Presence of fish on the shallow flooded margins of a small intermittently open estuary in South Eastern Australia under variable flooding regimes

Shallow water habitats within estuarine systems are believed to be important areas for small fish. While a wide variety of shallow habitats have been studied, the land that becomes inundated by the damming effect after the closure of intermittently open mouths has previously been overlooked. Fish were sampled monthly from both the main channel and flood zone of an intermittently open estuary between July 2004 and June 2005 using minifyke nets during the day and at night. A total of 7,787 fish were collected during the study representing 13 species and 11 families. Philypnodon grandiceps was the most abundant species and, together with Atherinosoma microstoma, Pseudogobius olorum, and Galaxias maculatus, made up 94% of the total catch. Inundation of the flood zone occurred in two discrete forms associated with mouth condition, which consisted of sporadic flooding while the mouth was open, to long-term flooding for 6 months after its closure. Large numbers of fish were captured on the flood zone, which included nine species; however, A. microstoma dominated the catch. A distinct shift in the flood zone fish assemblage occurred between the two mouth conditions, which is likely associated with changes in hydro-period and food availability of the flood zone and physico-chemical parameters in the main channel. There was no longitudinal variation in the fish assemblage in both the main channel and flood zone; similarly, the diel period was found to have little effect on the fish assemblage. The total catch per unit effort did not vary across seasons and suggests that fish abundance within the estuary is stable throughout the year. Unlike other estuarine systems where shallow water fish assemblages may be structured by variations in tide and elevation within the Surrey, freshwater inflow and, more importantly, mouth condition appear to have the greatest influence in composition of the shallow water flood zone fish assemblage of intermittently open estuaries.

Hydro-acoustic remote sensing of benthic biological communities on the shallow South East Australian continental shelf

Information regarding the composition and extent of benthic habitats on the South East Australian continental shelf is limited. In this habitat mapping study, multibeam echosounder (MBES) data are integrated with precisely geo-referenced video ground-truth data to quantify benthic biotic communities at Cape Nelson, Victoria, Australia. Using an automated decision tree classification approach, 5 representative biotic groups defined from video analysis were related to hydro-acoustically derived variables in the Cape Nelson survey area. Using a combination of multibeam bathymetry, backscatter and derivative products produced highest overall accuracy (87%) and kappa statistic (0.83). This study demonstrates that decision tree classifiers are capable of integrating variable data types for mapping distributions of benthic biological assemblages, which are important in maintaining biodiversity and other system services in the marine environment.

Deep identity, shallow time : sustaining a future in Victorian fishing communities

Like commercial fishers everywhere, it seems, those living in coastal communities of Victoria perceive themselves to be under threat from recreational fishers, environmentalists, imposed management regimes, and modernisation and globalisation of the industry. In responding to these threats they appeal to conventional props of tradition--to continuity in genealogical time, affiliation with place and specialised knowledge and practice. This seems paradoxical, given that most established fishers in Victoria are first or second generation members of an industry that, through its 150-year history, has been characterised by innovation and mobility. That paradox, we argue, is more apparent than real. Fisher identity is grounded primarily in engagement with an environment that is not familiar to outsiders. The paradox arises because fishers, like others who seek to sustain a future in the face of threat from outsiders, reshape strongly felt identity as tradition.

Fish and fisheries of large and medium-sized reservoirs in Vietnam

The study was undertaken in view of the importance of reservoir fisheries for Vietnam, and to fill gaps in the current knowledge in order to introduce affective management measures to optimise the fish yields from the reservoirs. Eight large and medium sized reservoirs , representing a cross section of reservoirs in Vietnam in the different climatic zones were studied.

Observations on metal concentrations in commercial landings of two species of tilapia (Oreochromis mossambicus and Oreochromis niloticus) from reservoirs in six river basins in Sri Lanka

Samples of the muscle of two species of tilapia (Oreochromis mossambicus and O. niloticus; 17-20 cm length) were obtained from at least one reservoir in each of the six river basins (Aruvi Aru, Kala Oya, Kirindi Oya, Ma Oya, Mahaweli, and Walawe Ganga catchments) in Sri Lanka. The metals Ca, Cu, Fe, K, Mg, Mn, Na, and Zn were consistently detected in the muscle tissue. Overall, there were few differences in the concentration of metals between the two species of fish, although there were also some statistically significant differences (p < 0.05) in the concentrations of some metals in fish obtained from some of the reservoirs. Aruvi Aru stands out as a river basin in which the two fish species have significantly lower concentration of metals when compared to other river basins. The concentration of the metals studied were below WHO and FSANZ guideline values for fish, suggesting that the consumption of the metals found in tilapia from these reservoirs poses little risk to human health.

Animal–plant–microbe interactions : direct and indirect effects of swan foraging behaviour modulate methane cycling in temperate shallow wetlands

Wetlands are among the most important ecosystems on Earth both in terms of productivity and biodiversity, but also as a source of the greenhouse gas CH₄. Microbial processes catalyzing nutrient recycling and CH₄ production are controlled by sediment physico-chemistry, which is in turn affected by plant activity and the foraging behaviour of herbivores. We performed field and laboratory experiments to evaluate the direct effect of herbivores on soil microbial activity and their indirect effects as the consequence of reduced macrophyte density, using migratory Bewick’s swans (Cygnus columbianus bewickii Yarrell) feeding on fennel pondweed (Potamogeton pectinatus L.) tubers as a model system. A controlled foraging experiment using field enclosures indicated that swan bioturbation decreases CH₄ production, through a decrease in the activity of methanogenic Archaea and an increased rate of CH₄ oxidation in the bioturbated sediment. We also found a positive correlation between tuber density (a surrogate of plant density during the previous growth season) and CH₄ production activity. A laboratory experiment showed that sediment sterilization enhances pondweed growth, probably due to elimination of the negative effects of microbial activity on plant growth. In summary, the bioturbation caused by swan grazing modulates CH₄ cycling by means of both direct and indirect (i.e. plant-mediated) effects with potential consequences for CH₄ emission from wetland systems.

Habitat utilization by juvenile hawksbill turtles (Eretmochelys imbricata, Linnaeus, 1766) around a shallow water coral reef

Contemporary studies of sea turtle diving behaviour are generally based upon sophisticated techniques such as the attachment of time depth recorders. However, if the risks of misinterpretation are to be minimized, it is essential that electronic data are analysed in the light of first-hand observations. To this aim, we set out to make observations of juvenile hawksbill turtles (Eretmochelys imbricata, Linnaeus, 1766) foraging and resting in a shallow water coral reef habitat around the granitic Seychelles (4°'S, 55°'E). Data were collected from six study sites characterized by a shallow reef plateau (<5 m) and a flat sandy area at the base of the reef face (<10 m). Observation data were categorized into the following behaviours: (1) stationary foraging; (2) active foraging; (3) resting; and (4) assisted resting. Central to this investigation was the development of a technique for accurately estimating the size of sea turtles in situ based upon previously tested techniques for reef fishes. This revealed that through calibration, the curved carapace length (CCL) of marine turtles can be consistently estimated to within 10 cm of their actual size. Although rudimentary, this has advantages for assessing the residency or absence of specific life history stages from particular environments. Indeed, our data supported previous claims that following the reproductive season, adult hawksbills in the region may move away from the nesting beaches to alternative foraging grounds whilst immature turtles (following the pelagic juvenile stage) may opt to reside in areas close to their natal beaches. With regards to habitat utilization, juvenile hawksbills displayed an alternating pattern of short, shallow foraging dives followed by deeper, longer resting dives. These findings are consistent with previous electronic studies of free-range diving in this species and suggest that the maximization of resting duration may be an important factor driving this behaviour.

Optimal sensor placement and measurement of wind for water quality studies in urban reservoirs

We collaborate with environmental scientists to study the hydrodynamics and water quality in an urban district, where the surface wind distribution is an essential input but undergoes high spatial and temporal variations due to the complex urban landform created by surrounding buildings. In this work, we study an optimal sensor placement scheme to measure the wind distribution over a large urban reservoir with a limited number of wind sensors. Unlike existing sensor placement solutions that assume Gaussian process of target phenomena, this study measures the wind which inherently exhibits strong non-Gaussian yearly distribution. By leveraging the local monsoon characteristics of wind, we segment a year into different monsoon seasons which follow a unique distribution respectively. We also use computational fluid dynamics to learn the spatial correlation of wind in the presence of surrounding buildings. The output of sensor placement is a set of the most informative locations to deploy the wind sensors, based on the readings of which we can accurately predict the wind over the entire reservoir surface in real time. 10 wind sensors are finally deployed around or on the water surface of an urban reservoir. The in-field measurement results of more than 3 months suggest that the proposed sensor placement and spatial prediction approach provides accurate wind measurement which outperforms the state-of-the-art Gaussian model based or interpolation based approaches.

Evaluation of management scenarios for controlling eutrophication in a shallow tropical urban lake

Urban lakes are typically smaller, shallower, and more exposed to human activities than natural lakes. Although the effects of harmful algal blooms (HABs) associated with eutrophication in urban lakes has become a growing concern for water resources management and environmental protection, studies focussing on this topic in relation to urban lakes are rare and knowledge of the ecological dynamics and effective management strategies for controlling eutrophication in urban lakes is lacking. This study applied an integrated three-dimensional hydrodynamics-ecological model for a small shallow tropical urban lake in Singapore and evaluated various management scenarios to control eutrophication in the lake. It is found that in-lake treatment techniques including artificial destratification, sediment manipulation and algaecide addition are either ineffective or possess environmental concerns; while watershed management strategies including hydraulic flushing and inflow nutrients reduction are more effective and have posed less environmental concerns. In this study, inflow phosphorus reduction was found to be the best strategy after evaluating the advantages and drawbacks of the management strategies studied. Runoff from the watershed exerts significant influence on urban lakes and thus an integrated water resources management at the watershed level is critical for the control of eutrophication