John D. Koehn

Fish, flows and flood plains: Links between freshwater fishes and their environment in the Murray-Darling River System, Australia.

Knowledge of the biology of native fishes of the Murray-Darling Basin is based largely on studies conducted under hatchery conditions and on a limited number of recreationally important species. From observations that increases in water level in aquaculture ponds initiate spawning in some species, and from limited studies of wild fishes and studies in overseas floodplain river systems, a perception has emerged of the importance of flooding and the flood plain in the life cycles of Murray-Darling fishes in general. However, there is little confirmatory evidence of the use of temporary floodplain habitats by larvae, juveniles or adults. The significance of in-channel habitats, especially for rearing, has received little attention. Murray-Darling fish species can be placed into three life history modes, based mainly on spawning style and time and developmental intervals of larvae at first feeding. Fish in each group may be able to take advantage of floods if the timing is right and prey are plentiful, however, the larvae of some species are able to recruit under non-flood conditions within the main river channel. This forms the basis of the ‘low flow recruitment hypothesis’, which attempts to explain why some species spawn during the warmest months and lowest flows and how they are able to recruit under these conditions. This hypothesis is then placed in the context of the current state of knowledge of the relationships between flow and the biology of Murray-Darling fishes, specifically cues for spawning, movement and recruitment. The lack of widespread evidence for floodplain use by any life history interval of fish may be due to a paucity of study, however, there are some fundamental factors, such as the predictability of timing and duration of high flow events as well as the lack of coincidence of high flows and high temperatures in some regions of the Basin, which may be important in determining the use of floodplain habitats by fish.

Climate change and Australian marine and freshwater environments, fishes and fisheries: synthesis and options for adaptation

Anthropogenic climate change is already apparent and will have significant, ongoing impacts on Australian fishes and their habitats. Even with immediate actions to reduce greenhouse gases, there will be sustained environmental changes. Therefore, it is necessary to consider appropriate adaptations to minimise detrimental impacts for both fishes and the human populations that utilise them. Climate change will have a range of direct effects on the physiology, fitness, and survivorship of Australia’s marine, estuarine and freshwater fishes, but also indirect effects via habitat degradation and changes to ecosystems. Effects will differ across populations, species and ecosystems, with some impacts being complex and causing unexpected outcomes. The range of adaptation options and necessary levels of intervention to maintain populations and ecosystem function will largely depend on the vulnerability of species and habitats. Climate change will also have an impact on people who depend on fishes for food or livelihoods; adapting to a new climate regime will mean trade-offs between biological assets and socioeconomic drivers. Models can be used to help predict trends and set priorities; however, they must be based on the best available science and data, and include fisheries, environmental, socioeconomic and political layers to support management actions for adaptation.

Priority management actions for alien freshwater fish species in Australia

Abstract In Australia, alien freshwater fish are continuing to steadily increase in number of species (reported in this paper to be 43), abundance, and distribution. In general however, their impacts are not well quantified in either environmental or economic terms and current management to reduce their impacts is limited and lacking direction. Although carp Cyprinus carpio have received some attention, very little is known about the impacts and even the distribution of most species. There is a lack of recognition of the problem, inconsistency in legislation, policy, and approaches across jurisdictions, and no nationally coordinated on‐the‐ground management actions. Where legislation and policy is available it is not always used to good effect. This paper provides a synthesis of existing knowledge of alien fishes in Australia, suggests a new management approach, and recommends priority management actions.

Contribution of climate change to degradation and loss of critical fish habitats in Australian marine and freshwater environments

Australiasaquaticecosystemsareunique,supportingahighdiversityofspeciesandhighlevelsofendemism; however, they are also extremely vulnerable to climate change. The present review assesses climate-induced changes to structuralhabitatsthathaveoccurredindifferentaquaticecosystems.Climaticimpactsareoftendifficulttodiscernagainst the background of habitat degradation caused by more direct anthropogenic impacts. However, climate impacts will become more pronounced with ongoing changes in temperature, water chemistry, sea level, rainfall patterns and ocean currents. Each of these factors is likely to have specific effects on ecosystems, communities or species, and their relative importance varies across different marine and freshwater habitats. In the Murray-Darling Basin, the greatest concern relates to declines in surface water availability and riverine flow, owing to declining rainfall and increased evaporative loss.OntheGreatBarrierReef,increasingtemperaturesandoceanacidificationcontributetosustainedandongoinglossof habitat-forming corals. Despite the marked differences in major drivers and consequences of climate change, the solution is always the same. Greenhouse-gas emissions need to be reduced as a matter of urgency, while also minimising non- climatic disturbances. Together, these actions will maximise opportunities for adaptation by species and increase ecosystem resilience.

Observations on the distribution and abundance of carp and native fish, and their responses to a habitat restoration trial in the Murray River, Australia

Abstract A native fish strategy has been initiated to rehabilitate native fish populations in the Murray‐Darling Basin, Australia. The reintroduction of large woody debris (LWD) into the Basins large lowland rivers is one of the restoration activities in the strategy. The results from three separate studies undertaken on the Murray River between Yarrawonga and Tocumwal are presented on the relationship between carp (Cyprinus carpio), native species, and LWD to examine whether native species and carp compete for LWD habitat. The first study reports on the relative abundance of carp and native fish in a river reach. Since 1995 carp abundance has declined, whereas the abundance of native fish populations has remained relatively constant providing little support for the hypothesis that competition for LWD habitat is having effects at the population level effects. The second study reports on the relationship between LWD, river channel position, and its use as habitat by carp and native species. A statistically significant relationship was observed between native fish, LWD, the location within a meander, and curvature of the meander. There was no statistically significant relation between carp and any of these parameters indicating that carp utilise a variety of riverine habitats, whereas native species were strongly associated with LWD. The third study reports on an experiment that tested the response of carp to the placement of new LWD habitat. The response from carp was statistically inconclusive. The combination of these studies suggest that it is unlikely that carp and native species are directly competing for LWD habitat and it is unlikely that carp will inundate restored LWD habitats and preclude native species.

Using biological information to support proactive strategies for managing freshwater fish during drought

This paper provides an assessment of the biological attributes of fish species in south-eastern Australia and rates their potential risk from the impacts of drought. We used scientific literature and expert opinion to conduct a semiquantitative assessment of attributes considered to influence species resistance and resilience to drought for 15 freshwater fish species found in south-eastern Australia. We also present a conceptual framework to guide management of fish populations during drought. The framework focuses on (1) quantifying spatial variation in the severity of drought impacts on particular habitats (rivers, wetlands etc.), (2) assembling information on drought sensitivities of regionally important species, (3) identifying high risk areas (based on species sensitivity and drought severity), (4) determining and implementing appropriate management actions (pre-emptive, responsive), (5) monitoring outcomes and (6) disseminating information on outcomes. In many regions, historic population declines will serve to exacerbate the impacts of drought, and thus are a major threat to successful recovery from drought. Although we discuss both long-term, pre-emptive planning and short-term, responsive management actions, we contend that a long-term view is required to successfully address the threats posed by drought. Furthermore, although droughts clearly represent a severe disturbance to fish populations, ultimately it is anthropogenic factors that exacerbate drought and constrain recovery pathways (at global, regional and local scales), rather than drought per se. These factors must be addressed if we are to ensure the long-term viability of fish populations in inland aquatic ecosystems.

Collection and distribution of the early life stages of the Murray cod (Maccullochella peelii peelii) in a regulated river

The Murray cod (Maccullochella peelii peelii) is a large fish species keenly sought by anglers. However, this species has declined in distribution and abundance and is now listed nationally as vulnerable. This study was undertaken in the Ovens and Murray rivers, to collect larvae and age-0 Murray cod and determine the distribution of larval Murray cod around the mid-Murray River irrigation storage of Lake Mulwala. Murray cod larvae were collected from 17 of 18 sites: main channels and flowing anabranch channels of regulated and unregulated rivers, sites upstream and downstream of the lake, in the upper and lower reaches of the lake, and in the outflowing Yarrawonga irrigation channel. Larval Murray cod were collected only by methods that sampled drift in flowing waters. Age-0 Murray cod were collected by electrofishing in the main river, but not in off-channel waters, suggesting that cod are likely to settle into habitats in the main channel at a post-larval stage. The widespread occurrence of drifting larvae suggests that this species may be subject to previously unrecognised threats as they pass through hydro-electric power stations or become stranded in anabranch and irrigation channels. Results of this study are likely to be applicable to other species with drifting larval stages, and are relevant to other locations in the Murray–Darling Basin.

Improving ecological response monitoring of environmental flows.

AbstractEnvironmental flows are now an important restoration technique in flow-degraded rivers, and with the increasing public scrutiny of their effectiveness and value, the importance of undertaking scientifically robust monitoring is now even more critical. Many existing environmental flow monitoring programs have poorly defined objectives, nonjustified indicator choices, weak experimental designs, poor statistical strength, and often focus on outcomes from a single event. These negative attributes make them difficult to learn from. We provide practical recommendations that aim to improve the performance, scientific robustness, and defensibility of environmental flow monitoring programs. We draw on the literature and knowledge gained from working with stakeholders and managers to design, implement, and monitor a range of environmental flow types. We recommend that (1) environmental flow monitoring programs should be implemented within an adaptive management framework; (2) objectives of environmental flow programs should be well defined, attainable, and based on an agreed conceptual understanding of the system; (3) program and intervention targets should be attainable, measurable, and inform program objectives; (4) intervention monitoring programs should improve our understanding of flow-ecological responses and related conceptual models; (5) indicator selection should be based on conceptual models, objectives, and prioritization approaches; (6) appropriate monitoring designs and statistical tools should be used to measure and determine ecological response; (7) responses should be measured within timeframes that are relevant to the indicator(s); (8) watering events should be treated as replicates of a larger experiment; (9) environmental flow outcomes should be reported using a standard suite of metadata. Incorporating these attributes into future monitoring programs should ensure their outcomes are transferable and measured with high scientific credibility.

A Bayesian Belief Network Decision Support Tool for Watering Wetlands to Maximise Native Fish Outcomes.

Wetlands are productive and diverse habitats for native fish but can be highly degraded, particularly in the Murray-Darling Basin (MDB), south-eastern Australia. Wetland management requires tools and processes that facilitate the synthesis and application of knowledge for decisions concerning the allocation of environmental water to wetlands to improve environmental outcomes. This paper describes the development of a Decision Support Tool (DST), based on a Bayesian Network designed to provide the best available science and support adaptive management of environmental flows into wetlands. The DST predicts the probability of improvements in fish population health as defined by abundance, population structure and fish condition for introduced common carp and three native species of fish: carp gudgeon, Australian smelt, and golden perch. Model sensitivity and validation showed that fish response varied depending on model inputs, but that responses from the DST were an accurate reflection of fish responses in wetlands based on field data. Ultimately, the success of this DST is dependent on its adoption by wetland managers. Throughout the entire development process, adoption of the DST has been promoted through engagement with managers and subsequently, through initiatives to integrate it into current management initiatives.

Using radio telemetry to evaluate the depths inhabited by Murray cod (Maccullochella peelii peelii)

Radio telemetry is widely used in studies of freshwater fishes, but the vertical position of fish in riverine environments is rarely reported. The present study tested the application of radio transmitters fitted with depth sensors to determine the vertical position of Murray cod in the lower Ovens River in south-eastern Australia. As the scale of depths in rivers is usually limited (<10 m in the present study), there is a greater need to assess measurement error. The study first involved trials to define depth measurement errors, and a mean relative bias of 9% (range 1.5–14.8%) towards greater depth was recorded. These data were then used to correct the depths recorded from tagged fish. Although data from this preliminary study are somewhat limited, results from the tagged fish showed that by day they all occupied the lower 15% of the water column, indicating that Murray cod exhibit demersal behaviour, using bottom rather than mid-water habitats. Although the present study highlights the importance of tag trials in determining errors, it also indicates the potential application of this technique to understanding the depth-integrated habitat preferences of Murray cod and other species.