Since the beginnings of modern marine fisheries management, allowable harvests have been based on the principle of sustainable yield for commercially important species. Yet the continuing decline of many valued species--North Atlantic cod are just one example--suggests that this approach has serious shortcomings. In "Ecologically Sustainable Yield," Richard W. Zabel, Chris J. Harvey, Stephen L. Katz, Thomas P. Good and Phillip S. Levin argue that a new, more holistic approach--one that recognizes the importance of the entire ecosystem in which a target species lives--is required. True "sustainability" depends on understanding and respecting the complex links between the various organisms that make up oceanic food webs.