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:m2) filed o be out- ated gent ~rep- rep- over fish as- rt to rant ent. ain- egal ntal His lan- stic tion ~pti- and tted :rre- pro- and gave e to ical sig- iver :hat flu- ing, that sent ma- re- tion Lion and 85 ). Direct Control of Fauna Even with the most efficient and effective fish culture programme, the success of planted fish depends equally on the water quality of the river system into which they are introduced. Many factors interact with the fish as they strive to establish themselves within the existing fish communities and their environment. Nutrient concentrations and the resulting pri- mary productivity of a river limits the growth and development of the hatchery fish. Correlations between fish production and nutrients in streams have been well documented (Welcomme 1985). Many water quality and physical characteristics affect the survival and growth of fish introduced into river systems. In fact, the concentrations of certain pazameters will dictate whether or not a hatchery-supported fisheries can ever be success- ful. For example, the penetration of light and its association with primary and secondary produc- tion is a key component to the survival of salmonids (Lloyd 1987). Besides affecting the quality and quantity of light penetration, sus- pended particles in the water column influence the proficiency with which fish see and catch prey. Also, particles, especially colloidal clay materials, can accumulate on gill filaments and other body parts to such an extent that fish die or are easy prey for larger predators. Readers should refer to .Walling and Webb (1992) and Webb and Walling (1992) for more detailed descriptions of water quality parameters and their ranges ex- pected in riverine systems. Habitat suitability Essential to this matching of fish with habitat is the need to understand the effects on fish produc- tion of physical processes in rivers (Heede & Rinne 1990). Similarly, the generation, transport and deposition of organic and inorganic particles, so much related to hydrological processes, can affect the success of fish stocking into rivers (Newcombe•8t MacDonald 1991). River and basin management schemes also in- fluence the quantity and size of sediment that travels suspended and/or settles in the river bed. These factors also have great influence on the survival, growth and reproductive potential of hatchery-reared and wild fish (Reiser & White 1988). Lazge rivers move large particles, and es- 395 pecially during flood events, can redefine very large portions of river bottoms. These major al- terationsfrequently remove and destroy essential spawning, nursery and staging areas for riverine fish. Losses of gravel, for example, preferred for spawning sahnonids, could mean the demise of any annual recruitment based on natural re- production. Deforestation of headwaters of tri- butazies to Lake Ontario in North America created severe erosion that eventually covered spawning habitat for landlocked Atlantic salmon with several metres of sand, silt and clay. Similar changes to the quality and quantity of essential habitat are well-documented worldwide (e.g. Ward & Stanford 1989). The essence of successful fisheries manage- ment in rivers is the matching of fish stock with suitable habitat. In many cases, however, habitat requirements for many fish species, especially needs for early-life survival and growth, are not usually understood. The interrelationships of riverine fishes with their environments, and the spatial and temporal scales one must use to under- stand these relationships and how fish species have adapted, are reviewed in detail by Bayley and Li (1992). Allocation /overharvest Management of riverine fish stocks involves more than just planting hatchery-reared fish and har- vesting these stocks for food, recreation and revenue. Certain basic decisions are necessary before committing resources to hatcheries and fish production. First, are artificially-reared hatchery fish the best means to optimize fish production or should managers be rehabilitating habitat and changing fishing scenarios to allow existing stocks to stabilize and thus optimize the potential for riverine production based on those existing stocks? Inherent in this decision is the question of how much of the annual production of fish should be allocated to the long-term main- tenance of the resource. Of the remainder of fish production, what quantity of fish would be eco- logically and economically sound to allot to fishing, and when and how could this resource extraction take place that would maintain these two principal allocations? Welch and Noakes (1991) designed an optimal