AbstractThe new millennium marks a time when scientific opinion and environmentalist sentiment are at last converging on the perception that the world's natural marine heritage is facing grave threats. What environmentalists have come to call the 'marine biodiversity crisis' is a pervasive and by now ell-documented phenomenon, until recently occurring largely unnoticed beneath the deceptively unchanging blanket of the ocean's surface. The fact that this problem is essentially an invisible one makes it all the more insidious, and our terrestrial bias makes combating the problem a huge and difficult task. Human impacts on our seas take many forms and result not only from activities that affect species directly - such as overfishing, in-filling of wetlands and coastal deforestation - but also from activities that affect oceans indirectly, such as through land-based sources of pollution, freshwater diversion from estuaries, invasive species and climate change. In tackling fisheries issues, most organizations attempt to base their projects and advocacy on the best available scientific information. The key scientific information underpinning campaigns and field projects addresses three facets of sustainability: (i) the levels of resource removal that can be realized without adverse impact on the ecosystem, given the particular environmental condition of the ecosystem at time of harvest; (ii) the least invasive means by which that harvest can be undertaken at desired levels of harvest, such that habitat impacts and by-catch are minimized; and (iii) the most appropriate stocks for large-scale harvest, namely protecting stocks that are sole representatives of genetically unique organisms and stocks whose ecological role is critically important and so not redundant. Environmental groups, however, are as diverse in their character, approach and constituencies as the environmental problems they address. They function variously as purveyors of information, as translators of scientific and management language to the vernacular, as honest brokers (although their own value systems cause some to question their honesty), as advocates and lobbyists for certain types of reform or regulatory measures, and as adversaries to management agencies and industry when invoking environmental litigation. If a common environmentalist response to fisheries-induced loss of marine biodiversity can be said to exist (and this is a dangerous assumption, given the diversity of groups and their approaches), it is to synthesize existing information, communicate it, and advocate change in policy and regulations where felt necessary. In addition, some groups go beyond fisheries-by-fisheries management reform to advocate: (i) shifting the burden of proof when evaluating fishing impacts on ecosystems; and (ii) establishing strictly protected marine reserves to further our understanding of and protect species, habitats and ecological processes. Such reserves are implemented in a variety of fashions: as components within larger, multiple-use protected areas that seek to accommodate a wide array of users; as single elements in scientifically designed reserve networks; and as one tool of many used in corridor approaches, coastal management and regional planning. Additionally, environmental groups will need to recognize and support real willingness among governmental agencies and decision makers to protect areas needed for fish spawning, feeding and migration through marine reserves, and help such forward-thinking agencies to enter into enforceable international agreements to protect shared or commons resources. The central element in these initiatives is a holistic approach - one that considers renewable living resources as part of a wider, interconnected ecosystem, one that evaluates all aspects of production or development and one that treats humans as bone fide elements of living systems. Holistic solutions are those that recognize these connections and try to minimize ecological, environmental and social costs, while maximizing the benefits (and benefit sharing) that can accrue from engagement in well-managed marine resource use.