of top-level predators that are beyond the ability of most ecologists to evaluate. There has also been a great deal of name-calling, such as referring to Myers’s and Worm’s calculations as “folly” and “fantasy” (Walters, 2003), and outrage about the publicity that their article received from the press (Polacheck, 2006). Nevertheless, the NRC report acknowledged declines in the range of 65–80% (NRC, 2006) that are much greater than anyone was admitting to before Myers’s and Worm’s article was published.
Ward and Myers (2005) subsequently evaluated the status of 19 oceanic fisheries species in the central Tropical Pacific between the 1950s and the 1990s using scientific survey and official observer data. There were 12 species of large predatory sharks, tunas, and billfishes and 7 smaller species <17 kg. All 12 large predators showed significant declines in biomass, and 11 of the 12 species decreased in average body mass by 29–73%, whereas 5 of 7 smaller species showed no significant change and skipjack tuna significantly increased (Ward and Myers, 2005). Moreover, the pelagic stingray Dasyatis violacea and pomfrets, which were absent in the 1950s, appeared in even greater abundance than any of the original smaller species. Overall, biomass declined 89.7% and large predators declined by 90.3%—the same as the declines originally reported by Myers and Worm (2003). Perhaps more important than the actual magnitude of decline, however, is the clear shift in species composition and relative abundance in the pelagic community reminiscent of the increase in mesopredators in the northwest Atlantic and Gulf of Mexico (Shepherd and Myers, 2005; Myers et al., 2007). Pelagic fisheries are a vast uncontrolled experiment whose ecosystem consequences are still unknown. Nevertheless, Ward’s and Myers’s results clearly point toward the potential for strong trophic cascades and significant declines in mean trophic level as fishing erodes top-down control.
Warming and acidification of the pelagic realm due to the rise of CO2 comprise another uncontrolled experiment on a global scale (Feely et al., 2004). Sea-surface warming increases the stratification of the oceans because warmer and lighter surface waters inhibit upwelling of cooler and denser nutrient-rich waters from below (Schmittner, 2005). Increased stratification may have already caused the drop in productivity in the northern Pacific that is widely described by biologists as a “regime shift” in the composition of open-ocean plankton communities (McGowan et al., 2003). Moreover, climate models suggest that the oceans may move into a permanent El Niño condition (Wara et al., 2005; Fedorov et al., 2006). Uncertainties abound regarding the degree to which upwelling could be permanently suppressed, but if ocean productivity declines, there will