Murray cod and modern fish screens: influence of water velocity and screen design on the entrainment and impingement of larval and young-of-year fish at water offtakes

SummaryGlobally, the extraction and diversion of water from river systems has had substantial impacts on aquatic ecosystem health and ecological processes. One such impact is the entrainment of fish at pump offtakes that can result in vast quantities of fish being permanently removed from rivers. Exclusion screens to prevent fish entrainment at pump offtakes are therefore an important management consideration. In this study, impingement and subsequent injury and mortality of a juvenile freshwater perciform, Golden Perch (Macquaria ambigua), was assessed in the laboratory using a simulated fish exclusion screen under a range of velocities and impingement durations. A 2 mm wedge‐wire screen eliminated the entrainment of 44‐day‐old Golden Perch that were exposed to approach velocities between 0.05 and 0.3 m/s. However, impingement rates of Golden Perch increased significantly with increased approach velocities and rates of injury and mortality increased with impingement duration. Results from this study indicate the primary mechanisms to reduce fish loss at pump offtakes are to design pump offtakes, fitted with fish exclusion screens, which limit approach velocities or impingement duration. Further studies are required to examine a range of species with varying swimming ability at early life‐history stages. Such data will contribute to the growing body of knowledge that supports adaptive management plans to prevent fish loss at water offtake pumps.

Recreational fishery management aims to prevent species decline and provide sustainable fisheries. Overfishing has been frequently suggested as a cause of historic fishery declines within the Murray–Darling Basin (MDB), Australia, but there have been few quantitative surveys for providing fishery-dependent data to gauge status. The Murray Cod Maccullochella peelii and the Golden Perch Macquaria ambigua are important species targeted by recreational fishers across the MDB. The fisheries are controlled by size and bag limits and gear restrictions (both species) as well as a closed season (Murray Cod only). A complemented fisher survey design was used to assess the recreational fishery for both species in a 76-km reach of the Murrumbidgee River in 2012–2013. Progressive counts were used to quantify boat- and shore-based fishing effort. Catch and harvest rate information was obtained from shore-based fishers via roving surveys and from boat-based fishers via bus route surveys. Murray Cod catch rates (fish/angler-hour) were 0.228 ± 0.047 (mean ± SE; boat based) and 0.092 ± 0.023 (shore based), and harvest rates (fish/angler-hour) were 0.013 ± 0.006 (boat based) and 0.003 ± 0.001 (shore based). Golden Perch catch rates were 0.018 ± 0.009 (shore based) and 0.002 ± 0.001 (boat based), and harvest rates were 0.006 ± 0.002 (shore based) and 0.001 ± <0.001 (boat based). The Murray Cod fishery had maximal catch and harvest during the 5-month period after the closed season ended. The closed season aims to protect spawning Murray Cod, but this strategy's effectiveness may have been influenced by high fishing effort and deliberate bycatch during the closure period. To sustain and improve these MDB fisheries, we suggest quantification of catch-and-release impacts on spawning Murray Cod, provision of fish passage, re-stocking of Golden Perch, and education on fishing techniques that minimize Murray Cod bycatch during the closed season. Received October 22, 2014; accepted March 6, 2015

Fish screens can help prevent the entrainment or injury of fish at irrigation diversions, but only when designed appropriately. Design criteria cannot simply be transferred between sites or pump systems and need to be developed using an evidence-based approach with the needs of local species in mind. Laboratory testing is typically used to quantify fish responses at intake screens, but often limits the number of species that can studied and creates artificial conditions not directly applicable to screens in the wild. In this study a field-based approach was used to assess the appropriateness of different screen design attributes for the protection of a lowland river fish assemblage at an experimental irrigation pump. Direct netting of entrained fish was used along with sonar technology to quantify the probability of screen contact for a Murray-Darling Basin (Australia) fish species. Two approach velocities (0.1 and 0.5 m.sec−1) and different sizes of woven mesh (5, 10 and 20 mm) were evaluated. Smaller fish (<150 mm) in the assemblage were significantly more susceptible to entrainment and screen contact, especially at higher approach velocities. Mesh size appeared to have little impact on screen contact and entrainment, suggesting that approach velocity rather than mesh size is likely to be the primary consideration when developing screens. Until the effects of screen contacts on injury and survival of these species are better understood, it is recommended that approach velocities not exceed 0.1 m.sec−1 when the desire is to protect the largest range of species and size classes for lowland river fish assemblages in the Murray-Darling Basin. The field method tested proved to be a useful approach that could compliment laboratory studies to refine fish screen design and facilitate field validation.

The Murray Cod Maccullochella peelii and Golden Perch Macquaria ambigua are important recreational species in Australia's Murray–Darling Basin (MDB); both species have declined substantially, but recovery is evident in some areas. Minimum length limits (MLLs)—implemented to ensure fish could spawn at least once prior to harvest eligibility—have increased three times in the past decade. We quantified variation in length at 50% maturity (LM50), age at 50% maturity (AM50), and von Bertalanffy growth parameters (k = Brody growth coefficient; L∞ = asymptotic length; t0 = theoretical age at zero length) of these species within two rivers and two reservoirs of the MDB; to investigate whether fish length is a suitable surrogate for AM50 in setting MLLs. Between 2006 and 2013, we collected 1,118 Murray Cod and 1,742 Golden Perch by electrofishing and gillnetting. Values of k and L∞ were greater for reservoir fish than for riverine fish. For both species, AM50 was generally greater in rivers than in reservoirs; for Murray Cod, LM50 was greater in reservoirs than in rivers. A yield-per-recruit model demonstrated that smaller Murray Cod MLLs would be required for rivers and that an MLL at or below 600 mm (the existing MLL) across all populations could lead to overfishing in some systems. The differences in growth rate and the onset of reproductive maturation between riverine and reservoir populations suggest that system-specific regulations would be more effective at reducing the overfishing risk and meeting fishing quality objectives. Received August 18, 2014; accepted September 10, 2015

Genetic variation is critical to the persistence of populations and their capacity to adapt to environmental change. The distribution of genetic variation across a species' range can reveal critical information that is not necessarily represented in species occurrence or abundance patterns. We identified environmental factors associated with the amount of intraspecific, individual-based genetic variation across the range of a widespread freshwater fish species, the Murray cod Maccullochella peelii. We used two different approaches to statistically quantify the relative importance of predictor variables, allowing for nonlinear relationships: a random forest model and a Bayesian approach. The latter also accounted for population history. Both approaches identified associations between homozygosity by locus and both disturbance to the natural flow regime and mean annual flow. Homozygosity by locus was negatively associated with disturbance to the natural flow regime, suggesting that river reaches with more disturbed flow regimes may support larger, more genetically diverse populations. Our findings are consistent with the hypothesis that artificially induced perennial flows in regulated channels may provide greater and more consistent habitat and reduce the frequency of population bottlenecks that can occur frequently under the highly variable and unpredictable natural flow regime of the system. Although extensive river regulation across eastern Australia has not had an overall positive effect on Murray cod numbers over the past century, regulation may not represent the primary threat to Murray cod survival. Instead, pressures other than flow regulation may be more critical to the persistence of Murray cod (for example, reduced frequency of large floods, overfishing and chemical pollution).

Pacific Northwest National Laboratory evaluated Gardena Farms, Little Walla Walla, and Garden City/Lowden II Phase II fish screen facilities and provided underwater videography beneath a leaking rubber dam in the Walla Walla River basin in 2006. Evaluations of the fish screen facilities took place in early May 2006, when juvenile salmonids are generally outmigrating. At the Gardena Farms site, extended high river levels caused accumulations of debris and sediment in the forebay. This debris covered parts of the bottom drum seals, which could lead to early deterioration of the seals and drum screen. Approach velocities were excessive at the upstream corners of most of the drums, leading to 14% of the total approach velocities exceeding 0.4 feet per second (ft/s). Consequently, the approach velocities did not meet National Marine Fisheries Service (NMFS) design criteria guidelines for juvenile fish screens. The Little Walla Walla site was found to be in good condition, with all approach, sweep, and bypass velocities within NMFS criteria. Sediment buildup was minor and did not affect the effectiveness of the screens. At Garden City/Lowden II, 94% of approach velocities met NMFS criteria of 0.4 ft/s at any time. Sweep velocities increased toward the fish ladder. The air-burstmore » mechanism appears to keep large debris off the screens, although it does not prevent algae and periphyton from growing on the screen face, especially near the bottom of the screens. In August 2006, the Gardena Farm Irrigation District personnel requested that we look for a leak beneath the inflatable rubber dam at the Garden City/Lowden II site that was preventing water movement through the fish ladder. Using our underwater video equipment, we were able to find a gap in the sheet piling beneath the dam. Erosion of the riverbed was occurring around this gap, allowing water and cobbles to move beneath the dam. The construction engineers and irrigation district staff were able to use the video footage to resolve the problem within a couple weeks. We had hoped to also evaluate the effectiveness of modifications to louvers behind the Nursery Bridge screens when flows were higher than 350 cubic feet per second, (cfs) but were unable to do so. Based on the one measurement made in early 2006 after the modified louvers were set, it appears the modified louvers may help reduce approach velocities. The auxiliary supply water system gates also control water through the screens. Evaluating the effect of different combinations of gate and louver positions on approach velocities through the screens may help identify optimum settings for both at different river discharges.« less

In 2006, Pacific Northwest National Laboratory (PNNL) researchers evaluated 27 Phase II fish screen sites in the Yakima and Touchet river basins. Pacific Northwest National Laboratory performs these evaluations for Bonneville Power Administration (BPA) to determine whether the fish screening devices meet those National Marine Fisheries (NMFS) criteria for juvenile fish screen design, that promote safe and timely passage of juvenile salmonids. The NMFS criteria against which the sites were evaluated are as follows: (1) a uniform flow distribution over the screen surface to minimize approach velocity; (2) approach velocities less than or equal to 0.4 ft/s protects the smallest salmonids from impingement; (3) sweep velocities that are greater than approach velocities to minimize delay of out-migrating juveniles and minimize sediment deposition near the screens; (4) a bypass flow greater than or equal to the maximum flow velocity vector resultant upstream of the screens to also minimize delay of out-migrating salmonids; (5) a gradual and efficient acceleration of flow from the upstream end of the site into the bypass entrance to minimize delay of out-migrating salmonids; and (6) screen submergence between 65% and 85% for drum screen sites. In addition, the silt and debris accumulation next to the screens should be kept to a minimum to prevent excessive wear on screens, seals and cleaning mechanisms. Evaluations consist of measuring velocities in front of the screens, using an underwater camera to assess the condition and environment in front of the screens, and noting the general condition and operation of the sites. Results of the evaluations in 2006 include the following: (1) Most approach velocities met the NMFS criterion of less than or equal to 0.4 ft/s. Of the sites evaluated, 31% exceeded the criterion at least once. Thirty-three percent of flat-plate screens had problems compared to 25% of drum screens. (2) Woody debris and gravel deposited during high river levels were a problem at several sites. In some cases, it was difficult to determine the bypass pipe was plugged until several weeks had passed. Slow bypass flow caused by both the obstructions and high river levels may have discouraged fish from entering the bypass, but once they were in the bypass, they may have had no safe exit. Perhaps some tool or technique can be devised that would help identify whether slow bypass flow is caused by pipe blockage or by high river levels. (3) Bypass velocities generally were greater than sweep velocities, but sweep velocities often did not increase toward the bypass. The latter condition could slow migration of fish through the facility. (4) Screen and seal materials generally were in good condition. (5) Automated cleaning brushes generally functioned properly; chains and other moving parts were typically well-greased and operative. (6) Washington Department of Fish and Wildlife (WDFW) and U.S. Bureau of Reclamation (USBR) generally operated and maintained fish screen facilities in a way that provided safe passage for juvenile fish. (7) Efforts with WDFW to find optimal louver settings at Naches-Selah were partly successful. The number of spots with excessive approach velocities was decreased, but we were unable to adjust the site to bring all approach values below 0.4 ft/s. (8) In some instances, irrigators responsible for specific maintenance at their sites (e.g., debris removal) did not perform their tasks in a way that provided optimum operation of the fish screen facility. Enforcement personnel proved effective at reminding irrigation districts of their responsibilities to maintain the sites for fish protection as well as irrigation. (9) We recommend placing datasheets providing up-to-date operating criteria and design flows in each site's logbox. The datasheet should include bypass design flows and a table showing depths of water over the weir and corresponding bypass flow. A similar datasheet relating canal gage readings and canal discharge in cubic feet per second would help identify times when the canal is taking more water than it should. This information is available at some of the sites and assists operators in determining if the site is running within the site specific design criteria. (10) Data were collected at Gleed when the protective metal plates were set down to the forebay floor and when they were raised to expose most of the screens. These data were sent to USBR personnel for use in looking for ways to reduce high approach velocities and erratic flow pattern at Gleed. (11) Alternatives to a screen site at Taylor are apparently being considered. A lot of effort was spent in 2005 and 2006 trying to increase water to the site, but it still was unable to operate within NMFS criteria for much of the year and may be a hazard to juvenile salmonids at times.

Short‐term (≤4 days) post‐release mortalities of two large, culturally and ecologically important Australian freshwater teleosts golden perch Macquaria ambigua (Richardson) and Murray cod Maccullochella peelii (Mitchell) were investigated. There was no angler‐induced mortality among golden perch that were immediately released in winter and spring, but 24% of this species and 15% of Murray cod died after delayed release in summer. Significant predictors of mortality were limited to times caught and total length for golden perch, and restraint methods and recovery times for Murray cod, but other parameters were also implicated as cumulative influences. The estimated mortalities may be sufficient to produce population‐level impacts for these two long‐lived species but could be considerably reduced through revisions of tournament regulations.

Combining bio-telemetry and underwater imagery to elucidate the reproductive behaviour of a large, long-lived Australian freshwater teleost

Because of the high costs of collecting field data, many species recovery and management plans do not include a monitoring feedback component to measure the success of interventions and refine management strategies. Here, we demonstrate how leveraging existing monitoring data can provide broad-scale, cost-effective information about a threatened fish species, the Murray Cod Maccullochella peelii, which is of cultural and recreational importance in Australia. We applied a Bayesian hierarchical model of abundance to Murray Cod catch data collected as part of broad-scale, general condition monitoring in the Murray–Darling Basin. The model uses replicated sampling at spatially independent sites to disentangle the confounding effects of detection probability and abundance on catch data. We demonstrate the reliability of the analysis for determining trends in abundance with a simulation study, and we show that basinwide abundance of Murray Cod declined by over 50% between 2010 and 2013. We found that detection probability of Murray Cod can vary substantially across space and through time, suggesting that accounting for variable detection will be important in any future evaluation of Murray Cod populations. This study highlights variable detection as an issue in monitoring regimes and demonstrates a method for the cost-effective use of existing monitoring data to evaluate species abundance trends.

In 2009, Pacific Northwest National Laboratory (PNNL) evaluated the Touchet Consolidated Facility to determine if it is designed, constructed, operated, and maintained to effectively provide juvenile salmonids with safe passage past the diversion and back to the Touchet River. Completed in 2008, the Touchet Consolidated Facility combined two irrigation diversions with an existing intake for the Touchet Acclimation Facility. The consolidated facility includes a separate fish screen and intake for each user, a pool and chute fishway, and an adult fish trap. The fish screens portions of the facility were evaluated on April 20, 2009, using underwater videography, acoustic Doppler velocimeter measurements, and visual observations while water was diverted to the acclimation facility alone and again as water was diverted to the irrigation system and pond together. The facility is in good condition and is well maintained, although water velocities within the site do not meet the criteria set by the National Marine Fisheries Service (NMFS). Approach velocities above 0.4 ft/s at the upstream end of the facility and decreases in sweep velocity toward the bypass are likely caused by the proximity of the upstream screen to the spill over stoplogs that control flow at the upstream end of themore » forebay. We recommend working with Touchet Acclimation Facility staff to try different configurations and heights of forebay stoplogs while PNNL staff measure water velocities, allowing real-time monitoring of changes in approach and sweep velocities resulting from the configuration changes. It may be possible to bring approach and sweep velocities more in line with the NMFS criteria for juvenile fish screens. We also recommend evaluating the facility later in the year when river levels are low and the irrigation district is the only water user. During the site visit, it was noted that the upstream end of the fishway has relatively closely spaced louvers that point downstream. During higher river levels such as on April 20, the orientation of the louvers causes a headloss of up to 1 ft or more. Fish must maneuver through this hydraulic jump and between the louvers. The Washington Department of Fish and Wildlife is considering alternatives to this configuration; if needed, we would be available to offer technical assistance.« less

Each year, millions of fish are extracted from Australian waterways by the pumping and diversion of water into irrigation systems. Fish protection screens can help reduce these losses but are largely untested in Australian rivers. In this study, a large, gravity‐fed irrigation offtake on Gunbower Creek, Victoria, Australia, was investigated for fish and debris entrainment. Experiments were performed under screened and unscreened conditions across various river flows. Mark–release–recapture experiments were undertaken with fingerlings of two recreationally significant fish species, Murray cod (Maccullochella peelii) and golden perch (Macquaria ambigua), together with wild fish community assessments, to determine how effective the screen was at reducing fish entrainment into the irrigation channel. The mean percentage of recaptured fingerlings was significantly lower when the irrigation channel offtake was screened compared with unscreened. Entrainment of released fish into the irrigation channel was reduced by &gt;98%. Similarly, wild fish entrainment was significantly lower when the irrigation channel was screened. When screened, fewer wild species dominated the sampled fish community, and entrained fish were generally &lt;40 mm in length. Debris loads decreased significantly in the irrigation channel owing to the screen, indicating the economic benefits of fish screens. Implementing screens could aid in native fish conservation efforts in riverine environments.

Murray cod is a top-order carnivore with high culture potential. Currently, there are no commercial diets formulated specifically for Murray cod. In this study, results of two growth trials on Murray cod (80–83.5-g mean initial weight), conducted in commercial settings, using two laboratory-formulated diets (DU1 and DU2; 48.9% and 49.1% protein, and 16.9% and 16.1% lipid, respectively, on a dry matter basis), and two commercial diets, formulated for other species (salmon – CD/S and barramundi – CD/B) but used in Murray cod farming are presented. The two commercial diets had less protein (46.6% and 44.4%) but higher lipid (21.7% and 19.5%). The energy content of the feeds tested was similar (about 20–22 kJ g−1). The growth performance and feed utilization of Murray cod did not differ significantly amongst the diets, but the food conversion ratio and % protein efficiency ratio in fish fed the DU1 and DU2 diets were consistently better. There was significantly less carcass and muscle lipid deposition in fish fed with the latter diets. Of the fatty acids in muscle, the lowest amounts (in μg mg lipid−1) of n-3 (262.5±2.9), n-6 (39.8±0.9) and polyunsaturated fatty acid (PUFA) (302.3±3.8) were observed in fish fed CD/S, and the highest in fish fed DU2 and CD/B. Fatty acids 16:0 and 18:0, 18:1n-9 and 16:1n-7, and 22:6n-3, 20:5n-3, 22:5n-3 and 18:2n-6 were the dominant fatty acids amongst the saturates, monoenes and PUFA, respectively, and accounted for 80.8–88.7% of all identified fatty acids (23) in muscle of Murray cod. The study showed that Murray cod could be cultured successfully on a diet (DU2) containing 20% soybean meal without compromising growth and/or carcass quality. Differences in the proximate composition and fatty acid composition of muscle of wild and farmed Murray cod were observed, the most obvious being in the latter. Wild Murray cod had significantly less (P<0.05) saturates (192.6±1.84 vs. 266.3±3.51), monoenes (156.5±8.7 vs. 207.6±6.19), n-3 (145.2±5.24 vs. 261.8±3.2) but higher n-6 (144.3±2.73 vs. 48.3±1.38) in muscle (all values are in μg mg lipid−1) than in farmed fish. Wild fish also had a much lower n-3 to n-6 ratio (1.0±0.03 vs. 5.4±0.09).

The use of freshwater for human consumption and agriculture has resulted in many wetland ecosystems being some of the most seriously impacted ecosystems in the world. In attempts to rehabilitate wetland ecosystems environmental flows are used to restore parts of the hydrological regime altered by human water use. The use of environmental water intends to improve ecosystem health, but frequently aims to have specific outcomes for populations of higher-order consumers such as iconic fish and bird species. To date, research and monitoring has mainly focused on understanding ‘flow-ecology’ relationships, without investigating the mechanisms underlying them. We sought to understand the importance of different basal food sources to the growth of the endangered Murray cod in temporary wetland systems using fatty acid biomarkers. We flooded replicate mesocosms with two different wetland soils to produce sufficient zooplankton prey to sustain and grow Murray cod larvae for approximately 2 weeks. The fatty acid profiles of Murray cod and percentages of different biomarkers were compared at the start and finish of the experiment and our results suggest that the most important basal food source is green algae. However, the biomarkers of diatoms, cyanobacteria and bacteria also increased and differed between wetlands with different hydrological regimes. It is unclear if our results can be extended to other wetland systems and we encourage further research both into the relationship between length of wetland flooding and invertebrate densities in other systems. We also encourage research into the mechanistic pathways in which green algae carbon is transferred through food webs to higher order consumers in wetland systems to help generalise our results to other wetlands and support the management of wetlands through the timing and duration of flooding from environmental water.

Sampling Murray Cod (Maccullochella peelii) Larvae in an Upland River