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This paper applies concepts of landscape ecology and patch dynamics to lotic systems. We present a framework for the investigation of pattern and process in lotic ecosystems that considers how specific patch characteristics determine biotic and abiotic processes over various scales. Patch characteristics include: size, size distribution within the landscape, juxtaposition, diversity, duration, and mechanisms affecting patch formation. Several topics of current interest in lotic ecology are examined from a patch-dynamics perspective: (1) response of periphyton communities to nutrient patches; (2) effects of patch dynamics on nutrient spiralling; (3) riparian patch dynamics and effects of leaf litter characteristics on lotic food webs; (4) beaver-induced patch dynamics; and (5) patch dynamics of river floodplains. We conclude that a patch-dynamics perspective coupled with a strong experimental approach can enhance the utility and predictive power of unifying concepts in lotic ecology, such as the river continuum hypothesis and nutrient spiralling, through its focus on organismal and process-specific building blocks of lotic systems. The effectiveness of a patch-dynamics approach as a framework for the study of lotic systems lies in the strength of the linkage between reductionist and wholestream perspectives.

The reported annual yield from inland capture fisheries in 2008 was over 10 million tonnes, although real catches are probably considerably higher than this. Inland fisheries are extremely complex, and in many cases poorly understood. The numerous water bodies and small rivers are inhabited by a wide range of species and several types of fisher community with diversified livelihood strategies for whom inland fisheries are extremely important. Many drivers affect the fisheries, including internal fisheries management practices. There are also many drivers from outside the fishery that influence the state and functioning of the environment as well as the social and economic framework within which the fishery is pursued. The drivers affecting the various types of inland water, rivers, lakes, reservoirs and wetlands may differ, particularly with regard to ecosystem function. Many of these depend on land-use practices and demand for water which conflict with the sustainability of the fishery. Climate change is also exacerbating many of these factors. The future of inland fisheries varies between continents. In Asia and Africa the resources are very intensely exploited and there is probably little room for expansion; it is here that resources are most at risk. Inland fisheries are less heavily exploited in South and Central America, and in the North and South temperate zones inland fisheries are mostly oriented to recreation rather than food production.

Articles Overfishing, environmental degradation, and redistribution of surface water have placed great stress on inland fisheries throughout the world. Human activities usually shift the balance among fish species, causing the extirpation of many indigenous species and the dominance of a reduced set of often introduced fish species. The result has been a massive reshaping of fish communities in the world's fresh waters over the past few centuries, with the pace of change quickening of late in the tropics.It has been known for some time that fishes react to environmental degradation and fishing pressures with a characteristic series of changes. If too much of the brood stock is caught, fewer and fewer recruits appear in the population in succeeding years. This is called recruitment overfishing. The impact is somewhat different if the large fish in a population are taken first, then smaller ones, and so on. The mean size of individuals drops, and there is selection for individuals that mature at a smaller and less fecund size. This is growth overfishing. Each of these phenomena has a counterpart corresponding to effects that become apparent when more than one species or stock is taken into consideration.Three decades ago, Regier and Loftus (1972) observed a multispecies analog to growth overfishing while they were researching the anthropogenic transformation of fish communities in the Great Lakes of North America. What they described-the successive removal of the largest-bodied species-was later generalized Henderson 1973, Welcomme 1995) and has been called the "fishing-down Uganda, Box 343, Jinja, process." Greater fishing pressure can initially bring about a higher catch, followed by a plateau over a range of increasing exploitation as component fish stocks are serially depleted. First large, and then successively smaller, species are removed and their places taken by even smaller and faster-growing ones, producing an illusion of sustained productivity that conceals deep changes in community and food web structure. Eventually there are no more economically exploitable stocks, and both the fishery and the fish community collapse or are changed beyond recognition (Welcomme 1995(Welcomme , 2003. John S. Balirwa is acting director of the Fisheries Resources Research Institute ofIn Africa, overfishing is a recurrent problem closely tied to environmental conditions. Africa has suffered food crises for decades, exacerbated in the Sahelian zones by prolonged drought through the late 1970s and the 1980s. When severe drought compromises production of livestock, rural communities turn to hunting and fishing to satisfy their protein needs. What worked for a long time when people were relatively few can have quite different impacts on wildlife at the currently very high human population densities. Thus, food crises, together with a political orientation of open access to wild resources such as fish, have led to a rapid increase in fishing pressure. This effect is further compounded by the rapid improvement and disseminat...

The form, hydrology and functioning of rivers worldwide have been increasingly modified by a range of human activities. The impacts of these changes on the fish faunas of rivers need to be assessed for biodiversity conservation and fisheries management. Reliable and cost effective indicators of fish assemblage responses to hydrological, morphological and functional changes in a river are required. Given the large number of fish species present in many rivers, reliance on a single indicator species is problematic. The present paper proposes the use of environmental guilds for this purpose. Building on prior studies, we propose a series of environmental guilds based on common patterns of response by fish species to changes in river flow and geomorphology. A general framework consisting of two upland stream guilds, three lowland lentic guilds, four lowland lotic guilds, two generalist guilds and five estuarine guilds is proposed. Considering the large numbers of species present in many river and estuarine systems and the flexibility of their behaviour, many species will be difficult to classify. Further development of the proposed guild classification at the level of individual basins is anticipated, particularly in river systems with highly variable hydrology and many opportunistic species. Nevertheless, this general scheme would be easily and rapidly applied to a wide variety of local circumstance, as well as to the description of the general trends in fish population and assemblage structure occurring during river development.