The need for managing non-lethal effects on wildlife is becoming increasingly important as global human-wildlife interactions are now more frequent and more diverse. We developed a mechanistic model for minke whales (Balaenoptera acutorostrata) to measure the effects of behavioural disturbances caused by whalewatching activities on foetal growth. The model illustrates the pathway through which behaviourally-mediated effects of anthropogenic disturbance might influence female reproductive success in an iteroparous capital breeding mammal. We found that although the behavioural disruptions caused by whalewatching interactions were substantial, the cumulative exposure of individuals to whalewatching boats was low, resulting in an effect on foetal growth no different from natural variability. This highlights the importance of considering all aspects of disturbance when evaluating effects of human disturbance on wildlife. Our mechanistic model can also be used to simulate different management scenarios to predict the long-term consequence of disturbance on vital rates, to help inform management decisions.This article is protected by copyright. All rights reserved.