Peter C. Gehrke

Large-scale patterns in species richness and composition of temperate riverine fish communities, south-eastern Australia

Riverine fish in New South Wales were studied to examine longitudinal trends in species richness and to identify fish communities on a large spatial scale. Five replicate rivers of four types (montane, slopes, regulated lowland and unregulated lowland) were selected from North Coast, South Coast, Murray and Darling regions. Fishwere sampled during summer and winter in two consecutive years with standardized gear that maximized the range of species caught. The composition of fish communities varied among regions and river types, with little temporal variation. Distinct regional communities converged in montane reaches and diverged downstream. The fish fauna can be classified into North Coast, South Coast, Murray and Darling communities, with a distinct montane community at high elevations irrespective of the drainage division. Species richness increased downstream in both North Coast and South Coast regions by both replacement and the addition of new species. In contrast, species richness in the Darling and Murray regions reached a maximum in the slopes reaches and then declined, reflecting a loss of species in lowland reaches. The small number of species is typical of the freshwater fish faunas of similar climatic regions world-wide. Fish communities identified in this study form logical entities for fisheries management consistent with the ecosystem-focused, catchment-based approach to river management and water reform being adopted in Australia.

Australia's tropical river systems: current scientific understanding and critical knowledge gaps for sustainable management

Australia’s tropical river systems are poorly understood in comparison with Australia’s temperate freshwater and tropical marine systems. Tropical rivers convey ~70% of the continent’s freshwater runoff, and are increasingly being targeted for development. However, existing knowledge is inadequate to support policy for tropical regions that avoids repeating the environmental problems of water use in southern Australia. This paper summarises existing knowledge on the hydrogeomorphic drivers of tropical catchments, fluxes of sediments and nutrients, flow requirements and wetlands. Key research issues include improved quantification of available water resources, hydrological, biogeochemical and ecological linkages at systems scales, understanding and valuing ecosystem processes and services, and projecting the effects of long-term climate change. Two special considerations for tropical Australia are the location of major centres of government and research capacity outside the tropical region, and the legal title of much of tropical Australia vesting in Aboriginal communities with different cultural values for rivers. Both issues will need to be addressed if tropical research is to be effective in supporting resource management needs into the future. Systems-scale thinking is needed to identify links between system components and coastal enterprises, and to protect the environmental, social, and economic values of Australia’s tropical river systems.

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.

Acute Cardio-respiratory responses of Spangled Perch, Leiopotherapon unicolor (Gunther 1859), to Sublethal concentrations of Zinc, Temephos and 2,4-D

Spangled perch, Leiopotherapon unicolor, were exposed to concentrations of 5.0, 10 or 20 mg 1-1 zinc, 0.1, 1.0 or 10 mg 1-1 temephos or 0.1, 1.0 or 10 mg 1-1 2,4-D at 25oC for 2 h, during which time ventilation rate, heart rate and oxygen consumption were continuously monitored. Fish exposed to 10 and 20 mg 1-1 zinc demonstrated a significant increase in ventilation rate; those exposed to 20 mg 1-1 also developed a significant bradycardia. Exposure to 10 mg 1-1 temephos caused an immediate reduction in ventilation rate and oxygen consumption, and also reduced heart rate during the second hour of exposure. Fish exposed to 10 mg 1-1 temephos died within 12 h. Responses of fish to 2,4-D gave no indication of toxic effects on the cardio-respiratory system. Cardio-respiratory responses to zinc are attributed to damage caused to the gill epithelium, which results in impaired gas exchange and lowered oxygen tension in arterial blood. Effects of exposure to temephos correspond to cholinesterase inhibition in nerves supplying the respiratory musculature and the heart.

Sustainable futures for Australia's tropical rivers: introduction to current research and information needs

The Forum on Sustainable Futures for Australia’s Tropical Rivers was held at Charles Darwin University in Darwin in February 2004. The concept emerged in response to increasing social, political and business interest in the water resources of northern Australia, recognising the need for science to be proactive in providing the knowledge to guide current and future policy and decision making on the use of these rivers. Pressures on tropical systems worldwide are increasing and Australian systems are not isolated from this reality.The papers within this issue focus onAustralia, but the lessons learned and conclusions drawn are relevant to many parts of the world. There is a long history of interest in development of northern Australia and this is currently being fuelled by increasing pressure on water supply and river systems in southern regions. Tropical rivers and groundwater systems contain roughly 70% of Australia’s freshwater resources. Water availability has been the driver of many grand schemes in the past and there are many examples that have proven to be non-feasible, or which have had significant unforeseen environmental impacts. Further development of water resources in tropical Australia is likely to result in conflicting opinions concerning risks to environmental goods and services and cultural values, as well as the intended social and economic benefits. Land use across the Australian tropical region is dominated by grazing, agriculture, Aboriginal tenure and traditional use, mining and tourism, with significant fishing interests in estuaries and coastal waters. Current management priorities are focussed on water-resource planning, water quality, fisheries, invasive plants, salinity, conservation, grazing and fire management. Outside of catchments such as the Ord and Burdekin, which have existing irrigation areas, estimates of existing water use as a percentage of sustainable yield are low. Scientific understanding of rivers in southern Australia has largely developed in a reactive fashion as unforeseen consequences of earlier development decisions have become apparent. While some tropical catchments have been extensively developed and are now the focus of environmental management efforts, many catchments are relatively unchanged from their historical condition under traditional ownership. The combination of growing interest in water at a national level, development aspirations in the tropics and the relatively good ecological condition of tropical rivers provides an opportunity for science to lead the information needs for sound management of Australia’s tropical rivers into the future. The objectives of the forum were to assemble and synthesise existing scientific knowledge of Australia’s tropical river systems and to identify critical knowledge gaps for future research priorities. The forum covered catchments spanning tropicalAustralia from Broome in WesternAustralia to Rockhampton in Queensland, adopting a system-scale approach to the functioning of tropical rivers, their wetlands, floodplains, estuaries and near-shore environments, and the impacts of land use, water use and other activities. Forum themes covered present and future use and management of tropical rivers, aquatic ecosystem assets and threats, tropical aquatic ecosystem processes, the role of flow and connectivity in tropical rivers and information needs to protect tropical rivers in the face of increasing development pressure. Erskine et al. (2005) review the geomorphological template of tropical Australian rivers and present a detailed typology of characteristic reaches. The template provides a sequential spatial framework for the ecological function of tropical rivers, with clear implications for the fish communities likely to be encountered in each region. Wetlands are characteristic geomorphic habitat features of tropical Australia that support high levels of biodiversity, but large areas of wetlands have been lost or are under threat from human activities in some regions. Finlayson et al. (2005) offer an analysis of the drivers behind the changing face of tropical wetlands, including both direct drivers and the less direct social attitudes that encourage or allow wetlands to be degraded. They propose a model based on inventory, assessment and monitoring to maintain the character of tropical