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Twenty-five fin whales (Balaenoptera physalus) were individually studied in their Ligurian Sea feeding grounds to describe and measure short-term responses to the close approach of a fast-moving inflatable craft from which biopsy samples were collected. Passive tracking was performed with a new technique based on simultaneous determination of (1) position of the observation vessel, (2) laser-measured distance between the target animal and the observation vessel, and (3) azimuth of the target animal with respect to the observation vessel. Tracking was combined with timing of the surfacing intervals. Two different swimming-surfacing patterns supposed to be related to feeding and traveling, respectively, were observed. Supposed feeding whales reacted to disturbance by changing their behavior into traveling. Two different avoidance strategies were performed simultaneously by the whales: travel at increased velocity and reduction of the time spent at the surface. After the disturbance ceased, the surfacing activity never completely reverted to predisturbance conditions during one hour of postexposure control and supposed feeding behavior appeared to be suspended indefinitely. Our results suggest the need for whale watching regulations in the Ligurian Sea, particularly as far as presumed feeding whales are concerned. [ABSTRACT FROM AUTHOR]