Responses by Hector's dolphins to boats and swimmers in Porpoise Bay, New Zealand

Theodolite cracking (61 d; 251 h) was used to quantify dolphin reactions to boats and swimmers in the austral summers of 1995-1996 and 1996-1997. Dolphins were accompanied by swimmers (within 200 m) for 11.2% of the total observation time, whereas boats, accounted for an additional 12.4%. Dolphins were not displaced by either of these activities. Swimmers caused only weak, non-significant effects, perhaps because dolphins could very easily avoid them. Reactions to the dolphin-watching boat were stronger. Analyses of relative orientation indicate that dolphins tended to approach the vessel in the initial stages of an encounter but became less interested as the encounter progressed. By 70 min into an encounter dolphins were either actively avoiding the boat or equivocal towards it, approaching significantly less often than would be expected by chance. Analyses of group dispersion indicate that dolphins were significantly more tightly bunched when a boat was in the bay.