Robert G. Doupé

Effects of salinisation on riparian plant communities in experimental catchments on the Collie River, Western Australia

Although the salinisation of streams has long been recognised as one of Western Australias most serious environmental and resource problems, there is very little published information on the effects of salinisation on riparian flora and fauna. We studied riparian vegetation in three experimental catchments on the Collie River in Western Australia. The catchments are situated within a 5-km area of state forest and are geologically and botanically similar, but differ in the extent of clearing, groundwater levels and stream salinity. In each catchment, transects were taken perpendicular to the direction of streamflow, and 4-m2 quadrats taken along each transect. Within each quadrat, soil salinity was measured, all plants were identified to species level and percentage cover estimated. The catchments differed significantly in soil salinity, with salinity being greatest in the most extensively cleared catchment and increasing towards the floor of the valley. Plant-species richness, species diversity and species composition were significantly related to soil salinity, both among catchments and among quadrats within the most extensively cleared catchment. Plant-species richness and diversity decreased with increasing soil salinity, an effect that may be partly due to a decline in perennial herb and shrub species. This may have an impact on other components of the riparian ecosystem.

Parasites of native and exotic freshwater fishes in south-western Australia

In this study, 1429 fishes of 18 different species (12 native and six exotic) were sampled from 29 localities to compare the levels of parasitism between native and exotic fish species and to examine the relationship between environmental degradation and parasite diversity. Forty-four putative species of parasites were found and most of these appear to be native parasites, which have not previously been described. Two parasite species, Lernaea cyprinacea and Ligula intestinalis, are probably introduced. Both were found on or in a range of native fish species, where they may cause severe disease. Levels of parasitism and parasite diversity were significantly greater in native fishes than in exotic species, and this may contribute to an enhanced demographic performance and competitive ability in invading exotics. Levels of parasitism and parasite diversity in native fishes were negatively related to habitat disturbance, in particular to a suite of factors that indicate increased human use of the river and surrounding environment. This was due principally to the absence in more disturbed habitats of a number of species of endoparasites with complex life cycles, involving transmission between different host species.

Larval anisakid infections of some tropical fish species from north-west Australia

Despite the commercial and zoonotic importance of larval anisakid infestations of teleosts, their distribution among Australias diverse marine fish fauna is poorly understood. A preliminary survey of Australias tropical north-west revealed a generally high prevalence of larval anisakids representing four genera (Anisakis, Terranova, Thynnascaris and Raphidascaris) among only seven fish species. The potential impact of high larval anisakid infections on both the health of recreational fishermen and aquaculture environments is discussed.

Rethinking the land: The development of inland saline aquaculture in Western Australia

Inland saline aquaculture may offer an opportunity for income diversification and a potentially productive use of land that can no longer support traditional agriculture in salt-affected parts of inland Australia. Interest in inland saline aquaculture is increasing in Western Australia, however, production and investment levels are characteristically low. Inland saline aquaculture presents a continuum of production and investment options for landholders and investors, from being a small-scale, hobby-like remedial use of salinised farmland to a novel and legitimate agricultural industry. Successful progress toward the latter depends on a number of factors: appropriate production technology; identification and establishment of sustainable markets; establishment of environmentally sustainable production systems; and industry management. We use preliminary data from finfish aquaculture in inland Western Australia to consider why industry success requires concurrent development across all these fields.

Efficacy of exclusion fencing to protect ephemeral floodplain lagoon habitats from feral pigs (Sus scrofa).

Foraging by feral pigs can strongly affect wetland vegetation assemblages and so too wider ecological processes, although their effects on freshwater ecosystems have seldom been studied. We assessed the ecological effects of pig foraging in replicate fenced and unfenced ephemeral floodplain lagoons in tropical north-eastern Australia. Pig foraging activities in unfenced lagoons caused major changes to aquatic macrophyte communities and as a consequence, to the proportional amounts of open water and bare ground. The destruction of macrophyte communities and upheaval of wetland sediments significantly affected wetland turbidity, and caused prolonged anoxia and pH imbalances in the unfenced treatments. Whilst fencing of floodplain lagoons will protect against feral pig foraging activities, our repeated measures of many biological, physical and chemical parameters inferred that natural seasonal (i.e. temporal) effects had a greater influence on these variables than did pigs. To validate this observation requires measuring how these effects are influenced by the seemingly greater annual disturbance regime of variable flooding and drying in this tropical climate.

Justification for genetic improvement in growth rates of black bream (Acanthopagrus butcheri): a partial budgeting analysis

Abstract Black bream (Acanthopagrus butcheri) appear an ideal candidate for the developing saline aquaculture industry of inland Western Australia. However, current maximum growth rates of 150g/annum are too slow for profitable production. This study investigated whether enhanced growth rates of black bream would improve profitability and justify a genetic improvement program. A partial budget analysis was conducted for two different fish production systems; a commercial operation that incurred more operating expenses due to costs associated with farm initiation (stand‐alone farm model), and an existing farm that diversified into aquaculture using the saline water resources of established farm dams (integrated farm model). Sensitivity analyses indicated that a 33 per cent increase in growth rate to at least 200g/annum would allow either production system to return a profit at a farm‐gate price of AUS

The potential of a salt-tolerant plant (Distichlis spicata cv. NyPa Forage) to treat effluent from inland saline aquaculture and provide livestock feed on salt-affected farmland

6/kg whole fish, with fish survival rates of 98 per cent for the stand‐alone farm, and 65 per cent for the integrated farm model. These results are discussed in the context of the genetic and economic consequences of selection for improved growth rates, and for developing breeding objectives and a genetic improvement program for black bream.

Investigational piscivory of some juvenile Australian freshwater fishes by the introduced Mozambique tilapia Oreochromis mossambicus

Dryland salinity is a major problem affecting food production from agricultural land in Australia and throughout the world. Although there is much interest in using saline groundwater to grow marine fish on salt-affected farmland, the disposal of nutrient enriched, saline aquaculture effluent is a major environmental problem. We investigated the potential of the salt-tolerant NyPa Forage plant (Distichlis spicata L. Greene var. yensen-4a) to trap nutrients from saline aquaculture effluent and subsequently to provide a fodder crop for livestock. Sub-surface flow wetlands containing NyPa Forage were constructed and their efficacy in removing total nitrogen, ammonia, nitrite/nitrate, total phosphorus and orthophosphate was monitored under different levels of nutrients and salinity. The wetlands removed 60-90% of total nitrogen loads and at least 85% of ammonia, nitrite/nitrate, total phosphorus and orthophosphate loads, with greater efficiency at high nutrient and low salinity levels. The above-ground yield, sodium, crude protein (CP) and in vitro dry matter digestibility (DMD) of NyPa Forage plants were measured after fertilisation with different nutrient levels and cropping at different frequencies. Yield of plants increased with increased nutrient, while nutritive value was greater when nutrients were applied but did not differ among nutrient levels. Yield was not affected by cropping frequency, but nutritive value was greatest when plants were cropped at intervals of 21 or 42 days. At optimum nutrient addition and cropping levels, the plants had a mean CP content of 16.7% and an in vitro DMD of 67.6%, equivalent to an energy value of 9.5 MJ kg(-1). Assuming an equivalent fibre content and voluntary food intake as grass hay, and no accumulation of other toxic minerals, these nutritive values would be sufficient for maintenance or moderate liveweight gains in dry adult sheep or cattle.

Potential Environmental Impacts From Farming Rainbow Trout Using Inland Saline Water in Western Australia

Experimental tanks were used to observe predatory effects in three different size classes of Mozambique tilapia Oreochromis mossambicus (one of the worlds most widespread exotic species and generally regarded to be a herbivore or both herbivore and detritivore) when tested against 10 juvenile Australian freshwater fish species, and significant levels of predation against all were recorded. There was a general trend for larger O. mossambicus to kill more prey and this was also reflected in a separate series of experiments using juvenile barramundi Lates calcarifer over a range of size classes. Predatory effects by O. mossambicus broadly reflected the accepted models of predator-prey interactions, being that mortality (and survival) was closely related to relative body size and mouth gape limitation. Experimental evidence for piscivory in O. mossambicus was supported by field sampling that detected prey fish remains in 16% of all fish surveyed (n = 176). The recognition of active piscivory by O. mossambicus in laboratory and field situations is the first such evidence, and suggests a need to re-evaluate the nature of their effects in introduced environments.

Preliminary Comparisons of Yield and Profit Achieved from Different Rainbow Trout, Oncorhynchus mykiss, Production Systems in Inland Western Australia

Secondary salinisation, caused by rising water tables as a result of land clearing, has led to large areas of unproductive agricultural land in Australia. Throughout the Western Australian wheatbelt, there is interest in the culture of rainbow trout (Oncorhynchus mykiss) and other fish species using saline groundwater on salt-affected farmland. We surveyed farmers and interviewed representatives of resource management agencies, to determine potential environmental impacts associated with this form of aquaculture. Four types of culture units have been used to grow trout: farm dams, constructed ponds, natural lakes and tanks. Our analysis of their water flow characteristics suggests that dams, ponds, lakes and tanks are likely to produce qualitatively similar environmental impacts. Farmers and resource managers identified the same potential environmental impacts from inland trout farming, but their perceptions of the importance of these impacts differed. In general, farmers ranked on-farm impacts more highly than off-farm impacts, while the reverse was true for resource managers. The regulation of environmental impacts in inland saline aquaculture is complicated by the diversity of government agencies involved and by the small scale of the industry. This suggests that economic instruments, facilitated by the voluntary development and application of environmental management guidelines, might be a better management tool than regulation, but there is a need to more precisely define and internalize many of the external environmental costs.