Human disturbance may cause both short-term behavioral disruption and permanent impairment of cetaceans. For resident dolphins in Hong Kong, they are only seen in the western waters (i.e. the brackish areas of Pearl River Estuary) probably because of feeding demand. Huang et al. (1978) reported that humpback dolphin primarily fed on estuary fishes, squids and shrimps. Because there appears to be no alternative area meeting the ecological requirements of dolphins, they are probably forced to tolerate human disturbance and bear the consequence of behavioral disruption. A single event of stress may cause a short-term disruption that can be recovered when the stress disappears. Accumulation of short-term disruption, however, may lead to permanent impairment of behavior and social life (Parsons, 1998). Therefore monitoring short-term behavioral disruption of the animals helps to prevent the onset of unrecoverable consequences