Population dynamics of the intertidal mussel population in the River Exe estuary, Devon (UK) over 7 yr (1976 to 1983) are described. There was no significant trend in adult numbers, and annual variations were small (1.5-fold, minimum to maximum). In contrast, the density of 'spat' mussels (0-year) varied uldely ( l ?~) , suggesting that a strong damping process acted during the first year. Considering just first-year mortality, failure to settle on the beds (k3) had the greatest influence on annual variations in total mortality (K). But losses in the first winter after settlement (k5) were strongly and positively denslty dependent. k3 was inversely density dependent, but only in 6 out of 7 yr. Other first-year losses were independent of density. After the large first-winter mortality (mean 68 %), there were only small gains in summer and small losses in winter for the next 4 yr. Thereafter, increasingly large losses occurred (mean 39 % ) each summer after spawning and each winter (mean 24 ?h), due mainly to bud predation. Some of the over-summer and over-winter changes in adult densities were density dependent, but their effect was small and only served as a 'fine tuning' mechanism keeping densities within very narrow limits. Though mortalities at various stages were correlated with the weather, the main feature of the population was its pronounced stability, due mainly to the powerful regulation acting during the first year on the mussel beds.

Atlantic salmon, Salmo salar L., smolts are vulnerable to entrainment in a variety of man‐made structures as they migrate downstream. The ability of acoustic bubble screens to deflect smolts from potential hazards was assessed. Screens were deployed, in turn, across one of the two identical channels through which the millstream of the River Frome flowed and the efficiency of these screen systems was tested by counting smolts by video recording in each channel. It was concluded that these screens deflected a significant number of smolts. Efficiencies were greater at night than in daylight because of smolt behaviour.

This paper summarizes the results from a study of historical stream salinity trends and catchment salt balances within the Murray–Darling Basin, Australia. A broad analysis of stream salinization was necessary to assist prediction of the increase in the effect and extent of dryland salinity across the basin. The sparseness of the water-quality data necessitated the development of an innovative statistical trend technique that also allowed for the high autocorrelation of the stream salinity data which was often present.Results showed the spatial distribution of stream salinization and identified regions of concern. The salinization characteristics of four distinct geographical regions were identified by providing a spatial analysis of catchment salt balances and stream salinity trends. The salinization behaviour of each region was also related to distinct physical processes. The most significant rising trends and catchment salt output/input ratios were in the zone with 500–800 mm year–1 rainfall in the southern and eastern dryland region.

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JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. British Ecological Society is collaborating with JSTOR to digitize, preserve and extend access to Journal of Animal Ecology. Summary 1. The predictions of an empirical model were tested, based on a game theory approach that describes how a population of oystercatchers Haematopus ostralegus, in which individual birds vary in their competitive ability and foraging efficiency, becomes distributed over its spatially variable mussel Mytilus edulis food supply. Model predictions on the distribution of the birds over the main mussel beds of the Exe estuary, on where particular cohorts of birds feed and on their intake rates and local dominance ranks were tested against already published data. 2. The model predicted quite well the preference ranks of the 12 beds; the spreading out of birds over more mussel beds as oystercatcher numbers increased; the decrease in immature oystercatcher numbers on the most preferred beds as adult numbers increased; the higher proportion of immatures on the lower ranked beds; the high rate of movement between beds of birds with low dominance scores; and, on the most preferred beds, the higher intake rates of dominant individuals and the similarity between the intake rates of adults and immatures with the same dominance. 3. Although, with a few exceptions, the qualitative trends were predicted correctly, their magnitudes were sometimes under-predicted, suggesting that some parameter values need to be refined. None the less, the model tests were considered encouraging. Future work should aim to incorporate into the model other aspects of the birds' behaviour, such as the effect on dominance of familiarity with a feeding area, and prey depletion. 4. By assuming that birds require a certain minimum rate of food intake, either to remain on the estuary or to survive the winter, and by running simulations over a wide range of initial population sizes, it was demonstrated how such a model can be used to predict (i) the carrying capacity for oystercatchers of beds of different preference rank, and of all the mussel beds combined, and (ii) the parameter values of the overwinter density-dependent mortality function. These findings, in turn, can be used to predict the local and global population consequences of winter habitat loss.