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396 Management Options economic and resource protection policy for har- vesting Adams River sockeye salmon (Oncor- hynchus nerka). The policy proposed that a subdotxrinant run be fished at 50% harvest rate in the first year and a moratorium be imposed on fishing', off-year runs for a period o~ 8-12 years. This proposal would put all the gains from a reduced rate of harvest into increasing the size of the spawning population. When an optimal escapement level was achieved, harvesting would be reinitiated. Unfortunately, senior manage- ment appeared to be more sensitive to the reduc- tion in fishing times and local employment, so the policy was considered impractical even though the proposal could contribute up to $600 million'(Can) to the net value of the fish stock. Major river diversions on the scale of those in Siberia and northern Quebec (Kierans 1988; Berkes 1989) present different hazards to fish management dependent on fish stocking. As well as significant shifts in habitat, in local climates and in stage discharge patterns, diversions even- tually change the character of the native fish assemblages such that new or existing species increased by fortuitous habitat shifts may prevent the successful management of the intended fish species. ~teliance on cultured fish to offset these changes is inevitably misplaced. However, once major ecologically profound changes have been accomplished within a river catchment, fisheries managers have to get on with the. job of managing this altered environ- ment to maximize fish production on a sustain- able basis. In many cases, fish are an essential food item so that restoration of fish production as soon as possible is often close to an emergency. At the same time, it would be a risky investment to take just any approach. Planning will lead one through a logical sequence asking questions and seeking answers until the best solution can be identified for the management of the fish com- munity in the new environment. Conflicting land/water use The best fish culture strategies and practices in the world' rarely offset the detrimental results of major land and water management practices which destroy certain components of a river sys- tern essential to the production and maintenance of fish stocks. For example, Raymond (1988) showed that major alterations in dam and im- poundment management combined with lazge releases of smolt from hatcheries offset the decline of steelhead (Oncorhynchus mykiss) in the Columbia River, but failed to compensate for ma- jorlosses of returning Chinook (O. tschawytscha). Also, most returning adults were of hatchery origin, suggesting native gene pools had also been lost. Here may be a case for arguing for the estab- lishment of hatchery stocks from broodstocks of local origin. Management of established reservoirs can in- fluencethe survival and growth ofhatchery-reazed fish. Fisheries previously dependent in the main on hatchery productions can be boosted and even made self-sufficient by changes and innovations in reservoir management. In mid-western America, populations of centrachids (Centrachidae) do- minate impoundment fisheries and aze enhanced by increased time of storage of flood waters (Mitzner 1981). At the same time, cool and cold- waterfish populations usually decline so that any maintenance of these species becomes almost exclusively hatchery dependent. Even Coldwater tailrace fisheries are usually based on stocking. Genetic integrity of wild and hatchery stocks The overall fitness of any species and of any of its many stocks should be a major concern of a man- agerusing hatchery fish to rehabilitate and main- tain a riverine fish community. Undoubtedly, there are major differences among various species and stocks in their predilection to adapt to rigor- ous environmental conditions in any river over any annual cycle. Testing of stocks Eor these abilities would be an ideal screening mechanism to increase probability of returns of planted fish and also to reduce costs for fish culture pro- grammes. Challenge-testing of stocks and their responses to success=limiting stresses showed stocks of coho salmon (O. kisutch) had different capabilities (McGeer et al 1991). Such. differ- ences should influence which stock is chosen to culture. The danger to native populations from large- scale escapes of farmed fish reflects the same hay hat No sal. bre seq for Mo alw fury gen may est. spry asst gra: Mir of lati all we] Effr Res acc fair leuc nay by a late beep affe grog grar fish toxi tam C ages rive to ma} any ma} on ~ they toxi