Category Archives: Techniques & methodology

Assessing fishway options for weirs of the northern Murray-Darling Basin

Key words: Fish passage, fish migration, fisway, prioritisations, northern Murray-Darling Basin

Threats and Impacts: Barriers to migration have been identified as a major contributor to the decline of native fish species within the Murray-Darling Basin. The Murray-Darling Basin Authority have made significant investment in improving fish passage along the Murray River and associated anabranches through the Lake Hume to the Sea program and the Living Murray Initiative. Despite the improvements along the Murray River, this investment has not been matched in the Northern Murray-Darling Basin. At present, the movement of fish within and between river systems north of Menindee Lakes remains significantly restricted by dams and weirs without adequate fish passage. 

Broad aim and methods: This project set out to develop concept designs and engineering costings for the highest priority weirs in the Northern Murray-Darling Basin.

A review of literature was undertaken initially to assess the likely composition and migratory requirements of the fish fauna in the Northern Basin. An analysis of available options for fish passage was undertaken, and justification provided for the preferred options in terms of the ecological, hydraulic and technical design constraints associated with each weir.

Assessment of structures within the northern Basin identified 12 priority sites within four sub-catchments. These structures were identified as priority sites due to their impact on migrating fish fauna, their potential benefit-cost ratio, and the river length that would be reinstated should the fish passage be provided at the site.

Of the 12 priority weir sites identified, five were investigated for feasibility of fishway installation and identification of fishway designs that would be directly applicable to five of the other sites plus generic types of weir (e.g. sheet pile with rock-fill face) in the northern Basin.

Of the two remaining sites, one has existing detailed design and cost estimates (Bourke Weir), while the second (Chinchilla Weir and gauge) requires further investigations – the costs of which were not possible within the budget for this project.

Fishway concept designs were developed at key representative sites which were specifically designed to suit the fish assemblage and semi-arid ecology of the northern Basin. Designs considered constructability, materials, regional context, maintenance and ownership, and allowed the development of cost estimates, with contingencies, to enable the financial and practical scope of the project to be assessed.

Figure 1 - Priority structures identified in the Northern Murray-Darling Basin

Figure 1 – Priority structures identified in the Northern Murray-Darling Basin

Figure 2 - Cunnamulla Weir, one of the priority sites identified for fish passage remediation in the northern basin. Photo courtesy of Scott Nichols

Figure 2 – Cunnamulla Weir, one of the priority sites identified for fish passage remediation in the northern basin. Photo courtesy of Scott Nichols

Findings: The river reaches where the weirs are located were noted to have high ecological value, with known native fish populations, high quality fish habitat, and long river reaches that would be reinstated for migration, either because of few nearby barriers or because of nearby weirs with fishways.

Spanning river systems in both NSW and Queensland, 12 high priority sites were identified, together with concept designs and investment costs to fix the top five barriers to fish passage. These weirs were chosen because of their anticipated high benefit/cost ratio.

The project identified that there are two feasible approaches to rehabilitating fish passage in the northern Basin:

  • provide fish passage at the top 11 priority structures to reinstate 2,086 km of river channel. The total cost was estimated at $14.56 m.
  • provide a strategic, holistic, program re-establishing broad-scale river connectivity of over 3,242 km. The total cost was estimated to be approximately $70 m.

The key features that make a fish passage program feasible in this area are:

  • the main-stem barriers are not numerous (42 for a broad-scale program reinstating over 3,200 km of river).
  • most of the barriers are low-level weirs between 1.5 m and 4.5 m high, with the exception of only eight structures.
  • most of the sites are relatively easy to work with.

Lessons learned and future directions: This project has provided a clear direction for strategic investment to deliver substantial improvements in fish passage connectivity, reducing fragmentation of fish populations in the northern Murray-Darling Basin. Fishway concepts were specifically designed to suit the fish assemblage and semi-arid ecology of the northern Basin and considered the feasibility of construction, materials, regional context, maintenance and ownership. 

Stakeholders and Funding bodies: This project was funded through the Murray-Darling Basin Authority’s Native Fish Strategy.

Contact: Scott Nichols, Fisheries New South Wales, (02) 66261396, scott.nichols@industry.nsw.gov.au, 1243 Bruxner Highway, Wollongbar, NSW 2477

Link: http://www.dpi.nsw.gov.au/__data/assets/pdf_file/0020/456203/Fishway-Options-for-Weirs-of-the-Northern-MDB-FINAL-for-web-Jan13.pdf

 

 

Counting Murray-Darling fishes by validating sounds associated with spawning

Key words: fish counting, spawning, Murray-Darling Basin, Native Fish Strategy

Over 700 fish species worldwide produce sounds, and the unique sounds made by fish species can often detected using underwater microphones. Most sounds are produced during courtship, for communication or identification, and they can be useful if attempting to locate fish, make abundance estimates, or direct habitat management. Prior to this project however, there had been little consideration given to use of sounds produced by fish for these purposes in Australian rivers.

Broad aim and methods: The specific objectives of this project were:

  • To trial a bioacoustic (fish noises) technology to determine whether captive large-bodied native fish (Murray Cod (Maccullochella peelii), Golden Perch (Macquaria ambigua), and Silver Perch (Bidyanus bidyanus) produce sounds associated with artificial or pond spawning, and whether spawning population counts can be obtained.
  • To isolate individual spawning sounds produced by each fish species and its associated behaviours, for example, do individual species produce unique, distinguishable sounds for male dominance, courtship, spawning or distress?
  • To test for soniferous sounds in wild collected adult carp spawned in captive conditions.
  • To scope passive bioacoustics as a tool for measuring the relative abundance of fish in key habitats and potentially in fishways.

 A series of trials were undertaken initially to benchmark or sound truth ambient noises within the experimental environment. In an initial trial, a hydrophone was placed into a tank with no fish to record noises. A second trial involving the same procedure but with a single fish was undertaken. The final experimental phase was to benchmark the noises from a number of fish (mixed sexes) Four fish that had been injected with hormones (two male and two female) were placed into a tank and recorded for 24 hours (Figs 1 – 2). A DIDSON camera was also set up to provide vision of the spawning fish.

Figure 1 - A sonogram of acoustic signals recorded in a tank with spawning Golden Perch. The noise could not be specifically isolated to the fish. (Courtesy of Ivor Stuart)

Figure 1 – A sonogram of acoustic signals recorded in a tank with spawning Golden Perch. The noise could not be specifically isolated to the fish. (Courtesy of Ivor Stuart)

Figure 2 - Researcher Jonothan Doyle listening to fish. (Photo courtesy of Ivor Stuart)

Figure 2 – Researcher Jonothan Doyle listening to fish. (Photo courtesy of Ivor Stuart)

Findings: Several acoustic noises were isolated during the project and although these were absent from the controls they could not specifically be attributed to the fish. These results demonstrate that some Murray-Darling Basin native fish potentially produce noises. Further research and replication is needed to clarify the mechanism of fish sound production, individual variation in vocalisation and the utility for research and management. The sonogram data did appear to include biological noise, but the DIDSON camera proved unsuitable in hatchery tanks and further work with fixed video cameras is needed to link sound production with fish behaviour.

Murray Cod appear to provide a model species for further acoustic trials as these fish have complex social behaviour that can be observed in the semi-natural conditions of a hatchery pond. The suggested protocol is to set up a DIDSON camera or video recorder and hydrophones within the spawning drum (used by fish as a laying site). This method would allow visual confirmation of fish making noises, and the hydrophone would be placed in an optimal position to capture any vocalisations.

Lessons learned and future directions: The preliminary results of this project suggest that using a hydrophone to detect native fish is plausible, but requires further work. If further trials are successful this technology would be useful for detecting native fish spawning which would be used to determine fish habitat preferences for both conservation and rehabilitation. 

Stakeholders and Funding bodies: This project was funded through the Murray-Darling Basin Authority’s Native Fish Strategy.

Contacts: Ivor Stuart, Kingfisher Research P/L.,0408 619 126, ivor.stuart@gmail.com

Link: http://www.mdba.gov.au/sites/default/files/pubs/MDBA-13088-Soniferous-Reportv2.pdf

Preliminary investigation of an “Achilles Heel” for control of Redfin Perch in New South Wales

Key words: Perca fluviatilis, Redfin Perch, invasive species, physical removal, control strategy, Native Fish Strategy.

Threats and Impacts: Redfin Perch (Perca fluviatilis) is an alien fish species that has been established in Australia for more than 150 years. Although a popular recreational angling target in some regions, it has a range of deleterious impacts on native fish, through predation and competition for resources, and as a vector for a virus (epizootic haematopoietic necrosis virus). Despite the threat posed by this species, there are major deficiencies in current knowledge and policies in regards to controlling existing populations and responding to new infestations. In New Zealand and Australia the control of Redfin Perch has been found to be most effective in small lakes and ponds using physical removal techniques such as nets and traps, as well as mid-water trawling and electrofishing at night.

Project objectives and methods: The objectives of this project were to:

  1. undertake a detailed literature review of species biology to identify weaknesses that could be exploited in control programmes;
  2. conduct field trials of potential control techniques;
  3. complete an investigation of behaviour and movement using acoustic technologies; and,
  4. provide recommendations for a future control programme, including scoping of sterile feral technology.

This study included a detailed literature review of Redfin Perch biology to identify any potential weaknesses that could be exploited in control programs. Field trials were then performed in an impoundment (Suma Park Reservoir) on the central tablelands of New South Wales, known to contain an abundant population of Redfin Perch, and a riverine site in the Gwydir catchment. The trials were designed to investigate the effectiveness of physical removal of Redfin Perch using a combination of electrofishing, panel (gill) netting (with and without herding), fyke nets and clover-leaf traps with several attractants (laser lights, glow sticks, magnets and berley). The study also used underwater acoustic cameras (DIDSON) to examine Redfin Perch behaviour in response to each of the attractants. Separate trials were undertaken in winter and summer. Additional field trials were undertaken in a riverine site in the Gwydir catchment during summer.

Given the limited understanding of the species movement patterns and the importance of this information to targeting control techniques, an acoustic tagging study was undertaken in Suma Park Reservoir.

Figure 1 A cloverleaf trap such as those used during field trials (Photo courtesy of Dean Gilligan)

Figure 1 A cloverleaf trap such as those used during field trials (Photo courtesy of Dean Gilligan)

Figure 2 The focus species for this study, Redfin Perch (Photo courtesy of Dean Gilligan)

Figure 2 The focus species for this study, Redfin Perch (Photo courtesy of Dean Gilligan)

Findings: The review of Redfin Perch biology highlighted several key aspects that could be exploited in future control programmes:

  •  timing of reproduction – target removal prior to or during spawning events;
  • inducible sterility – sterile feral technology;
  • spawning behaviour – removal/reduce availability of spawning substrate;
  • self regulation of populations – bio-manipulation or sterile technology; and,
  • schooling behaviour – target control efforts.

In the removal trials, catch rates in fyke nets and cloverleaf traps were relatively low across all three trials (winter and summer in reservoir and summer in river) with standard panel nets and electrofishing being the most effective methods. The clover-leaf traps were not effective at catching Redfin Perch, either with or without attractants within the traps. Catch rates in cloverleaf traps and fyke nets were too low to draw any conclusions relating to improvements in catch efficiency resulting from the use of the attractants trialled. However, assessment of the response of Redfin to the various attractants using DIDSON imagery revealed that glow sticks and lasers do have the potential to be used as attractants, particularly at night.

The acoustic telemetry study indicated that most fish occupied the downstream end of the dam, with only up to two individuals spending extensive periods of time within the upstream reaches of the impoundment. Overall, fish spent 90% of the time within the top 10 m of the water column, possibly due to lower dissolved oxygen concentrations below this depth.

Lessons learned and future directions: Overall this project has resulted in the compilation of valuable information on Redfin Perch that can contribute to its future management. In particular:

  • passive fishing techniques/traps that rely on luring/attracting fish into a certain area (e.g. clover-leaf traps) are not very effective;
  • they appear to be much more susceptible to being caught in nets that target/intercept fish while moving (fyke and panel nets);
  • electrofishing is effective in the short-term and on a small scale, but may not be cost effective/practical in the long term as abundance of the target population declines;
  • glow sticks and laser lights were found to be effective attractants at night, but optimal deployment methods need to be established that minimise trap-avoidance of those fish attracted;
  • juveniles form large schools, whereas adults were more solitary; and,
  • movement data indicates the top 10 m of the water column and areas around the deeper downstream reaches of impoundments are occupied most frequently and may be appropriate areas to target removal efforts. 

Stakeholders and Funding bodies: This project was funded through the Murray-Darling Basin Authority’s Native Fish Strategy.

Contacts: Dr Dean Gilligan, New South Wales Department of Primary Industries. Tel: + 61 2 4478 9111, Email: dean.gilligan@industry.nsw.gov.au

Design and installation of a novel wetland Carp harvesting set up at Lake Bonney, South Australia

Key words: Carp, pest fish control, Lake Bonney, Native Fish Strategy

During 2009–2010, Lake Bonney (near the township of Barmera in SA) received 26 gigalitres of environmental water from the Murray River. It was anticipated that Carp (Cyprinus carpio) would accumulate in large numbers at the lake inlet as water was delivered (Fig1), providing a unique opportunity to trial a wetland Carp separation cage (WCSC) for controlling the estimated 50–100 tonnes of this species in the lake, as well as a number of designs for screening fish. Although numerous types of screens have been used to restrict the movement of fish either into or out of wetlands, most do not achieve the best environmental outcome in terms of allowing the free passage of native fish and other fauna while restricting the movement of Carp and other unwanted species.

Project aim and methods: Fishing/tagging activities and monitoring in the lake proper were undertaken in association with delivery of an environmental watering to Lake Bonney, and installation of a prototype wetland carp separation cage, to evaluate:

  • The population of Carp and other large-bodied native fish (>250mm total length at maturity) in Lake Bonney including Murray Cod (Macculochella peelii), Golden Perch (Macquaria ambigua), Silver Perch (Bidyanus bidyanus), Freshwater Catfish (Tandanus tandanus) and Bony Herring (Nematalosa erebi).
  • The response of Carp and native fish during the provision of environmental water, and therefore the need to accommodate the passage of large-bodied native fishes during future water allocations; and
  • The species diversity, abundance and size structures of captured fish (Carp and large-bodied fishes)

Two new carp exclusion screens (jail bars with 31mm apertures between the bars and square grid-mesh with 44 x 44 mm internal dimensions) (Fig 2) were trialled in the culverts to evaluate:

  • their effect on flow velocity; and,
  • whether an angle-mount and the high flow-velocities in the culvert would combine to clear the screens by pushing debris towards the water’s surface (and potentially over the top of the screen).

Findings: Scientific sampling and commercial fishing activities within the lake and inflow point, combined with fish tagging, allowed estimation of the resident population of several large-bodied fish species (native and alien), and their response to inflow. The size of the resident adult Carp population was estimated via a Peterson mark-recapture tagging experiment at 44,606 individuals. A similarly large but unquantified biomass of Bony Herring was also detected. Otherwise, only three large Freshwater Catfish and two Golden Perch were recorded, suggesting the lake’s large-bodied native fish population is very low (with the exception of Bony Herring).

Carp were observed to aggregate in large numbers around the inflow point, and spawning activity was observed within 24 hrs. Their efforts to exit the lake via the culverts was blocked by the carp screen. In contrast, relatively few large Bony Herring and no other large-bodied native fish were captured near the inflow point, however thousands of juvenile Bony Herring were observed in January 2010 when Carp were absent.

Significant refinements to strengthen Carp screens; enable them to pivot; and, prevent public access were required to enable carp screens to operate without fouling with debris, and to prevent vandalism. When set to an angle of ~33° fouling and flow constriction was significantly reduced. Most entrained fish and turtles were also able to pass over the top of this design.

Figure 1 Carp in Lake Bonney (Photo courtesy of Leigh Thwaites)

Figure 1 Carp in Lake Bonney (Photo courtesy of Leigh Thwaites)

Figure 2 Carp cage installed at Lake Bonney (Photo courtesy of Leigh Thwaites)

Figure 2 Carp cage installed at Lake Bonney (Photo courtesy of Leigh Thwaites)

Lessons learned and future directions: Although the cage operated according to its intended design and function during the 2010 trial, some operational issues were observed, necessitating refinements that have resulted in a pragmatic, adaptable and safe device.

Fixed screens such as grid mesh and the ‘jail bar’ design should not be used at wetlands like Lake Bonney that have high flows and easy public access, because:

  • impeding Carp movement is inefficient and often obstructs native species
  • regular maintenance is required
  • they tend to deteriorate over time, and can be easily vandalised
  • they can compress Carp into wetlands (ie juvenile Carp pass through a screen and grow to a point where they cannot move out though the screen).

While commercial fishing can be a valuable tool for controlling Carp, it is of limited use as a ‘stand alone’ technique as netting a proportion of adult fish does not stop Carp from spawning.

The level of by-catch (356 Bony Herring, as well as a few Golden Perch, Goldfish (Carrassius auratus) and Birds) signals the need to survey the resident native fauna on a site-by-site basis prior to installing any Carp management infrastructure. Also, the motivation of Carp to migrate out of the lake decreased over time, suggesting that harvesting should occur in the early stages of the lake being filled.

 

Stakeholders and Funding bodies: This project was funded through the Murray-Darling Basin Authority’s Native Fish Strategy.

Contacts: Dr Leigh Thwaites, South Australian Research and Development Institute. Tel: + 61 8 8207 5495, Email: leigh.thwaites@sa.gov.au.

Link: http://www.sardi.sa.gov.au/__data/assets/pdf_file/0019/153226/Proof_of_concept_of_a_novel_wetland_carp_separation_cage_at_Lake_Bonney,_South_Australia.pdf

Quantifying and mitigating the impact of weirs on downstream passage of native fish in the Murray-Darling Basin

Key words: downstream, migration, fish injury, undershot weir, Native Fish Strategy.

Fish communities of the Murray-Darling Basin (MDB) are highly migratory. Significant numbers of fish undertake large-scale downstream movements as adults, as well as during egg and larval life phases. With any type of migration, it is essential that fish are able to negotiate any barriers without delay or injury.

There are an estimated 10,000 barriers installed in the MDB. Two major weir designs are constructed on Australian waterways. Undershot weirs are usually operated via steel gates and water is released underneath the gates, whereas overshot weirs are usually constructed from concrete or wood and water cascades over the weir crest. Preliminary studies have shown that undershot designs, common throughout the MDB, have been shown to contribute to high mortality in larvae of some native fish species. The need was identified to determine if such mortalities occur across all species and size classes of native fish.

Broad aim and methods: This controlled field study aimed to determine the impacts of downstream fish passage of common MDB fish species through undershot and overshot weir designs at a range of flows to determine fish welfare impacts. It was hoped that this information, combined with modelling to understand hydrodynamic stresses that occur at these weirs, would help to inform development of appropriate mitigation measures.

A number of native fish species at various stages in their life history were introduced upstream of an experimental weir structure configured to function either as an undershot or overshot weir, operating at different water levels/gate openings. A fyke net was installed downstream to collect all experimental fish. Rates of injury and survival were compared between the different weir designs.

A key aspect of this project was to use computational fluid dynamics (CFD) modelling to investigate potential sources of injury. Modelling parameters such as pressure differentials, shear stresses, velocity and turbulence were used to link observed fish injuries with environmental parameters.

Findings: Passage through overshot weirs was associated with substantially greater survival in all species compared to undershot weirs. Few fish died and the main welfare issues arose when water from overshot weirs fell into shallow water, where fish became physically injured when impacting the downstream weir apron. These results indicate that the construction of overshot weirs with deep plunge pools would provide safe conditions for many fish species and sizes moving downstream.

Most Golden Perch (Macquaria ambigua) and Silver Perch (Bidyanus bidyanus) larvae, and more than half of Murray Cod (Maccullochella peelii) larvae died during undershot weir passage. Small-bodied native fish such as Australian Smelt (Retropinna semoni) and Unspecked Hardyhead (Craterocephalus stercusmuscarum) displayed extremely high mortality when passing through undershot weirs. Adult life stages of large-bodied species were also affected by undershot weirs but to a much lesser degree, with most adult Golden Perch and Silver Perch and a third of Murray Cod suffering minor injuries when passing through small gate openings. Undershot weirs were characterised by higher values of shear, turbulence and pressure changes. Modifications were made to undershot gates to try and reduce these impacts, but unfortunately none of the trials successfully mitigated effects on native fish.

Injuries such as this can be sustained by fish attempting passage through an undershot weir (Photo Lee Baumgartner NSW DPI).

Figure 1. Injuries such as this can be sustained by fish attempting passage through an undershot weir (Photo Lee Baumgartner NSW DPI).

Figure 2. Weir designs such as this one at Balranald can impact on downstream passage of native fish (Photo Jamin Forbes).

Figure 2. Weir designs such as this one at Balranald can impact on downstream passage of native fish (Photo Jamin Forbes).

Lessons learned and future directions: The findings of this study are particularly relevant for the MDB, given that over 80% of main channel weirs in most inland rivers now use undershot weirs. Continuing upgrades to undershot weir structures in smaller creeks and tributaries are being carried out to improve water delivery efficiency, but may substantially increase injury and mortality of native fish over a large spatial scale. Options to design and fit undershot weirs with ‘fish friendly’ flow modifications should be explored to minimise these threats to native fish. It is important that any such structure should protect all life history stages and have applicability over a large spatial scale. These modification options should be seen as a priority area for future research work.

Stakeholders and Funding bodies: This project was funded through the Murray-Darling Basin Authority’s Native Fish Strategy.

Contacts: Dr Lee Baumgartner, Fisheries NSW, 02 6958 8215, lee.baumgartner@dpi.nsw.gov.au.

Link: Report not yet published.

Evaluation of carp exclusion screens at wetland inlets

Key words: pest fish control, European Carp, exclusion screen, Native Fish Strategy

Threats and Impacts: Wetlands are sites of high primary and secondary production and contain diverse flora and fauna. Indeed, many riverine species are wholly or partially dependent on wetlands for food, shelter or habitat during some part of their life cycle. Carp (Cyprinus carpio) dominate the alien fish fauna of the Murray–Darling Basin, and are believed to impact on native fish communities by increasing turbidity, disturbing and redistributing benthic seeds and invertebrates, up-rooting delicate shallow-rooted vegetation, competing with native fishes and other aquatic fauna for food and space, and indirectly promoting the development of toxic algal blooms (Fig 1).

In the Murray-Darling Basin, up to 98% of Carp are produced in wetlands connected to the main rivers. Carp Exclusion Screens (CES), which are mesh barriers that are installed at inlets to wetlands to exclude large fish from enterin (Figs 2-3), provide a management tool that has been applied to protect ecologically important areas from the impacts of Carp. However, little work has been undertaken to validate the effectiveness of CES in managing Carp, and concerns about possible detrimental effects of CES on native aquatic fauna have been raised.  

Broad aim and specific objectives: The project had three broad aims:

  1. evaluate the effectiveness of CES at wetland inlets;
  2. assess possible impacts of existing screen configurations on native fish communities that would normally access wetlands; and,
  3. design (if possible) an optimised CES to allow small and medium sized native fish to pass in and out of wetlands whilst denying access to mature carp.

Methods: The aims of this project were achieved by undertaking six key research activities:

  1. a desktop literature review and a field reconnaissance to evaluate the existing diversity in the design and management of CES within the Murray–Darling Basin;
  2. analysis of available data from recent comprehensive wetlands surveys (the 2004–2007 South Australian River Murray Wetlands Baseline Surveys) to evaluate differences in the relative abundances of carp and native fishes in wetlands with and without CES;
  3. identification of the species composition and sizes of fishes and other aquatic fauna that make lateral migrations through wetland inlets and which might, therefore, be affected by the use of CES;
  4. modelling to establish the size range of large-bodied fish that could pass through different screen mesh dimensions;
  5. calculation of ‘optimised’ mesh designs that would prevent the passage of mature, breeding-size carp (>250 mm TL) whilst allowing the passage of a majority of small and medium sized native fishes that use wetlands; and,
  6. laboratory and field trials of the most common existing screen mesh designs versus the optimised designs.
Figure 1: Carp accumulating downstream of a Carp exclusion screen at Sweeneys wetland. (Photo courtesy SARDI)

Figure 1: Carp accumulating downstream of a Carp exclusion screen at Sweeneys wetland. (Photo courtesy SARDI)

Figure 2: Carp Screens installed on a channel at Riverglades SA.  (Photo courtesy Leigh Thwaites)

Figure 2: Carp Screens installed on a channel at Riverglades SA. (Photo courtesy Leigh Thwaites)

Figure 3: Pivoting carp screen adjustment at Ramco SA. (Photo courtesy of Leigh Thwaites

Figure 3: Pivoting carp screen adjustment at Ramco SA. (Photo courtesy of Leigh Thwaites

Findings: The current CES designs and management regimes were noted to have been ineffective in reducing the numbers and biomass of Carp in wetlands.

A diverse and abundant native fish community (14 species) was found to utilise wetlands and wetland inlets. Some existing exclusion screen designs are detrimental to native fish (by excluding most sizes and life history stages), including species of conservation significance. Other aquatic fauna, such as turtles, are also likely to be impacted.

Two types of screens that will optimise the exclusion of large, sexually mature carp were designed:

  • A square grid mesh with 44 mm gaps
  • A “jail-bar” design with 31.4 mm gaps.

The jail bar design was found to collect less debris, trap more Carp and less native fish, and had little effect on flow velocity.

Lessons learned and future directions:CES may be beneficial as part of an integrated Carp management regime in some wetlands. Presently, there is no benefit in using CES in permanently inundated wetlands, unless other Carp reduction measures are also employed.

  • The use of CES alone should be considered for use at seasonal/ ephemeral wetlands that dry every 1-2 years. They may also be suited to permanent shallow wetlands that remain filled for >2 years at a time, if it can be shown that all adult Carp migrate from wetlands to overwinter in deeper river water.
  • The jail bar CES with 31 mm apertures between bars screen passed more native fish, including the greatest proportion of Bony Herring (Nematalosa erebi) (>90%), which are the key large-bodied native fish found to use wetlands and wetland inlets.
  • All CES need to be regularly maintained to ensure that they are functioning as intended and are not altering channel hydrodynamics or impeding the passage of native fauna.

Stakeholders and Funding bodies: This project was funded through the Murray-Darling Basin Authority’s Native Fish Strategy.

Contacts: Dr Leigh Thwaites, South Australian Research and Development Institute. Tel: + 61 8 8207 5495, Email: leigh.thwaites@sa.gov.au.

Link: Not yet published.

An assessment of a Dual-Frequency Identification Sonar (DIDSON) to complement fish migration studies in the Murray Darling Basin.

Key words: Fish counting, fish passage, DIDSON, sonar, Native Fish Strategy.

A major limitation to studying the behaviour of fish in the rivers of the Murray-Darling Basin is high turbidity (muddy) water, which prevents direct observation of fish. The dual-frequency identification sonar (DIDSON) is a unique, high-definition piece of equipment that uses sound beams to produce almost photographic quality underwater images. For fish studies, the DIDSON can be used to study fish movements, depths, fish behaviour and number and size of fish and does not require clear water for viewing.

Broad aim and methods: This project aimed to determine the feasibility of using the DIDSON to help assess fish behaviour in two types of fishways in the Murray-Darling Basin. The trial also tested the ability of the DIDSON (and its software) to automatically count and measure fish.

Experiments conducted at three locations (Murray Barrages, Yarrawonga fish lift fishway and Lock 8 vertical slot fishway) to determine whether the DIDSON could produce images sufficient for species recognition. Individuals of known-length were also used to assess ability for automatic length-recording. The DIDSON sonar was applied under a range of conditions in the Yarrawonga fish lock during different stages of fishway cycling (including in fishways with traps deployed to assess behaviour in response to traps).  The purpose was to consider behavioural responses and implications for fishway operation (a) at the fishway exit to consider the possible fate of exiting fish, and (b) in a vertical slot fishway under different river levels to determine its influence on successful fish ascent of fishways.

Figure 1. The output of a DIDSON sonar on a laptop. (Photo courtesy Lee Baumgartner NSW DPI)

Figure 1. The output of a DIDSON sonar on a laptop. (Photo courtesy Lee Baumgartner NSW DPI)

Figure 2, a fish casting a shadow using the DIDSON sonar. (Photo courtesy Lee Baumgartner NSW DPI)

Figure 2, a fish casting a shadow using the DIDSON sonar. (Photo courtesy Lee Baumgartner NSW DPI)

Findings: The trial concluded that DIDSON was a powerful tool for observing freshwater fish. When used in conjunction with conventional trapping techniques, the DIDSON consistently provided additional data on fish behaviour that otherwise would not be determined. However, when compared to trapping data collected, total fish numbers were frequently underestimated and estimated fish lengths were quite variable. Further development of the operating software could alleviate these problems.

Lessons learned and future directions: DIDSON was identified to be a useful tool for monitoring the efficiency of fishways and how fish behave at the entrance to fishways (e.g identifying whether they approach but not enter fishways or if they enter but not proceed any further). Such information may lead to modification of fishways to increase fish passage in the MDB. The trial also highlighted that this technology may be useful for a range of other fish research projects in Australia.

Stakeholders and Funding bodies: This project was funded through the Murray-Darling Basin Authority’s Native Fish Strategy.

Contacts: Dr Lee Baumgartner, Fisheries NSW, + 61 2 6958 8215,  Email: lee.baumgartner@dpi.nsw.gov.au

Link: http://www.dpi.nsw.gov.au/__data/assets/pdf_file/0009/136665/Output-686_DIDSON-Report_FORMATTED.pdf

Assessing the costs and benefits of re-snagging to enhance fish communities downstream of Yarrawonga on the Murray River.

Key words: re-snagging, fisheries enhancement, habitat, cost/benefit, Native Fish Strategy

Trunks, branches and root masses (known as large woody debris or snags) have a significant role in the species composition, primary production and habitat structure of many freshwater systems. Although the extensive removal of snags from the Murray Darling Basin (MDB) in the last 150 years for riverboat navigation, water conveyance and infrastructure protection was recognised at the time of this study as a threat to native fish species; it was not known whether native fish populations would increase following ‘re-snagging’.

Broad aim and specific objectives: The aim of this project was to conduct a scientific trial of re-snagging on the Murray River downstream of Yarrawonga and devise a cost-benefit model to assist river managers with future re-snagging of large lowland rivers.

Methods: Monitoring was undertaken of three native fish – Murray Cod (Maccullochella peelii), Trout Cod (Maccullochella macquariensis), and Golden Perch (Macquaria ambigua) – across three river reaches (Fg 1). One of these reaches was the target of re-snagging efforts(Fig 2), while the other two acted as controls. Monitoring of populations of these species took place before and after re-snagging was undertaken. Experiments were undertaken over seven years between 2007-2013 to enable comparison of changes between each area.

Electrofishing was used to collect information on length frequency data at each site. Age structure was inferred from length frequency data collected, and validated through collection and analysis of otoliths (fish ear bones). Electrofishing and mark-recapture methods were used to measure changes in population size over time, and also provided a secondary source of data to estimate annual population growth. Fish over 200mm were tagged with Passive Inductive Transponder (PIT) tags and a subsample was also fitted with radio-transmitters to provide additional information on fish movement. Fishery dependent data collected through an angler logbook program provided Catch per Unit Effort and species composition data.

ARI researcher Jarod Lyon implanting a radio transmitter in Murray Cod.  (Photo courtesy Joanne Kearns)

Figure 1. ARI researcher Jarod Lyon implanting a radio transmitter in Murray Cod. (Photo courtesy Joanne Kearns)

This project has helped increase understanding of the benefits received through reintroducing large snags to the Murray River.  (Photo courtesy Martin Casey)

Figure 2. This project has helped increase understanding of the benefits received through reintroducing large snags to the Murray River. (Photo courtesy Martin Casey)

Findings: The results from this long-term project clearly demonstrated that native fish respond positively to the addition of snags. All three native fish targeted used the re-snagged sites within 12 months of the re-snagging, and all size classes were represented in those sites. Native fish also responded positively to the density of snags in a site.

The optimal location for snag placements depended on the target species. If re-snagging activities are targeting Murray Cod then maximum benefit is likely to be obtained by re-snagging within 15m of the bank. Although re-snagging this inner area will also deliver benefits for Trout Cod, the re-snagging of mid river areas will preferentially but not exclusively benefit Trout Cod in large waterways such as the Murray River. The creation of habitat in depositional zones of meanders had lower rates of utilisation in comparison to other zones.

Two models were developed to allow cost-benefit analysis to be undertaken, one that examined costs and benefits at the landscape scale and the other at a local scale. The benefits of habitat created through re-snagging are influenced by the size of the existing resident population of fish and the extent of connectivity with alternate source populations.

Lessons learned and future directions: Increased scientific understanding of the importance of snags to native fish and river health has led to significant efforts to reverse the loss of this vital habitat. The most obvious way to achieve this is to put the snags back in the streams. Although conceptually simple, there is a lot of science and engineering behind the placement of snags. Consideration must be given to the type, size, shape and quantity of snags needed, as well as their position and orientation in the river. This level of detail is necessary to ensure that the structures are placed to maximise outcomes for fish communities.

Another component of this program has been the establishment of a data set that will provide estimates of the growth rates and population statistics of Murray Cod, Trout Cod and Golden Perch. This has already been used to assist with advancing the management of Murray Cod in the Basin.

Stakeholders and Funding bodies: This project was funded through the Murray-Darling Basin Authority’s Native Fish Strategy and The Living Murray initiative.

Contacts: Dr Jarod Lyon, Arthur Rylah Institute for Environmental Research. Tel: + 61 3 9450 8678, Email: jarod.lyon@depi.vic.gov.au.

Development of fish screening criteria for water diversions in the Murray-Darling Basin.

Key words: irrigation, extraction, water diversion, fish screening, Native Fish Strategy.

Threats and Impacts: There is mounting evidence to suggest that significant numbers of fish are being lost from Australian rivers via water extraction. One of the most common tools used to combat this loss internationally are fish screens on irrigation intake pipes. Prior to this project there were no guidelines for intake screens in the Murray-Darling Basin (MDB).

Broad aim and specific objectives: This project aimed to undertake experiments to develop physical design criteria for fish screens at water diversions in the MDB as well as undertaking a scoping study of fish screening programs elsewhere in the world to make recommendations on how to best initiate a successful program in the Basin.

Methods: A combination of field and laboratory-based experiments at simulated intake screens was used to test how approach velocities (water velocities in front of and at right-angles to the screen face) and screening materials affected potential injury and mortality of native fish species. An experimental water pump was used, to which screens of varying mesh size could be fitted, enabling comparisons in fish entrainment to be identified. Dual-frequency identification sonar was also used to quantify the number and nature of fish interactions with the experimental screen. Lastly, a review of fish screening programs elsewhere in the world was undertaken to aid identification of key factors for successful implementation of an effective program in the MDB

Experimental fish screen being moved into place (Photo courtesy of Craig Boys)

Figure 1. Experimental fish screen being moved into place (Photo courtesy of Craig Boys)

Experimental pumping station showing typical deployment into water adjacent to a gravel bar (Photo courtesy of Craig Boys)

Figure 2. Experimental pumping station showing typical deployment into water adjacent to a gravel bar (Photo courtesy of Craig Boys)

Setup of research site (Photo courtesy of Craig Boys)

Figure 3. Setup of research site (Photo courtesy of Craig Boys)

Findings: It was found that the installation of fish screens has great potential to significantly reduce fish entrainment at intakes. Mortality at an experimental intake was reduced from over 90% (unscreened) to less than 2% (when screened) in the laboratory. Approach velocities of up to 0.4m/sec were effective in reducing entrainment of juvenile Golden Perch (Macquaria ambigua) and Silver Perch (Bidyanus bidyanus) in laboratory trials, with very little injury or mortality resulting from incidental screen contacts or impingement. In comparison, field observations of an assemblage of fish at a screen demonstrated that even modest increases in approach velocity (from 0.1 to 0.5 m/sec) produced a significant increase in the rate of screen contact for fish less than 150 mm, with the impact being more marked for smaller fish. There was little difference in the rate of screen contact or entrainment when using three different sizes of woven wire mesh. Together, these findings suggest that screening material may not be as important as approach velocity when designing screens for protecting fish.

A review of successful screen programs in the USA found that coordinating committees are a key factor to success. Government-irrigator cost-share programs have proven to be strong incentives to screen diversions elsewhere in the world and their use should be further explored for the MDB.

DIDSON (sonar) output, showing experimental screen (Photo courtesy of Craig Boys)

Figure 4. DIDSON (sonar) output, showing experimental screen (Photo courtesy of Craig Boys)

Lessons learned and future directions: This study highlighted that approach velocity is a key determinant of potential injury or mortality associated with contact with intake screens. Screen material was not found to influence potential injury or mortality of fish.

The findings of this project should be used to develop guidelines for water abstraction that will have significant benefits for native fish by reducing the number of fish lost to irrigation off takes and injury and mortality associated with fish contact with intake screens. This has the potential to significantly assist in native fish population rehabilitation by protecting smaller bodied fish (including early life history stages of large bodied species).

There is a need for a fish screening coordinating committee for the MDB to provide guidance regarding the setting and refinement of screen design criteria, identify funding opportunities and identify priority intakes for implementation.

Stakeholders and Funding bodies: This project was funded through the Murray-Darling Basin Authority’s Native Fish Strategy.

Contacts: Dr Craig Boys, Fisheries New South Wales. Tel: + 61 2 4916 3851, Email: craig.boys@dpi.nsw.gov.au.

Link: http://www.dpi.nsw.gov.au/__data/assets/pdf_file/0016/438001/2204_Development-of-fish-screening-criteria-for-water.pdf

Investigating strategies to improve post release survival of hatchery-reared threatened fish species

Key words: fish stocking, threatened fish, post release survival, training, Native Fish Strategy

Fish stocking can be used to help restore threatened fish stocks. However hatchery-reared fish can have some behavioural deficits related to domestication which hinder their survival in the wild. Pond-reared fingerlings seem to retain live food foraging skills and some bird avoidance behaviours, but they are naïve in avoiding predatory fish. Fish reared to larger sizes in grow out facilities tend to be fed on artificial pellet diets and are protected from birds and other predators, so are inexperienced in foraging for live foods and poor at avoiding predatory birds in the wild. Pre-release training of hatchery-reared and grow-out facility reared fish is one strategy available to improve survival after stocking into the wild.

Broad aim and specific objectives: The value of pre-release training was evaluated in this study. Specific objectives were:

  1. to determine if hatchery reared threatened fish species native to the Murray-Darling Basin can be trained to reduce hatchery domestication effects and test if this leads to improved survival in the wild.
  2. to determine if release in predator exclusion cages (soft release strategy) to overcome transport stress, leads to improved post stocking survival.

Methods: The effectiveness of tank-based training was assessed by exposing fingerlings of Murray Cod (Maccullochella peelii), Silver Perch (Bidyanus bidyanus) and Freshwater Catfish (Tandanus tandanus) en masse to predatory fish and chemical alarm signals from fish skin extract. Sub-adult Murray Cod and sub-adult Silver Perch from grow-out facilities (where they were reared on pellet diets and protected from bird exposure) were also trained to avoid simulated cormorant (Phalacrocoracidae) attacks (Figs 1-3). Training used a combination of: bird models to harass and chase fish; cormorant odour; and, alarm signals from fish skin extract. Sub-adult Murray Cod and adult Silver Perch (~300 mm total length) from grow-out facilities were also trained to take live food. To assist this process a wild Murray Cod or Silver Perch was introduced into each training tank to help cue the behaviours of the fish from the grow-out facilities.

Stocking trials at three sites in the northern Murray-Darling Basin were used to test if pre-release training improved survival of stocked fingerlings of Silver Perch and Murray Cod. Predator free release cages were also tested as a stocking method to improve survival.

A juvenile Murray cod with VIE tag ready for release. Vie tagged Murray cod. Note green tag at base of anal fin. (Photo courtesy of Michael Hutchison.)

Figure 1. A juvenile Murray cod with VIE tag ready for release. Note green tag at base of anal fin. (Photo courtesy of Michael Hutchison.)

Training tank within which predators were separated from fingerlings. (Photo courtesy of Michael Hutchison.)

Figure 2. Training tank within which predators were separated from fingerlings. (Photo courtesy of Michael Hutchison.)

Findings: Tank-based validation experiments confirmed that training significantly improved the predator response behaviour of all three species compared to untrained fish. At least 72 hours training was required for Murray Cod and Silver Perch fingerlings and 48 hours training for Catfish fingerlings to significantly change predator avoidance behaviour.

Trained sub-adult Silver Perch showed significant behavioural changes in response to simulated Cormorant attack compared to untrained groups. However sub-adult Murray Cod showed no significant change in behaviour. Sub-adult Silver Perch readily adapted to taking live shrimp in the training tank, but pellet-reared cod failed to take live shrimp over a one month training period.

Predator release cages seemed to disadvantage the survival of stocked Murray Cod fingerlings. Predator free cages neither advantaged nor disadvantaged stocked Silver Perch.

Silver Perch fingerlings in a training tank, separated from predator by partition. (Photo courtesy of Michael Hutchison.)

Figure 3. Silver Perch fingerlings in a training tank, separated from predator by partition. (Photo courtesy of Michael Hutchison.)

Lessons learned and future directions: Pre-release training of fingerlings led to a significant improvement in survival of trained Murray Cod compared to untrained control fish. At locations where predators were more abundant, the survival of trained Murray Cod was up to four times higher than untrained Murray Cod. Across all locations the average survival rate of trained Murray Cod was twice that of untrained Murray Cod.

There were no significant differences detected between trained and untrained Silver Perch fingerlings stocked into the wild. This may have been because of the schooling nature of this species, and amalgamation of Silver Perch into mixed schools of trained and untrained fish, leading rapid social learning of the untrained fish from the trained fish.

Predator abundance had a significant impact on survival outcomes for both Murray Cod and Silver Perch fingerlings. Survival was lowest in locations with high predator abundance. The patchiness of predator distributions within a site means it is best to use several release points at a site.

Sub-adult and adult Silver Perch seem to be highly trainable, but sub-adult Murray Cod are not. Silver Perch are a social schooling species and this may enhance training. In contrast Murray Cod tend to be territorial and solitary. The use of long term pellet reared sub-adult Murray Cod in conservation restocking programs should be avoided. If large fish are required for conservation stocking, translocation of wild caught sub-adults or adults may be a better option.

Stakeholders and Funding bodies: This project was funded through the Murray-Darling Basin Authority’s Native Fish Strategy and undertaken by a research team from the (now) QLD Department of Agriculture Fisheries and Forestry.

Contact:  Michael Hutchison, Queensland Department of Agriculture, Fisheries and Forestry, +617 3400 2037, Michael.hutchison@daff.qld.gov.au

Link: http://www.mdba.gov.au/sites/default/files/pubs/Strategies-to-improve-post-release-survival-of-hatchery-reared-threatened-fish-species.pdf