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Review of diadromous fish distribution in the upper Thomson River system
W. Koster and T.A. Raadik
2010
Arthur Rylah Institute for Environmental Research
Client Report
Arthur Rylah Institute for Environmental Research Client Report
Review of diadromous fish distribution in the upper Thomson River system
W. Koster and T.A. Raadik
Arthur Rylah Institute for Environmental Research 123 Brown Street, Heidelberg, Victoria 3084
2010
Arthur Rylah Institute for Environmental Research Department of Sustainability and Environment
Heidelberg, Victoria
Report produced by: Arthur Rylah Institute for Environmental Research
Department of Sustainability and Environment
PO Box 137
Heidelberg, Victoria 3084
Phone (03) 9450 8600
Website: www.dse.vic.gov.au/ari
© State of Victoria, Department of Sustainability and Environment 2010
This publication is copyright. Apart from fair dealing for the purposes of private study, research, criticism or review as
permitted under the Copyright Act 1968, no part may be reproduced, copied, transmitted in any form or by any means
(electronic, mechanical or graphic) without the prior written permission of the State of Victoria, Department of
Sustainability and Environment. All requests and enquiries should be directed to the Customer Service Centre, 136 186
or email customer.service@dse.vic.gov.au
Citation: Koster, W. and Raadik, T.A. 2010. Review of diadromous fish distribution in the upper Thomson River
system. Report to West Gippsland Catchment Management Authority. Department of Sustainability and Environment,
Heidelberg, Victoria (unpublished).
Disclaimer: This publication may be of assistance to you but the State of Victoria and its employees do not guarantee
that the publication is without flaw of any kind or is wholly appropriate for your particular purposes and therefore
disclaims all liability for any error, loss or other consequence which may arise from you relying on any information in
this publication.
Front cover photo: Australian Grayling (Tarmo A. Raadik) and upper Thomson River (Wayne Koster).
Authorised by: Victorian Government, Melbourne
Printed by: Snap Printing, Heidelberg
iii
Contents
Acknowledgements............................................................................................................................v
Summary............................................................................................................................................1
1 Background .............................................................................................................................3
2 Distribution of Australian Grayling and other diadromous fish in the upper Thomson
River system.......................................................................................................................................4
Australian Grayling (Prototroctes maraena) ......................................................................................5
Lampreys (Mordacia mordax and Geotria australis ) ........................................................................5
Eels (Anguilla australis and A. reinhardtii) ........................................................................................6
Broad-finned Galaxias (Galaxias brevipinnis)....................................................................................6
Common Galaxias (Galaxias maculatus) ...........................................................................................7
Australian Bass (Macquaria novemaculeata) .....................................................................................7
Tupong (Pseudaphritis urvillii)...........................................................................................................8
3 Factors impeding the distribution of Australian Grayling and other diadromous fish in
the upper Thomson River system ....................................................................................................9
4 Restoring connectivity of fish passage for Australian Grayling and other diadromous
fish in the upper Thomson River system.......................................................................................12
5 Conclusions and recommendations .....................................................................................15
iv
v
Acknowledgements
The West Gippsland Catchment Management Authority (WGCMA) funded this project. Thanks to
David Stork from WGCMA for his role in the coordination of the project. David Crook, Jason
Lieschke, Jeremy Hindell and Matthew Jones from the Arthur Rylah Institute for Environmental
Research (ARI) provided valuable comments on an earlier version of this document. Thanks to
David Dawson from ARI for his assistance in collating fish distribution data.
vi
Review of diadromous fish distribution in the upper Thomson River system
Arthur Rylah Institute for Environmental Research Client Report 1
Summary
This report documents the findings of a review of the distributions of diadromous fish in the upper
Thomson River system in West Gippsland. Diadromous fish undertake migrations between
freshwater and marine environments and comprise about 70% of the native freshwater fish species
in the Thomson River system. They are currently considered to be confined largely to the lower
and mid reaches (Hall 1989, Raadik 1996, Koster and Crowther 2003).
Specifically, the aim of this project was to determine the distributions of the nationally threatened
Australian Grayling (Prototroctes maraena) and other diadromous fish species in the upper
Thomson and Aberfeldy rivers, and identify, where possible, any factors potentially impeding
diadromous fish distribution, based on a review of fish survey data and published and grey
literature (including technical reports).
The results of this review indicate that Australian Grayling and most other diadromous fish species
in the Thomson River system are confined to the lower and mid reaches. Exceptions include eels
and lampreys, which are capable of climbing over barriers. Based on historic, current and potential
distributions of diadromous fish species, including comparisons with the fish communities present
in nearby catchments (e.g. Mitchell, Tambo, Snowy), Australian Grayling and several other
diadromous fish species should be found in the upper reaches of the system.
A range of factors are potentially impacting diadromous fish distribution in the mid to upper
Thomson River. The Thomson Dam has modified the hydrology and water temperature of the
river, which could result in the loss or disruption of important biological cues (e.g. high flows) for
fish migrating into the system or throughout the river (TMEFT 2004). Issues with coldwater
releases have been alleviated to some degree by the use of a multi-level offtake to maintain release
water temperatures within target levels. The presence in the upper Thomson River of the
diadromous Short-finned Eel (Anguilla australis), Long-finned Eel (Anguilla reinhardtii) and
lampreys (Mordacia mordax, Geotria australis) suggests that suitable migration/attraction cues
(i.e. flows) exist in the upper reaches. The presence of self-sustaining populations of non-
migratory native fish species (e.g. Southern Pygmy Perch Nannoperca australis, River Blackfish
Gadopsis marmoratus, Australian smelt Retropinna semoni) in the Thomson River below the dam
also indicates that water temperature and flow are not preventing the establishment of fish
populations in the upper Thomson River and that native fish are able to survive in this reach.
The degree of impact of recent fires on fish habitat in the upper Thomson River catchment is
unknown, but is not likely to be a major cause of the lack of diadromous fish species in that part of
the system. Given that diadromous fishes in south-eastern Australia typically undertake annual
upstream migrations from marine environments into rivers, and different species migrate at
different times, at least some diadromous fish species should be present at any given time. Even if
habitat was extremely unsuitable, small numbers of fish would be present, replaced by new
recruits (Lyon and O’Connor 2008). Surveys conducted in the Thomson River since the fires have
collected the diadromous species Australian Grayling, Tupong (Pseudaphritis urvillii) and
Common Galaxias (Galaxias maculatus) at various sites in areas that were burnt (e.g. Coopers
Creek, C5 Track, Bruntons Bridge), but not from sites upstream of the Horseshoe Bend Tunnel.
The Horseshoe Bend Tunnel on the upper Thomson River has been identified in the Victorian
State Fishway Program as a barrier to fish movement (McGuckin and Bennett 1999). The tunnel
was constructed in 1911–12 with most of the river flow diverted through the tunnel and bypassing
the one kilometre reach of the Thomson River known as Horseshoe Bend (LCC 1991).
Opportunities for fish to migrate through the old river channel are limited, as the flow in the
channel is estimated to occur about 3% of the time (Koster and Crowther 2003). In contrast,
diadromous fishes in south-eastern Australia migrate over an extensive time frame encompassing
Review of diadromous fish distribution in the upper Thomson River system
2 Arthur Rylah Institute for Environmental Research Client Report
much of the year (Koehn and O’Connor 1990). Migration of fish through the tunnel would also be
impeded, particularly by steep gradients and sudden drops in height. Water velocities within the
tunnel (1.2–6.2 m/sec) are also known to far exceed the swimming capabilities of small
diadromous fishes (Saddlier and O’Connor 1997, Boubee et al. 1999). Natural light within the
tunnel is also severely reduced, which can be a behavioural impediment to fish movement
(O’Brien 1999, Thorncraft and Harris 2000, Fairfull and Witheridge 2003).
Restoring fish passage connectivity around the Horseshoe Bend Tunnel along the old course of the
Thomson River would increase the opportunities for the Australian Grayling and other diadromous
fish species to access the upper reaches of the system. Restoring fish passage past the tunnel
supports the need to restore access to rivers for Australian Grayling in accordance with the
National Recovery Plan for Australian Grayling (Backhouse et al. 2008) and represents an
important step toward restoring connectivity and biodiversity of native fish communities in the
Thomson River system. Restoring fish passage past Horseshoe Bend Tunnel would facilitate
access to a further 22 km of the Thomson River upstream to the Thomson Dam, 63 km of the
Aberfeldy River, and numerous tributary streams, including streams in the Baw Baw National
Park. Recommendations on the timing and magnitude of flows to facilitate fish passage along the
old course of the Thomson River around Horseshoe Bend Tunnel are also provided.
Review of diadromous fish distribution in the upper Thomson River system
Arthur Rylah Institute for Environmental Research Client Report 3
1 Background
Approximately 70% of native freshwater fish species in coastal catchments in Victoria exhibit
diadromy (Harris 1984, Koehn and O’Connor 1990, Raadik 1995, Drew 2008) - they undertake
migrations between freshwater and marine environments (McDowall 1988). Several different
kinds of diadromy exist, including anadromy, catadromy and amphidromy (Myers 1949,
McDowall 1988). Anadromous fish enter rivers as mature adults and migrate to upstream
spawning grounds, with juveniles later migrating downstream to the sea (e.g. Short-headed
Lamprey Mordacia mordax, Pouched Lamprey Geotria australis, Australian Whitebait Lovettia
sealii) (McDowall 1999). Catadromous fish enter rivers as juveniles, and adults return to the sea to
spawn (e.g. Tupong Pseudaphritis urvillii, Short-finned Eel Anguilla australis, Long-finned Eel
Anguilla reinhardtii). Adult amphidromous fish live and spawn in fresh water, and the larvae drift
downstream to the sea and later migrate back into fresh water (e.g. Australian Grayling
Prototroctes maraena, Broad-finned Galaxias Galaxias brevipinnis) (McDowall 1999).
In all categories of diadromy, migrations are undertaken by different life-history stages, and
consequently by different sizes of fish (e.g. adults, juveniles and larvae). Swimming ability varies
with each life history stage and between species and consequently the speed of movement and the
degree of penetration (or distance inland) upstream into freshwater environments varies.
Migratory freshwater fish comprise about 70% of the native freshwater fish fauna of the coastal-
draining Thomson River system in West Gippsland. The current distribution of Australian
Grayling and most of the other migratory fish species is considered to be confined to the lower and
mid reaches (Hall 1989, Raadik 1996, Koster and Crowther 2003). Australian Grayling is a
nationally threatened species, and is listed as vulnerable under the Commonwealth Environment
Protection and Biodiversity Conservation Act 1999 and threatened under the Victorian Flora and
Fauna Guarantee Act 1988. Key threats to Australian Grayling include barriers to migration,
altered flow regimes and habitat loss and degradation (Backhouse et al. 2008, DEWHAC 2010). In
the national recovery plan for the Australian Grayling, preservation of the Thomson River
population is identified as necessary for the long-term survival and recovery of the species
(Backhouse et al. 2008).
The aim of this project was to determine the distributions of Australian Grayling and other
diadromous fish in the upper Thomson and Aberfeldy rivers, and identify, where possible, any
factors potentially impeding diadromous fish distribution, based on a review of published and grey
literature (including technical reports) and fish survey data (Victorian Aquatic Fauna Database
managed by the Arthur Rylah Institute for Environmental Research - ARI). The report also
addresses a number of particular concerns (e.g. alien fish species, fish stocking) regarding
reinstating or improving diadromous fish passage in the system.
Review of diadromous fish distribution in the upper Thomson River system
4 Arthur Rylah Institute for Environmental Research Client Report
2 Distribution of Australian Grayling and other diadromous fish in the upper Thomson River system
Data on fish distributions in the Thomson River basin, and from more widely in coastal Victoria,
where applicable, has been sourced from the Victorian Aquatic Fauna Database and published and
grey literature (including technical reports). Survey data extends back to the mid 1960s. Earlier
surveys (i.e. pre mid 1980s) were typically focused on recreational angling species (native and
exotic), and may not have targeted or recorded all native non-angling species. The actual
distributions of native non-angling species in the Thomson River system in this earlier period may
therefore be under-represented. Data on the occurrence of native migratory species in adjacent or
nearby similar coastal catchments were included to provide support for possible historic ranges
within the Thomson River system. More recent surveys conducted in the Thomson River system
have been designed to provide representative information on species distributions or biodiversity
(e.g. Saddlier and Doeg 1998, 2002, Koster and Crook 2006, Koster and Dawson 2008, Koster et
al. 2009, Lieschke unpublished [Sustainable Rivers Audit - SRA] data). No fish survey data was
available for the upper Thomson River system prior to construction of the Horseshoe Bend Tunnel
(1911–12), located on the upper Thomson River upstream of Coopers Creek.
Ten native freshwater migratory fish species have been recorded from the Thomson River basin to
date (Table 1), including the Australian Smelt (Retropinna semoni), which was recently found to
be partly diadromous (Crook et al. 2008a). As diadromy appears to be facultative (not obligatory)
in Australian Smelt because only some individuals or populations undertake migrations, this
species was not considered further in the review.
Table 1. Common and scientific names of migratory freshwater native fish recorded from the
Thomson River basin, including migratory phases.
Migration direction and life stage
Common Name Scientific Name Downstream Upstream
Short-headed Lamprey Mordacia mordax Juvenile Adult
Pouched Lamprey Geotria australis Juvenile Adult
Short-finned Eel Anguilla australis Adult Juvenile
Long-finned Eel Anguilla reinhardtii Adult Juvenile
Broad-finned Galaxias Galaxias brevipinnis Larvae Juvenile
Common Galaxias Galaxias maculatus Adult + larvae Juvenile
Australian Grayling Prototroctes maraena Adult + larvae Juvenile
Australian Smelt Retropinna semoni Larvae Juvenile
Australian Bass Macquaria novemaculeata Adult + larvae Juvenile
Tupong Pseudaphritis urvillii Adult Juvenile
Review of diadromous fish distribution in the upper Thomson River system
Arthur Rylah Institute for Environmental Research Client Report 5
Australian Grayling (Prototroctes maraena)
Australian Grayling adults undertake downstream migrations to the lower reaches of rivers during
autumn to spawn, usually coinciding with rises in flow, then migrate back upstream (Koster and
Dawson 2010a,b). The larvae are washed downstream to the sea, where they remain for about five
months before returning back upstream as juveniles into the freshwater reaches of rivers in spring–
summer (Berra 1982, 1987; Crook et al. 2006).
Australian Grayling have been recorded in the Thomson River as far upstream as Walhalla, where
a single individual was collected near the bridge on the Walhalla Road in 1985 at 220 metres
above sea level (masl) (approx. river distance inland 160 km). This is the only known record of the
species in the system upstream of the Horseshoe Bend Tunnel, despite numerous recent surveys
(i.e. late 1990s onwards) in the upper Thomson River designed to provide representative
information on species distributions or biodiversity (e.g. Saddlier and Doeg 1998, 2002, Koster
and Crook 2006, Koster and Dawson 2008, Koster et al. 2009, Lieschke unpublished SRA data).
Australian Grayling have been recorded, however, at several nearby sites (e.g. Coopers Creek –
200 masl, C5 Track – 190 masl, Bruntons Bridge – 190 masl), but these are all downstream of the
tunnel in surveys since the mid 1980s. The sites at Coopers Creek, C5 Track and Bruntons Bridge
are located approximately one, three and nine kilometres downstream of the tunnel, respectively.
Throughout its range, the Australian Grayling is known to occur at high altitudes and is able to
move large distances inland. For example, Australian Grayling have been recorded in the
Wonnangatta River to 400 masl (approx. river distance inland 230 km), the Tambo River near
Bindi Station at 440 masl (approx. river distance inland 160 km) and in Craigie Bog Creek (Snowy
River system) to 760 masl (approx. river distance inland 340 km). Australian Grayling could be
expected to occur in the upper reaches of the Thomson River system to about 400–450 masl,
including the lower reaches of the Aberfeldy River. This is much higher than the current range of
190–220 masl. It should also be noted that this range is based on records following construction of
the Horseshoe Bend Tunnel (1911–12).
Lampreys (Mordacia mordax and Geotria australis )
Two species of lamprey have been recorded from the Thomson River system — the Short-headed
Lamprey and Pouched Lamprey. Adult lampreys migrate upstream in winter–spring and spawn in
the upper reaches of rivers (Koehn and O’Connor 1990, McDowall 2000). Juveniles gradually
migrate downstream and go to sea the following winter, remaining there for 3–4 years before
returning to fresh water as adults (McDowall 2000).
Short-headed Lamprey have been recorded at several sites upstream (e.g. The Narrows, Walhalla
Road Bridge) and downstream (e.g. Coopers Creek, C5 Track, Bruntons Bridge) of Horseshoe
Bend Tunnel in various surveys from the mid 1980s to the present. Pouched Lamprey have been
recorded in the Thomson River upstream to The Narrows in the mid to late 1980s, and
occasionally farther downstream in the system (e.g. Bruntons Bridge, Cowwarr, Rainbow Creek).
Throughout their range, both species of lamprey are known to penetrate large distances inland and
upstream to high altitudes. For example, Short-headed Lamprey have been recorded in the Tambo
River near Bindi Station to 440 masl (approx. river distance inland 160 km) and Menaak Creek to
350 masl (approx. river distance inland 155 km). Pouched Lamprey have been recorded in the
Brodribb River to 240 masl (approx. river distance inland 85 km) and up to 300 masl in the Yarra
River system (approx. river distance inland 130 km).
Review of diadromous fish distribution in the upper Thomson River system
6 Arthur Rylah Institute for Environmental Research Client Report
Both species of lamprey should occupy the lower to mid reaches of the Thomson River system,
with Pouched Lamprey upstream to about 300 masl and Short-headed Lamprey penetrating farther
upstream to over 400 masl, including the lower reaches of the Aberfeldy River. Lampreys are
known to climb wet rocks and vertical surfaces (Harris 1984, Sloane 1984), so they can be found
upstream of instream obstacles.
Eels (Anguilla australis and A. reinhardtii)
Two species of eels — the Short-finned Eel and Long-finned Eel — are found in the Thomson
River system. Adults migrate downstream to the sea to spawn during summer–autumn with
migration documented as being associated with high flow events (Koehn and O’Connor 1990,
Crook et al. 2008b). Juveniles enter fresh water during spring and summer (Koehn and O’Connor
1990). Short-finned Eels can withstand periods out of water and can climb over substantial
barriers, although this behaviour is most common in the juvenile phase (<120 mm) (McDowall
2000).
Short-finned Eel have been recorded in the Thomson River as far upstream as the Thomson–
Jordan Divide Road, upstream of Thomson Dam in 1988 (500 masl, approx. river distance inland
200 km) and have been recorded at several sites (e.g. Beardmores Track, The Narrows, Walhalla
Road Bridge) upstream of Horseshoe Bend Tunnel, as well as in the Aberfeldy River, in various
surveys since the late 1970s. Short-finned Eel have also been recorded downstream of Horseshoe
Bend Tunnel at several nearby sites (e.g. Coopers Creek, C5 Track, Bruntons Bridge) in various
surveys since the late 1970s. Long-finned Eel have been recorded at several sites upstream (e.g.
The Narrows, Walhalla Road Bridge) and downstream (e.g. Coopers Creek, C5 Track, Bruntons
Bridge) of Horseshoe Bend Tunnel in various surveys between the 1980s and the present.
Throughout their range, Short-finned and Long-finned Eels are known to penetrate to high
altitudes and large distances inland, and Short-finned Eel may penetrate as far as headwater
reaches. For example, Short-finned Eel have been recorded in the Wonnangatta River to 400 masl
(approx. river distance inland 230 km), the Tambo River north branch and Bendoc River to
960 masl (approx. river distance inland 185 km and 355 km respectively), with individuals found
as high as 1340 masl in the upper Snowy River system (approx. river distance inland 350 km).
Long-finned Eel have been recorded in the Crooked River to 370 masl (approx. river distance
inland 200 km), the Tambo River south branch to 560 masl (approx. river distance inland 170 km)
and Butchers Creek (620 masl, approx. river distance inland 110 km), with the highest recorded
elevation in the Snowy River catchment at 755 masl (approx. river distance inland 360 km).
Consequently, Short-finned Eel are expected to be found throughout the Thomson River
catchment, including the upper reaches, with Long-finned Eel penetrating upstream to
approximately 450–500 masl including the lower and mid reaches of the Aberfeldy River.
Broad-finned Galaxias (Galaxias brevipinnis)
Broad-finned Galaxias adults spawn in the upper reaches of streams during autumn on high flows
(O’Connor and Koehn 1998). Larvae are then washed downstream to the sea and move into rivers
and migrate upstream as juveniles about six months later, during spring (Koehn and O’Connor
1990, McDowall 2000). Broad-finned Galaxias are also known to form landlocked populations in
many lakes (McDowall 2000).
Only a single individual Broad-finned Galaxias has been recorded in the Thomson River, from the
mid reaches near Cowwarr in 2002. The species is relatively uncommon in the entire Gippsland
Review of diadromous fish distribution in the upper Thomson River system
Arthur Rylah Institute for Environmental Research Client Report 7
Lakes catchments (Tambo, Mitchell, LaTrobe and Thomson River basins) with only a few
populations known from the lower Mitchell and Avon River systems, though a landlocked
population exists in Lake Tarli Karng in the Macalister River system (Thomson River basin).
Given the difficulty in identification of Broad-finned Galaxias in the juvenile stage
(morphologically similar to other Galaxias spp.), the available dataset for this species in the
Thomson River system is considered to be poor.
Throughout its range in Victoria, Broad-finned Galaxias are known to penetrate large distances
inland and upstream to high altitudes. They have been reported to 1625 masl (approx. river
distance inland 400 km) in the upper Snowy River system, reaching to 620 masl in the Deddick
River (approx. river distance inland 170 km), to 360 masl (approx. river distance inland 210 km) in
the Mitchell River system, and to 850 masl (approx. river distance inland 230 km) in Lake Tarli
Karng in the Thomson River basin.
Broad-finned Galaxias is commonly found to 400 masl and above, and should occupy the lower
and mid reaches of the Thomson River system, with small, isolated populations possibly found
higher in the catchment. Broad-finned Galaxias are known to climb moist, vertical barriers by
using their downward facing pectoral and pelvic fins to adhere to substrates using surface tension
(McDowall 2003). Consequently they can be found in small, steep tributaries, and upstream of
waterfalls.
Common Galaxias (Galaxias maculatus)
Common Galaxias adults migrate downstream on the new or full moon, mostly during autumn,
and spawn on spring tides in the upper tidal reaches of estuaries (Benzie 1968, McDowall 1996).
The larvae then go to sea, and migrate back into the freshwater reaches of rivers as juveniles about
six months later, in spring–summer (McDowall 1996).
Common Galaxias have been recorded in the Thomson River as far upstream as Walhalla, where
21 were collected near the bridge on the Walhalla Road in 1988. This is the only known record of
the species in the system upstream of the Horseshoe Bend Tunnel. Common Galaxias have been
recorded, however, at several nearby sites (e.g. Coopers Creek, Bruntons Bridge), but these are all
downstream of the tunnel in surveys since the mid 1980s.
Throughout its range, the Common Galaxias is known to penetrate to high altitudes and large
distances inland. It has been recorded in the Wonnangatta River to 570 masl (approx. river
distance inland 250 km), the Tambo River near Bindi Station to 440 masl (approx. river distance
inland 160 km), the Suggan Buggan River to 370 masl (approx. river distance inland 155 km) and
to 410 masl (approx. river distance inland 165 km) in the Wentworth River.
Common Galaxias are usually found in the lower reaches of river basins, but are common to over
400 masl and could be expected to be found in the upper Thomson River system to above
450 masl, including the Aberfeldy River.
Australian Bass (Macquaria novemaculeata)
Australian Bass adults migrate downstream to estuaries during autumn and winter to spawn, before
returning upstream (Harris 1986). Juveniles migrate upstream in spring–summer. Males mostly
remain in lower tidal waters, while females travel farther upstream (McDowall 1996).
Downstream migration of adults has been linked to flooding (Harris 1986). Most Australian Bass
recorded in the Thomson River were found in the lower reaches around Myrtlebank and Longford.
Review of diadromous fish distribution in the upper Thomson River system
8 Arthur Rylah Institute for Environmental Research Client Report
There are surprisingly few records from the mid reaches to more upland regions of many streams,
considering that females are able to move long distances upstream (e.g. Snowy Falls, approx. 240
km river distance inland). Anecdotal angler reports from other coastal Victorian streams suggest
Australian Bass were once found up to about the mid reaches of many larger systems, to around
300 masl. Consequently, Australian Bass should be found in the Thomson River in the lower and
mid upper reaches, but not extending upstream as far as the Aberfeldy River.
Tupong (Pseudaphritis urvillii)
Tupong undertake downstream migrations to the sea during autumn and winter to spawn,
coinciding with increases in river flow (Koster and Dawson 2009, Crook et al. 2010). Juveniles
migrate upstream into rivers about six months later during spring–summer (Hortle 1979). Males
mostly remain in estuaries, whilst females travel further upstream (Hortle 1979).
Tupong have been recorded in the Thomson River as far upstream as Beardmores Track below the
Thomson Dam wall (290 masl, approx. river distance inland 190 km) and at several other nearby
sites upstream of Horseshoe Bend Tunnel (e.g. The Narrows, Walhalla Road bridge) in various
surveys since the late 1970s. They are more common downstream of Horseshoe Bend Tunnel,
having been recorded at several nearby sites (e.g. Coopers Creek, C5 Track, Bruntons Bridge) in
surveys since the late 1970s (Tunbridge 1997, Koster and Crowther 2003, Koster et al. 2009).
Throughout its range, the Tupong is known to penetrate to high altitudes and large distances
inland, such as the Wonnangatta River to 570 masl (approx. river distance inland 250 km), the
Tambo River north branch to 640 masl (approx. river distance inland 180 km), the Suggan Buggan
River to 690 masl (approx. river distance inland 170 km) and Thirty Mile Creek in the Mitchell
River basin to 890 masl (approx. river distance inland 220 km).
Most Tupong are found in the lower reaches of coastal river systems, but it appears that larger
females are found upstream (Hortle 1979). Consequently, Tupong should be found throughout the
Thomson River catchment, including the upper reaches to about 500 masl, including the Aberfeldy
River.
Review of diadromous fish distribution in the upper Thomson River system
Arthur Rylah Institute for Environmental Research Client Report 9
3 Factors impeding the distribution of Australian Grayling and other diadromous fish in the upper Thomson River system
Thomson Dam
The Thomson Dam has greatly modified the hydrology of the river downstream of the storage
(Gippel and Stewardson 1995, Cottingham et al. 2001, Earth Tech 2003, TMEFT 2004). Changes
to hydrology in the Thomson River most likely impact on the distribution of diadromous fishes
over the length of the river through the loss of important biological cues (e.g. high flows) for fish
migrating into the system or throughout the river (TMEFT 2004). There was also a short period in
1984–85 when hypolimnetic water at 9–11°C was released from the dam. However, a multi-level
offtake has since been used to maintain release water temperatures within target levels specified in
Schedule F5 of the State Environment Protection Policy (Waters of Victoria). Based on limited
data, excluding the period in 1984–85 when hypolimnetic water was released, Gippel et al. (1992)
reported that dam regulation increased mean water temperatures below the dam by around 3°C in
winter and reduced mean water temperatures by 3°C in summer. The reduction in summer water
temperatures persisted downstream to Coopers Creek, but winter temperatures were only increased
by 1°C at The Narrows and not at all at Coopers Creek (Gippel et al. 1992). The presence of the
diadromous Short-finned Eel, Long-finned Eel and lampreys, which are capable of climbing over
barriers, in the Thomson River below the dam nonetheless suggests that suitable migration and
attraction cues (i.e. flows) for fish exist in this reach. The presence of self-sustaining populations
of non-migratory native fish species (e.g. Southern Pygmy Perch Nannoperca australis, River
Blackfish Gadopsis marmoratus, Australian Smelt) in the Thomson River below the dam also
indicates that water temperature and flow are not preventing the establishment of fish populations
in the upper Thomson River and that native fish are able to survive in this reach.
Bushfires
The immediate impacts of fires such as increased water temperature and decreased dissolved
oxygen levels, as well as the associated effects of fires, such as sediment deposition into streams,
can impact fish communities by decreasing pool depth by filling with sediment, reducing food
supply and reducing the useable resting and spawning habitats. Impacts of fire usually decrease
with time as catchments recover and sediment is flushed from the system. The degree of impact of
recent fires (e.g. 2006-07) on fish habitat in the upper Thomson River catchment (and hence the
ability for the catchment to support diverse fish communities) is unknown, but is not considered a
major factor in lack of diadromous fish species in that part of the system. Given that diadromous
fishes in south-eastern Australia typically undertake annual upstream migrations from marine
environments into rivers, and different species migrate at different times, at least some diadromous
fish species should be present at any given time. Even if habitat was extremely unsuitable, small
numbers of fish would be present, replaced by new recruits (Lyon and O’Connor 2008). Surveys
conducted in the Thomson River since the fires have collected Australian Grayling, Tupong and
Common Galaxias at various sites in areas that were burnt (e.g. Coopers Creek, C5 Track,
Bruntons Bridge) (Figure 1), but not from sites upstream of the Horseshoe Bend Tunnel (e.g.
Koster and Dawson 2008, Koster et al. 2009).
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10 Arthur Rylah Institute for Environmental Research Client Report
Figure 1. Fish survey sites at C5 Track (a) and Bruntons Bridge (b) following the 2006-07 fires.
Horseshoe Bend Tunnel
The Horseshoe Bend Tunnel (Figure 2) on the upper Thomson River has been identified in the
Victorian State Fishway Program as a barrier to fish movement (McGuckin and Bennett 1999).
The length of the Thomson River downstream of the tunnel is approximately 128 km. The length
of river upstream of the tunnel is approximately 22 km to the Thomson Dam and 63 km to and
including the Aberfeldy River. The tunnel (approximately 220 metres in length) was constructed in
1911–12 with most of the river flow diverted through the tunnel and bypassing the one kilometre
reach of the Thomson River known as Horseshoe Bend (LCC 1991). The record of an Australian
Grayling and the records of other diadromous species upstream of the tunnel indicate that some
migratory fish have been able to move upstream, possibly taking advantage of infrequent but
appropriate flows through the old river channel. Opportunities for fish to migrate through the river
channel are extremely limited, however, because flow in the channel is estimated to occur only
about 3% of the time (Koster and Crowther 2003). Overflow into the bend occurs only during high
flow events typically only two to three times per year and usually lasting only for a few days on
each occasion (Koster and Crowther 2003). In contrast, the timeframe over which upstream and
downstream migration of diadromous fishes in south-eastern Australia occurs is far more
extensive, encompassing much of the year, with different species also migrating at different times
of the year, and under varying flow conditions (Koehn and O’Connor 1990).
Migration of fish through the tunnel would also be impeded. Reluctance of fish to move through
tunnels has been reported for a range of fish species (Ahmad et al. 1962, Pavlov 1989). The
Horseshoe Bend Tunnel presents several major impediments to upstream and downstream fish
passage, including steep gradients and sudden drops in height (Figure 1). At the upstream and
downstream ends of the tunnel the surface comprises smooth rock and gradients exceed 15°. Baker
and Boubee (2006) found that juvenile and adult Common Galaxias were unable to pass over
ramps 1.5 m long, sloped at 15° with a bare surface. At the upstream end of the tunnel there is also
a turbulent cascade and large drop (>200 mm) in height. Various studies suggest that juveniles and
adults of Common Galaxias are prevented from moving upstream by vertical drops of only 100
mm and 200 mm respectively (McDowall 2000, Baker 2003). The white water and turbulence at
the upstream end of the tunnel would also disorientate fish and provides no resting areas for
several metres. Boubee et al. (1999) predicted that Common Galaxias had a maximum burst
swimming distance of only 3.3 m at a velocity of 0.70 m/sec, which declined to 2.1 m at 1.0 m/sec.
Water velocities within the tunnel (see below) exceed these values.
In addition to steep gradients and drops in height, the tunnel presents several other impediments to
fish passage. Water velocities within the tunnel have been measured under low flow conditions
(a) (b)
Review of diadromous fish distribution in the upper Thomson River system
Arthur Rylah Institute for Environmental Research Client Report 11
(240 ML/day) and range from 1.2 to 2.5 m/sec (Thiess Environmental, unpublished data). For a
high flow period (1682 ML/day), data modelling indicates water velocities of approximately
6.2 m/sec in the tunnel (Snowy Mountains Engineering Corporation, unpublished data). This range
of velocities (1.2–6.2 m/sec) is known to far exceed the swimming capabilities of small
diadromous fishes (Saddlier and O’Connor 1997, Boubee et al. 1999). Saddlier and O’Connor
(1997) found that juvenile Tupong were unable to negotiate an artificial channel 2 m long at
velocities ranging from 1.1–1.9 m/sec, although some larger fish (190–200 mm in length) could
negotiate the channel. The ability of Common Galaxias to negotiate the channel at velocities
greater than 1.0 m/sec was also severely reduced, with a 90% failure rate (Saddlier and O’Connor
1997).
Natural light within the tunnel is also severely reduced, which can be a behavioural impediment to
fish movement (O’Brien 1999, Thorncraft and Harris 200l0, Fairfull and Witheridge 2003). Recent
research has shown that the upstream movement of a range of small native Australian fishes
(Australian smelt, unspecked hardyhead Craterocephalus fulvus, bony herring Nematalosa erebi,
carp gudgeon Hypseleotris spp.) is adversely impacted by low light intensity (Jones in prep).
Several recent studies have also shown that the upstream migration of diadromous galaxiids
(e.g. Common Galaxias, Spotted Galaxias Galaxias truttaceus) through fishways occurs
predominantly during daylight (Morgan and Beatty 2006, Zampatti et al. in prep). The installation
of ‘windows’ (e.g. steel grating) within barriers such as road culverts to provide light is
increasingly incorporated into fish passage improvement works (e.g. Cumberland River at Lorne,
Tahbilk Lagoon at Nagambie) in recognition that many species require natural daylight patterns
for movement and that darkened areas such as tunnels and culverts create behavioural barriers
(Thorncraft and Harris 2000).
Although other potential obstacles to fish movement exist in the upper Thomson River (e.g. rapids
at Bruntons Bridge, The Gorge), the physical and hydraulic complexity of these natural structures
produces low velocity resting areas and reduces the distances travelled between rests at high
velocities, thereby enabling the successful upstream passage of fish. In addition, during high flows
rapids are ‘drowned’, which also provides important opportunities for fish to move around any
obstacles to movement (Baker 2003).
Figure 2. Upstream (a) and downstream (b) ends of the Horseshoe Bend Tunnel and (c) old river
channel.
(a) (b) (c)
Review of diadromous fish distribution in the upper Thomson River system
12 Arthur Rylah Institute for Environmental Research Client Report
4 Restoring connectivity of fish passage for Australian Grayling and other diadromous fish in the upper Thomson River system
Native fish species
Restoring fish passage connectivity around the Horseshoe Bend Tunnel along the old course of the
Thomson River will enable diadromous fish species, including the nationally threatened Australian
Grayling, to move into large areas of habitat upstream. Australian Grayling has declined in
distribution and abundance throughout its range due to factors such as barriers to movement and
habitat loss and degradation (Backhouse et al. 2008, DEWHAC 2010). A National Recovery Plan
for Australian Grayling has been developed by an expert panel to address these threats and
includes as a key recovery objective increasing the length of rivers available by facilitating fish
passage past barriers (Backhouse et al. 2008). Improved access for Australian Grayling and other
diadromous fish would be available to a further 22 km of the Thomson River upstream to the
Thomson Dam, 63 km of the Aberfeldy River, and numerous tributary streams, including streams
in the Baw Baw National Park. It is recognised that the Thomson Dam will continue to restrict
diadromous fish distribution upstream of the dam wall. Nonetheless, a substantial increase in the
opportunities for diadromous fish to access the upper reaches of the system will be achieved
through restoring fish passage past the tunnel, which supports the need to restore access to rivers
for Australian Grayling in accordance with the national recovery plan for the species, and
represents an important step toward restoring connectivity and biodiversity of native fish
communities in the Thomson River system.
The extent to which fish would use the upper Thomson River, or tributaries such as the Aberfeldy
River, following the reinstatement of fish passage around Horseshoe Bend Tunnel would depend
on a complex range of factors such as flow and habitat conditions, which are likely to vary
considerably through time. In the upper Thomson River system, flow in the Thomson River
generally exceeds flow in the Aberfeldy River, which might encourage more fish to continue
migrating up the Thomson River. On the other hand, the unregulated Aberfeldy River which has a
more natural flow regime, generally comprises a large proportion of flow in the upper Thomson
River system during high flow periods (i.e. spring – early summer), which represents the key
upstream migration period for diadromous fishes in south-eastern Australia (Koehn and O’Connor
1990). The presence of the diadromous Short-finned Eel in the upper Thomson and Aberfeldy
rivers is evidence of the upstream colonisation of both stream systems, and also suggests that
suitable migration and attraction cues (i.e. flows) exist in both rivers.
Alien fish species
Two alien fish species — Brown Trout (Salmo trutta) and Rainbow Trout (Oncorhynchus mykiss)
— have been recorded in the upper Thomson River system. Trout have been implicated in the
decline of native fishes worldwide, including galaxiids and Australian Grayling (Crowl et al. 1992,
McDowall 2006). Trout are widespread in the Thomson River, including upstream and
downstream of Horseshoe Bend Tunnel. As they are already found upstream and downstream of
the tunnel, the reinstatement of flows around the tunnel would not result in a range expansion of
either species. Allowing additional native fish species upstream into waters containing alien
species may increase predatory or competitive interactions, though often the degree of interaction
is related to habitat complexity and fish density. Another two alien species, Common Carp
(Cyprinus carpio) and Redfin Perch (Perca fluviatilis), are restricted to the mid to lower reaches of
the Thomson River around Cowwarr. Habitat conditions in the upper Thomson system (i.e. fast
flowing riffle/run habitats) are not considered favourable to the establishment of these species,
Review of diadromous fish distribution in the upper Thomson River system
Arthur Rylah Institute for Environmental Research Client Report 13
though some individuals may penetrate further upstream. The positive benefits of allowing native
diadromous fish species access to a relatively large expanse of upstream habitat, including smaller
tributary streams, out-weighs any possible negative impacts from alien species.
Timing of fish movement
The upstream migratory period of diadromous fishes in south-eastern Australia encompasses an
extensive time frame (Koehn and O’Connor 1990), although the migration of different species
from marine habitats into lower freshwater reaches of rivers is concentrated around late spring –
early summer (Sloane 1984, Gehrke et al. 2002, Raadik et al. 2001, Zampatti et al. 2003). In the
Thomson River, fish must first migrate various distances within the Gippsland Lakes, then up the
Latrobe River system before they enter the Thomson River itself, before moving upstream through
the lowland section to the gorge section commencing at Cowwarr Weir. During migration over this
distance, some species may move at different speeds and some movements may be continuous or
erratic, so the timing of diadromous fishes reaching the upper Thomson River system upstream of
Cowwarr Weir is unclear.
Environmental flow recommendations have been developed for the Thomson River which include
providing flows for fish passage (Earth Tech 2003, TMEFT 2004). In particular, low flow freshes
have been recommended in the period December to April to provide localised fish movement in
the upper reaches. A continuous low flow has also been recommended between December to April
(Earth Tech 2003, TMEFT 2004). Given the uncertainty about the timing of diadromous fishes
reaching the upper reaches, a continuous low flow along the channel of the Thomson River around
the Horseshoe Bend Tunnel for upstream fish migration may be more effective in facilitating
upstream fish passage than short-duration peak flows. The flows provided need to be of sufficient
depth to allow for localised fish passage but also to provide refuge. A depth of >0.4 m has been
recommended in the environmental flows determination for the Thomson River (Earth Tech 2003)
as being the minimum water depth for fish habitat.
Recent research has shown that adult Australian Grayling undertake downstream spawning
migrations to the lower reaches of rivers around April–May, coinciding with rises in flow or
‘freshes’, followed by return upstream migrations (Koster and Dawson 2010a, b). Similarly, adult
Tupong migrate downstream to the sea for spawning around May–August, coinciding with
relatively high flows (Koster and Dawson 2009, Crook et al. 2010). Providing freshes is therefore
recommended during April–August to facilitate the downstream (and return upstream) migration
of some adult diadromous species. High flow freshes (i.e. >800 ML/d) have been recommended in
the period May–November as part of the environmental flow recommendations for the Thomson
River (Earth Tech 2003, TMEFT 2004).
Regulating flow through Horseshoe Bend Tunnel
Flow rates are one of the important factors limiting the upstream movement of fish. Although flow
rates through the tunnel could be reduced, there are other impediments to fish movement through
the tunnel, such as steep gradients, sudden drops in height and lack of light. Consequently, altering
flow rates alone would have little effect on fish migration. In contrast, the natural river channel of
the Thomson River around Horseshoe Bend provides greater opportunities for fish movement
because of the complexity of flow patterns (riffle, run, pool, glide, etc.) which provide
opportunities for fish to move over short or long distances at a time, aswell as areas of useable
resting and foraging habitat.
Review of diadromous fish distribution in the upper Thomson River system
14 Arthur Rylah Institute for Environmental Research Client Report
Fish stocking
The recruitment of diadromous fishes relies on complex migrations from freshwater environments
to the sea and vice versa. Given that most diadromous fish species in the Thomson River are only
short-lived (e.g. Australian Grayling: 2–5 years, Common Galaxias: 1–2 years), if diadromous fish
species such as Australian Grayling were irregularly stocked upstream of the tunnel they would
persist for only a short period and would not be able to develop self-sustaining populations in the
upper reaches unless the critical migration pathway between fresh water and the sea was restored.
Review of diadromous fish distribution in the upper Thomson River system
Arthur Rylah Institute for Environmental Research Client Report 15
5 Conclusions and recommendations
The results of this review indicate that Australian Grayling and most other diadromous fish species
in the Thomson River system are confined to the lower and mid reaches, but would naturally also
be found in the upper reaches of the system if they had access. The presence in the upper Thomson
River system of the diadromous Short-finned Eel, Long-finned Eel and lampreys, which are
capable of climbing over barriers, suggests that suitable migration/attraction cues (i.e. flows) exist
in the upper reaches. The presence of self-sustaining populations of non-migratory native fish
species also indicates that water temperature and flow are not preventing the establishment of fish
populations in the upper Thomson River and that native fish are able to survive in this reach.
A major barrier to fish passage into the upper reaches of the Thomson River systems is the
Horseshoe Bend Tunnel. Opportunities for fish to migrate through the old river channel are
limited, with flow in the channel estimated to occur only about 3% of the time. Migration of fish
through the tunnel would also be impeded by steep gradients, sudden drops in height and excessive
water velocities. A lack of natural light in the tunnel poses a further impediment to fish passage.
Restoring fish passage connectivity around the Horseshoe Bend Tunnel along the old course of the
Thomson River will enable diadromous fish species, including the nationally threatened Australian
Grayling, to move into large areas of habitat upstream.
The following recommendations are made based on the findings of this study:
• Restore fish passage connectivity along the old course of the Thomson River around
Horseshoe Bend Tunnel. The environmental flow recommendations developed for the
Thomson River should be used as a basis for determining the flows required for fish passage.
Given the extended migratory period and uncertainty about the exact timing of diadromous
fishes reaching the upper Thomson River system, providing a continuous low flow for fish
migration may be more effective in facilitating upstream fish passage than short-duration peak
flow events. Providing ‘freshes’ is recommended during April–August to facilitate the
downstream (and upstream return) migration of adult diadromous species, although for
Australian Grayling the key period for adult migration is April–May. It is recommended that
the environmental flow recommendations developed for the Thomson River be used as a
guide for water depth (e.g. > 40 cm).
• Design and implement a long-term monitoring program to assess the re-establishment of
diadromous fishes. This should include pre-intervention and post-intervention monitoring in
the upper Thomson River, Aberfeldy River, tributaries, and the mid reaches of the Thomson
River near Cowwarr, to provide an indication of fish migration into the system.
Review of diadromous fish distribution in the upper Thomson River system
16 Arthur Rylah Institute for Environmental Research Client Report
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