Year

1998

Degree Name

Master of Science (Hons.)

Department

School of Geosciences

Abstract

This study primarily investigated the spatial temporal relationship between the estuarine geomorphology and five shorebird species (Aves: Charadriiformes) at Shoalhaven River on the southern coast of New South Wales, Australia. Population data on five shorebird species (Pacific Golden Plover, Lesser Sand Plover, Double-banded Plover, Red-capped Plover and Red-necked Stint) have been collected since 1970. Preliminary analysis of these data suggested a cyclic trend in annual population numbers that may be linked to estuarine geomorphological processes. The entrance to the Shoalhaven River is often blocked by a barrier dune, periodically being breached by floodwaters. Once opened the entrance channel is slowly closed by tidal pumping through Berry's Canal, sediment transport along the beach front and aeolian derived sands. Preliminary investigations suggested this opening and closing regime is cyclic. Thus the questions being asked include determining if the entrance condition is cyclic and whether there is temporal and spatial variation in seven habitat types within the entrance basin (marine waters, estuarine waters, intertidal flats, supratidal sands, saltmarsh, dune vegetation, other land). Finally I explore the relationship between temporal changes in the estuarine morphology and the five shorebird populations. To determine spatial changes in the estuary morphology and the seven habitat classes I interpreted thirteen aerial photographs taken between 1970 and 1996. This study period covered two complete cycles of open (1974-1980 and 1988-1995) and closed (1970-1974, 1981-1988 and 1995-96) entrance condition. Each photograph was first georectified with a digital image processing package (DIMPLE) to correct for spatial distortions that occur during the aerial photographic process. Habitats in the final images were then interpreted via digitising into the seven habitat classes within a Geographic Information System (GIS). Two GISs were used during the course of spatial analysis, ERMS and SPANS GIS. Within the GIS, areas of each habitat within each year of image capture were determined. These data are regressed against time since entrance opening to examine trends in habitat change. Additionally, inferential data was available from several sources on the general entrance condition using a trinomial classification (open, closing, closed) since 1936. This data was analysed for cyclic trends using the contingency periodogram. Data from this time series were also compared against the El Niño Southern Oscillation Index (SOI) and Sunspot activity index for correlation's between these mesoscale phenomena and the entrance condition. Finally data derived from these analyses were correlated against the population time series of each species and the five species combined. The results show there is a quasi-septennial cycle in the entrance condition since 1936, with open and closed regimes lasting for 6-9 years. The data can be loosely related to strong positive and negative deviations in the SOI. There was no obvious relationships with sunspot activity. Concomitantly, all the estuarine habitats (except other land) changed dramatically through the study period. The study was able to graphically illustrate the direction, development and vegetative invasion of a major dune on the southern side of the entrance channel, the development and expansion of saltmarsh communities, the alteration and subsequent realignment of the beach front after breaching and substantial changes in the intertidal flats. Correlation with shorebird populations was more difficult to establish, although several species do correlate well with temporal and spatial changes in the available area of intertidal flats and saltmarsh. There was however an obvious correlation between shorebird populations and the general condition of the entrance channel, with larger populations being present during the closed phased and the lowest numbers present during the open phase of the channel. Issues in relation to the findings of this study and shorebird conservation in the Shoalhaven Estuary are discussed. The study demonstrated that temporal and spatial patterns in habitat and estuarine geomorphology can be readily interpreted from remotely sensed data and suitably analysed with a GIS. Whilst determination of correlation's between shorebird populations and these biotic processes was more difficult to determine, a casual link was readily established.

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