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The Enhancement of Drained Salmonid Rivers in Ireland 21 the authors have been guided by the extensive literature on trout stream enhancement programmes in North America since the 1930's (Duff, 1988 and others). Some adaptation of the American techniques have been nec- essary to take account of the specific ecology of Irish systems and to make allowance for the fact that, on most cases, we were dealing with mixed atlantic salmon and brown trout popu- lations. A degree of pragmatism is required in approaching rehabilitation pro- grammes. Drainage requirements or channel conditions post-drainage may prohibit one from undertaking mean- ingful fisheries rehabilitation pro- grammes in certain areas or prevent one from recreating the specific hab- itat type which was present pre- drainage. Post-drainage fisheries rehabilitation programmes should al- ways be flexible enough to accommo- date and address such difficulties. Fisheries losses in one area can often be offset by improvements in other zones particularly where one is deal- ing with the overall management of relatively large catchments. 5d. The Cost Effectiveness of Rehabilitation Rehabilitation costs will be very vari- able depending as they do on drainage scheme design require- ments, and the quantity and type of materials needed to restore a partic- ular ecotype. A typical example of the type of works undertaken in Irish rivers and the benefits which have accrued in fisheries terms are pre- sented (table 1). Some aspects of the costs and re- turns presented in Table 1 require elaboration. On the costs side the de- sign expenditure figure is generous. This facet would cost less if the chan- nel are in question was being en- hanced as part of a programme for an overall subcatchment. The return data are minimal figures. For instance one could also make some allowance for the added value in trout and sal- mon tourist angling terms as a con- sequence of the increased fish stocks. There are also social as well as monetary gains - a functional sal- monid stream is a valuable local amenity. The annual fish production Table 1. - An example of the costs and benefits of salmonid stream enhancement pro- grammes in Ireland Benefits - Measured in terms Capital costs of annual fish production post-works Materials - 1,000 tonne stone/gravel £ 4,500 500 S2 Smolts £ 1,500 Machine Hire (80 hrs. @ £ 18/hr.) £ 1,440 100 S' Smolts £ 200 Design and Supervisory Costs £ 2,000 1,000 1 Y.O. trout £ 400 600 2 Y.O. trout £ 840 300 3 Y.O. trout £ 600 TOTAL £ 7,940 TOTAL £ 3,540