Inland Fisheries

3.4.1 Introduction

Dams interrupt stream flow, and generate hydrological changes along the integrated continuum of river ecosystems that ultimately can be reflected in their associated fisheries. The extent to which fisheries can be developed, sustained or protected along these modified riverine ecosystems reflects basin topography, geological features, watershed hydrology, and climate, as well as engineering features of the dam itself, and operational programmes for retention and release of water from the reservoir, through the dam and into the tail waters. Fundamental considerations must include establishment and maintenance of habitat for spawning, recruitment and maturation of the fish stocks, and provisions for passage by fishes that during certain phases of their life cycles, depend on longitudinal movements along the stream continuum.

Compensation for loss in yield from river fisheries can be difficult to achieve through development of reservoir fisheries. The larger the river, and the more downstream the location of the dam, the less the potential there is for a reservoir fishery to compensate in terms of yield for losses sustained by the river fishery. Compensation potentials apparently are higher in shallower reservoirs in tropical regions than they are in deeper reservoirs and in more northern latitudes. Even if compensation is achieved from a fishery perspective, specific needs of fish species not included in the fishery, and/or that may be threatened or endangered, must be considered to avoid negative impacts to these fishes.

River fishery production is dependent on length of river, catchment area and, for specific sections of rivers, the position of the segment along the river continuum. If altered hydrology resulting from dams curtails or eliminates normal, historical downstream flooding, overall fisheries production throughout the system can be negatively impacted. The effects of the interference may be variously harmful, beneficial or indifferent depending on the particular situation and fish fauna inhabiting the rivers concerned.