The effectiveness of interpretive signage as a means of modifying visitor behaviour to reduce negative impacts on wildlife was tested empirically at a seal watching site on Vatnsnes peninsula in North West Iceland. From July to September 2014, the actions of 2440 visitors were observed and their behaviour recorded. To test the importance of how interpretive information is presented, signs with either ontological (instructions without explanation) or teleological (instructions with explanation) information were positioned along the path towards the site. A control group, to which no signs were provided, was also observed. Our results show that the majority of the tested behaviour was influenced when signs were present and that under some conditions teleological signs were more effective than ontological. The type of visitor group was found to significantly influence behaviour, with families having the most intrusive behaviour compared to singles, couples or other groups. The findings of this study contribute to a better understanding of how interpretative signage can modify tourist behaviour to facilitate sustainable wildlife tourism. The use of teleological signs for managing wildlife tourism activities is recommended because they are more effective than ontological signs in terms of modifying the general visitor behaviour. In addition, signage and other management strategies should address the different needs and responses relevant to the nature of the tourist group visiting the site. Special focus should be placed on families when signs are designed because this group type showed the highest probability of causing disturbance at the site.