Yield, growth and mortality rate of the Thai river sprat, Clupeichthys aesarnensis, in Sirinthorn Reservoir, Thailand

The Thai river sprat, Clupeichthys aesarnensis Wongratana, is a clupeid with a short life span, and supports artisanal fisheries in a number of reservoirs in the Mekong Basin. The growth parameters, mortality rates and the status of the Thai river sprat in Sirinthorn Reservoir (28 800 ha), NE Thailand (15°N; 105°E), are presented. The fishery is based on lured lift-nets, operated 7–14 days in the new moon period, September to April each year. It was shown that the von Bertalanffy growth function (VBGF) model was L_t (mm) = 78.43[1 − exp{−0.211[t − (−0.7996)]}] and its growth conformed to an isometric pattern. Natural mortality rate (month−¹) was 0.13 month−¹. Total mortality rates ranged from 0.69 to 1.53 month−¹ depending on the weather and the fishing season. Recruitment was continuous throughout the year but peaked in June and July. The yield per recruit model indicated that the exploitation rate of this fishery is probably too high.

Effect of flooding on estuarine bivalve populations near the mouth of the Hopkins River, Victoria, Australia

The densities of two common intertidal/shallow subtidal bivalves, Soletellina alba and Arthritica helmsi, were sampled in vegetated and unvegetated habitats of the Hopkins River estuary on three occasions during the  autumn/winter 1995.Winter flooding coincided with mass mortalities of the infaunal bivalve S. alba, but not A. helmsi. Mortalities were apparent for individuals living deeper in the sediment (≈35 cm) in vegetated and unvegetated habitats, but small S. alba (<1mm) were less susceptible to mortality than larger individuals (>1mm). Mortalities were similar across different habitat types and sediment depths, and at multiple sites within close proximity to the estuary mouth.

Spatial, temporal and size-class variation in the diet of estuary perch (Macquaria colonorum) in the Hopkins River, Victoria, Australia

The dietary importance of prey of estuary perch (Macquaria colonorum; Percicthyidae: Günther) was examined spatially, temporally and among size classes. Fish were collected from the Hopkins River, south-western Victoria, from September 1998 to February 1999. The species is a euryhaline, euryphagic carnivore with spatial, temporal and size class variations in diets. Fish caught from estuarine locations consumed primarily Paratya australiensis (40% IRI) while freshwater fish consumed mostly Tricopteran larvae (63.5% IRI). In both freshwater and estuarine locations, the relative importance of P. australiensis decreased with increasing length of fish. Diet changed seasonally, indicating opportunistic changes in prey. The species selected particular prey items relative to environmental availability (P. australiensis, Amarinus lacustrine).

Public land use planning using bioregions and other attributes : determining the study area of the VEAC river red gum forests investigation

In order to plan for the best use of public land at a regional scale the determination of an appropriate regional boundary is important for ecological, resource use and recreational reasons. The study area for the Victorian Environmental Assessment Council's (VEAC) River Red Gum Forests Investigation incorporated bioregional boundaries, modelled pre- I750 vegetation distribution, recent public land use investigations, and the distribution of public land. This paper outlines how ecological attributes and past land use studies were used to inform the boundary for this major study of public land along the Murray River in northern Victoria.

Recruitment of the infaunal bivalve Soletellina Alba (Lamark,1818) (Bivalvia: Psammobiidae) in response to different sediment types and water depths within the intermittently open Hopkins River estuary

Studies examining recruitment processes for soft-sediment macroinvertebrate fauna in intermittent estuaries are rare and most studies of active habitat selection have been tested in the laboratory rather than the field. The present field study examined whether recruitment of the infaunal bivalve Soletellina alba was influenced by water depth and sediment particle size in the intermittent Hopkins River estuary, southern Australia. The number of recruits in sediment trays differed between water depths, but active habitat selection was not evident across treatments of varying sediment particle size. The use of sediments with varying particle sizes also provided an opportunity to identify potential discontinuities in body-size distributions of recruits associated with varying habitat architecture. The length (mm) of recruits was converted to the same scale used to express sediment particle size (i.e. phi units: phi = − log2 of sediment particle size). The size of recruits differed across water depths, but did not differ across treatments with fine (phi = 3) versus coarse (phi = 1) sediment, and no relationships were apparent between bivalve size and sediments consisting of varying particle size. These patterns of recruitment do not correspond with the distribution of adult S. alba within the Hopkins River estuary. Previous sampling has shown that abundances of juvenile and adult S. alba are variable across time, site and water depth, but are often greater at the deeper water depth (1.05 m below the Australian Height Datum). However, recruitment during the present study was greatest at the shallower water depth (0.05 m below AHD), and the apparent absence of active habitat selection suggests that the distribution of adults is unlikely to be attributable to differences in recruitment associated with sediments of varying particle size.

Spatial and temporal changes in abundance of the infaunal bivalve Soletellina alba (Lamark, 1818) during a time of drought in the seasonally-closed Hopkins River Estuary, Victoria Australia

The infaunal bivalve Soletellina alba is susceptible to mass mortalities during annual winter flooding in the Hopkins River Estuary, southern Australia. Periods of low salinity (≤1) are the likely cause of these mass mortality events, which can occur in seasonally-closed estuaries when high winter flows are sufficient to flush all salt water from the estuary. Core samples of S. alba were collected from two water depths across four times and at three sites near the mouth of the estuary. Minimal to zero abundances of large S. alba (>1 mm) were expected to be sampled, particularly at the shallower water depth, during a typical winter flood event. However, the present study occurred during a period of drought, which led to the absence of winter flooding. This absence of winter flooding prevented the occurrence of lethal salinities (i.e. ≤1) in the estuary during this period and a greater number of living S. alba adults were sampled. Abundances of juvenile and adult S. alba were still variable, even in the absence of winter flooding, and reflected an interaction between date, site and water depth. However, no mass mortalities of adults were observed during the drought conditions in contrast to what occurs during typical winter flood events and provides support for the hypothesis that winter flooding is responsible for past mass mortalities.

Evaluation of SWAT for modelling the water balance of the Woady Yaloak River catchment, Victoria

Future land use change will have a profound effect on the water balance of agricultural and rural catchments in Australia. It is therefore imperative that any such consequences likely to arise from impending land use changes are predicted accurately so that strategies can be implemented to minimise or prevent undesirable impacts to the water balance of catchments. SWAT is a comprehensive hydrologic model developed to predict the impacts of land use change on water balance. SWAT has been applied in Australia but it has not yet been widely adopted. The application of SWAT to the Woady Yaloak River catchment in southwest Victoria is described in this paper. SWAT is being evaluated to determine whether it is suitable for modelling the water balance of catchments in the southwest region of Victoria and to determine if it could be adopted as a planning tool to manage land use change. The results achieved in this initial application of SWAT were very pleasing. However it is shown that the groundwater and tree growth components of the model are not entirely adequate. These shortcomings with SWAT affect its ability to accurately model the water balance of catchments in Australia. It is recommended that both these components be modified to improve model performance.

Conflict resolution and policy making mediation in the Mekong River Basin

The Mekong River serves China, Myanmar, Thailand, Laos, Cambodia and Vietnam covering an area of approximately 795, 000 square kilometres and the Mekong River basin is a delicate eco-system rich in natural resources and bio-diversity. Competing demands for increasingly scarce supplies of water, the reciprocal impacts of land and water uses and inadequate governance arrangements have given rise to conflicts that has to be resolved by policy making to facilitate a process, whereby the main principles adopted in the Mekong River Agreement can be implemented.

Conflict resolution and sustainable water use in the Mekong River Basin

In this paper it is argued that increased demands for water use in the Mekong River Basin makes this region vulnerable to conflict. Strategies to both prevent and manage conflict are necessary for sustainable water use in this region. Community development is integral to sustainable development. Community development strategies are particularly useful in recognising knowledge and expertise within local communities. They also assist in involving local communities - particularly members of minority groups in collaborative efforts for sustainable natural resource use and conflict management. It is essential that local communities are active partners in the development of conflict resolution and sustainable development strategies. Active and meaningful participation of local communities in the planning, and management of local water use development activities will increase the likelihood of sustainable outcomes.

Application of SWAT to model the water balance of the Woady Yaloak River catchment, Australia

The widespread land use changes that are expected to occur across the Corangamite region in southwest Victoria, Australia, have the potential to significantly alter the water balance of catchments. Adoption of the Soil and Water Assessment Tool (SWAT), which is a long-term water balance model, as a tool for predicting land use change impacts on catchment water balance for the Corangamite region is currently being considered. This paper describes the initial application of SWAT to the Woady Yaloak River catchment, located within the Corangamite region, to carry out an evaluation of its abilities for simulating the long-term water balance dynamics of the catchment. The performance of the model for predicting runoff at annual and monthly time scales was found to be very good. The excessive recharge of the shallow aquifer that occurred during winter, despite the subsoil being relatively impermeable, ultimately contributed to overestimation of baseflow and underestimation of interflow. The actual evapotranspiration from hydrologic response units (HRU s) containing eucalyptus trees was significantly less than that from HRUs containing pasture, a problem attributed to the incorrect simulation of Leaf Area Index (LAI) and biomass by the model for mature stands of eucalyptus trees and also to assigning inadequate values for two parameters that directly influence evapotranspiration. SWAT has very good potential for being used as tool to study land use change impacts across the Corangamite region provided that several modifications are made to the model to overcome some of the shortcomings and deficiencies that were identified in this initial application.

River pilots for time`s flow: identifying factors to guide on-line distance education students in the use of their learning time

This research draws on recent studies of student time perception and use.
Case studies are used contrast the time use experiences of tertiary distance
education (on-line) students with tertiary students studying in traditional faceto-face classes with an online component. Previous studies and experience highlight a mismatch between the measurable and hence ”real” amount of time students spend at their computer and online, with the perceived” (and resented) time spent in online learning. This study uses investigates the recognition and application of factors affecting student perception of time spent in studying and learning online. It also compares the effectiveness of these factors when applied to distance education based wholly online classes, and face-to-face classes with an online component.
Some of the factors were measurably successful in reducing students’
perceptions of time “wasted” online, while others produced considerable
insight into face-to-face students perceptions of time used in study. The
factors included much greater focus on the person who was a student and
their expectations and time/life experiences while learning; the support and
use of alternative technologies such as mobile phones as learning and
communication too; a higher level of administrative and academic technical
support for the students; convergence of delivery methods; and strategic
involvement of teaching staff in design and delivery of learner management
systems.

Sea-level changes and palaeo-ranges: reconstruction of ancient shorelines and river drainages and the phylogeography of the Australian land crayfish Engaeus sericatus Clark (Decapoda: Parastacidae )

Historical sea levels have been influential in shaping the phylogeography of freshwater-limited taxa via palaeodrainage and palaeoshoreline connections. In this study, we demonstrate an approach to phylogeographic analysis incorporating historical sea-level information in a nested clade phylogeographic analysis (NCPA) framework, using burrowing freshwater crayfish as the model organism. Our study area focuses on the Bass Strait region of southeastern Australia, which is marine region encompassing a shallow seabed that has emerged as a land bridge during glacial cycles connecting mainland Australia and Tasmania. Bathymetric data were analysed using Geographical Information Systems (GIS) to delineate a palaeodrainage model when the palaeocoastline was 150 m below present-day sea level. Such sea levels occurred at least twice in the past 500 000 years, perhaps more often or of larger magnitude within the last 10 million years, linking Victoria and Tasmania. Inter-locality distance measures confined to the palaeodrainage network were incorporated into an NCPA of crayfish (Engaeus sericatus Clark 1936) mitochondrial 16S rDNA haplotypes. The results were then compared to NCPAs using present-day river drainages and traditional great-circle distance measures. NCPA inferences were cross-examined using frequentist and Bayesian procedures in the context of geomorphological and historical sea-level data. We found distribution of present-day genetic variation in E. sericatus to be partly explained not only by connectivity through palaeodrainages but also via present-day drainages or overland (great circle) routes. We recommend that future studies consider all three of these distance measures, especially for studies of coastally distributed species.

Estimating post-release survival and the influential factors for recreationally caught Black Bream (Acanthopagrus butcheri) in the Glenelg River, south eastern Australia

Black bream (Acanthopagrus butcheri) is the main target species amongst the estuarine recreational fisheries of Victoria, Australia. The A. butcheri fishery is managed through legal-minimum length and daily bag limits. The success of this management strategy requires that the survival rate for released fish is high. This study used the most common angling practices to estimate post-release survival and identify influential factors for undersized A. butcheri in Victoria. In total 1557 and 923 A. butcheri were caught and monitored for initial (≤1 h) and delayed (72 h) survival, respectively. Fish were caught across 3 years, with each year separated into cold and warm water periods with 8 fishing trial days in total. Only 1 of the 266 controls used to assess confinement effects died. Total survival was 95% (S.E. ± 0.8%) for shallow- and 74% (S.E. ± 3%) for deep-hooked fish and decreased as fish length increased. A post-mortem (PM) procedure was developed and showed that throat and gill injuries were the most frequent cause of deep-hooking death. It revealed that 97% of hooks left in fish remained there after 72 h and identified hooking location inaccuracies recorded at the time of capture. Total survival for deep-hooked fish was 20% higher when hooks were left in the fish. Deep-hooked fish were more likely to bleed when hooks were removed and total survival was lower for fish that bleed (58%) than fish that did not bleed (80%). Shallow-hooking rates decreased as fish length increased and were higher during warm water compared to cold water trials. The high shallow-hooking and survival rates observed suggest that A. butcheri survival in the fishery would be high, but deep-hooking has the potential to undermine the management strategy. Determining the shallow-hooking rate in the fishery would help clarify the impact of these findings at the fishery level.