Chapter 10: Habitat Improvement in Altered Systems
Mark A. Pegg and John H. Chick
Most freshwater ecosystems have been altered by human activities such as channelization, increased nutrient inputs, and shoreline development. Human activities can change fish habitat so that a system may not be able to achieve fishery management objectives, thus providing impetus to improve habitat conditions. Changes in habitat quantity and quality have been identified as primary reasons for declines in fish populations in North America (Ricciardi and Rasmussen 1999; Venter et al. 2006). There has been a recent, marked increase in support from resource managers and the public to initiate activities to improve habitat for fishes. For example, the number of habitat improvement projects reported in the National River Restoration Science Synthesis database has increased from a few dozen projects in 1985 to nearly 6,000 projects in 2005 (Bernhardt et al. 2005). A standardized approach to coordinate, plan, and implement habitat improvement projects is difficult to apply given the differences among ecosystems and the causes of habitat loss throughout North America. However, a systematic and logical management approach to mitigate or restore habitats that meets fisheries management objectives can streamline the process and is needed.
The concept of habitat improvement is complex and dynamic because it occurs across multiple spatial and temporal scales (Bohn and Kershner 2002; Feist et al. 2003). For example, habitat improvements can occur at a local scale, such as placement of habitat-forming structures in a stream segment during a single year, or at a watershed scale, with habitat improvements made throughout a system over many years. Habitat improvement at small spatial scales is generally conducted at a single lake, stream segment, or reservoir; requires little coordination by fisheries managers with other entities; and is performed with relatively limited personnel and resources. Habitat improvements at larger scales, such as whole streams or entire watersheds, often require considerable planning and coordination because large systems have diverse management and interest groups and are subjected to many different alterations.