Chapter 4: Freshwater Aquatic Habitat Measurements
William L. Fisher, Michael A. Bozek, Jason C. Vokoun, and Robert B. Jacobson
Habitat is one of the most recognized and appreciated aspects of fisheries biology, management, and conservation (Orth and White 1993; Summerfelt 1993; Naiman and Latterell 2005; Rice 2005). Fisheries management agencies throughout North America support habitat inventory, monitoring, and enhancement programs to evaluate, protect, and improve aquatic habitats to enhance fish stocks (Bain and Stevenson 1999; Fisher and Burroughs 2003). In fact, the role of habitat is so well established in the fisheries discipline that many citizen groups actively participate in habitat restoration and enhancement efforts under the guidance of trained professionals. Stream habitat restoration (Palmer et al. 2005; Alexander and Allan 2006), artificial reef construction (Bassett 1994; Rogers and Bergesen 1999), and riparian management (Beschta 1991; Naiman et al. 2000) are examples of some of the high-profile habitat enhancement activities that are part of fisheries management programs (Grove et al. 1991). However, such management can be complicated and requires a comprehensive understanding of the role of habitat in the function of aquatic ecosystems.
Whereas the concept of fish habitat management is a well-accepted tenet of fisheries biology, in practice considerable variation exists in how it is integrated into management. General concepts of habitat quality have led to development of useful biotic indices to gauge habitat quality (Karr 1981), but understanding the specific cause(s) of degraded conditions or developing predictive models useful for habitat rehabilitation has been more difficult (Stoneman and Jones 2000). Quantification of fish population responses to habitat modification, which would be useful for assessing limiting factors and essential for restoration and enhancement projects, is still in its infancy. Identifying any one key habitat component that may be limiting a fish population (and thus requisite to see population level responses to management) from among so many in aquatic systems can be daunting. Moreover, habitat is only one dimension of ecosystems; ecological (e.g., productivity and predator–prey dynamics), climatic, and sociological (e.g., angling harvest and regulations) interactions can often mask or override population responses to habitat (Forney 1974; Lackey and Hubert 1977), which, in many cases, may not actually be limiting. For example, the abundance of adult walleye in Escanaba Lake, Wisconsin (1951 to 2002), varied widely among years because of density-dependent year-class strengths (Figure 4.1) while physical habitat including water levels, littoral zone substrates, water quality conditions, and macrophyte occurrence and abundance remained relatively stable. Thus, direct manipulation of habitat may not result in any measurable changes in fish populations in streams (Hunt 1988) or lakes (Neuswanger and Bozek 2004) above natural levels of variation and can be masked by other processes, such as redistribution or concentration of individuals (Smokorowski et al. 1998).