River dolphins are among the world’s most threatened mammals, and indeed the baiji (Lipotes vexillifer), a species endemic to China's Yangtze River, is likely extinct. Exploitation for products such as meat, oil, and skins has been a lesser feature in the population histories of river dolphins compared to most large mammals. Habitat factors are therefore of particular interest and concern. In this paper we attempt to describe the population-level responses of river dolphins to habitat transformation. We find circumstantial but compelling evidence supporting the view that, at a local scale, river dolphins are opportunists (generalists) capable of adapting to a wide range of habitat conditions while, at a river basin scale, they are more appropriately viewed as vulnerable specialists. The same evidence implies that the distributional responses of river dolphins to basinwide ecological change can be informative about their extinction risk, while their local behaviour patterns may provide important insights about critical ecological attributes. Empirical studies are needed on the ecology of river cetaceans, both to inform conservation efforts on behalf of these threatened animals and to help address broader concerns related to biodiversity conservation and the sustainability of human use in several of the world's largest river systems. 1. Introduction In this paper, we attempt to evaluate the ability of river dolphins to adapt to environmental change. This evaluation is necessarily speculative and largely theoretical. Our goal is to develop ideas and terminology that will facilitate a rigorous debate and stimulate field researchers and resource managers to look at these animals with fresh eyes. Our evaluation is far from academic because the fluvial systems occupied by dolphins have been and continue to be subjected to dramatic environmental changes associated with water development, a general decline in the availability and quality of fresh water, and global climate change. Regarding this last, although global warming will generally result in increased precipitation, the effects will be spatially and temporally uneven, and declines are expected in some areas . Also, sea-level rise is expected to result in the loss of dolphin habitat in the lower reaches of rivers due to salinity encroachment and increased sedimentation . The recent extinction of the Yangtze River dolphin or baiji Lipotes vexillifer  adds a sense of urgency for understanding the vulnerability and resilience of freshwater dolphins to environmental change. Although fishery
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