater mussels were found, population densities were determined using a stratified random sampling design from Strayer & Smith (2003). Mussel density was determined in four 4 x 12.5 m transects by counting the number of mussels within each of 10 randomly placed 1 x 1 m PVC quadrats per transect (Figure 1). Mussels were collected by a combination of sieving and hand-collection. Stream sediment, benthic habitat and riparian vegetation characteristics were noted for each quadrat. Mussels collected from each transect were measured with calipers according to the methods prescribed by McMichael & Hiscock (1958). Statistical and graphical analysis was undertaken using Sigma Plot™ 12.0 software.

Results & Discussion Transect characteristics Transects 1 and 3 were characterized by riparian vegetation composed a mixed variety of alien and native trees, sedges and weeds that provided the stream with shade. The stream flowing through Transect 2 was well shaded by Flooded Gum (Eucalyptus rudis) but banks lacked trees in some areas. Within the stream, coarse sand was the dominant sediment type with mud along the edges of the banks. A thick layer of organic sludge (~25 cm deep) was characteristic of the open channel in Transect 4. Woody debris and leaf litter were most prevalent in Transects 1 and 3, but less common in Transects 2 and 4. Table 1 Average density (± standard error) of freshwater mussels (Westralunio carteri) at four stratified-randomly sampled transects within Yule Brook between Kenwick Link and Albany Highway.

Transect number Transect description Mussel density (number/m2)

Transect 1 Heavily vegetated; steep banks; variety of feral and native trees 0.7 (±0.34)

Transect 2 Combination of open spaces and areas shaded by Eucalyptus rudis 2.2 (±0.84)

Transect 3 Heavily vegetated; steep banks; feral vegetation abundant 0.1

Transect 4 Straight channel with no trees and very little shade 0

Freshwater mussel ecology Average densities within each transect are given in Table 1. Mussel densities within each quadrat are presented in Figure 2. The exposed submerged tree roots of flooded gums, which are well known habitats for native fish and crayfish species, also contained the densest mussel colonies. This was particularly apparent in Transect 2 where native Nightfish (Bostockia porosa), a known host fish species for the glochidia of W. carteri were also observed. Mussels were virtually non-existent in areas where alien plant root mats, such as Willows (Salix spp.), covered the bottom of the stream, making it virtually impenetrable to mussels or other aquatic fauna. Organic sludge and exceptionally deep layers of leaves also appeared to be unfavourable for mussels. Although the effects of alien vegetation on W. carteri are largely unknown, pharmaceuticals derived from some plants have been known to cause problems in freshwater mussel physiology. In Willows, salicylic acid derived from the sap is used in the production of aspirin and other medications, such as novobiocin and morphine, respectively used as an antibiotic and an analgesic, cause reduced immune system function in freshwater mussels (Elliptio complanata) in the St. Lawrence River, North America (Gagné et al., 2006).

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Transect 1

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Figure 2 Densities of Carter’s Freshwater Mussel observed in each stratified-random sampling transect (numbered 1 to 4 on left) within Yule Brook. Transects were measured from downstream to upstream (left to right in each diagram) and from the right to left bank (bottom to top in each diagram).

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Population structure of living mussels in the study area Within the study area, live freshwater mussels were dominated by individuals within the 70 - 80 shell length range (Figure 3). There was evidence of recent recruitment. Two small juveniles (5 and 15 mm long) were located near the foot bridge in Transect 2 in coarse sand, in shallow water exposed to sunlight. The scarcity of smaller mussels (40-60 suggests either that the population is extremely fast growing or (more likely) that the population is aging. No information on the growth rates, age or longevity of W. carteri in Yule Brook is currently available. Populations of W. carteri downstream from Kenwick Link and extending upstream to above Royal Street in the Canning River are presumed to be extinct (Klunzinger et al. 2011). The location of this viable population represents probably the only living representatives of W. carteri from the Canning River catchment downstream from around Homestead Park / above Royal Street. There were no differences in average size of mussels occurring in the various strata nor within the various transects. Abundance of juveniles was not determined in this survey due to the logistical challenges associated with their collection.

Shell length (mm)0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95

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Figure 3 Length-frequency histogram of freshwater mussels (W. carteri) collected during this survey within Yule Brook.

n = 30


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Conclusions & Recommendations

1) A follow-up study should be undertaken during late August-October to determine the extent to which freshwater fishes utilize Yule Brook for spawning and to what extent W. carteri concurrently release glochidia onto host fishes.

2) Following fish sampling, sites should be sampled for juvenile W. carteri during March to test recruitment strength.

3) Water quality should be monitored for changes in salinity, temperature, pH and dissolved oxygen. This should coincide with management activities within the Canning River, particularly during placement or removal of the weir boards at Kent Street.

4) The effects of biochemicals from feral plant species (such as Willows) on freshwater mussel physiology and reproduction should be considered for further research.

5) Maintaining this population of W.carteri will require reducing or eliminating

sedimentation, improving habitats by revegetation and maintaining water levels with salinities in the <1.0-2.0 ppt range as well as encouraging freshwater fish to utilize spawning habitats and remain in favourable habitat for glochidia metamorphosis and juvenile settlement.

6) Development of captive rearing techniques for W. carteri should be considered while seed stock is available from the wild.


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References

Gagné, F., C. Blaise, M. Fournier, and P.D. Hansen. 2006. Effects of selected pharmaceutical products on phagocytic activity in Elliptio complanata mussels. Comparative Biochemistry and Physiology, Part C 143: 179–186. Klunzinger, M.W., Strebel, D., Beatty, S.J., Morgan, D.L. and Lymbery, A.J. (2011). Baseline survey of freshwater

mussel populations for the urban waterways renewal project. Centre for Fish & Fisheries Research (Murdoch University). Report to SERCUL.

McMichael, D.F. and Hiscock, I.D. (1958). A monograph of the freshwater mussels (Mollusca: Pelecypoda) of the Australian Region. Australian Journal of Marine and Freshwater Research 9: 372-507.

Strayer, D.L. and Smith, D.R. (2003). A Guide to Sampling Freshwater Mussel Populations. American Fisheries Society Monograph 8. Bethesda, MD, USA.

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