Marine-ecosystem management is not simple. In order to predict the effects of any management activities on other components of the system, complex ecological modelling is often required. Marine reserves have been suggested as a conservation tool that can bypass the need for complex and often controversial ecological models. To date, marine predators have attracted significant attention in ocean conservation planning, but they have primarily been used as figureheads, largely obscuring any potential ecological role as indicator species. Their distribution can help identify productive ocean areas, the protection of which will encompass a high measure of biodiversity within the underlying ecosystem. In this chapter, I review the evidence supporting marine reserves over ecosystem modelling approaches, and discuss the potential to use marine megafauna in order to identify sensitive marine habitats.

The seas have been increasingly altered by the effects of humans (Jackson et al. 2001) and the risk of extinction to marine species is far greater than has often previously been thought (Roberts & Hawkins 1999). The most pervasive of these effects is over-fishing; but other significant threats include pollution, degradation of water quality, habitat destruction and anthropogenic climate change. Fisheries now consume an estimated 24% to 35% of primary production (Pauly & Christensen 1995). In many cases this has resulted in extinctions both of target species that are directly harvested (e.g. Myers et al. 1997) or of incidentally caught species additional to the target catch (e.g. Casey & Myers 1998).