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Common dolphins Delphinus sp. are frequently targeted by tourism operations in NewZealand waters, yet there is a paucity of data on potential impacts faced by this species. Transitionmatrix models, used widely in population ecology, have recently been applied to behaviouraltransitions in order to provide successful management guidelines. We detail the use of Markov chainmodels to assess the impact of tourism activities on the behavioural state of common dolphins in theHauraki Gulf, New Zealand. First-order time discrete Markov chain models were used to describetransition probabilities in both control and impact scenarios. The effect of boat interactions wasquantified by comparing transition probabilities of both control and impact chains. Foraging and restingbouts were significantly disrupted by boat interactions to a level that raises concern aboutthe sustainability of this impact. Both the duration of bouts and the overall time spent in these 2 behaviouralstates decreased. Foraging dolphins took significantly longer to return to their initialbehavioural state in the presence of the tour boat. There was also an increased preference to shiftbehaviour to socialising or milling after tour boat interactions. Impacts identified in the present studyare similar to those previously reported for bottlenose dolphins, a coastal species typically consideredto be more susceptible to cumulative anthropogenic impacts.