Male and female bottlenose dolphins Tursiops spp. have different strategies to avoid interactions with tour boats in Doubtful Sound, New Zealand

I assessed the short-term reactions of bottlenose dolphins Tursiops spp. to interactions with tour boats, and their long-term implications. Vertical avoidance of boats, showed by an increase in time spent underwater, is a typical response in cetaceans, and has been likened to predator avoidance strategies. This study looked at the variation in diving pattern of bottlenose dolphins in Doubtful Sound, New Zealand, in relation to boat interactions. An observing vessel was used to collect the data. A regressive approach showed that this vessel did not have a significant effect on the diving pattern of the dolphins. The analysis would have allowed the detection of a small difference (6.35 s) in dive interval (percentage of variance, PV = 0.05) with high certainty (power = 0.86). Dolphins avoided tour boats vertically by increasing their mean diving interval. Dolphins started to react before boats were in visual contact. An information theoretic approach indicated that the behaviour of the boat was the predominant factor affecting the diving interval. Males and females responded differently to interactions with boats. Males started to avoid boats as soon as they were present, while females switched to a vertical avoidance strategy only when interactions became intrusive. This difference in avoidance strategy may be related to the different metabolic regime of the sexes. Males would be more likely to meet the cost of vertical avoidance of boats because of their greater energy stores. Females vertically avoid boats, an energetically expensive exercise for them, only when the risk incurred by this interaction is high.