Aquasave Consultants 2011

TECHNICAL NOTE

Ecological implications for freshwater fishes arising from specific hydrological changes to the lower ,

July, 2011

Common galaxias from the River Torrens

Correspondence in relation to this report contact Dr Michael Hammer Aquasave Consultants Tel: +61 429 098 920; Email: [email protected]

Disclaimer

This report was commissioned by the Adelaide and Natural Resources Management Board. It was based on the best information available at the time and no warranty express or implied is provided for any errors or omissions, nor in the event of its use for any other purposes or by any other parties.

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Introduction

The Adelaide and Mount Lofty Ranges Natural Resources Management Board (herein the ‘Board’) takes an active role in the integrated management of aquatic habitats including for the River Torrens which is a prominent feature of the landscape and mindset of Adelaide. Aquasave Consultants was engaged to provide technical science based advice on two scenarios being considered by the Board relevant to native fishes of the lower River Torrens, principally concerning potential hydrological changes.

Scenario 1 – Flow manipulation via reservoir release (city-gorge) The Torrens Lake is a show piece for the city precinct, and the quality of this body of water is linked to recreation activity, tourism and public sentiment. Poor water quality and especially algal blooms are a major management issue, and dilution/flushing flows via release of water from the upstream Kangaroo Creek Reservoir is being considered as one of a combination of actions to improve water quality. The implementation and exact nature of this action is still to be determined, but in principal would involve sustained flow release over summer months as a steady base flow (~several hundred to low thousands of ML per day). Water would thus run from the reservoir through the Gorge weir and along the section of the Torrens to the City Weir, being picked up in water harvest schemes prior to reaching the mouth. The ecological implications of this base flow are to be considered.

Scenario 2 – Stormwater harvesting (city to sea) Several large stormwater reuse projects are being developed in the Adelaide region that aim to extract water in the reach of the River Torrens watercourse downstream of the City Weir. Currently under the draft Western Mount Lofty Ranges Water Allocation Plan extraction limits for licensed users in the lower Torrens are set at a threshold flow rate to provide at least 100mm depth of water flow. Commentators have indicated this simple extraction rule to (a) not be reflective of the highly modified nature of the stream reach (e.g. disconnected from natural flow regime due to considerable water supply infrastructure, major stormwater input from an urban landscape, wide concrete and/or artificial channels requiring large water volumes to meet threshold values), and (b) be overly restrictive on the capacity to harvest water for reuse schemes which could struggle to capture flashy flow peaks. Subsequently advice has been sought on minimum flow requirements and ecological implications tailored to the specific situation (i.e. more flexible rules based extraction).

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Regional fish objective: Consideration of issues in the current assessment refer to the overarching objective used in recent environmental water projects for the Mount Lofty Ranges (VanLaarhoven and van der Wielen 2009; VanLaarhoven 2010), i.e. maintaining self-sustaining populations of existing species that are resilient to times of drought.

Project objectives: 1) To assemble information and expertise that can review the nature of the proposed hydrological changes then identify and consider possible effects both positive and negative to native fishes. 2) Identify opportunities to ameliorate potential threats or enhance current conditions to achieve desirable outcomes for native fish populations and management. 3) Develop testable hypotheses that can form the basis for event based and condition monitoring that evaluates the effects of proposed hydrological changes, and that could ultimately fo rm part o f adaptive processes for decisions on water delivery or extractio n.

The emphasis for these objectives is very much at a level and time frame to inform the feasibility of projects and related management rather than acting as a detailed risk assessment.

Project approach: Consideration of ecological response first required collation of information on ecological assets, environmental water requirements and observed flow ecology to provide a basis for assessing likely ecological response (literature review, Aquasave data and personal communication with other experts). Indicative hydrological data to frame the magnitude and scale of proposed interventions was provided through access to gauged flow data from the Department for Water (DfW) Surface Water Archive (www.e-nrims.dwlbc.sa.gov.au/swa), the Board’s online Water Monitoring Network supplied by Water Data Services (www.wdapp.com) and other specific analyses facilitated through the Board (Australian Water Environments, AWE).

A small expert panel was convened to assemble loca l o n-ground expertise regarding the nature of flow events, habitats and barriers to provide a context for the assessment and to canvas the implications of the scenarios from different perspectives. The panel, which was assembled for an on-site meeting and tour of the lower catchment and peer review, included: • Alan Ockenden (Board) – project management & hydrology. • Michael Hammer (Aquasave) – project assessment & fish ecology. • Geoff Fisher (AWE) – hydrology and engineering. • Jason VanLaarhoven (DfW) – ecology, water requirements and policy linkage. • Peter Shultz (formerly of the Board) – ecology and local habitat expertise. • Da le M cNe il (SARDI) – fish ecology and restoration, local expertise.

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1. Assessment of ecological impacts

1.1. Importance of the Lower Torrens for fishes

Despite its position within the heart of a major city populated by over one million people, the section of the River Torrens between Kangaroo Creek Reservoir through the end of the Torrens Gorge to its current mouth at the sea at Breakout Creek still contains key fish related ecological assets for inclusion within natural resource management. A strong information base comes from baseline survey data (Rowntree and Hammer 2004; Gray et al. 2005; Hammer 2005; Hicks and McEvoy 2005), targeted ecological studies (McNeil et al. 2010; McNeil and Schmarr in prep.), and museum and other opportunistic records (Edmeades 1999; Mathews et al. 2004; McNeil and Hammer 2007; Hammer et al. 2009). Records are shown visually in Figure 1.

Fish related ecological assets for the Lower Torrens include: • High fish species richness. • Representation of threatened species. • Significant populations. • Multiple functional groups. • Diverse habitat.

A total of 15 native freshwater fish species have been recorded (Table 1). Four estuarine species are included in the species list as they have been recorded upstream of the Breakout Weir on occasion, or have been recently recorded immediately below the Breakout Creek weir and could potentially occur upstream. There are several other essentially marine species not included in the list but which also occur in the small section of estuary between the sea and the weir (e.g. Australian salmon). Fishes alien to the Torrens include five translocated Australian native species (three are well established in the Lower Torrens), and six species exotic to Australia (Table 1).

Six of the native fishes known to currently occur in the Lower Torrens are considered threatened at the state level (Hammer et al. 2009)( Tab le 1). There is also a translocated population of threatened freshwater catfish from the River Murray which is doing well in the Torrens and may have conservation value as refuge and for ecological research.

In addition to important species composition, the value of the Lower Torrens is enhanced as regional population centres or outlying populations for several species. Most notable is a population of mountain galaxias in lowland habitat downstream of the gorge (e.g. downstream of Gorge Weir and S ilke ’s Road area). A landlocked population of common galaxias occurs in the Gorge Weir area, possibly a relic from a natural Torrens system pre its many weirs which fragmented connectivity through to the sea. Significant populations of diadromous fish have been retained (e.g. pouched lamprey) or have returned to the lower reaches following installation of the fish ladder at Breakout Creek (e.g. common galaxias and congolli). Most diadromous species are threatened at the state level (Table 1) so any additional security offered by creating more suitable habitat in the Lower Torrens will foster significant populations.

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Four different functional groups of fishes are represented in the stream section, with the functional group of individual species listed in Table 1: • Obligate freshwater, stream specialised: restricted to life in freshwater, with specialised flow or habitat requirements. Landlocked populations of diadromous fish are best described by this group. • Freshwater, generalists: non-specific or flexible flow and habitat requirements, also with broad salinity tolerance. Some species are comfortable in fresh or salt water (euryhaline). • Estuarine: species that predominantly occur in estuaries showing some requirement for or association with freshwater discharge. • Migratory, diadromous species: species that require migration to and from the sea or estuary as part of their life-cycle.

A list of species (specific ecological assets) is provided for the different sections of the Lower Torrens by functional group. Alien species are listed for inclusiveness and as they are considered in several flow processes (i.e. suppression).

Scenario 1 – Flow manipulation via reservoir release (city-gorge): • Specialist obligate freshwater (mountain galaxias, landlocked common and climbing galaxias). • Generalist freshwater (flathead gudgeon). • Alien (trout, carp, redfin, Gambusia, rainbowfish, carp gudgeon, freshwater catfish).

Scenario 2 – Stormwater harvesting (city to sea): • Generalist freshwater/euryhaline (flathead gudgeon, bluespot goby). • Diadromous (common galaxias, climbing galaxias, lampreys, shortfinned eel, congolli). • Estuarine (black bream, yelloweye mullet, jumping mullet, hardyhead, gobies). • Alien (carp, goldfish, Gambusia, rainbowfish, carp gudgeon, freshwater catfish).

Broad habitat diversity occurs as a transition from mid-pool channel habitat in the gorge through to lowland channel and then estuarine habitat. At finer scales the stream section is reasonably heterogeneous with different habitats including those dominated by rock, riffles and runs, deep well vegetated pools and developed wetlands.

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Figure 1. Fish distr ibut ion data for the Adelaide region showing records for galaxias species.

Table 1. Fishes recorded in the Lower Torrens, upstream of the Breakout Creek Weir along with life history, local distribution notes and conservation status (note other estuarine/marine species have been recorded in the small section downstream of the weir). [CREN = Critically Endangered, EN = Endangered, VU = Vulnerable, RA = Rare, P = Protected]

Fisheries Action Plan Common name Scientific name Life history Lower Torrens distribution notes Act 2009 Mountain galaxias Galaxias olidus Freshwater specialist Patchy and low abundance upstream of city VU Southern purple-spotted gudgeon Mogurnda adspersa Freshwater specialist Locally extinct P CREN Flathead gudgeon Philypnodon grandiceps Freshwater generalist Common to abundant throughout Shortfinned eel Anguilla australis australis Diadromous Rare in lower reaches RA Climbing galaxias Galaxias brevipinnis Diadromous Rare lower and upper reaches RA Common galaxias Galaxias maculatus Diadromous Lower reaches and at start of Gorge Pouched lamprey Geotria australis Diadromous Rare mouth to city weir EN Shortheaded lamprey Mordacia mordax Diadromous Rare mouth to city weir EN

Native Congolli Pseudaphritis urvillii Diadromous Lower reaches VU Western bluespot goby Pseudogobius olorum Freshwater generalist (euryhaline) Lower and mid reaches Smallmouthed hardyhead Atherinosoma microstoma Freshwater generalist (euryhaline) Estuary section, occassional us weir Tamar River goby Afurcagobius tamarensis Estuarine Estuary section Black bream Acanthopagrus butcheri Marine/estuarine Estuary section Yelloweye mullet Aldrichetta forsteri Marine/estuarine Estuary section, occassional us weir Jumping mullet Liza argentea Estuarine Estuary section Dwarf flathead gudgeon Philypnodon macrostomus Freshwater generalist Above Kangaroo Creek, may occur in reach Carp gudgeons Hypseleotris spp. Freshwater generalist Common throughout Barramundi Lates calcarifer Marine/freshwater One off record in city weir Freshwater catfish Tandanus tandanus Freshwater specialist Common below city weir, rare upstream P EN

Translocated Murray rainbowfish Melanotaenia fluviatilis Freshwater generalist Common throughout Goldfish Carassius auratus Freshwater generalist Common throughout Common carp Cyprinus carpio Freshwater generalist Common throughout Gambusia Gambusia holbrooki Freshwater generalist Common throughout Oncorhynchus mykiss

Exotic Rainbow trout Freshwater specialist Occasional records in upper reach Redfin Perca fluviatilis Freshwater generalist Common above city Brown trout Salmo trutta Freshwater specialist Common upper reach

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1.2. Environmental Water Requirements

Environmental Water Requirements (EWRs) for freshwater fishes of the Mount Lofty Ranges have recently been the subject of a detailed assessment process (VanLaarhoven and van der Wielen 2009). This outlines requirements for habitats and species scaled up to broad reach types as the basis for water allocation planning to maintain water-dependent ecosystems at an acceptable level of risk in the face of hydrological development. Extraction limits have been devised for the Western Mount Lofty Ranges (VanLaarhoven 2010) that are in turn linked to a draft Water Allocation Plan (WAP) which also covers the lower urban River Torrens.

A specific consideration for the Lower Torrens is that it “has changed significantly due to hydrological modification (i.e. occurring downstream of Kangaroo Creek Reservoir) and urbanisation, and complete ecological functioning is no longer possible or desired (e.g. overbank flow risk flooding in urbanised areas)” such that key water requirements for existing ecological assets only have been targeted in the WAP. Consequently the key term of reference for the current assessment relates to EWRs to facilitate fish passage to sustain populations of diadromous fishes and as a surrogate for broader ecosystem components (VanLaarhoven 2010). Nevertheless opportunities or impacts relating to other EWRs for lowland stream reaches are also investigated for holistic consideration of sustainable fish populations (e.g. maintenance of refugia, spawning cues, suppression of exotic fishes).

The process of assigning EWRs (VanLaarhoven and van der Wielen 2009) involved several key steps of data collection and analysis, and it is worthwhile reviewing the specific information inputs used and to detail specific information available at the current time for the Lower Torrens.

Water requirement tables For each functional group important ecological processes are matched to required aspects of the flow regime. Tables 2 and 3 are an adaption of the EWRs for fishes of lowland habitats of the Mount Lofty Ranges (VanLaarhoven and van der Wielen 2009), selective for the particular flow periods (Figure 2) likely to be impacted under the two aspects of hydrological alteration i.e. Scenario 1 - low flows and freshes during the low flow season; Scenario 2 – lo w flows and freshes throughout the year, particularly from transition to or from high flow (T1 and T2: Figure 2).

Figure 2. Typical ranges for flow seasons discussed in environmental water requirements (taken from VanLaarhoven and van der Wielen 2009).

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Table 2. Summary of Environmental Water Requirements relevant to the addition of baseflow during summer to the Torrens between Kangaroo Creek and the City. These are all supplementary to the key term of reference regarding migration of diadromous fishes as access to this section is blocked by multiple barriers.

Flow Season Flow component Functional group Ecological process Flow purpose (objective) Likely impact Low Flow Low flow All Variable flows discourage exotics Some aliens thrive on warm stable conditions Positive All Persistent water in pools Maintain habitat and refuges Positive All Maintain shallows Habitat diversity to offset impacts of exotics Positive Freshwater generalists Promote spawning Adult and larvae conditioning Positive/negative Fresh All Refill pools, maintain WQ Maintain habitat and refuges Positive Stream specialist Clean substrate Aids egg deposition of mountain galaxias Positive All Fish movement between pools Maintain local population processes Neutral/positive All Variabl e fl ows dis courage exoti cs Some aliens thrive on warm stable conditions Positive

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Table 3. Summary of Environmental Water Requirements relevant to the extraction of low flows for stormwater harvesting in the Torrens below the City. Those specific to the key term of reference regarding migration of diadromous fishes are shaded, others represent supplementary objectives for holist ic management.

Fl ow Season Fl ow component Functional group Ecological process Fl ow purpose (objecti ve) Likely impact Low Flow Low flow Diadromous Sus tained flow connectivity Upstream migration Negative All Persistent water in pools Maintain habitat and refuges Neutral All Variable flows discourage exotics Some aliens thrive on warm stable conditions Negative All Maintain shallows Habitat diversity to offset impacts of exotics Negative Generalists/estuarine Promote spawning Adult and larvae conditioning Neutral/negative Fresh All Refill pools, maintain WQ Maintain habitat and refuges Neutral All Fish movement between pools Maintain local population processes Neutral All Variable flows discourage exotics Some aliens thrive on warm stable conditions Neutral T1 Low flow Diadromous Sus tained flow connectivity Downstream migration Negative All Persistent water in pools Maintain habitat and refuges Negative All Variable flows discourage exotics Some aliens thrive on warm stable conditions Negative All Maintain shallows Habitat diversity to offset impacts of exotics Negative Generalists/estuarine Promote spawning Adult and larvae conditioning Neutral/negative Fresh Diadromous Small rises and oxygenation Fish conditioning/spawning cues Negative All Refill pools, maintain WQ Maintain habitat and refuges Neutral All Fish movement between pools Maintain local population processes Neutral All Variable flows discourage exotics Some aliens thrive on warm stable conditions Neutral Hi gh flow Low flow Diadromous Sus tained flow connectivity Ups tream & do wns trea m migra tio n Neutral Fresh Diadromous Raised water levels Promote spawning success Neutral Diadromous Fl ow to es tua ry Attract diadromous fish to catchment Neutral All Fish movement between pools Maintain local population processes Neutral T2 Low flow Diadromous Sus tained flow connectivity Upstream migration Negative All Fish movement between pools Maintain local population processes Neutral

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1.3. Local flow ecology data

Flow processes are informed by collation of broader literature and expert opinion of those working closely in the field (for the Mount Lofty Ranges see McNeil and Hammer 2007; Hammer 2009; VanLaarhoven and van der Wielen 2009). The applied knowledge of flow processes to specific assessments relies on some level of local data collection. In addition to base line studies of distribution mentioned earlier, two specific projects provide important insight by having sampled in the Lower Torrens. The first is an initial assessment of the effectiveness of the fishway installed at Breakout Creek Weir involving intensive trapping in September and October of 2006 and 2007 (McNeil et al. 2010). The second is a flow ecology study monitoring site based populatio ns between 2006-2008 of major rivers in the Adelaide region, including sites in the Lower Torrens immediately upstream of the Breakout Creek Weir (to Henley Beach Road), others midmay between the city and the Gorge (Paradise at Silke’s Road), and just above the Gorge Weir (McNeil and Schmarr in prep.). S uch study provides information on the ecological response to flow such as refuge availability, water quality and flow seasonality. Base line data to assess population s tatus o f common galaxias and congolli is provided in the Appendix.

With regard to the key term of reference for facilitating fish passage, the broader literature and local specific data for migration of diadromous fishes provides an indication of the range and peak times of movement as well as suitable conditions (Table 4). Diadromous fishes have a dependence on connectivity in autumn to allow access to the lower river and/or sea ( flo w season T1), and/or later winter and spring (flow season high flow/T2) to allow movement from the sea into freshwater. For anadromous fishes like lampreys, sub-adults move downstream to the sea in autumn and return several years later in spring to access freshwater habitat to spawn. Catadromous fishes like congolli move to the sea to spawn in autumn and juveniles return in spring. Amphidromous fishes like common galaxias spawn in the lower reaches of freshwater and their eggs or larvae drift out to sea, before returning in late winter/spring as whitebait.

The collective migration window for different modes of diadromy covers a full calendar year (Table 4). The best current indication of peak migration activity for the Torrens is mid April- early June (downstream) and late August-early November (upstream). The fish passage study suggested that fish were passed in higher numbers on (a) the declining edge of flow events and (b) low flows due to these providing the best attractant flows to the fish ladder. The peaks of flow events which display high velocity and turbulence are unlikely to support active fish migration for the generally small species or small sized individuals (except perhaps adult lampreys) that are trying to migrate upstream in the Torrens due to issues with burst swimming ability, sustained swimming performance and the scale of factors relative to size (Mallen-Cooper 1992; Angermeier 1995; Warren and Pardew 1998). However the ability of different species to pass particular stream sections and barriers in the Torrens remains a specific area for future research. Overall since the fish ladder has been installed up until 2008 ( i.e. prior to Breakout Creek wetland stage 2 works) diadromous fishes have returned to the Lower Torrens up to a barrier just downstream o f Henley Beach Road (McNeil and Schmarr in prep.). There are currently two new barriers downstream and many upstream of Henley Beach road that likely impede or prevent fish migration.

With respect to other flow processes, flow or freshes in the low flow season have been little studied owing to that most of the recent research has been during extended drought. Nevertheless data on the condition of refuges, and subsequent resilience of fish populations, suggests that flows that maintain and refresh refuges are beneficial, especially for stream specialists (i.e. galaxias species upstream of the city). Page 10 of 25

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Table 4. Broader literature and local observations (in bold) on the migration of diadromous fish species recorded from the River Torrens (modified from McNeil and Hammer 2007). Question marks (?) show that specific investigation into migration in the Torrens have only been conducted during September and October.

Migration into estuary Upstream (us) migration Downstream (ds) migration * Peak movment * * * * * * Species Migration type J F M A M J J A S O N D Where Source Pouched lamprey Upstream migrants SW WA M Torrens R SAM, Hammer (2005) ? ? ? Torrens R McNeil et al (2010) LSE SA Hammer (2008) Downstream migrants SE Australia K SW WA M Shortheaded lamprey Upstream migrants * * * SE Australia K Anadromous Yarra R Vic Zampatti et al. (2003) ? * R. Murray, SA Jennings et al. (2008) Downstream migrants SE Australia K Shortfinned eel Glass eels into estuary SE Australia K Central Vic K Western Vic K Elvers upstream SE Australia K & M Yarra R Vic Zampatti et al. (2003) LSE SA Hammer (2008) Adults to estuary SE Australia K Congolli Juveniles us from sea Tas K

Catadromous ? ? ? Torrens R McNeil et al (2010) * R. Murray, SA Jennings et al. (2008) LSE SA Hammer (2008) Adults ds to spawn SE Australia M Tas K Common galaxias Juveniles us from sea Aust K Yarra R Vic Zampatti et al. (2003) ? ? ? ? * * ? ? Torrens R Hammer (2005);McNeil (2010) * * R. Murray, SA Jennings et al. (2008) * * LSE SA Hammer (2008) Aust M Adults ds to spawn Vic K * LSE SA Hammer (2008) Climbing galaxias Juveniles us from sea SE Australia K & M Amphidromous ? ? Torrens R McNeil (2010) Yarra R Vic Zampatti et al. (2003) LSE SA Hammer (2008) Larvae swept to sea SE Australia M

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1.4. Likely impacts of hydrological change

The likely impact of the two scenarios of hydrological change are presented against flow seasons and processes in Tables 2 and 3 and are discussed in more detail below.

Scenario 1: Flow manipulation via reservoir release

Additional water availability during the low flow season will likely have mos tly positive effects on the local fish community. While the diadromous life cycle is not currently supported in this reach due to the presence of numerous barriers downstream which prevent access to species from the sea, base flow from October onwards (100mm depth threshold) would allow upstream movement of diadromous species to important habitat such as potential spawning areas for lampreys in the perennial Sixth Creek. There are several flow processes for current ecological assets that would be enhanced by sustained base flow provided that the released water is not episodically on/off, not at high velocity, has lo w suspended solids, is well oxygenated and has a thermal range similar to what might have been expected naturally (e.g. as compared to any inflows upstream of Kangaroo Creek or out of Sixth Creek). Very warm flows would favour alien fishes such as Gambusia and carp. Provided these conditions are met, addition of baseflow would secure the permanency and quality of refuges, increase available habitat by wetting shallow pools and edges and by preserving important s ha llo w riffle habitat and cater for the water requirements of current ecological assets (i.e. cool, oxygenated water for galaxias species, and flushing of spawning habitat for mountain galaxias) (Table 2). The potential for restoration is highlighted by a near lack of these types of flows in summer months in recent years (Figure 3).

Possible negative effects of sustained flow release in summer are that it (a) may not align with the requirements of generalist native species (flathead gudgeon) which have recruitment tied to lo w-flow recruitment and (b) may support population processes for alien species, especially redfin. Such impacts may be offset by greater overall habitat availability provided by base flow for generalist native species to find suitable areas to breed and recruit and all native species to avoid interaction with alien species (e.g. occurrence in riffles or edge vegetation).

Figure 3. Gauged flow data from the Gorge Weir on the Torrens, note the lack of flows in summer periods (DfW unpublished data).

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2.2. Scenario 2: Stormwater harvesting

The context for assessing negative impacts of this scenario is related to risks of extraction that would decrease certain flow events be lo w a depth threshold of 100mm (i.e. towards cease to flow). This flo w depth threshold is designed to allow connectivity through points of constriction (e.g. shallow habitat sections), and can be converted to different flow rates depending on channel width (e.g. ~1350L/s at Seaview Road, AWE unpublished data). The nature of flow harvesting itself is likely to have a limited capacity to influence the magnitude of flow peaks or total flow volume. The Board has indicated the lo ng-te r m harvest capability across the whole reach to be ~900L/s, which is a small portion of most flow peaks as shown in representative hydrographs in Figures 4-7. Hence the key consideration is competing demands for low flows, and possible risks therein to meeting the regional fish objective.

Under the current habitat structure of the lowermost reaches of the Torrens which has (a) fish ladder which does pass fish but with noted performance deficiencies, (b) long se ctio n of channel with wide threshold points for connectivity, with few resting/refuge points and little cover, (c) numerous other barriers to block passage at least under low-med ium flo ws, and (d) an overall small area of habitat occupied by diadromous fish (sea to Henley Beach Road), it would be expected that the diadromous fish population would display a low resilience to hydrological changes that might further limit connectivity. This is especially so for the particular life stages that migrate upstream and their noted behaviour (e.g. movement detected on the declining edge of flows at the lower end of the flow spectrum). Hence there are risks to sustaining diadromous fish populations associated with reducing the flow threshold for extraction during peak times of movement (mid-late autumn and spring).

The current best available model on migration windows (and note that fish movement has not been specifically examined outside September-October for the Torrens) suggests that there could be less risk if the threshold flow depth limits for extraction were lowered during winter as this is outside the peak movement period for diadromous fishes. The impact on other flow processes such as refuge maintenance during the high flow season (winter) is also likely to be low due to extraction being buffered by a high volume and frequency of unharvestable flo w (Figure 4). Moreover in wet periods the indicative extraction capacity is unlikely to affect low flows to any major degree (Figure 5). The flow threshold is thus more flexible at this time as there is less risk of impacting migration, but low flows should not be eliminated (e.g. cease to flow frequency should not be greatly increased and some regular frequency of 100mm flow depth should be maintained). The absolute minimum flow depth threshold should be sufficient to maintain regular operation of the fish ladder in current or future modified fo rm ensuring that current migration patterns are at the least maintained. An indicative minimum flow rate at Seaview Road to support this function has been provided as ~150L/s (Table 5).

Harvesting low flows below the threshold during summer and early autumn could impact flow processes such as refuge permanency and refuge availability, primarily for isolated and small rainfall events and during drought (e.g. Figure 7).

An assoc ia ted d irec t r isk o f extraction is through entrainment of fish in pumping infrastructure (i.e. fish getting sucked through inlets). This has been shown to be a cause of significant mortality overseas and in New South Wales (Baumgartner et al. 2009). Specific investigation on pump entrainment mortality at different periods and fish size would be needed to assess the nature and significance of this risk.

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Table 5. Different scenarios modelled for the Lower Torrens based on flow depth at the fish ladder, calculated using a broad crested weir equation. The q200 scenario is representative of the flow rate required for operation (200mm reference depth) of the fish ladder, and the q800 scenario is roughly equivalent to that required to maintain the 100mm threshold (=1350L/s) across the concrete channel at Seaview Road (AWE unpublished data).

Breakout Creek (Flow over broad-crested weir)

id Reference depth of flow at fishway(m) Flowrate (L/s)

q200 0.2 152

q400 0.4 431

q600 0.6 792

q800 0.8 1220 q1000 1 1705

Figure 4. Indicative winter hydrograph ( low-moderate flow period) for end of system flows in the River Torrens (Water Data Services, unpublished data). The inset depicts lower flow rates, and includes (a) green line marking the modelled flow rate at Seaview Road providing the 100mm flow depth threshold (i.e. 1350L/s), with green shading indicating extraction capacity (i.e. 900L/s), and (b) a yellow line marking the modelled flow rate to support fish ladder function (i.e. 150L/s), with yellow shading indicating extraction capacity (i.e. 900L/s).

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Figure 5. Indicative winter hydrograph (high flow period) for end of system flows in the River Torrens (Water Data Services, unpublished data). The inset depicts lower flow rates, and includes (a) green line marking the modelled flow rate at Seaview Road providing the 100mm flow depth threshold (i.e. 1350L/s), with green shading indicating extraction capacity (i.e. 900L/s), and (b) a yellow line marking the modelled flow rate to support fish ladder function (i.e. 150L/s), with yellow shading indicating extraction capacity (i.e. 900L/s).

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Figure 6. Indicative spring hydrograph for end of system flows in the River Torrens (Water Data Services, unpublished data). The inset depicts lower flow rates, and includes a green line marking the modelled flow rate at Seaview Road providing the 100mm flow depth threshold (i.e. 1350L/s), w ith green shading indicating extraction capacity (i.e. 900L/s). The purple line indicates the flow volume required for 100mm of flow depth if the channel was reduced to 5m width: there are considerably greater opportunities for fish movement under this scenario.

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Figure 7. Indicative summer hydrograph for end of system flows in the River Torrens (Water Data Services, unpublished data). The inset depicts lower flow rates, and includes a green line marking the modelled flow rate at Seaview Road providing the 100mm flow depth threshold (i.e. 1350L/s), w ith green shading indicating extraction capacity (i.e. 900L/s).

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2. Threat mitigation and restoration opportunities

The previous section flagged specific threats and points of vulnerability from scenarios which alter stream hydrology. Opportunities to ameliorate threats or enhance local conditions are briefly considered to propose possible management options to ensure that the regional fish objective is met under any alteration of current conditions.

2.1 Flow management strategies

Rules based water extraction Extraction below a 100mm flow depth threshold for the Lower Torrens (Scenario 2) that then might reduce the frequency and duration of these types of low flows has different levels of risk to sustaining diadromous fishes across different broad flow seasons. Lower risk in winter mo nths suggests the potential to relax the threshold and develop and test an adaptive management framework for rules based extraction during this period. Specific rules are outside the scope of this report (i.e. assessing feasibility) but they should focus on: • A threshold to maintain fishway operation at a regular frequency and duration. • No great increase in cease to flow events at multiple points in the reach. • Preservation of the 100mm depth threshold for some frequency in the high flow season, especially close to the T1 and T2 flow seasons. • Event-interval based thresholds for extraction in summer and early autumn.

Fish ladder performance Reducing flow volumes potentially creates a greater reliance on fishway performance at Breakout Creek (and thus a risk to migration) through reduced duration of operation that may restrict access or affect timing of access (e.g. not being operation at appropriate tide cycles, tide heights or times of day). Hence specific amelioration with any alteration of low flows could be achieved by implementing fishway improvements and further refining fishway operation. Some key issues gleaned from previous investigatio n (McNeil et al. 2010) and from the fishway site visit include: • Improving passage for small congolli e.g. increasing surface roughness. • Improving attractant flows to allow fish to detect and enter the fishway. • Assess other performance reasons that might be limiting use by fish which reach the ladder but do not ascend (e.g. small modifications to account for behavioural factors). • Ongoing maintenance to ensure unobstructed passage. • Improved design to assist easy maintenance and occupational health and safety.

Channel modification There would be specific advantage in re-modelling the artificial section of channel downstream of Tapleys Hill Road. A narrower channel or the development of pools with restricted connecting points would reduce the flow rate required to maintain a minimum 100mm of flow depth. Thus for the same flow types, there might be extended periods of appropriate flow allowing greater opportunities for fish movement and migration, especially in spring. For example in October 2010 there were only three occasions that flows reached higher than a 100mm flow depth (Figure 7). Table 6 describes the flow volume required to maintain the 100mm threshold depth of flow for different widths of channel rated for end of system flow and conditions. A reduction in channel width from 20m to 5m reduces the flow volume required for 100mm flow depth by a corresponding 75% (Table 6). Some increase in the frequency of these very low flow events resulting from channel and/or flow control modifications will build stronger populations/resilience, and then provide scope for rules based extraction limits to be applied across the year.

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2.2. Complimentary works

Habitat enhancement The artificial and simplified section of channel upstream of the fishway encompassing a section of concrete (Figure 6) then low shallow pools with poorly define channel upstream to Tap le ys Hill Road offers little cover and a reduced pathway for migration. This presents a current significant risk to sustaining populations, which may be worsened with loss (extraction) of certain low flows. Hence extending the design principals of upstream wetlands to the lower section has a high potential for benefit to increase the area and quality of suitable habitat for fishes. This could be as simple as constructing a channel through the concrete to offer better cover and passage, through to restoring the reach as estuarine. A series of constructed deeper pools would allow greater fish population size to be maintained through refuges during summer, allow resting points for migrating fish and assist in the protection of spawning aggregations of common galaxias. Adding riparian vegetation would also increase habitat and food availability (e.g. surface insects), and the addition of physical structure such as snags or rock piles serves as cover from flows and predators, increased food resources (e.g. surfaces for macroinvertebrates) and spawning sites.

Fish passage at a reach scale The small section of habitat currently available to diadromous fishes in the Lower Torrens elevates the risk of local declines, especially during harsh drought conditions. To increase the area of habitat currently available a program should be continued to address fish passage at Breakout Creek, other current priority barriers, and any future structures (e.g. working upstream from the river mouth). This will be guided by a current project being undertaken by SARDI for the Board which is mapping artificial instream barriers (D. McNeil pers. comm.), and other mapping is needed which identifies natural barriers at low and cease to flow conditions (e.g. inter-pool connecting points such as riffles or rock bars). A taskforce drawing together local stakeholders and expertise in fish ecology, hydrology, engineering and management would be an ideal way to co-ordinate a ‘City to Sea’ fish passage program for the Torrens. This can draw from a similar program well established for the River Murray system (Barrett and Mallen-Cooper 2006) and would have a high potential to increase the amenity of the Torrens by providing a tangible improvement in the linear park instream environment. Some key factors for consideration in fishway design are slope, surface roughness, attractant flows, channel velocity, run length, resting areas, approach and exit cover and function at different depths of flow (e.g. Mallen-Cooper 2004). Providing for fish passage at multiple flow heights or migration points is an important local consideration due to the peaky hydrology.

2.3. Linkage between the scenarios Any low flows from reservoir release that reach the section of River Torrens below the city are likely to aid connectivity and improve habitat conditions for diadromous fishes. Specific environmental water allocation in late spring to early summer in particular, could be another mechanism to improve the resilience of the fish community.

2.4. Fish screens on pumps Filtering inflowing water through fish screens should be investigated to prevent entrainment of fishes from pump point sources. F is h screens should ideally be self cleaning (debris-free) and not harm aquatic life through entrapment or damage. At the least a fine mesh (<10mm) could be used to prevent larger fish from being entrained. Most of the technology and expertise on fish screens is centred in the US (e.g. driven by EPA and legislation on cooling

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Aquasave Consultants 2011 water intake screens), see for example www.intakescreensinc.com and www.pump-rite.com. However there is currently a NSW Fisheries research project through the Murray-Darling Basin Authority looking at screening irrigation off takes to prevent loss of larval native fish from rivers to terminal habitats (Baumgartner et al. 2009) which could have applicable outco mes.

2.5. Other technology Any technology advances that would allow harvesting of flow peaks could help reduce competing demands for low flows. There are several technologies which could assist with suppression of alien species, such as traps for harvesting carp when attracted to barriers (Stuart et al. 2006).

Figure 6. The very lower section of the River Torrens in spring 2008. Note the harsh concrete section immediately upstream of the fish ladder and the lack of permanent pools or defined migration channel.

Table 6. Depth and flow rate at different channel width scenarios, calculated using a Manning’s Equation (AWE unpublished data). The flow volumes match the ‘q’ scenarios of Table 5. Green shading shows how the 100mm flow depth threshold reduces for different channel widths. Breakout Creek (Flow Depth & Channel Width) Flowrate

Reference channel width (m) 152L/s = q200 431L/s = q400 792L/s= q600 1220L/s = q800 1705L/s = q1000 Flow depth (mm) Flow depth (mm) Flow depth (mm) Flow depth (mm) Flow depth (mm) 1 208 433 687 970 1280 3 96 183 269 355 442 5 70 131 191 249 307 10 46 85 123 160 196 20 30 56 81 105 128

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3. Ecological research to support management Improved data and targeted monitoring is a key part of adaptive management. The main points of research needed to underpin adaptive flow management in the Lower Torrens and relevant objectives for assessment are provided below.

3.1. Long-term monitoring Performance criteria: the distribution and relative abundance of key ecological assets to be similar or enhanced, and the relative abundance of exotic species similar or reduced, compared to baseline conditions. Condition monitoring should have a focus on spatial and temporal replication and assess population trends. The current baseline data for assessment is reasonable, however the previous sites of McNeil and Schmarr (i.e. three sites, each with three pools) should be re-instigated and the addition of one or more monitoring sites between Henley Beach Road and the city would better assess diadromous fish status.

3.2. Migration data Performance criteria: free access into and through the Lower Torrens for diadromous fishes. This firstly requires validation of the lo ca l movement window including peak activity, and could be assessed relatively easily by extending the previous fishway study as well as targeting spawning aggregations of common galaxias and congolli in the lower stream reach. Spatial investigation would be achieved by event and season based monitoring at a range of other barriers, and temporal replication across years could indicate response to particular flow or climatic conditions (e.g. lampreys moving on full moons or during storms). Mapping natural and artificial barriers in the flatter western reaches of the urban Torrens will he lp id e ntify critical points of connectivity and local flow volume requirements for fish passage.

3.3. Fish passage ecology Performance criteria: fishways in the Lower Torrens which pass all sized fish and aggregations. Understanding of the specific behaviour and dispersal ability of the migratory stages of local fish species will provide the necessary data to improve and design fishways. Flume based trials in the lab provide opportunities to measure the swimming ability of fish (e.g. velocity maximum, velocity v. time) as well as simulated trials of conditions in the wild (e.g. design of v-notch weirs for galaxias passage: Cantone et al. 2002). Field testing o f the performance at barriers is then necessary to indicate success or need for further refinement.

3.4. Specific flow response Performance criteria: positive or neutral response of native fishes to flow alteration. This primarily relates to the Scenario 1 flow supplementation (but also low flow extraction for maintaining refuges), where demographic data assessing recruitment and survivorship linked to flo w events can indicate ecological response. Data requirements are partially fulfilled through long-term monitoring as above, but should also include seasonal monitoring or event based observations such as habitat use and fish spawning condition. Such assessment should be informed and incorporated within a broader ‘eflows’ project currently underway involving delivering and monitoring environmental flows from reservoirs in the western Mount Lofty Ranges being undertaken by the Board, SA Water, DfW and various others partners.

3.5. Alien species Performance criteria: no major increase in the baseline of exotic species richness and abundance. Suppression or potential exploitation of alien species relies on a good knowledge of their local response to low flows and flow manipulation (e.g. (relative abundance, recruitment, migration and breeding cues). The primary targets in terms of impacts to key ecological assets include redfin, Gambusia and trout, with carp an additional target based on waterway health and community perceptions.

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Conclusion

The current tailored assessment highlights that there are important ecological values in the Lower Torrens which ensure that detailed consideration and management of the aquatic environment will have meaningful outcomes. Assessment of environmental water requirements for fishes with respect to potential hydrological changes identifies some key areas that may exhibit ecological response both positive and negative. Supplementing a base flow in summer is likely to have largely positive effects, while extraction down to very lo w flows in the lowermost reaches could have negative impacts to the ecology of diadromous fishes. Key points of management include: • Extraction below the 100mm reach scale threshold in mid to late autumn and spring would pose a high risk to diadromous fish migration and thus sustainability. • Very specific rules would need to be placed on additional extractions over summer to ensure refuge persistence. • There is flexibility in winter to lower the 100mm threshold at a determined frequency and to an absolute minimum end of system flow threshold to support regular fishway operation in the order of 150L/s. • Certain modification could aid ecological and management outcomes, specifically the flow depth threshold of 100mm can be translated into lower flow volumes where appropriate channel and/or flow control modifications are possible. There is an opportunity to do this at the Torrens outlet structure to more effectively connect the fishway with the natural channel. • River restoration could enable a greater environmental resilience and capacity for extraction across all flow seasons.

The general approach towards adaptive management should be validated with and informed by on-going targeted research and monitoring.

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References

Angermeier, P. L. (1995).Ecological attributes of extinction-prone species: loss of freshwater fishes of Virginia. Conservation Biology 9, 143-158. Barrett, J., and Mallen-Cooper, M. (2006).The Murray River’s ‘Sea to Hume Dam’ fish passage program: progress to date and lessons learned. Ecological Management and Restoration 7, 173-183. Baumgartner, L. J., Reynoldson, N. K., Cameron, L., and Stanger, J. G. (2009).Effects of irrigation pumps on riverine fish. Fisheries Management and Ecology 16, 429-437. Cantone, V., Kon, D., MacGillivray, E., and Mittiga, L. (2002) Engineering and ecology: enhancing fish passage at V-profile crump weirs. Fourth Year Research Project thesis, The University of Adelaide. Edmeades, R. J. (1999) Fish of the Torrens and Onkaparinga rivers and environmental engineering to promote their conservation. MSc thesis, University of Adelaide. Gray, S., Howell, S., and Maxwell, S. (2005). Ecological Survey of the Torrens River Wetlands at Breakout Creek and within the Horse Agistment Area: Integrated report to the Torrens Catchment Water Management Board. Australian Water Quality Centre, Bolivar. p. 32. Hammer, M. (2005). Adelaide Hills Fish Inventory: distribution and conservation of freshwater fishes in the Torrens and Patawalonga catchments, . Report to Torrens and Patawalonga Catchment Water Management boards. Native Fish Australia (SA) Inc., Adelaide. p. 68. Hammer, M. (2009). Freshwater fish monitoring in the Eastern Mount Lofty Ranges: environmental water requirements and tributary condition reporting for 2008 and 2009. Report to the SAMDB NRM Board. Aquasave Consultants, Adelaide. p. 160. Hammer, M., Wedderburn, S., and van Weenan, J. (2009). Action Plan for South Australian Freshwater Fishes. Native Fish Australia (SA) Inc., Adelaide. p. 206. Hicks, D. C., and McEvoy, P. (2005). Biological and stream condition survey of the eastern urban Torrens from Gorge Weir to Gilberton. Report to the Torrens Catchment Water Management Board. Australian Water Quality Centre, Bolivar. Mallen-Cooper, M. (1992).Swimming ability of juvenile Australian Bass, Macquaria novemaculeata (Steindachner) and juvenile barramundi, Lates calcarifer (Bloch) in an experimental vertical slot fishway. Australian Journal of Marine and Freshwater Research 43, 823-834. Mallen-Cooper, M. (2004). Concept design for a fishway on the Torrens River Outlet Weir (Breakout Creek). Fishway Consulting Services. p. 7. Mathews, G., Walker, G., Mathwin, R., and Hammer, M. (2004).Spring tides, galaxias and the River Torrens, South Australia. Fishes of Sahul 19, 177-186. McNeil, D., and Schmarr, D. (in prep.). Fish community and flow ecology in the Western Mount Lofty Ranges. SARDI Aquatic Sciences, Adelaide. McNeil, D. G., and Hammer, M. (2007). Biological review of the freshwater fishes of the Mount Lofty Ranges. SARDI publication number: F2006/000335. South Australian Research and Development Institute (Aquatic Sciences), Adelaide. p. 104. McNeil, D. G., Wilson, P. J., Fredberg, J. F., and Westergaard, S. (2010). Fish passage at the Breakout Creek Fishway, River Torrens, South Australia. Report to the Adelaide & Mount Lofty Ranges Natural Resources Management Board. SARDI Publication No. F2009/000409-1. SARDI Aquatic Sciences, Adelaide. p. 25. Rowntree, J., and Hammer, M. (2004). Freshwater fish survey of the central urban River Torrens, Adelaide South Australia. Report to the Adelaide City Council. Native Fish Australia (SA) Inc., Adelaide. p. 15.

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Stuart, I., Williams, A., McKenzie, J., and Holt, T. (2006). The Williams’ cage: a key tool for carp management in Murray-Darling Basin fishways. Final report to the Murray- Darling Basin Commission. Arthur Rylah Institute for Environmental Research, Victoria. p. 31. VanLaarhoven, J. (2010). Environmentally sustainable extraction limits for the Western Mount Lofty Ranges Prescribed Watercourse Area. Technical Report DFW 2010/01. Department for Water, South Australian Government, Adelaide. p. 45. VanLaarhoven, J., and van der Wielen, M. (2009). Environmental water requirements for the Mount Lofty Ranges prescribed water resources areas. Department of Water, Land and Biodiversity Conservation & South Australian Murray-Darling Basin Natural Resources Management Board, South Australian Government, Adelaide. p. 95. Warren, M. L., and Pardew, M. G. (1998).Road Crossings as barriers to small-stream fish movement. Transactions of the American Fisheries Society 127, 637-644.

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Appendix

40 20 i) autumn 2006 i) autumn 2006 - low flow, high 30 - low flow, high baseflows w/ 15 multiple flushes over summer baseflows w/ multiple flushes over summer

20 10 No. of Individuals of No. No. of individuals of No. 10 5

0 0 0-10 11-20 21-30 31-40 41-50 51-60 61-70 71-80 81-90 91-100

40 101-110 111-120 121-130 131-140 141-150 151-160 161-170 171-180 0-10 >250 11-20 21-30 31-40 41-50 51-60 61-70 71-80 81-90 91-100

Size Classes 101-110 111-120 121-130 131-140 141-150 151-160 161-170 171-180 181-190 191-200 201-210 211-220 221-230 231-240 241-250 20 ii) spring 2006 Size class (mm) 30 - disconnected pools, ii) spring 2006

baseflows over winter w/ 15 - disconnected pools, large flush prior to surveys baseflows over winter w/ No. of Individuals 20 large flush prior to 10 surveys No. of Individuals of No.

10 individuals of No. 5

0 0 0-10 11-20 21-30 31-40 41-50 51-60 61-70 71-80 81-90 91-100 0-10 >250 101-110 111-120 121-130 131-140 141-150 151-160 161-170 171-180

40 11-20 21-30 31-40 41-50 51-60 61-70 71-80 81-90 91-100 Size Classes 20 101-110 111-120 121-130 131-140 141-150 151-160 161-170 171-180 181-190 191-200 201-210 211-220 221-230 231-240 241-250 iii) autumn 2007 - iii) autumn 2007 30 moderate flow, minimal flow - moderate flow, minimal over summer but large flush 15 prior to surveys flow over summer but large flush prior to 20 surveys 10 No. of Individuals of No. No. of individuals of No. 10 5

0 0 0-10 11-20 21-30 31-40 41-50 51-60 61-70 71-80 81-90 91-100 0-10 >250 101-110 111-120 121-130 131-140 141-150 151-160 161-170 171-180 40 11-20 21-30 31-40 41-50 51-60 61-70 71-80 81-90 91-100

20 101-110 111-120 121-130 131-140 141-150 151-160 161-170 171-180 181-190 191-200 201-210 211-220 221-230 231-240 241-250 Size Classes (mm) Size class (mm) iv) spring 2007 iv) spring 2007 30 - disconnected pools, 15 baseflows w/ regular flushes - disconnected pools, over winter baseflows w/ regular flushes over winter 20 10 No. of Individuals of No. No. of individuals of No. 10 5

0 0 0-10 >250 0-10

11-20 21-30 31-40 41-50 51-60 61-70 71-80 81-90 11-20 21-30 31-40 41-50 51-60 61-70 71-80 81-90 91-100 91-100 101-110 111-120 121-130 131-140 141-150 151-160 161-170 171-180 181-190 191-200 201-210 211-220 221-230 231-240 241-250

40 101-110 111-120 121-130 131-140 141-150 151-160 161-170 171-180 20 Size Classes (mm) v) autumn 2008 v) autumn 2008 30 - disconnected pools, 15 - disconnected pools, minimal flow w/ small minimal flow w/ small flushes over summer flushes over summer 10 20 No. of individuals of No. No. of Individuals of No. 5 10

0 0 0-10 >250 11-20 21-30 31-40 41-50 51-60 61-70 71-80 81-90 0-10 91-100

11-20 21-30 31-40 41-50 51-60 61-70 71-80 81-90 40 101-110 111-120 121-130 131-140 141-150 151-160 161-170 171-180 181-190 191-200 201-210 211-220 221-230 231-240 241-250 91-100

350 101-110 111-120 121-130 131-140 141-150 151-160 161-170 171-180 Size Classesvi) spring 2008 35 vi) spring 2008 300 - disconnected pools, 30 - disconnected pools, baseflows w/ low regular baseflows w/ lo w 250 25 flushes over winter regular flushes over

200 20 winter

15

150 individuals of No. 10 No. of individuals No. 100 5

50 0 0-10 >250 0 11-20 21-30 31-40 41-50 51-60 61-70 71-80 81-90 91-100 101-110 111-120 121-130 131-140 141-150 151-160 161-170 171-180 181-190 191-200 201-210 211-220 221-230 231-240 241-250 0-10 11-20 21-30 31-40 41-50 51-60 61-70 71-80 81-90

91-100 Size Classes (mm) 101-110 111-120 121-130 131-140 141-150 151-160 161-170 171-180

Size class (mm)

Lengths of common galaxias (left) and congolli (right) at Breakout Creek (mouth of Torrens River) over six survey seasons, from autumn 2006 to spring 2008. Note, light blue bars indicate fish captured in estuarine waters (from McNeil and Schmarr in press).

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