Academic literature on the topic 'Carp Murray-Darling Basin'

Salinisation in the Murray–Darling Basin, Australia, may affect aquatic flora and fauna, including the common carp, an alien species that has become the most common fish in the river system. This study describes the responses of juvenile carp (31–108 mm total length) to salinity levels that prevail in some wetlands of the lower reaches of the River Murray. Carp are moderately tolerant of salinity (direct transfer LC50: 11 715 mg L–1), particularly after slow acclimation (LC50: 13 070 mg L–1), but sub-lethal effects are evident at lower salinities. These include effects on osmoregulation (>7500 mg L–1), behaviour (7500–12 500 mg L–1) and sperm motility in mature fish (150–300 mm) (8330 mg L–1). Salinities in some Murray–Darling Basin wetlands already approach half seawater (17 500 mg L–1) and carp populations in these important nursery areas could be impacted through sub-lethal effects on adults and lethal effects on juveniles, eggs and sperm.

Regionalisations based on species assemblages are a useful framework for characterising ecological communities and revealing patterns in the environment. In the present study, multivariate analyses are used to discern large-scale patterns in fish assemblages in the Murray–Darling Basin, based on information from the Murray–Darling Basin Authority’s first Sustainable Rivers Audit (SRA), conducted in 2004–2007. The Basin is classified into nine regions with similar historical fish assemblages (i.e. without major human intervention), using data that combine expert opinion, museum collections and historical records. These regions are (1) Darling Basin Plains, (2) Northern Uplands, (3) Murray Basin Plains, (4) Northern Alps, (5) Central East, (6) Avoca Lowland, (7) Southern Slopes, (8) Southern Alps and (9) South-Western Slopes. Associations between assemblages and physical variables (catchment area, elevation, hydrology, precipitation, temperature) are identified and used to reinforce the definitions of regions. Sustainable Rivers Audit data are compared with the historical assemblages, highlighting species whose range and abundance have changed since the early 19th century. Notable changes include declines in native species such as silver perch, river blackfish, mountain galaxias, Macquarie perch, trout cod and freshwater catfish, and the advent of alien species including common carp, eastern gambusia, goldfish, redfin perch, brown trout and rainbow trout. Less significant declines are evident for native carp gudgeons, golden perch, two-spined blackfish, bony herring and flathead gudgeon. Changes are evident even in regions where habitats have been little disturbed in the past 200 years.

Non-native common carp (Cyprinus carpio L.) are the most abundant large-bodied fish in the Murray–Darling Basin. The abundance of common carp larvae and young-of-the-year appears to increase after flooding, although the relative contribution of floodplain habitats compared to riverine areas remains unresolved. Larval nets were used monthly from September 2000 to January 2001 to identify common carp spawning and recruitment areas in the regulated Murray River and floodplain around the Barmah–Millewa forest. Five non-native and five native fish species comprising 136 111 individuals were collected, with common carp constituting 88% of the overall catch. Less than 1% of common carp, however, originated from the Murray River upstream of the Barmah–Millewa floodplain. Consequently, this floodplain appears to be a major source of common carp recruitment in the mid-Murray area. Conversely, eggs from large-bodied native fish were only present in the Murray River and not the Barmah floodplain. There are opportunities for common carp control in this area, to potentially reduce populations in a wider river reach. Implementation of common carp control measures in the Barmah–Millewa floodplain should be further investigated, particularly with regard to seasonal irrigation flows, obligatory migration routes and in the timing of future large-scale environmental water allocations.

AbstractThere is a paucity of information on the diversity and occurrence of freshwater fish parasites in Australia. This study investigates the distribution and occurrence of a parasitic nematode of the genusContracaecumin freshwater fish from south-eastern Australia. Fish (n= 508) belonging to nine species and eight families were collected from eight wetlands associated with the Murrumbidgee River floodplain in the southern Murray–Darling Basin and subjected to laboratory examination. Third-stage nematode larvae were found in eight of the nine fish species. The exception was the fly-specked hardeyhead (Craterocephalus stercusmuscarum), although only one specimen of this species was examined. Nematode larvae were identified asContracaecum bancroftiusing a combined morphological and molecular approach. The parasite was most prevalent in weather loach (Misgurnus anguillicaudatus; 34.8%) and Australian smelt (Retropinna semoni; 21.4%), followed by carp (Cyprinus carpio; 9.5%), of which the former and latter are non-native species.Contracaecumprevalence differed between locations, with Two Bridges having the highest number of infected fish. This may be due to the higher number of suitable host species collected at these localities.Contracaecumspp. are parasites with low host specificity that have also been reported in Australian marine fish, humans and piscivorous birds. The high parasite prevalence in the two abundant non-native fish species in the region suggests that they act as a suitable host for this endemic parasite, resulting in the increase in the parasite population. It would be interesting to study host–parasite interactions in this area, especially if introduced fish populations declined dramatically in the attempt to eradicate them or control their population.

Common carp, Cyprinus carpio, is a highly invasive fish species across freshwater systems of south-eastern Australia, and especially in semi-arid floodplain wetlands. However, multi-component, large-scale experimental studies on carp effects on such ecosystems are scarce. This is in spite of demands to prioritise management and control of carp for the rehabilitation of habitats across the Murray–Darling Basin. A 2-year, large-scale field experiment in a terminal wetland of the lower River Murray (South Australia) evaluated the effects of free-ranging carp on water transparency, aquatic macrophytes (biomass and cover), zooplankton density, benthic invertebrates (density, richness and diversity) as well as native fish. Within 1 year since artificial inundation, transparency sharply decreased and this was accompanied by a decrease in aquatic macrophyte biomass and cover, a fluctuation in zooplankton density, and a decrease in benthic invertebrate richness and diversity. Also, the decreases in transparency and benthic invertebrate richness were significantly related to carp biomass, which averaged 68.0 kg ha–1 and induced a shift from clear- to turbid-water state. Following a flood event, increased connectivity caused carp to further access the newly inundated areas.

Macrobrachium rosenbergii nodavirus (MrNV)—the aetiological agent of white tail disease—is a major limiting factor of crustacean aquaculture as it causes up to 100% mortality in M. rosenbergii larvae and juveniles. Despite the importance of MrNV, there have been few studies on the phylogenetic diversity and geographic range of this virus in Australian waterways. Here, we detected MrNV genomes in common carp (Cyprinus carpio) metatranscriptomes sampled at five freshwater sites across the Murray-Darling Basin (MDB), Australia. We identified genetic divergence of the RNA-dependent RNA polymerase gene between MrNV sequences identified in the northern and southern rivers of the MDB. Northern viruses exhibited strong phylogenetic clustering with MrNV from China, whereas the southern viruses were more closely related to MrNV from Australia. However, all five viruses were closely related in the capsid protein, indicative of genetic reassortment of the RNA1 and RNA2 segments between Australian and introduced MrNV. In addition, we identified Macrobrachium australiense in two of the five MrNV-positive libraries, suggesting that these species may be important reservoir hosts in the MDB. Overall, this study reports the first occurrence of MrNV outside of the Queensland region in Australia and provides evidence for genetic reassortment between endemic and introduced MrNV.

There are over 6000 km of irrigation drains in the Murray-Darling Basin, Australia. The maintenance of aquatic plants may be critical to the utility of the watercourses in scavenging nutrients, yet the plants are often removed by extensive herbicide spraying and large-scale mechanical excavation and desilting. Results for four out of five experiments showed that water clarity improved when vegetation was left unmanaged. High concentrations of inflowing nitrate from subsurface tile drainage was quickly dissipated. There was an unexpectedly poor correlation between turbidity and phosphorus concentration overall; but in four experiments concentrations of total phosphorus declined during transport through vegetated stretches of channel. There was an important interaction between plant cover and sediment bioperturbation, since in bare stretches of channel the roiling of carp increased the concentrations of suspended sediments and nutrients. Irrigation drainage water quality may be improved by management of aquatic plants to trap suspended paniculate load and reduce the effects of carp.

Blackwater contains high levels of dissolved organic carbon that can be rapidly consumed by microbes, sometimes leading to extremely low levels of dissolved oxygen (hypoxia) and drastic consequences for aquatic life, including fish kills. Drought-breaking rains in late 2010 inundated large areas of the Barmah–Millewa Forest, southern Murray–Darling Basin, Australia, and resulted in a prolonged hypoxic blackwater event within the forest and the Murray River downstream. This study investigated the short-term effects of the blackwater event on fish and crayfish. Compared with non-affected sites, blackwater affected sites had: significantly higher abundances of emerged Murray crayfish (Euastacus armatus) that were vulnerable to desiccation, predation and exploitation; large numbers of dead or dying shrimp and yabbies; significantly reduced abundances of native fish; but contained similar abundances of alien fish species (particularly common carp, Cyprinus carpio). The nature of the mechanisms that caused these changes and the longer term significance of the event on the river system remains an important area for future research. We also propose a range of management considerations for reducing the blackwater impacts, such as the timing of environmental water delivery after prolonged drought and the importance of maintaining river–floodplain connectivity during flood periods.

Six rivers within the upper Mumbidgee catchment were sampled for larval and juvenile fish. The rivers represented both regulated and unregulated flow regimes and varied widely in size. There was wide variation in the larval fish communities supported by each river, both in terms of the species diversity and total abundance of fish sampled. The highly regulated reach of the Mumbidgee River sampled during this study had the highest numbers of native species and native individuals of any river sampled. In the two rivers selected for further study, the Murmmbidgee and Goodradigbee, there was a high level of inter-annual consistency in the species composition within the reaches sampled, despite considerable change in the temperature and flow regimes of both rivers. This indicates that at least some spawning of those species sampled may occur each year, regardless of environmental conditions. Estimates of the relative abundance of each species sampled changed markedly between years, and it is argued, on the basis of growth information contained in the otoliths, that differential survival of larvae and juveniles was largely responsible for this shift in relative abundance. Otolith microstructure provided information on the date of spawning and early growth patterns of all species sampled in the upper Mumumbidgee catchment. In addition to determining the age and thus 'birth-date' of an individual, the effect of a particular event or series of events has on growth, and subsequent survival, is permanently recorded in the otolith microstructure. This enables accurate back-calculation and correlation to management actions or natural events. No other research tool has this ability to retrospectively assess, on a daily basis, the impacts of management actions on condition and subsequent survival of fish larvae. Species sampled could be separated into three groups based on spawning requirements; those linked with flow, those linked with temperature and generalist species that appear to have river independent cues, such as photoperiod or moon phase. Patterns in growth rate during the early life history stages enabled quantification of the consequences of variation in environmental conditions on the survival and recruitment of various species. Growth was not always highly correlated with water temperature, in fact, for mountain galaxias, high temperatures appear to negatively affect larval condition and subsequent survival. Conversely, carp exhibited a strategy more consistent with common perceptions, with growth and survival increasing with increasing temperature. The study uncovered spawning and growth patterns that were unexpected. Age analysis of western carp gudgeon demonstrated that they had undertaken a mid-winter spawning, when the water temperature in the main channel was far lower than that at which spawning was previously recorded for this species. Redfin perch from the unregulated Goodradigbee River exhibited growth rates exceeding the published upper limits for this and other closely related species. This growth could not be correlated with either temperature or flow, indicating that there are additional factors that dominate growth rates of redfin perch in the Goodradigbee River. The proportion and abundance of native species alone is not necessarily indicative of a 'healthy' or pristine system; some native species may be positively affected by river regulation, at least as juveniles. Comparison of the current larval fish community with likely pre-European fish communities does provide an indication of change to the system. The results of this study suggest that larval fish growth rates can be strongly influenced by environmental conditions, thus providing a powerful tool for monitoring future change and the factors which cause it. This study has demonstrated the value of larval and juvenile fish age and growth information, derived from otolith microstructure techniques, for many aspects of river management. Current river management priorities for which these techniques provide unique information include the determination of environmental flow regimes and the control of undesirable exotic species such as carp.

<em>Abstract</em>.—The Murray-Darling basin produces about 40% of the total value of Australia’s agricultural output from 1.9 million ha of irrigated agriculture that represents around 75% of the nation’s total irrigation. Major reservoirs in the southeastern states regulate the basin’s river systems for irrigation but also provide recreational fisheries. One of these storages is Lake Eppalock in the state of Victoria, a multi-use impoundment built in 1964 covering 3,230 ha and holding 312,000 ML at full supply level. It has been actively developed as a mixed species recreational fishery (golden perch <em>Macquaria ambigua </em>and Murray cod <em>Maccullochella peeli</em>) and is a popular angling water. The principal recreational target species in the lake compete with invasive pest species (common carp [also known as European carp] <em>Cyprinus carpio</em>). Drought is part of the natural variability of the Australian climate and its rainfall history features several periods of a decade or longer that have been distinctly drought-prone. Eastern Australia was in the eighth year of the latest drought cycle in 2007, and Lake Eppalock had fallen to less than 1% of its full supply level. These conditions highlighted increasing competition for water and brought into focus the interdependence and linkages between fisheries management and water needs, both for irrigation and for the environment. Fisheries managers faced a very strong likelihood of extensive fish deaths in the lake and elsewhere that could cause significant long-term impacts requiring many years to recover the recreational fishery. A planned partnership approach with the storage water authority was adopted in 2006 for integrated fisheries and water management, with response actions targeted to achieve storage conditions ensuring the maximum survivability of key recreational angling species in the lake through the drought. The framework for cooperation established in this study provides an example for future water allocation disputes.