Impact of dredging on the volute Cymbiolacca pulchra and its environment at Heron Island, Great Barrier Reef, Australia

The impact of dredging operations on the volute Gastropod (Cymbiolacca pulchra) population of a coral reef atoll (Heron Island, Great Barrier Reef, Australia) was investigated using data from annual surveys of the population and its environment Comparisons were made of pre-dredging (1984 to 1986), during-dredging (1987) and post-dredging (1988 and 1989) summer densities and size distributions of volutes at eight locations on the reef. There was significant variation among the sites in the pre-dredging years with volutes restricted to four sites characterised by a combination ofre1ative1y low bommie cover « 2%) and high sand cover (> 75%). All four sites were influenced by the dredge plume during dredging operations (September to November 1987 and February 1988). Volute densities declined significantly during dredging (1987) compared to the pre-dredging years. In the following year (1988) the difference was highly significant with zero densities recorded. By 1989 there had been a recovery with no significant difference in the overall density of volutes although the density of small volutes was greater and larger volutes smaller compared to pre-dredging densities. From June 1985 to May 1986 monthly counts were made at all sites to examine seasonal patterns of recruitment Recruitment into the population occurred over much of the year, though it tended to be higher in the autumn months (March to May), presumably following summer breeding. We suggest that the declines in volute densities were probably due to a failure of recruitment during dredging coupled with a loss of large volutes which may have resulted from natural mortality, emigration, or dredging. The recovery probably followed immigration of large volutes from less affected areas. The environmental factors of percent cover of sand, rock, rubble, coral, bommies and macroalgae were also monitored and there were significant changes in the cover of algae, coral, sand and rubble. These changes are interpreted as covariates rather than causes of observed changes in volute densities. Post-dredging increases in the cover of algae persisted beyond the termination of this study

Factors influencing the eastern curlew's distribution and choise of foraging sites among tidal flats of Moreton Bay, South eastern Queensland

The use of feeding habitat by eastern curlews in Moreton Bay was examined by means of quantitative density assessment at 26 sites from 13 locations. The sites were chosen to encompass variation in width (area) of tidal flat, seagrass density, and substratum type. Each site was visited four times: during each of a neap and a spring low tide, in January and February 1992. The total curlew count per site was strongly positively correlated with the width of the tidal flat, and had little or no relationship with seagrass density, substratum type or tidal phase. Wide flats also showed more variation than narrow flats in total curlew numbers. Curlew density, measured by the number of birds within 100 m of each side of the water's edge, was also greater on wide tidal flats, showed little relationship to seagrass density or substratum type, but was higher during neap low tides than spring lows. The data suggest that curlews choose soft-sediment intertidal feeding sites on the basis of potential foraging area, and may be particularly sensitive to the lower and infra-littoral areas. A better understanding of foraging site selection by the eastern curlew requires information on site fidelity, feeding success in relation to tidal zonation, diet and the influence of social interactions

Discrimination of sex in the White-bellied Sea-Eagle, Haliaeetus leucogaster, using genetic and morphometric techniques

The White-bellied Sea-Eagle, Haliaeetus leucogaster, is monomorphic for adult plumage colouration, but in body size displays reversed sexual dimorphism, with female birds significantly larger. Analyses of morphometric data from 37 individuals from Australia and Papua New Guinea revealed a latitudinal cline in body dimensions, with individuals larger in the south. A discriminant function based on 10 morphometric characters was 100% effective in discriminating between 19 males and 18 females that had been sexed using molecular genetic methods. Reclassification using a jackknife procedure correctly identified 92% of individuals. The discriminant function should be a viable alternative to genetic sexing or laparoscopy for a large proportion of individuals within the Australo-Papuan range of this species; and can also be used to identify a small proportion of 'ambiguous' individuals for which reliable sexing will require those other techniques

Long-term variation in the distribution of the White-bellied Sea-Eagle (Haliaeetus leucogaster) across Australia

The White-bellied Sea-Eagle Haliaeetus leucogaster (Accipitridae) is widespread within Australia. However, in a number of states it is thought to be declining locally in response to human induced disturbance. Here we analyse the Australian Bird Atlas data to identify the extent and pattern of change in range and density of the species between three Atlas Periods (1901-1976, 1977-1981 and 1998-2001) using a new standardized frequency measure, the Occupancy Index (OI) for 1° blocks (approx. 100 km2) across the continent. At the continental scale, there was no significant difference in the spatial extent of occupancy between Atlas Periods. However, there were considerable changes in frequency and range extent between defined regions, and there were distinct differences in the pattern of change in OI between coastal and inland blocks over time. Coastal blocks showed much more change than inland blocks, with a clear increase in the use of coastal blocks, accompanied by a decrease in inland blocks, during the 1977-1981 Atlas Period, relative to both other Atlas Periods. While there were slight (and not statistically significant) trends for OI to increase in areas containing dams, and to decrease in urbanized coastal areas, the over-riding factor associated with distributional shifts and frequency changes was apparently climatic fluctuation (the 1977-1981 period showing the influence of El Niño associated drought). Within this study, the impression of abundance was strongly dependent on both the temporal and spatial scale of analysis. This highlights the importance of large-scale analysis in interpreting change in distribution and abundance of widespread species

Contemporary Status of the White-Bellied Sea Eagle in Australia: A Tale of Many Scales

Considered to have a declining world population, concern has been expressed in recent years over the conservation status of the White-Bellied Sea-Eagle (Haliaeetus leucogaster) within Australia. Although widespread, regionally it is thought to be declining in response to human induced disturbance. We used mitochondrial control region sequence data and the Australian Bird Atlas data to investigate the current genetic and spatial distribution of the species at the continental level and within and between specified regional units. At ecological timescales the Atlas Data was used to identify the extent and pattern of change in range and density of the species between three Atlas Periods (1901-1976, 1977-1981, and 1998- 2001) using a new standardized frequency measure, the Occupancy Index (OI). Sequence data were obtained from 128 individuals describing 15 haplotypes. Overall, genetic diversity was low and although there were regional differences, AMOVA results failed to provide any significant level of genetic subdivision. We suggest that the population expanded from a bottleneck approximately 160,000 years ago during the late Pleistocene, and spread throughout the continent through a contiguous range expansion. At the continental scale, there was no significant difference in the spatial extent of occupancy between Atlas Periods. However, there were considerable changes in frequency and range extent between defined regions, and there were distinct differences in the pattern of change in OI between coastal and inland areas over time. The over-riding factor associated with distributional shifts and frequency changes was apparently El Nino driven climatic fluctuation. It is clear from the combined analyses that there are signatures of both historical and contemporary processes effecting the current distribution, and that the high level of genetic exchange between regions bodes well for the long-term survivorship of the species within Australia. This study reinforces the importance of multiscale analyses both temporally and geographically

Conservation status of the White-Bellied Sea-Eagle Haliaeetus leucogaster in Australia determined using mtDNA control region sequence data

Considered to have a declining world population, concern has been expressed in recent years over the conservation status of the White-bellied Sea-Eagle Haliaeetus leucogaster (Gmelin, 1788) within Australia. We used mitochondrial (mtDNA) control region sequence data to investigate the current distribution of genetic variation in this species at the continental level and within and between specified regional units. We were specifically interested in identifying breaks in genetic connectivity between the west and east of the continent and between Tasmania and the Australian mainland. We also investigated the likelihood of a bottleneck at the time of colonisation, and propose hypotheses regarding colonisation history. Sequence data were obtained from 128 individuals describing 15 haplotypes. Overall, diversity was low and AMOVA results failed to provide any significant level of genetic subdivision between regions. We suggest that the population expanded from a bottleneck approximately 160,000 years ago during the late Pleistocene, and spread throughout the continent through a contiguous range expansion. There is insufficient evidence to suggest division of the population into different units for conservation management purposes based on the theoretical definition of the 'evolutionary significant unit'. It is clear from the analysis that there are signatures of both historical and contemporary processes affecting the current distribution. Additional sampling and confirmation of the perceived pattern of population structure using a nuclear marker is recommended to validate conservation monitoring and management at a continental scale