Predicting the effects of whalewatching activity on the vital rates of Eastern North Pacific blue whales
Enrico Pirott and Leslie New
International Whaling Commission
Interactions with whalewatching vessels can cause baleen whales to change their behaviour, but the management of these activities requires an assessment of how short-term responses affect the survival and reproduction of individuals and, ultimately, the dynamics of the overall population. In this study, we use an existing model for the consequences of disturbance on the vital rates of Eastern North Pacific blue whales (Balaenoptera musculus) to investigate the effects of various scenarios of whalewatching activity on the survival and reproductive output of females in this population. Moreover, we assess the relative influence of environmental variability, and the potential synergy with increases in whalewatching intensity. Our results suggest that disturbance is likely to primarily affect female reproduction, while individual survival appears to be more robust. When environmental conditions are also simulated to change, the compound decrease in reproductive output is more apparent, but predicted effects are only additive. Finally, our study highlights that the simulated severity of the effects of interactions with whalewatching vessels has the highest influence on the predictions. Considering the outstanding uncertainties on the behavioural response process, the underlying environmental conditions and resource dynamics, and the exposure rates of individuals, these results cannot be used to inform direct management actions for the population. However, modelling approaches like the one used in this study will allow moving beyond descriptions of the short-term effects of whalewatching on the behaviour of individual whales and towards predictions of the consequences of multiple, cumulative stressors on the overall population.