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394 Management Options lines for each generation may be carried out in a single yeaz, or as is preferred for longer-living species, in three successive years (Fig. 20.2. Evaluation Evaluation of success of programmes that re- habilitate or introduce species using hatchery fish is fraught with many problems in river man- agement. Sampling is very difficult, especially for small fish, and population estimates are usually very unreliable except by direct count methods of migratory fish at fishways (McMenemy & Kynard 1988;; Beamesderfer & Rieman 1988. Sampling people who catch or eat fish may provide useful information about riverine fish, especially with artisanal fisheries (Bayley & Petrere 1989 but the quantitative methods to estimate fish production, survival and yield are poorly developed relative to approaches for the same parameters for lakes, small' streams and reservoirs. Casselmann et al (1990 surveyed 73 scientists from l2 countries for their experience in sampling large river sys- tems. This survey reviewed and evaluated many types of sampling gear but concluded that none was suitable for sampling large river systems in all types of habitat and situations. 20.3 FACTORS INFLUENCING SUCCESS As stated earlier in this chapter, there must be a commitment by river catchment managers to include fisheries management as a component of their plans. Therefore, the catchment planning process becomes the most important factor that could influence the success of any fish stocking scheme. From the very beginning of this process, it should be evident from the catchment plan as to what quality and quantity of fish habitat will be delivered by the plan. Further, the plan must indicate where the various fish habitats will be in the catchment, what variability can be expected and when, in any one year, those changing con- ditions are likely to occur. Nelson et al (1992) used a hierazchical system to classify locations and sites in northeastern Nevada, USA. The sys- tem is based on the integration of geology, geo- morphology and local habitat features. The authors were able to develop preliminary criteria for assessing a fishery on a large scale (km2) to save time and money, by analysing detailed habitat attributes on those sites most likely to be important for the chosen fish community. The application of the ideas and concerns out- lined in the remainder of this section is predicated singularly on the forewarning any catchment plan should provide. It is at this level of prep- aration that the public and their legislative rep- resentatives become involved. Consultation over and acceptance of catchment plans and their fish management components provide greater as- surance that fiscal resources and commitment to sustainability will be forthcoming. The concept of sustainability is an important pazt of planning for fisheries in a river catchment. Gardiner (1991) argues for ecological sustain- ability that includes social, political and legal components where economic and environmental sustainability are very much interrelated. His paper is an excellent treatise on the value of plan- ning at the catchment level to achieve holistic management of riverine systems. Water quality and quantity Water-quality management for fish production and survival of hatchery fish includes the opti- mizing of not only discharges for current and volume, but also of the water levels and wetted margins of streams. The complicated interre- lationships between instream flow and fish pro- duction have caused many problems in fish and river management. Often fisheries managers have had neither expertise nor data readily available to help plan for the effects of changes in hydrological regimes. However, Gustard (1992 reported sig- nificant advances in the understanding of river regimes, including international databases that could help in the understanding of global influ- ences on floods and their frequency. Water abstraction schemes, e.g. cooling, drinking-water supplies, especially those that withdraw large volumes (>500 m3 min-1 f, present major hazards to fish, and could 'harvest' ma- jor portions ~ :f planted species intended to re- habilitate ariver system. Various fish protection devices have been designed for water extraction systems, but few, if any, prevent entrapment and impingement of all species offish (Fletcher 1985.