Fish on the run: facilitating fish passage from drying floodplains

In the Murray-Darling Basin, river managers are implementing site-scale managed floodplain inundations for vegetation outcomes but there is a risk of native fish stranding during floodplain recession due to the absence of natural cues. In 2014, at the 5,000 ha Gunbower floodplain, central Murray River, we devised a fish exit strategy which included: (i) a fish ‘exit hydrograph’, a designed recession to cue fish to leave the floodplain, (ii) evaluation of a new fishlock to facilitate fish passage from the floodplain to the permanent Gunbower Creek. During our evaluation of the exit strategy we collected 113,099 fish exiting the fishlock at up to 20,000 fish/hr, with juvenile non-native carp, native Australian smelt and native carp gudgeons dominating the catch. Fish were 15-500 mm long. Native fish exited the floodplain during the initial drop where carp exited during the later half of the recession. In addition, 30 golden perch were acoustic tagged to identify their floodplain exit pathways. The implications of our results are discussed in the context of maximizing safe exit of fish from other temporary floodplain habitats

Optimisation of Fishway Entrance and Exit Conditions Using Physical Modelling: SARFIIP Pike Floodplain Regulator and Fishway Designs

As part of SARFIIP, Jacobs and Kingfisher Research prepared designs for two integrated regulator and fishway structures at the Pike floodplain for SA Water, DEW and the MDBA. These structures will enable the future managed inundation watering of Pike during regulated river flows to restore floodplain health and fish passage connectivity through the floodplain. A successful floodplain flow regulator and fishway design requires that fish are able to readily locate and enter the downstream entrance. The entrance must be located at the ‘limit of fish migration’, represented by either a wall or a line of turbulence below the regulator gate that fish cannot pass. The upstream fishway exit must be located where fish are not drawn back downstream over the gates. To confirm the optimal fishway entrance and exit arrangements, a 1:15 scale physical model was constructed and tested at the UniSA AFMG facilities. The model was designed to enable the performance of critical elements to be identified and if necessary, quickly adjusted. The sheet-metal model incorporated six lay-flat regulator gates and an adjustable downstream fishway entrance. The model was tested for variable scaled passing flows up to 3,000 ML/d. The modelling revealed the existence of complex hydraulics and the need to maintain the integrity of attraction flows to the fishway entrance. A ‘flow straightening wall’ was incorporated to ensure positive velocity vectors downstream of the entrance. A nib wall was provided across the regulator below the overshot gates to form the ‘limit of fish migration’, aligning with the fishway entrance. The location of the fishway upstream exit was also confirmed and the optimised arrangements demonstrated to the client. In summary, low-cost physical modelling was undertaken to optimise the fishway designs and provide certainty to the biological functionality of the structures and this helped maximise ecological value for investment

Control of globally invasive common carp: a 10 year commercial trial of the Williams\u27 carp separation cage in a Murray River fishway

Common carp Cyprinus carpio, are a highly migratory pest fish in Australia, North America, New Zealand and parts of Europe. Fishways built to facilitate native fish passage also benefit invasive carp. The Williams’ cage was developed to separate carp from native fish as they pass through fishways by exploiting their unique jumping behaviour. We report on a 10-year commercial application in a fishway on the lower Murray River (SE Australia) where a high biomass of carp resides. Between November 2007 and April 2017, the automated Williams’ cage was installed and operated at Lock 1 by a collaborative team of river managers, weir keepers, commercial fishers and researchers. To date, over 700 tonnes of adult carp, (approx. 350,000 fish) have been removed at a maximum rate of 5 tonnes per day. The income generated from the sale of the fish has far exceeded set up costs. Catches and separation efficiencies were highest in spring (Austral) when fish were migrating to spawn. During the cage design phase, refinements helped reduce bycatch of non-target native fish to practically zero (0.03%) and informed future designs, application and operation. The Williams’ cage has now successfully moved from an experimental idea to full commercial viability and could play a key role in controlling the dispersal and abundance of carp where high abundances preside and collaborative management alliances can be formed

Exploring ways to deliver better fishway management

Victorian Waterway Management Strategy provides the framework for government, in partnership with the community, to maintain or improve the condition of rivers, estuaries and wetlands so that they can continue to provide environmental, social, cultural and economic values and includes actions specifically aimed at fishway management in Victoria. This presentation discusses the history (and issues) with many of our current fishways and future fishway management in the context of the policy and actions outlined in the Strategy. Actions and approaches to achieve these outcomes include recently released guidelines outlining contemporary performance, design and monitoring of fishways in Victoria and exploring ways to deliver better fishways. These fishway guideline documents are intended to create a consistent approach to fishway management across the state and together with potential future management strategies will ensure improved river connectivity into the future

Cost Effective Modelling to Improve the Functionality of the Broken Creek Rice’s Weir and Kennedy’s Weir Vertical Slot Fishways

Acknowledgement Goulburn-Murray Water Broken Creek in north-central Victoria flows into the River Murray upstream of Barmah. There are 10 low-head (\u3c2 m high) weirs on Broken Creek which all have vertical slot fishways however these have high turbulence (i.e. 75 W/m3) and thus limited functionality for several species of native small and medium sized fish (i.e. \u3c300 mm long). In late 2017, the Victorian government (DELWP) engaged Jacobs and Kingfisher Research to hydraulically model the Rices and Kennedy’s Weir fishways to prepare conceptual designs for retro-fitted ‘key-hole’ slots to reduce pool turbulence and demonstrate potential for improvement in functionality to pass much smaller fish (i.e. \u3e50 mm long). Jacobs applied a Microsoft Excel based fishway model which takes fishway geometry, calibrated slot discharge coefficient data, and headwater/tailwater ranges, and uses these data to predict individual pool turbulence, depth and slot velocity. These hydraulic outputs were combined with fish swimming ability, maximum allowable turbulence, and minimum water depth to graphically demonstrate water level ranges for which each fishway could pass small, medium and large-sized native fish. Conceptual level ‘key-hole’ slot designs were then developed, reducing slot areas and flow rates and enabling passage of all fish sizes. The modelling showed that The theoretical implementation of ‘key-hole’ slots effectively halved the fishway discharge and reduced the pool turbulence to 35 W/m3, the known threshold suitable for passage of small-sized native fish. This project demonstrated the efficiency of Microsoft Excel based modelling to bring together both fishway hydraulics and fish biology, with novel design options rapidly evaluated for a low cost. Graphical fishway operation tables were automatically produced for the full range of site operational conditions without the need for costly post-processing of model results. GBCMA propose to retrofit key-hole slots to Rice’s and Kennedy’s weir fishways to improve their performance during 2018

A cautionary tale about the inhibitory effects of gated culverts on fish passage restoration efforts

Connectivity between river-floodplain habitats has been heavily constrained in many large tropical river systems by the construction of regulators, levees and other physical barriers. Fishways are being constructed to ameliorate the effects of these barriers; but it is important that all aspects of fishway design cater for local target species. We investigated the lateral movement patterns of Lower Mekong Basin fish in Laos, through a fishway that incorporated a series of cones, resting pools, and a culvert with a vertical lift gate. Fish needed to negotiate all of these structures to move from the Mekong to an adjacent wetland. We tested the hypothesis that gated culverts may hamper the effectiveness of fishways, by comparing the abundance and species richness of fish at three locations along the path of the fishway and culvert: (1) the fishway entrance; (2) the fishway exit; and (3) the culvert exit (i.e. immediately upstream of the culvert). There were no marked differences in the total abundance and species richness of fish between the fishway entrance and culvert exit while the river remained at levels where the culvert was only partially inundated. Nevertheless, the abundance and species richness of fish were markedly lower at the culvert exit than at the fishway entrance and exit once the headwater levels rose to where the culvert was completely inundated. These findings indicate that fish were able to ascend the fishway but not the culvert once it became completely submerged, and thus support the hypothesis that gated culverts can hamper the effectiveness of fishways in facilitating the lateral movement of fish in large tropical systems. Fish passage at such installations can be enhanced through optimised operating regimes. Ensuring that headwater levels remain below the culvert ceiling is likely to be the best way to maximise fishway effectiveness

Populated and Remote Reefs Spanning Multiple Archipelagos Across the Central and Western Pacific

Comparable information on the status of natural resources across large geographic and human impact scales provides invaluable context to ecosystem-based management and insights into processes driving differences among areas. Data on fish assemblages at 39 US flag coral reef-areas distributed across the Pacific are presented. Total reef fish biomass varied by more than an order of magnitude: lowest at densely-populated islands and highest on reefs distant from human populations. Remote reefs (<50 people within 100 km) averaged ∼4 times the biomass of "all fishes" and 15 times the biomass of piscivores compared to reefs near populated areas. Greatest within-archipelagic differences were found in Hawaiian and Mariana Archipelagos, where differences were consistent with, but likely not exclusively driven by, higher fishing pressure around populated areas. Results highlight the importance of the extremely remote reefs now contained within the system of Pacific Marine National Monuments as ecological reference areas