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20: Direct Control of Fauna: Role of Hatcheries, Fish Stocking and Fishing Regulations D. P. DODGE AND C. C. MACK 20.1 INTRODUCTION This chapter .describes the benefits and defic- iencies inherent in directly controlling biological populations, as opposed to habitat manipulation, as pan of a scheme to manage riverine resources. Here, the use of hatchery-reared fish is discussed. The key to successful management of fish in any catchment is cut from three principles that sup- port all animal culturing whether intensive feed- lot operations for domestic stock or open-water harvest of pelagic fishes. First, a manager must have extensive under- standing of the habitat and general environmental conditions into which it is intended to introduce a reared species. Will the existing habitats limit the success of a stocking programme? Are the limiting factors irreversible, or can selected under- takingsalter conditions to increase the probability of success? Might extremes in environmental conditions occur that could prevent success even when average conditions appear suitable? Can these extremes be mitigated? Is there sufficient knowledge about the habitat requirements of the selected species in order to match them with location and quantity of riverine habitat? Secondly, the manager needs knowledge about the species to be cultured. How adaptable is the chosen species to episodes of stress resulting from extreme environmental fluctuations? Are there developed and tested gene pools or stocks of the species that are adapted to the kinds and quantities of habitat available in the river system? Does the manager want self-sustaining stocks or will the programme depend on reared stocks or on some combination of the two? Is the selected species compatible with native species in the system, or should one expect such success that diversity of native species will decline? Will the reared individuals interbreed with wild indi- viduals of the same species or with similar species to produce hybrids? Can any of these negative effects be mitigated? Finally, the public must be consulted and the manager must ensure that the public understands the risks and benefits of stocking. This chapter will propose answers to some of these questions. As will also become apparent, there may not be any answers to some of the questions, until assessments produce data about stocking activities sufficient to make adequate analyses of these kind of projects. Scope and context One cannot overestimate the value of planning, not only as a means of putting ideas on paper, but also as a way of testing those ideas. To realize the potential for fish production in any river system, managers should prepare plans for catchments which also have regard for creating and protecting stable and diverse fish assemblages as part of the bigger picture of water and land management. Also, a manager needs to appreciate that the pro- ductivity of a river depends on nutrients dissolved in the terrestrial systems of its catchment, and how these nutrients reach the aquatic environ- ment depends on the interface between land and water ~Zalewski et x11991 ~. Total reliance on fish culture for recruitment is fraught with as many pitfalls and subsequent disasters as for any other artificially sustained system. Wherever possible managers should select goals that advocate man- agingfish on the basis otself-sustaining, naturally 386