Overfi shing and Habitat Degradation

hroughout history, people have preferentially settled along coastlines, and they continue to do so today. Coastal people make up more than half of the total human population, and coastal settlements are transforming marine habitats at a rapid pace. Coastal people have also been long engaged in the extraction of marine resources, mostly animals such as marine mammals, fi sh, and invertebrates as well as some algae and higher plants (Lotze et al. 2006). The effects of fi shing and hunting on marine life forms have now spread from coastal areas to the continental shelves and the open ocean (Watson et al. 2012), and they are beginning to transform the largest ecosystem on Earth, the deep sea (Roberts 2002). While Chapter 8 describes these historical changes in detail, this chapter focuses on the current effects of fi shing and habitat alteration on marine communities. In doing so, it examines the role of humans as a top predator (Estes et al. 2011) and ecosystem engineer (Smith 2007) in marine communities. This chapter treats fi shing and habitat degradation together because they represent by far the most dominant human impacts on marine ecosystems. There is little doubt that fi shing—which we defi ne here as including all extraction of marine animals and plants—is the human activity that has historically had the most transformative impact on marine communities (Dayton et al. 1995, 1998; Jackson et al. 2001; Lotze et al. 2006; Halpern et al. 2008; Lotze and Worm 2009). The effects of fi shing, however, have often occurred in combination with habitat disturbance, either from the fi shing gear itself or from other unrelated impacts (Dayton et al. 1995; Watling and Norse 1998). According to a comprehensive analysis of the historical evidence, an estimated 96% of local extinctions in coastal environments involved fi shing and hunting and 39% the effects of habitat degradation (Lotze et al. 2006). In 42% of reviewed cases, multiple human impacts were involved. Another study of the factors that drive extinction risk today found that exploitation caused a majority of marine species losses (55%), followed closely by habitat loss (37%), while the remaining losses were linked to invasive species, climate change, pollution, and disease (Dulvy et al. 2003). Only recently, however, have ecologists begun to study the community-wide effects of fi shing and habitat degradation in much detail. Ecological theories and concepts that were developed in terrestrial, freshwater, and coastal ecosystems are now being applied to continental shelf and deep-water habitats. Fisheries-induced trophic cascades, for example, are well known to occur in lakes (Carpenter et al. 1985), rivers (Power 1990), and coastal regions (Estes and Palmisano 1974), but have only recently been described from large offshore marine ecosystems (see review by Baum and Worm 2009). Hence it appears that fi sheries that were historically managed with a single-species focus require a much broader community and ecosystem context within which their impacts can be understood and managed. The ecosystem approach to fi sheries (EAF) T