experience massive nutrient inputs, extended summer eutrophication and hypoxia, and population explosions of microbes (Diaz, 2001; Jackson et al., 2001).
The degrading effects of fishing, habitat destruction, introduced species, and eutrophication reinforce each other through positive feedbacks (Jackson, 2001; Jackson et al., 2001; Lötze et al., 2006). For example, oysters were nearly eliminated by overfishing, but their recovery is now hampered by hypoxia due to eutrophication, by introduced species that compete for space and cause disease, and by the explosive rise of formerly uncommon predators that were previously kept in check by now overfished species (Lenihan and Peterson, 1998; Myers et al., 2007). Much of the overall decline of the 80 species reviewed by Lötze et al. (2006) was due to multiple suites of drivers: 45% of depletions and 42% of extinctions involved multiple impacts. Nowhere have these drivers been brought under effective regulation or control.
Ecological degradation on continental shelves is almost as severe as in estuaries and coastal seas, and the drivers are similar, albeit in somewhat different proportions.
Longline fishing and trawling have removed 89% of the pristine abundance of prized large predatory fishes like cod, pollock, and haddock in the North Atlantic in the last 100 years, and cod have been depleted by 96% since 1852 (Table 1.1) (Christensen et al., 2003; Rosenberg et al., 2005). The effects on sharks have also been enormous (Table 1.1). Large sharks most commonly caught by pelagic longlines in the northwest Atlantic were reduced by 40–89% between 1986 and 2000 (Baum et al., 2003). Likewise, in the Gulf of Mexico, longline fishing and trawling reduced the four commonest large pelagic species by 45–99% in the 40 years between the 1950s and 1990s (Baum and Myers, 2004). Small coastal sharks in the Gulf of Mexico have also been severely reduced, except for some species that have experienced release from predation by the overfishing of their predators (Shepherd and Myers, 2005). Of the 23 species for which adequate data were available, 16 species declined between 1972 and 2002, and the declines were statistically significant for 9 species, 3 of which were reduced to <2% of their 1972 abundance. Seven species also increased,