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11.
Over the last ten years, there has been a major decline in the condition of the Coorong, the estuary for Australia's largest river system, the River Murray. This decline is due to prolonged drought combined with past management of the Murray-Darling Basin. In order to successfully manage the estuary in the future, predictions are needed to evaluate the effect of possible management actions on the Coorong ecosystem under a variety of climatic scenarios. The alternative stable state concept can be extended to non-equilibrium systems, allowing for modelling of condition. Rather than constraining the definition of alternative states to those that are stable, we identify a suite of ecosystem states that occur naturally, but also include those that arise during the decline of the system. Eight distinct states were defined, with thresholds between them based on a combination of environmental characteristics associated with co-occurring biota. Threshold values for environmental characteristics define the transition rules between states. Mapping these states allows us to characterise the condition of the estuary in both space and time. The distribution of these states, and the diversity of states supported can be used to create an ecosystem condition index. By calculating the value of the index over time, the trajectory of ecosystem condition merges, and predictions can be made about future condition, should the current situation continue. This trajectory modelling can then form a baseline against which to evaluate possible management actions under a variety of climatic scenarios to identify those most likely to improve the condition of the Coorong. 相似文献
12.
Pip Forer Dean Forbes Peter Fairweather David Mercer Richard Howitt Victor Prescott 《The Australian geographer》1993,24(2):89-96
AN INTRODUCTION TO URBAN GEOGRAPHIC INFORMATION SYSTEMS by W.E. Huxhold. 16 x 23 cm, xxiii and 337 pages. Oxford University Press, New York, 1991. (ISBN 0 19 506535 2) $44.95 (soft).
INDONESIA: resources, ecology and environment (Natural Resources of South‐East Asia Series) edited by J. Hardjono. 14 × 22 cm, xvi and 262 pages. Oxford University Press, Oxford, 1991. (ISBN 0 19 588992 4) $39.95 (hard).
THE UNIQUE CONTINENT: an introductory reader in Australian environmental studies edited by J. Smith. 13 × 20 cm, vi and 282 pages. University of Queensland Press, Brisbane, 1992. (ISBN 0 7022 2475 8) $14.95 (soft).
SPECIAL INTEREST TOURISM edited by B. Weiler and C.M. Hall. 15 × 23 cm, xi and 214 pages. Belhaven, London, 1992. (ISBN 1 85293 072 1) £35.00 (hard).
REMOTE POSSIBILITIES: the Aboriginal domain and the administrative imagination by T. Rowse. 18 × 25 cm, viii and 117 pages. North Australian Research Unit, Australian National University, Darwin, 1992. (ISBN 0 7315 1345 2) $15.00 (soft).
ANTARCTICA: an economic history of the last continent by M. Wilder. 21 × 29 cm, viii and 155 pages. Department of Economic History, University of Sydney, Sydney, 1992. (ISBN 0 86758 616 8) $20.00 (soft).
AUSTRALIAN RAINFORESTS (Oxford Monographs on Biogeography No. 6) by P. Adam. 19 × 25 cm, xiv and 308 pages. Oxford Science Publications/Clarendon Press, Oxford, 1992. (ISBN 0 19 854223) $170.00 (hard). 相似文献
13.
Caging and a mark–recapture design were used to estimate the growth rate of the brittle, infaunal bivalve Soletellina alba in the Hopkins River estuary. The growth of both caged and uncaged individuals was monitored at three sites near the mouth of the estuary over 180 days. Growth rates did not differ for caged and uncaged bivalves, or for bivalves subject to different amounts of handling, or between sites. Growth did differ between consecutive time intervals, which was attributable to negligible growth occurring during the colder months of autumn/winter. Comparisons of the condition (as indicated by total mass for length3) of S. alba were inconsistent between sites for caged and uncaged bivalves and for those subject to different amounts of handling. Soletellina alba is a rapidly growing bivalve with mean growth rates for the three time intervals being 0.04±0.002 mm day−1 in summer, 0.02±0.001 mm day−1 in autumn and 0.03±0.001 mm day−1 from summer to winter. Using existing literature, it was shown that a significant relationship exists between maximum shell length and onset of sexual maturity in bivalve molluscs. This relationship predicts that S. alba should reach the onset of sexual maturity at 15.8 mm length. Therefore, it appears that it may be possible for juvenile S. alba (<1 mm) to grow, reach sexual maturity and reproduce in between annual mass-mortality events caused by winter flooding. 相似文献
14.
Earlier research shows that between 1971 and 1981, the number of farmers in New Zealand increased and their average age decreased, whereas between 1981 and 1991, the opposite trend occurred. This article addresses the issue of change in the average age of farmers since 1991 using recent census data. It reviews the difficulties in obtaining good data and describes the adjustments need to be made to obtain a consistent data series from 1971 to 2006. The long-term trend for increasing age of farmers and farm workers continues. This demographic aspect of farm structural change is then discussed in terms of the sustainability of farming by reference to productivity and potential problems with succession. 相似文献
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The supply of detritus is an important food source for many soft-sediment invertebrates, but its importance for their growth and condition is rarely, if ever, tested directly using manipulative field experiments. Therefore, we designed such a study to: (1) test the importance of fine particulate organic matter for the growth and condition of the infaunal bivalve Soletellina alba; (2) indirectly test the feeding mode of S. alba, which has been assumed to be a deposit feeder like other members of the same superfamily (Tellinoidea); (3) compare growth rates across two summers with contrasting patterns of estuary mouth opening/closing; and (4) compare the condition of individuals used in two field studies (i.e. present versus past) and a past laboratory study. Neither growth nor condition differed when organic content of the sediments was varied, which suggests that S. alba is either a suspension feeder or capable of switching modes of feeding. There was considerable interannual variation in growth with greater growth occurring during the summer with a longer period of mouth opening. This suggests that periods of mouth closure may reduce secondary production within seasonally-closed estuaries. Potential artefacts associated with laboratory trials were also identified, with laboratory bivalves exhibiting poorer condition than those used in two field trials. The present study provides no evidence that variable quantities and qualities of organic matter within the sediments influence the growth and condition of S. alba, but future studies should focus on food supplied via the water column when the estuary is open versus closed. 相似文献
17.
T Jansen K Kristensen TP Fairweather P Kainge JN Kathena MD Durholtz 《African Journal of Marine Science》2017,39(3):349-361
Optimal and sustainable management of fish resources cannot be ensured without a thorough understanding of the migration patterns and population (demographic stock) structure. Recent studies suggest that these aspects of the economically and ecologically important deepwater hake Merluccius paradoxus are not reflected in the current assessment and management practices for the Benguela Current Large Marine Ecosystem. In this study, we compiled data from multiple demersal trawl surveys from the entire distribution area and applied state-of-the-art geostatistical population modelling (GeoPop) to estimate growth rate, mortality, and spatial and temporal distribution patterns of M. paradoxus. The data and the model enabled us to follow temporal and spatial changes in the distribution and infer movements from the recruitment/nursery areas, through the juvenile phase and the adults’ migration to the spawning areas outside/upstream of the nursery areas. The results indicated one primary recruitment/nursery area on the west coast of South Africa and a secondary less-productive recruitment/nursery area on the south coast near Port Elizabeth. Juveniles initially migrated away from the main recruitment area, followed by natal homing by larger individuals. This pattern was highly consistent through the time-series of the study. This perception of a, primarily, panmictic population that performs transboundary migrations between Namibia and South Africa corresponds largely to the hypothesis and data plots given in recent studies. We recommend that fisheries assessment, advice and management take into consideration these aspects of the distribution and population (stock) structure of M. paradoxus. 相似文献