Analysis and Interpretation of Freshwater Fisheries Data

17: Habitat Evaluation

Tammy J. Newcomb, Donald J. Orth, and Dean F. Stauffer


The demand for clean freshwater resources continues to grow with increasing needs for instream (hydropower) and offstream (agricultural, municipal, and industrial) uses of water. These activities influence water quality and habitat availability in river and lake habitats as well as the hydrologic processes that support them. Financial, cultural, and biological stakes can be high in water use and allocation decisions, so it is important to be able to quantify fish habitat made available by the presence of water as well as the quality of the habitat provided by that water. Even in water-rich places where allocation is not an issue, many human uses on the landscape can result in reductions in water quality or degradation of physical habitat.

Fish habitat is composed of physical and biological components required to support fish growth, survival, and reproduction. Habitat components can include specific attributes of a location occupied by a fish or the suite of areas required to complete life histories and sustain a population. More specific terms for fish habitat include essential fish habitat, critical habitat, and preferred habitat. Essential fish habitat is defined by the 1996 Magnuson–Stevens Fishery Conservation and Management Act as “those waters and substrate necessary to fish for spawning, breeding, feeding or growth to maturity” (16 U.S.C. §§ 1801 to 1882). Critical habitat is a term associated with the Endangered Species Act of 1973 (16 U.S.C. §§ 1531 to 1543) and represents the area required to conserve an endangered species. In a broader context, critical habitat areas provide habitat for sensitive life stages such as spawning or early life history (Pitlo 1989). Finally, preferred habitat is defined as those areas that organisms select with greater frequency than those areas occur in the environment (Johnson 1980).